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CCN Micro AD report - The Community Composting Network

1. 22 5 2 3 Temperature sseesssssseeesseeeseeee nenne nnne nnne nnne rn see ir sie s rase sra se snae se asian seis rasis rna anna 22 S24 Volatile fatty acids VEA us oedin coelo t E unen Ena admtkt una ok ka Vudkud es eo aus Mit pipa vex D es MR RES PSU dE 22 5 2 5 zl a A 23 5 2 6 Dry matter and organi altler is ie dunecanutu etta Eee tuper euren sens uncus uni dues usn ia PU RU eU 23 5 2 7 PANOT ON RR r A 23 53 Listofmontoring equlpimelll uui reri nu ene tiuict astu Dax tua cuota paquete puce bin ct au tu pt lacune a utut p Eds 24 o ois i em oo 0 ee ee ee ee 25 5 4 1 PEO MENT siesievo ce oan oectaceeiiee se a E E sees 25 5 4 2 FONO NEN TE 26 5 4 3 Floating layers NE EE T EHE LE 26 5 4 4 ME e eii ET nant dawhoabawslanseavansdaneengsaetau bands 26 5 4 5 Blockages Leakages NER TET EE C D m 26 5 4 6 Wc ic een eee eee nee eee Se eee eee eee te ere 26 5 4 7 Low gas production cccceccccececceeeeeeeeeseeeeneeeeseeeeseeeeseeeeseeeesaeessaeesseeeseaeessaeeeseeesseeesneees 26 5 4 8 VIGO COUR ME 2f 5 4 9 ACCESSING the digester isis ce rom uite rasiue sr equ oU o hd Ra uud Pork uu Mo Dewsuetutuemdiatas eu sd oue Pai su diGK EP ast 27 6 HACO ONS siicaetatisiscaecdes o E a 28 Annex 1 Determination of VFA with titration Method ccccccccceececeeeeeeeeeeeeseeeeeseeeeeeseeesseeeesaneeessaes
2. same stage of digestion process Temperature and time monitoring of pasteurization unit Catering waste is shred to a maximum particle size of 12 mm before pasteurization Calibration of temperature probes Maintenance of equipment All batches numbered clearly 2 During pasteurization input of untreated material is not allowed Cleaning and hygiene procedures Transported of pasteurized material takes place in closed pipes Unclean and clean areas are separated by concrete walling will this be the case for CCN biogas plants and leachates cannot pass between the two areas Anaerobic digestion takes place ina separate closed vessel Staff training CCN Micro AD Phase 2 Report 23 August 2010 CCP 15 Temperature of 70 C to be maintained over at least 1 hour CCP Catering waste to be shred to a particle size of no more than 12 mm before pasteurization CCP 16 Temperature probes to be calibrated every 3 months CCP Maintenance of equipment according to prescription of manufacturer CCP 17 No contamination of treated material with untreated material CCP 18 No contamination with material not at the same stage of the process CCP 19 No cross contamination of material not at the same stage of processing Temperature monitoring over time Data stored on computer Output from shredder to be inspected as discharged Calibration records to be stored on site Maint
3. Price depending 5 cor Wane polr ot Y Milder before and after 15mm length on material and Econosto 100 500 IN shredded waste to ded steel sedes pasteunzer pump as neede pipe leng p p LL Manufacturer Brand amp type Size or Volume Type of Other technical Alternative Rough price supplier material specifications equipment indication Dependent on Motor outside Y ABS flygt Two blade mixer exact digester Stainless steel digester or Flender 300 500 dimensions submersible 14 amping porusptor Hy me Plasson valves HI PVC AVM Efcon 100 digester Econosto 15mm Safety valve for 6 Spring loaded 72 inch 2 inch biogas in digester threaded valve Rass 0 5 1 0 bar D ems Pipes valves fittings Manual valves minimum PVC Stain less Price depending 13 ror transport of Y Milder before and after 15mm length on material and Econosto 100 500 digestate from digester HE ded steel belena to digestate storage pump PA DERE Pipe ieng 14 Digestate storage Y Polem Box atleastsame aS BE HDPE Closed container Polis 700 1000 feed storage Overtoom Pipes valves fittings ANUA did minimum l Price depending 5 cor return of egestate N Milder poloreand anem dSn denaii ee en msatenalatid Econosto 100 500 liquid from digestate pump ded steel ne lenath storage to shredder also check valve da Neede pipe leng Pump for transport of Verderflex depending on 16 digestate liquid from Desc uns peristaltic
4. although it is a requirement when residues of animal by products are digested A pathogen test kit is CCN Micro AD Phase 2 Report 23 August 2010 23 9 LeAF available from DelAgua and it measures thermotolerant faecal Coliform count Special kits for Salmonella testing on site are to best of our knowledge not available 5 3 List of monitoring equipment Table 5 1 lists the monitoring equipment mentioned in this chapter and their details Table 5 1 List of possible monitoring equipment Parameter Equipment Specifications of product example Example of Estimated supplier costs euro General Beakers gloves safety glasses Fisher Scientific Pipette glass graded Fisher Scientific 5 10 Pipette finnpipette type ThermoScientific 110 270 tips 10 30 1000x DH strips pH range 4 7 example Fisher Scientific 10 100x pH tester Electronic pH tester range O0 14 pH Fisher Scientific 40 100 pH meter Electronic pH meter incl electrode Fisher Scientific 300 600 pH range 0 14 Tempera Handheld Temperature range 50 C 150 C Fisher Scientific 30 ture thermometer Dr Lange Dr Lange spectrophotometer Hach Lange equipment test cuvettes LCK365 organic acids accessories Automated titration Automatic Titrator Fischer Scientific 700 5500 Traditional Laboratory glassware and chemicals titration method see annex 1 Dry matter Oven Drying oven Fischer Scientific 700 5000 Moist
5. taken the event of failure of a critical control point destined for processing in the factory will be sent of site if it cannot be processed within 48hours Retraining of site staff in procedure contaminants by approved laboratory Analysis results reviewed by project manager Visual inspection of end product on site reviewed daily by processing staff Daily review of inspection reports by site manager Weekly review of inspection reports by project manager Daily review of inspection reports by site manager Weekly review of inspection reports by project manager Cross contamination of final product with untreated catering waste Exposure to birds Contamination with material not at the same stage of processing equipment failure Repair and maintenance back up for processing equipment breakdown Removal of stored catering waste to a suitably licensed disposal facility in the event of equipment failure in excess of 48 hours Building vented through biofilter Negative air pressure maintained at all times by fans Door opening times kept to a minimum to allow for deliveries and vehicle exits only Untreated material delivered to site is received and processed in a separate area of the building The building container is divided in to a clean and unclean areas physically separated by concrete walling or other solid separation Leachate from waste
6. and an anaerobically very stable digestate and the former by a high VFA concentration usually in combination with a low pH in the digester and unstable digestate Moreover another explanation for low gas production could be the presence of toxic or inhibiting substances preventing the anaerobic process to proceed Check the quality of the food waste used to feed the digester Finally there may be leakages leading to a low amount of biogas captured in the gas system This must be fixed immediately 5 4 8 Malodour Malodour in anaerobic digestion is usually related to the formation of hydrogen sulphide gas which smells like rotten eggs and to the presence of VFA To prevent the release of malodorous compounds it is important to completely inspect all parts of the installation including the storage of feed digestate and biogas and all other equipment that at some point in the process contain these malodorous compounds Resolving malodour coming from the plant can involve checking the plant for any kind of leakages checking the gas cleaning device whether it is functioning properly e g if it requires replacement and checking the quality of the substrate e g presence of excessive amounts of sulphur rich substances in food waste 5 4 9 Accessing the digester It should be possible to access the digester if this is needed for troubleshooting In large reactors usually a man hole is installed for this purpose whereas small scale sys
7. digester contents Calcium carbonate is one of the chemicals that can be used for pH correction It can be found at garden stores as pulverised limestone known as garden lime e g Capital Gardens Vitax Garden Lime Soil Conditioner 20kg 15 It is a safe chemical to use because it is not aggressive and the equilibrium between water and carbonate prevents a too high pH increase Overdosing of calcium carbonate would result in precipitations which are unwanted because of the risk of clogging but it would not harm the biomass For pH correction of large volumes calcium hydroxide often called hydrated lime can be used which can be bought at home improvement stores It is more aggressive than calcium carbonate which could be a disadvantage but it is a bit cheaper e g B amp Q Blue Circle Hydrated Lime White 25kg 7 50 Both chemicals could be tried to see which is found preferable The suitability of a chemical is also influenced by the presence of impurities such as heavy metals The amount of lime that has to be added cannot be known beforehand because the buffer capacity of the reactor contents is unknown Therefore either the alkalinity buffer capacity of the digester contents can be tested by titration with acid or some extra calcium buffer can be added When the entire digester contents needs to be neutralised it is best to determine the quantity by neutralising a small amount first and then calculate how much would be needed fo
8. internet several sites exist where different articles can be found such as e http www labexchange com e http www lab equip com e http www colco co uk e http www dreamscience lab co uk e http www labx com e http www labstuff nl 5 4 Troubleshooting This section describes to most common problems that could occur during operation or start up of the digester and identifies possible solutions 5 4 1 Acidification Acidification of the digester is one of the most common situations in which the anaerobic digestion process steps are out of balance It can occur both during start up and during normal operation Acidification is characterized by a severe pH drop in the worst case down to a pH of 4 5 This is a result of the relationship between the processes of acidification and methane formation The methane producing organisms methanogens use acetic acid to eventually produce methane When there are not enough methanogens present to consume the acetate acids will accumulate in the digester It is not only the acetic acid that is not consumed but also the acids formed during acidogenesis that accumulate for further explanation see the phase 1 report These accumulated acids cause a pH drop in the digester which negatively affects the methanogens and can reach toxic levels As a result even less acid is transformed by methanogens This is a vicious circle which is started by feeding an excessive amount of easily acidif
9. mixing failure Visual observations of the digester contents may reveal formation of foam or poor mixing performance An overview of the described monitoring equipment is given in the next section section 5 3 5 22 pH The pH of a sample is preferably measured shortly after sampling because biological processes continue in the sample thereby affecting the pH If the pH analysis is not possible within a few hours after sampling the sample should be filtered and the filtrate the liquid fraction which is free of suspended solids should be stored in fridge for maximum of 1 day or freezer The pH can be monitored in several ways depending on the accurateness and the quality that is required Two options are described the use of indicators and the use of electrode pH strips pH strips are relatively cheap and easy to handle Usually a pH test strip with indicators is placed in a sample and colours specific for a certain pH appear on the strip pH strips with different pH ranges and accurateness are available For the digester system the range should be between 4 5 and 8 and the increase in pH steps preferably as small as possible pH electrode With the pH electrode pH can be analyzed electronically usually in one or two decimals The pH electrode should be calibrated regularly with standard pH solutions using calibration solutions of pH 7 and 4 Portable pH meters and testers are commonly available 5 2 3 Temperature The temper
10. pump desired time for storage to shredder Dura or VF pumping Pipes valves fittings minimum iz e plogee veneer Y Milder Three way valve 15mm length i Uepsnens Econosto 100 500 from digester to biogas ded on pipe length cleaning dis Pipes valves fittings minimum ie OF biogas transport Y Milder Valve 15mm length pice COpenamg Econosto 100 500 from digestate storage ded on pipe length to biogas cleaning iaa depends on Saturated Steel wool 19 Biogas cleaning Y Norit Activated carbon E E carbon Aedvstedresrbon activated carbon scrubber or gt 1000 7 device scrubber E disposed as Puxin Biogas properties i x d chemical waste desulpharize 10 Mixer for digester stainless steel must be able to PVC transport solids Manual transport 1500 2500 AVTI qm W CV Manufacturer Brand amp type Size or Volume Type of Other technical Alternative Rough price supplier material specifications equipment indication Pipes valves fittings 20 for biogas transport to biogas holder dd Price dependin Milder 3 way Valve 15mm length PVC l P 3 Econosto 100 500 on pipe length as needed Pipes valves fittings minimum 22 for biogas transport to Milder Valve 15mm length rie epe Econosto 100 500 on pipe length hot water boiler as needed PONNAIST OOrEr aNG Elco sede use 25 kW Elco Klockner a 7 11 2 n Rendamax circulation along SHES SIERI 20 50 mbar EK 01 B G F T a
11. 34 Annex 2 Measuring methane content of biogas using sodium hydroxide ssssssss 36 CCN Micro AD Phase 2 Report 23 August 2010 2 7 9 LeAF Summary This report describes the outcomes of phase 2 of the decentralised Micro Anaerobic Digestion AD project by the Community Composting Network CCN It describes a conceptual design of a suitable decentralized AD system for the scope specified by the CCN Steering Group a commercial component guide start up procedure and operational manual for the digester The micro anaerobic digester plant has a volume of 1 m and is designed to treat kitchen waste When operating the digester at a conservative retention time the digester would process around 25 kg kitchen waste d approximately waste of 10 15 households and produce about 3 m biogas d The overall system includes the digester and auxiliaries The component list identifies suitable components possible suppliers manufacturers alternative manufacturers and component details Before operating the digester at design loading rate first a start up procedure has to be followed The start up of the digester characterized as getting the reactor to work follows a step wise increase in feeding rate controlled by the volatile fatty acid VFA concentration and pH or only pH of the digester contents The daily operation of the digester involves feeding the digester at optimal loading rate monitoring most import
12. 470 Lettinga Associates Foundation LeAF for environmental protection and resource conservation Development of decentralised anaerobic digestion systems for application in the UK Phase 2 Community Composting Network CCN Client Cath Kibbler cath communitycompost org Date 23 August 2010 Lettinga Associates Foundation Project number 08 486 PO Box 500 Er cq o o o ood e 6700 AM Wageningen Authors Els Schuman The Netherlands lemke Bisschops SS Tel 31 317 482023 Revised by Henri Spanjers Fax 31 317 482108 eee a http www leaf water org Fiat Interim report 18 11 2009 7 9 LeAF Table of contents CITI ANY EE REO T m 3 1 PURO CUI EO RPM OT o e 4 2 Description of the Micro AD plant seeslsseesssseeeeeeeen nennen nnnm nnne nnne nn nnn nnn nnns 5 2 1 BUTT CVG O eoa E E E E E vo N 5 22 Qonceptual COSION se cicccesdrcrwenccansaccnnesstinnsscandisenavasenssasanasindndonbedsasleansedndnnavesteeneradusndivarehdawebeansewetes 5 29 Process CO SCION ERE m m t T 2 3 1 Pre treatment CQUIPMENT cccccccsscecesecceseceeeeceeeccaeeceeeceueeceeessusecsueessueessueesseeessesenaess T 2 3 2 DOCST RE m T 2 3 3 BIOO PET E E E E E O T ZAR RAE NAY OU E E E E E A E A O E E AA 8 3 Commercial component guide ticciei5cs225 00cc 9 4 Start up of anaerobic digester ee cece ccc eee
13. Daily checks on the level of fluid in the drainage tank will be recorded in the site diary raised in the event of a Treated material which procedure site staff In the event of cross contamination the effected material will be processed again Log sheet for each batch filled in and updated each time work carried out on bay 30 A non conformance to be control failure Details of corrective action recorded becomes contaminated will have to be returned to the beginning of the process Retraining of site staff in Disciplinary procedures for Details of all non conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken Daily inspection of procedures and critical control points by site supervisor Weekly inspection by project manager Daily site inspections and final product analysis 9 LeAF process bun lemc dm ee E Material will be returned to Data stored on Hygienisation transfer between dirty and clean side of the process Potential for 1 material not to be adequately 2 pasteurized Equipment failure 1 preventing 2 pasteurization Cross contamination between batches during pasteurization Contamination with 1 material not at the same stage of process Cross contamination with material not at the 12
14. and digestate can not flow within the building The clean and unclean areas are separated by sealed concrete walling and drainage channels are in front of each bay to take away any fluid to a sealed storage tank outside Use of a boot washes between clean and unclean areas for boots and tools When loading shovel handles final product it will first be cleaned and go through the wheel wash A dedicated bucket will be used for handling the finished product Signage on site Treated material which becomes contaminated will have to be returned to the beginning of the process Site staff training Loading takes place inside the building Loading takes place in a separate unclean area and cannot come into contact with processed material Flow of materials does not permit cross contamination CCN Micro AD Phase 2 Report 23 August 2010 catering waste to be stored inside the building container CCP 8 Preventative maintenance schedule in place and emergency repair and maintenance support available CCP 9 No cross contamination of treated product with untreated catering waste CCP 14 No cross contamination of treated and untreated material 9 4 Disciplinary procedures for inspections and site staff checks Daily site inspection carried out by site supervisor and findings recorded in site diary Daily inspection of control measures findings recorded in site diary
15. ant parameters and troubleshooting A list of monitoring equipment is included in the report for analyzing most important parameters during operation of the digester To comply with regulations especially the Animal By Product Regulations ABPR the AD system has to fulfil certain requirements which are taken into account in the conceptual design A Hazard Analysis and Critical Control Point HACCP plan is included a template to support the preparation of a HACCP plan for a specific situation This report and the Phase 1 report are both available for download from the CCN website at http www communitycompost org index php projects mad This work is licensed under the Creative Commons Attribution NonCommercial NoDerivs 3 0 Unported License Permissions beyond the scope of this license may be available by contacting info communitycompost org or CCN 67 Alexandra Road Sheffield 52 3EE UK To view a copy of this licence visit http creativecommons org licenses by nc nd 3 0 or send a letter to Creative Commons 171 Second Street Suite 300 San Francisco California 94105 USA We d love to hear from any organisations or individuals who have used this report passed it on or who have found it interesting informative Please get in contact with us by visiting http www communitycompost or CCN Micro AD Phase 2 Report 23 August 2010 3 7 9 LeAF 1 Introduction This report describes the outcomes of phase 2 of the decen
16. anufacturer Brand amp type Size or Volume Type of Other technical Alternative Rough price supplier material specifications equipment indication Box tank 100 litre HDPE PE Plastipro 400 500 container Insinkerator The Green ISE model 75 40 x 40 cm stainless steel 230V 0 75 PK 400 500 machine Verderflex depending on peristaltic pump desired time for Dura or VF pumping Pump for transport of shredded waste to pasteurizer Debu Wijk amp Boerma stainless steel must be able to PVC transport solids Verderpro VPS 1500 2500 cavity pump Pasteurizer Autoclave with Alfa Laval oa No standard size Stainless steel Custom m ade A 5000 7000 pasteurizer electrical temperature registration Verderflex depending on peristaltic pump desired time for Dura or VF pumping Pump for transport of pasteurized waste to digester Debu Wijk amp stainless steel must be able to Verderpro VPS PVC transport solids cavity pump 190074909 Boerma Pipes valves fittings for transport of pasteurized waste to digester Manual valves minimum PVC Stain less Price depending Milder before and after 15mm length oe on material and Econosto 100 500 pump as needed pipe length Double wall MEMANG Drocom i 1m HDPE PE connections and Polem 3000 4000 isolated sampling ports Insulated digester AVT qm W Pipes valves fittings Manual valves minimum PVC Stain less
17. ate has to be stored until use and the storage tank needs to be made sufficiently big to store that amount The stability of the digestate depends on the performance of the digestion process A well functioning digestion process that is optimised for biogas production as in production of biogas per volume of input will produce a digestate that still generates some biogas Digesters that receive more feed than they can optimally handle produce unstable digestate Only a digester that is underloaded from an optimisation point of view would produce digestate that forms no residual biogas As a result the digestate storage can be seen as a post digestion step and therefore is designed in this way For reasons of safety odour and greenhouse gas emissions the residual biogas is not allowed to escape to the atmosphere so the storage is gas tight The gas is then collected treated and used together with the main biogas stream from the digester Depending on the uses of the digestate a separation step may be needed for example when the liquid fraction is used in shredding of the feed or when the liquid and solid fraction will be applied separately as different fertilisers e g composting of solid fraction before application The method of separation of the liquid and solid parts of the digestate in the CCN system has yet has to be decided From the pilot tests it should become clear whether the digestate will separate by gravity or if mechanical separatio
18. atering waste that are destined for processing in the factory to be processed within 24hrs of delivery CCP 6 All by site staff and records kept in the site diary Waste will be rejected from Daily monitoring of process logs for waste delivery and processing dates Timetabled preventative maintenance schedule inspections and 4 checks Non conformance raised in Catering Waste that are through the process recorded on site Non conformance report raised Details of all non conformances recorded in site diary along with records of actions taken site Details of all non conformances recorded in site diary along with records of actions taken the event of failure of a critical control point destined for processing in the factory will be sent of site if it cannot be processed within 48hours Pest control measures increased if monitoring reveals a problem Retraining of site staff in procedure Disciplinary procedures for Pest control inspections carried out by a contractor on a monthly basis Daily site inspection carried out by site supervisor and findings recorded in site diary Daily monitoring of process logs for waste delivery and processing dates Daily Preventative maintenance 29 Non conformance raised in Catering Waste that are site staff Details of all non conformances recorded in site diary along with records of actions
19. ature is easily measured by thermometer or electronic temperature meters The range of the temperature meter should be minimally up to 40 C to be able to measure the temperature in the digester 35 C The pasteuriser will need a temperature meter range suitable for a desired temperature of 70 C 5 2 4 Volatile fatty acids VFA Volatile Fatty Acids VFA are not foreseen to be measured on site unless a laboratory is installed on the premises However if no onsite laboratory is available samples may be taken and sent for analysis to a lab Samples for VFA should be taken just before feeding and then filtered or centrifuged to remove suspended solids and stored in fridge maximum 1 day or freezer Although results of a VFA analysis are not instantaneous compared to pH they give valuable information on the performance of the digester Also in time the amount of data will grow and give the operator a feeling of which pH levels are to be considered safe with regard to digester operation CCN Micro AD Phase 2 Report 23 August 2010 22 9 LeAF When a small laboratory is available on site VFA can be determined with the titration method or by measurement of organic acids with Dr Lange kits It should be kept in mind that the titration method can be difficult for people without laboratory experience and it is not very precise results may even vary between different people executing the analysis The method is included as an appendix of
20. ceceeeeeceeeeecaeeeeeseeeeeseeeesaeeeeseaeeeseaeeeeseeeeseeeesaaeeeeenes 13 4 1 FF A AUN escalates H EE 13 4 2 Start up procedure eee eee 13 4 2 1 Filling the reactor with inoculum 1eeeeeeeeseeeeneeennennnnn nnne 13 4 2 2 Start up protocol applying both VFA and pH analyses ccccseececeeeeeeeeeeeeseeeeeaeeeeeas 14 4 2 3 Start up protocol applying only pH analyses ssseesssseeseeeeeennenn 16 4 2 4 Monitoring parameters other than pH and VFA cccccccceeeeeeeeceeeeseeeeseeeeseeeeseeeeseeeens 18 AP cim 18 5 Operatona manuak NETTE tt 20 MEE uo 20 5 1 1 DS ANS esconde dee cc acon eeatcesneaqcacaecenscasencaencccesaoseactaucedacenstenbact RERE ARR 20 5 1 2 Shredder and pasteurizer ccccccccceecccceeceeceeeeeeeeececeeeeesaeeeeeseeeeseeeeesseeeeeseeeeeseeeeeseeeeesees 20 5 1 9 Feeding the GIG OST MR E T UTD 21 5 1 4 DOSA esta 21 5 1 5 Biogas storage and CA GS ssepe dedo aum a ipse ubere du gene aa 21 5 1 6 axe m OH 21 9 M nlonng guidelines essees tae Ene astro nia sti ma Entum SE Quite can ru lux n Posi REex de a equa uL neu e edu Sa ens 21 5 2 1 Analysing 10 AN UU aguas boite aper iciu dnd deemanasateneaedeeeeaneetaoseeceieetescee 21 5 2 2 o
21. digester when measuring only pH In addition to the guideline presented in the decision support scheme Figure 4 2 the following comments are made o The initial feeding rate kg food waste d is set at 20 of the reactor design feeding rate 25 kg d that is 5 kg food waste per day similar to other start up scheme According to the decision support scheme the interval is increased remains constant or is decreased based on weekly analysis of pH o During the start up it is important to measure the pH regularly to verify the pH is 7 0 7 5 Especially during the first week of starting up it is recommended to measure the pH frequently i e at least every day If pH drops it is recommended to stop or reduce the feed for one week CCN Micro AD Phase 2 Report 23 August 2010 17 9 LeAF o Ifthe pH falls below 6 5 alkalinity should be added accompanied by a reduction in the feeding rate by 2 5 kg d Wait until pH and VFA are back to required values and increase from this moment the feeding rate possibly with steps of 2 5 kg d o Ifthe pH is below 6 but higher than 5 5 it can be tried to revive the digester by bringing the pH back to neutral and not feeding it until the excess VFA is consumed This will probably take time and the chances it works are uncertain No specific time limit exists but if it is felt it takes too long the inoculum should be replaced If the digester is emptied the contents can technically be used as part
22. e a known amount of biogas should be injected in the bottle and bubbled through the solution This results in a certain amount of liquid going out of the bottle With a measuring cylinder the solution going out of the bottle via the needle can be collected and measured This volume represents the volume of methane in the biogas A pinch of the indicator thymol blue can be added to determine when the solution of sodium hydroxide has to be replaced It is recommended to wear gloves lab coat and safety glasses CCN Micro AD Phase 2 Report 23 August 2010 36
23. e and decide on further increases in feeding rate based on the prevailing VFA concentration o When the VFA concentration exceeds 1000 mgCOD L the pH should be checked A pH drop below 6 5 should be prevented to avoid the risk of methanogenic inhibition due to non neutralized VFA o When the VFA concentration exceeds 1000 mg COD L and the pH does not fall below 6 5 reduce the feeding rate by 2 kg d and wait for one week Use the VFA concentration to decide on further increases in feeding rate o Ifthe pH falls below 6 5 alkalinity e g CaCO3 should be added accompanied by a reduction in the feeding rate by 5 kg d Wait until pH and VFA are back to required values and increase from this moment the volumetric feeding rate with steps of 3 kg d only o If for some reason the pH has dropped below 5 5 it is recommended to restart with fresh sludge Start up is completed if the design volumetric feeding rate 25 kg m d is reached and if during one week the VFA has been below 500 mg l 4 2 3 Start up protocol applying only pH analyses It may not be possible to measure VFA on a weekly basis but only the pH The disadvantage of controlling the start up with the pH is that there is not necessarily an immediate pH response to a increase in VFA It is possible that VFA levels are already too high while the pH is still acceptable depending on the buffer capacity of the reactor contents Even a relatively small pH drop may indicate acidification a
24. easure of the concentration of an ion or multiple ions in solution Similarly to N normal concentration it represents the molar M concentration of the charge of the ion s in question Milli means 10 and therefore 1000 Meq is equal to 1 N and if the charge of the ion is 1 such as in the case of acid it is also equivalent to 1 M CCN Micro AD Phase 2 Report 23 August 2010 35 9 LeAF Annex 2 Measuring methane content of biogas using sodium hydroxide There are several ways to measure the methane content of biogas using sodium hydroxide solution The methods are based on the principle that CO dissolves in the sodium hydroxide solution and the methane remains in the gas phase Therefore the biogas volume after contact with sodium hydroxide solution represents the volume of methane in the initial volume of biogas The following method is an example of measuring methane content using sodium hydroxide solution Materials Bottle rubber cover syringe needle about 3 sodium hydroxide solution Measuring cylinder ndicator thymol blue Method A bottle should be prepared e g 0 5 L bottle filled with certain volume e g 250 ml of 1 3 or 1 M sodium hydroxide solution and closed with a rubber cover Then it should be hold up side down and a small syringe needle should be put through the rubber Via the needle a small amount of solution will go out of the bottle Then keeping the bottle up side down with a syring
25. ecking for leakages and blockages 5 1 1 Substrate The food waste kitchen waste is composed of the food leftovers and the biodegradable waste from food preparation It does not include all biodegradable household waste only biodegradable food waste Moreover the feed to the digester should be of good quality and not contain inert material and or inhibitory contaminants Examples of inert or unwanted materials are e sand or grit e plastic e g packaging material e objects e g cutlery e elastics Inhibiting components are generally not present in food waste However it is important that the feed has a more or less constant and balanced composition 25 kg of food waste is fed each day which is likely to be food waste from at least several households and thus it is assumed that the composition in food waste will not strongly fluctuate or be out of balance Excessive amounts of one type of food waste are not preferred 5 1 2 Shredder and pasteurizer The shredder pasteurizer and their connections should be checked for blockages or leakages regularly Only feed of a good quality i e contamination free should be put through both pre treatment units Moreover in relation to the HACCP plan and ABPR compliance it is important that temperature and time are logged during operation of the pasteurizer Most shredders will need to receive liquid to work properly This additional flow will increase the volume of the feed The required a
26. eeding tima the inceulum should be replaced Replace inoculum 9 LeAF Figure 4 1 Decision support scheme for start up of anaerobic digester using both VFA and pH measurements In addition to the guideline presented in the decision support scheme the following comments are made The initial feeding rate kg food waste m day is set at 20 of the reactor design feeding rate 25 kg m d that is 5 kg food waste m d According to the decision support scheme the interval is increased remains constant or decreased based on weekly analysis of VFA Different methods for VFA determination will lead to different concentrations and or units of measurement It is recommended to use the pilot experience for refining of the VFA concentration limits specified in O the decision support scheme CCN Micro AD Phase 2 Report 23 August 2010 15 9 LeAF o During the start up it is important to measure the pH regularly to verify the pH is 7 0 7 5 During the first week of start up it is recommended to measure the pH frequently i e at least daily If pH drops below 6 5 it is recommended to reduce or postpone the feed for one week and add alkalinity in the form of calcium carbonate CaCQs o f after one week of daily feed the VFA is below 500 mg COD I the feeding rate can be increased with 2096 of the design feeding rate 7 5 kg d o If the VFA is in the range of 500 1000 mgCODI L wait one week before increasing the feeding rat
27. enance records to be stored on site Batch progress sheet monitored to show position of each batch daily Batch progress sheet monitored to show position of each batch daily Daily inspection and findings recorded in site diary the beginning of the process and reprocessed Investigate cause of failure and raise a non conformance report Recalibration of temperature probes Investigate causes of failure Reprocess waste if required In the event of batch cross contamination the batch will be returned to the start of the process In the event of batch cross contamination the batch will be returned to the start of the process In the event of cross contamination the contents of the anaerobic reactor will be returned to the start of the process 31 computer Details of all not conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken Daily review of temperature data by project manager Daily review of records by site supervisor Weekly review by project manager Daily revie
28. ges to regulation CCN Micro AD Phase 2 Report 23 August 2010 CCP 23 Final product to pass all bacterial tests CCP 9 Final product not to be cross contaminated with untreated waste CCP 24 HACCP plan review to ensure fit for purpose Temperature monitoring over time Data stored on computer Monitoring during loading and movement of materials Daily site inspections and findings recorded in site diary In the event of failure of a batch due to bacterial contamination it will be taken off site to a suitable licensed disposal facility or processed again from the start of the factory In the event that material becomes contaminated it will be processed again from the start Non conformance report raised Immediate action will be taken to correct any issues relating to batch failure In the event that material becomes contaminated it will be processed again from the start Non conformance report raised 33 All testing records will be dated kept on site and clearly linked to batches Details of all non conformances recorded in site diary along with records of actions taken Details of all non conformances recorded in site diary along with records of actions taken All records will be checked weekly by project manager Final product analysis Daily site inspections by site supervisor Weekly inspection by project manager Initially ongoing review of HACCP b
29. he end of a control failure Weekly inspection by T building by vehicle movements liquids that h f th k l Details of th t or liquids that have Stockpiles of material in the Waste reception required of the working day etai So e project manager not been cleaned corrective action and processing area to be shaped and kept up by staff or tidy using the loading shovel on a daily recorded vehicles basis Retraining of site Processing equipment to be cleaned weekly staff in procedure using a power wash as required Disciplinary All catering waste delivery vehicles to have procedures wheels and any contaminated body work washed before leaving building Company vehicles to be cleaned on a weekly basis relevant Site loading shovels to be cleaned weekly using a power wash Spillages in outside yard to be cleared immediately Bays to be cleaned with power washer after emptied every time And the integrity of seals to sides and backs of bays checked Wheel wash to be cleaned out every 2 weeks Staff and vehicles to pass through wheel foot wash when moving between dirty and clean areas Maintenance of Loss of records 1 3 monthly re calibration of probes carried CCP16 3 monthly checks 1 In the event of a breakdown Contract with Final product monitoring caused by temp out by suppliers on contract Temperature scheduled on probes in the probes suppliers analysis equipment probe failure probes to be pasteurizer
30. iable substrate such as food waste and sugars to the anaerobic digester Careful start up and correct process operation are the key to avoiding acidification problems Acidification is usually detected because of a drop in pH and or and increase in VFA concentration The quantity of gas produced is usually not a good indicator for detecting acidification because during acidification initially more CO is produced which compensates for the lower methane volume When a lower gas production is noted it is usually too late to reverse the process If gas composition is continuously measured the CO fraction of the biogas can be used alongside pH and VFA measurements to monitor digester stability Depending on the buffer capacity of the reactor contents it is possible that VFA levels are already too high while the pH is still acceptable This means that even a relatively small pH drop is a reason to reduce or postpone feeding as it could indicate the start of acidification When a large pH drop is observed it is usually too late to intervene Measuring VFA concentrations is a better method to monitor digester stability but is more expensive and more time consuming and for that reason it will probably not be done before each feed This leaves pH as the only parameter that is monitored before feeding and therefore it is indispensable to be very careful with increasing the amount or changing the type of feed When acidification is still not in its final
31. is allowed for 24 h There should be pest control and there should be clean and unclean areas which are physically separated Cross contamination of material in clean and unclean areas should not be possible at all 5 2 Monitoring guidelines 5 2 1 Analysing parameters The monitoring of the process performance during start up is described in chapter 4 After the start up period is finished analyzing certain parameters remains essential for keeping track of digester performance Depending on the stability of the process over time the process conditions should be monitored daily or weekly in order to evaluate whether the reactor is performing as expected The parameters to be analyzed may be different for the pilot plant and for the other micro AD plants The following parameters are useful to analyse e pH e VFA pilot plant e biogas production CCN Micro AD Phase 2 Report 23 August 2010 21 9 LeAF e biogas composition e temperature e pathogens Sampling is performed just before feeding of the reactor Sampling ports can be used to extract a small volume from the digester contents In general measuring pH temperature and to some extent biogas production and composition is recommended in all cases For the pilot plant it would be useful to analyse in addition the VFA and the biogas production and composition more elaborately In addition alarms and warning devices may be installed to alert for toxic gas H2S and CH foam and
32. lean area Placement of all system components should be well thought about For transport of material it is most convenient to have all equipment close together but at the same time the separation between clean and unclean areas should be respected Available space and the movement of people and materials are important factors in deciding the layout also because of safety issues and cross contamination of the clean area by movement from the dirty area CCN Micro AD Phase 2 Report 23 August 2010 8 C 9 LeAF 3 Commercial component guide LeAF subcontracted the company Landustrie Sneek B V to provide a list of components suitable for the micro AD system Table 3 1 next provides suitable components possible suppliers manufacturers alternative manufacturers and component details Next to the information received from Landustrie some additional information has been included mainly in the column of alternative equipment suppliers It was intended that all the components be off the shelf and for the total cost of the system to be in the region of 5000 but this goal has yet to be attained Equipment for monitoring the reactor performance contents is not included in this component list instead they are described in the section on monitoring Please note estimated costs are all in Euro s CCN Micro AD Phase 2 Report 23 August 2010 9 Table 3 1 Component guide Feed storage Transport of feed to shredder Shredder M
33. liquid from the digester or the introduction of oxygen in the digester Leakages could occur because of malfunctioning sampling ports and safety valves at pipeline connections or because of damage to materials or corrosion It is assumed that leakages can be prevented if standard procedures for plumbing and gas fitting are followed 5 4 6 Mixer failure Insufficient mixing could be due to failure of the mixing equipment This may be caused by failure of the equipment itself or by a too high solids content of the digester 5 4 7 Low gas production The biogas production may be lower then expected based on the applied feeding rate This can have multiple causes First of all the digester may be acidified characterized by a low pH see section 5 4 1 Secondly a too high concentration of VFA may be present inhibiting methanogens while the CCN Micro AD Phase 2 Report 23 August 2010 26 9 LeAF pH is still neutral This situation is related to the former and this situation may result in acidification of the reactor For troubleshooting of both situations section 5 4 1 is referred to The applied loading rate may also be cause for lower biogas production than expected There is an optimum in the loading rate A too high loading rate may result in a too short retention time of substrate in the system whereas a too low loading rate does not use the full digester capacity The latter is characterized by low VFA concentration in the digester
34. mount of liquid depends on the type of shredder used and on the composition of the waste e g presence of soup or sauce For kitchen sink food waste disposers such as the Insinkerator water consumption is reported to range from 1 to 4 5 litres per person per day University Karlsruhe 2006 A study was done with shredding of different types of vegetables resulting in water consumption figures of 5 6 tomato to 22 4 cauliflower leaves litres per kg wet weight It is likely that collected food waste will need less water because the material to be processed will already be decomposing and is also expected to contain cooked soft materials Nevertheless after ease of use water consumption could be a decisive point in the choice of a particular shredder CCN Micro AD Phase 2 Report 23 August 2010 20 9 LeAF For shredding either water can be used or digestate liquid The latter would have the advantage of containing some alkalinity but it might be impractical because it involves transport of the liquid from the clean side to the dirty side of the installation 0 1 3 Feeding the digester Feeding of the reactor should be performed daily In the proposed design the digester is loaded with 25 kg shredded food waste day This amount is ideally fed in small portions during the day However for practical reasons the amount can be fed in one or two portions during a day What is most important is that the digester is fed regularly 5 1 4 Dige
35. n is needed 2 3 3 Biogas Before usage the biogas quality is normally upgraded with a biogas cleaner in order to remove impurities like hydrogen sulphide The needed extent of upgrading depends on the actual biogas quality and the specifications of the equipment in which the biogas is used For example a special biogas boiler should be able to cope with raw biogas CCN Micro AD Phase 2 Report 23 August 2010 7 7 9 LeAF The biogas holder is used for collection of biogas If needed excess biogas can be stored but from a small scale digester of 1 m the amount of gas that can be obtained is limited Because energy is required for hygenisation pasteurization of the substrates and for heating the digester system it would make most sense to use the produced biogas for these processes 2 4 Plant layout In order to comply with the ABPR the plant area should be divided into a clean area and an unclean area It is stated in the regulations that preferably there should be some form of physical separation between these two areas e g a wall To prevent access by birds and vermin the reception area should be fully enclosed that is reception of waste should take place in a building However for very small facilities covered leak proof and lockable containers can be used instead The unclean area including the reception area should be easy to clean and disinfect and it should not be possible for liquids from the unclean area seep to the c
36. n site collect pilus bu An house number Analysis results metal plastic and a E operating R E reviewed by Project site processing bin glass which could 4 Bins seen to contain a high level of procedures for manager contaminate final contamination will be rejected at the kerbside catering product kerbside waste Visual inspection of 5 Staff training on what is suitable for the delivered product by composting process Processing staff Guideline on acceptable levels of contamination and staff training Delivery of Material may be Catering wastes are delivered in purpose CCP 2 Catering All delivery 1 Customers will be informed Details of all non All deliveries will be Catering Waste exposed to designed vehicles by collection staff waste deliveries vehicles will be of all site procedures before conformances monitored by site to facility scavenging birds 2 Customers delivering waste direct to site to will only be monitored by site trading with the company recorded in site staff daily and animals be instructed on the requirements for accepted if staff and any non Starts diary along with containing the waste Reception of catering takes place inside with the doors closed or in case of small customers may drop off amounts of kitchen waste covered leak 3 If there is a problem with proof and lockable containers are used for delivery vehicle suitability reception area customers will be contacted Pest control measu
37. nd base Balance Procedure The procedure consists of the following steps 1 Centrifuge 5 minutes at 5000 rpm the sample or filter it folded paper filter 2 Keep the supernatant filtrate 3 Puta 250 ml beaker on a balance and set it to O 4 Use a pipette to put a quantity V ml of the supernatant filtrate into this beaker This amount of sample should have a maximum of 3 meq of VFA If the VFA concentration is completely unknown this is a matter of trial and error 5 Add demineralised or distilled water to reach a volume of 100 ml 2100 g on the balance 6 Titrate the liquid with HCI until reaching pH 3 0 write down how much HCI was used a ml 7 Transfer the content of the beaker into the round bottom flask 8 Add some pumice stone and connect the flask to the cooler 9 Boilthe liquid for 3 minutes 10 Switch off the flame and wait for 2 minutes 11 Pour the liquid back into the beaker 12 Immediately titrate with NaOH to pH 6 5 write down how much NaOH was used b ml CCN Micro AD Phase 2 Report 23 August 2010 34 9 LeAF Calculation The following values are needed Quantity of sample used V from step 4 Quantity of HCI used a from step 6 Quantity of NaOH used b from step 12 bx101 a 100 First calculate the value of C C bx101 a 100 99 23 T l 100 Then calculate the concentration of fatty acids in meq per liter VFA meq l Cx Meq is an abbreviation for milliequivalents which is a m
38. nd caution with feeding rate should be taken When a large pH drop is observed it is usually too late to intervene Nevertheless the following scheme is proposed for start up of the digester with only pH measurements The same principle as above can be used only the pH determines whether the feed rate has to be increased maintained decreased or stopped Because problems in anaerobic process during start up of the digester are likely not directly observed when using the pH it is recommended to start up more carefully It is likely to take more time compared to the pH VFA approach as described above Pilot plant testing should reveal the applicability of only pH analysis for start up of food waste digester Moreover it is recommended to measure the pH frequently in order to detect as soon as possible pH decline in the system CCN Micro AD Phase 2 Report 23 August 2010 16 Set feeding at 5 kg d Apply current feed 9 LeAF for one week No Increase feed by Design feed 2 5 kg d reached Yes v Maintain design feed Regularly check pH and VFA Yes Reduce feed by 2 5 kg d S END Stop feeding Add alkalinity 6 5 pH 7 5 Stop feeding Replace inoculum If it is felt that this strategy takes too much time the inoculum should be replaced Figure 4 2 Decision support scheme for start up of the
39. ng liquid from the digestate more on digestate in 5 1 4 Recycling part of the liquid digestate to the process also increases process stability Secondly the substrate needs to be pasteurized at 70 C for at least 1 hour Shredded substrate is transported to the pasteuriser by hand by mechanical movement pump screw conveyor or under gravity The pasteurizer is equipped with a temperature control and monitoring device to keep a stable temperature of 270 C and to demonstrate that the temperature and time requirements were met The pasteurized material is pumped to the digester If the pasteuriser can be placed at a higher level than the digester feeding from the pasteuriser could be done by gravity This depends on the possibilities of emptying the pasteuriser An advantage of feeding by means of a pump is that pumping makes it easier to gradually feed the digester over a period of time 2 3 2 Digester The digester is a gas tight tank with several openings feed input digestate output biogas outlet gas pressure safety valve mixer opening sampling ports optional drain outlet sensor ports optional All connections are liquid and gas tight The digester is heated in order to facilitate the digestion process Ideally the digester content is mixed regularly When feeding with a certain amount of new substrate the same amount is removed from the digester by allowing an overflow of the digestate while preventing short cutting The digest
40. of the feed replacing kitchen waste o If for some reason the pH has dropped below 5 it is recommended to restart with fresh inoculum Start up is completed if the design feeding rate 25 kg d is reached and if during one week the pH is in the range of 7 0 7 5 4 2 4 Monitoring parameters other than pH and VFA During start up careful attention should be paid to the evaluation of parameters for monitoring the treatment performance and process conditions In addition to the pH and VFA measurements the biogas production and biogas composition may be used to evaluate reactor performance Biogas with a methane content of about 55 or more indicates a good process performance Lower methane concentrations and high carbon dioxide concentration may indicate acidification and a reduction of feeding rate may be applied 4 3 Alkalinity A good buffer capacity of the reactor contents prevents a severe pH drop in the reactor when acids are produced The processes in the digester should keep themselves balanced but it is possible that in certain cases the natural buffer capacity of the digester is exceeded and the pH drops too much When this happens the start up decision support scheme recommends the addition of alkalinity to increase the pH of the reactor contents Addition of alkalinity is usually done in the form of lime If that is not an option digested cow manure could be used but that would involve the replacement of quite a large part of the
41. on of 10 m gas bag is 2000 mechanical under overpressure protection up to 5 mbar is 1450 alternatively siphon and water lock are used connection materials 200 Another alternative is Chinese biogas bags e g Chongqing Xinshui Machine Manufacture Co Ltd a Digester heating system would resemble domestic central heating system including all equipment normally used in a central heating system Steel tubing placed along the reactor wall takes the function of the radiators Fully automatic regulation of the system could cause a price increase of 1000 2000 Euros Alternative biogas water heater from China Chongqing Xinshui Machine Manufacture Co Ltd 3 Single double Gas bag 10 m pheeas bud Flexible walled operating length 3 5 m 21 Biogas holder Y Westech Dependent on depends on l 2000 5000 legislation ia al SIRO 8 membrane pressure up to diameter 2 m 50 mbar Thecogas AVTI qm W 9 LeAF 4 Start up of anaerobic digester The purpose of this chapter is to describe the start up of the digester It is not a construction manual for the digester this will be an outcome of the test build phase of the project This chapter explains the steps to be taken after construction of the plant to get the digester running In addition the start up protocol will be refined based on the outcomes of the pilot plant tests 4 1 Preparation Checking hydraulics and gas capture Before start up the hydraulics and gas tigh
42. organisms are to be maintained Methanogenic bacteria that may be present at relatively low concentrations in the seed sludge inoculum should be enriched in the sludge The basic approach is that the feeding of the reactor is increased step wise based on the rate of conversion of feedstock As described in phase 1 Volatile Fatty Acids VFA are intermediate products in the anaerobic digestion process in which acetic acid is used by methanogens for biogas production The VFA concentration in the digester should be kept low thus preventing inhibition of methanogenesis To provide optimal conditions for the methanogens the step wise increase in feeding rate is determined by the VFA concentration and pH in the digester An increase in VFA concentration can result in a pH decline depending on the buffer capacity Moreover the VFAs are more toxic to the methanogens at low pH Therefore the VFA concentration and pH are important for assessing the performance of digester and it is recommended to analyse both during start up However when this is not possible pH may be used solely to determine reactor performance provided that a safety factor is applied because it is a less reliable method 4 2 1 Filling the reactor with inoculum To start fill the digester with water cow manure and or anaerobic slurry ideally from a digester that is operating well Again ensure that the reactor is gas tight The best results will be achieved if the anaerobic slurr
43. out 3 m biogas d It should be emphasized that the design in Figure 2 1 is conceptual For example the way to keep a certain liquid level and gas pressure in the digester depends on the way the digester is configured CCN Micro AD Phase 2 Report 23 August 2010 5 9 Zr Je o juoo dwa 5 JepJooey dwa Y L J0yeoipur dwa J L 9A E YOOYD Da SSOA p ejos Jaysobig jeuondo uod Buijdues zt Jesunejsed MK eDeJojs ejejsebiq 1 abesojs pee WA dung Jeppeuus esn ejejseDiq 4 ANN AXN m Es MK I ue v QUU pod Buidues Lo Safety valve oDeJojs ojejsoDip woy seboig ee J o XIN J109 13 eM JOH Jepjou seDoig PS Buiueao seDoig sesn seb JeujQ seb jsneux3 DS anjen Ajayes OX Safety valve Figure 2 1 Proposed digester system Simplified process flow diagram not to scale dashed connecting lines slurry liquid flow can be operated manually CCN Micro AD Phase 2 Report 23 August 2010 7 9 LeAF 2 3 Process description 2 3 1 Pre treatment equipment The feed food waste is stored in a closed container From the feed storage the food waste is transported to a shredder The shredder should reduce the particle size to a maximum of 12 mm in order to ensure Animal By Products Regulations ABPR compliance for catering waste in UK see as well phase 1 report For shredding extra liquid is needed which can be achieved by usi
44. phase meaning the pH is above 5 5 the acidification may be reverted by reducing the feeding rate if necessary to zero see startup protocol and by adding alkalinity for example adding CaCO3 to increase the pH to 7 decreasing the toxicity of the acids for methanogens pH and VFA analysis in time should tell whether acidification could be stopped and recovery of the digestion process was possible If this is the case the feeding rate can be increased again CCN Micro AD Phase 2 Report 23 August 2010 25 9 LeAF If the pH is below 5 5 it is recommended to restart with fresh inoculum as the methanogenic activity may have been completely lost and follow the complete start up procedure 0 4 2 Foaming Foaming is a common problem with many digesters It occurs in many forms and no general prevention or remediation rules exist When a foam layer is stable and reaches high enough it can block the gas outlets causing a pressure increase in the digester Remedies that can be tried are mixing the top layer or spraying water on the surface Changing the feed composition if possible can also reduce foaming 5 4 3 Floating layers Scum layers are formed by material floating on top of the liquid in the digester When thick enough this floating layer can cause blockages of effluent pipes and biogas outlets Fat is the most common cause of scum layer formation but also light materials such as straw can start to float Different floating mate
45. r 3 a component list is provided with details of relevant components based on recommendations of an experienced constructor The proposed start up of the digester is given in chapter 4 followed in chapter 5 by an operational manual in which daily operation monitoring guidelines and troubleshooting are discussed The last chapter chapter 6 includes an HACCP plan outline based on existing experiences by a CCN s members site which processes food waste in line with ABPR criteria CCN Micro AD Phase 2 Report 23 August 2010 4 7 9 LeAF 2 Description of the Micro AD plant 2 1 Introduction The micro anaerobic digester AD plant is a small scale system designed to treat kitchen waste in this report also referred to as food waste It is highly biodegradable material and therefore in principal suitable for anaerobic digestion For this case study it is assumed that there is sufficient kitchen waste available for feeding the digester The digester is designed such that it is relatively easy to build operate and maintain and that it fulfils the requirements set by legislation The overall system includes the anaerobic digester and its required auxiliaries 2 2 Conceptual design The conceptual design of the system is given in Figure 2 1 The digester has a volume of 1 m When operating at a conservative retention time 40 days the digester would process around 25 kg kitchen waste d approximately waste of 10 15 households and produce ab
46. r the entire digester The best practical way to carry out a neutralisation will maybe become clear during the pilot but in any case it is recommended to be cautious when adding chemicals to the digester Chemicals that increase alkalinity can also be used in a preventive way by adding a small amount with each feed It is impossible to predict the amount that should be used it should be just enough to CCN Micro AD Phase 2 Report 23 August 2010 18 C y NZ LeAF make stable operation easier It is possible to test a small portion of the digester contents by mixing it with a lime type product and see if and when pH increases above 8 Any amount of lime that does not increase the pH of the reactor above 8 is safe CCN Micro AD Phase 2 Report 23 August 2010 19 9 LeAF 5 Operational manual This chapter describes the daily operation of the digester the guidelines for monitoring the most important parameters and troubleshooting of the most common problems This chapter could be revised especially the section on troubleshooting after implementing and testing the pilot system in phase 3 The maintenance of the auxiliary equipment of the anaerobic digester system are not described in detail in this chapter as it is expected that this is done according to user manual provided by the manufacturer of the specific equipment 5 1 Operation The daily operation of the system involves feeding collecting digestate maintenance and ch
47. res in place within facility and reminded of their Bait boxes around the site and inside the responsibilities building Driver to complete a check sheet 4 Site will not accept further defect report weekly before leaving site with deliveries from offending collection vehicle To ensure that the vehicle company if they do not is suitable for purpose correct problems Deliveries from 1 Site staff to visually check load before CCP 3 Level of Daily monitoring 1 Loads which are heavily Details of allload Analysis of end customers acceptance contamination to of catering waste contaminated will not be put rejection will product for CCN Micro AD Phase 2 Report 23 August 2010 28 2 Site is not open to random Rer record of actions deliveries only approved taken transported in a conformance suitable vehicle recorded in the site diary other materials not suitable for digestion process Exposure to Catering waste animals and birds Low levels of contamination to be removed by site operatives A load which is heavily contaminated will be rejected from site Guidelines for acceptable levels of contamination and training given to site operatives Guidelines issued to customers who supply catering waste Site operatives to visually inspect waste prior to processing All catering waste kept inside the building in case of small amounts of kitchen waste covered leak proof and lockable con
48. rials can cling together causing a dense layer Adequate mixing of the reactor contents can prevent the formation of these layers and mixing can also be used to destroy the scum layer when it forms However mixing does not bring guaranteed success If scum layers are left for too long they can dry out and form a crust that is difficult to remove Ideally mixing is around a horizontal axis which can break the through the surface scum layer and also mix sediment into the tank 5 4 4 Sediment layer Sand grit and other inert materials can form a sediment layer on the bottom of the digester This layer can cause blockages and wear on the mixer but in any case it reduces the effective reactor volume the volume used for anaerobic digestion Introducing this type of materials in the digester should be avoided If a sediment layer is formed it should be removed before damage occurs or before the effective volume is reduced too much Ideally mixing is around a horizontal axis which can break the scum layer and also mix sediment into the tank 5 4 5 Blockages Leakages Blockages in the hydraulic system may be caused by large particles in the system In this case the functioning of the shredder should be checked Blockages of the hydraulic and gas pipe lines may be caused by foaming floating or sediment layers or as described in section 5 4 2 5 4 3 and 5 4 4 Leakages in the digester could result in the release of biogas to the atmosphere escape of
49. state When a certain amount of food waste is fed to the digester the same amount of digester contents digestate should be taken out e g by pumps or overflow which is stored in the digestate storage unit The digestate should be stored to allow further anaerobic stabilisation Storage time will depend on regulations and odour of the digestate After this it can be used Separation of the solid and liquid fraction of the digestate would allow for recycling of the liquid fraction to the feed providing extra buffering and alkalinity The solid fraction could be composted with green waste to facilitate ease of handling The excess liquid fraction could be applied as a liquid fertiliser Settling might be sufficient for solid liquid separation If not some mechanical separation could be applied or it might be decided to use the digestate without separation 5 1 5 Biogas storage and capture A careful daily inspection of the gas production is necessary Bad odours may indicate leakages in the system The biogas storage should be sufficient to store the expected production of biogas depending on the biogas use chosen and the biogas cleaning device should be maintained according to instructions of manufacturer 5 1 6 Hygiene In the APBR hygiene is a very important aspect Food waste should be stored in a building or in case of small scale system a covered leak proof and lockable container is sufficient Storage in the reception area normally
50. tainers are used Catering waste that are destined for processing in the factory will be processed within 24hrs of delivery Pest control within the facility Housekeeping and hygiene procedures Preventative maintenance system to reduce processing equipment failure Repair and maintenance back up for processing equipment breakdown Removal of stored catering waste to a suitably licensed facility in the event of equipment failure for in excess of 48 hours Process logs kept detailing waste deliveries and when waste processed Staff training on procedures and induction All catering waste are stored on site within a building or in case of small amounts of kitchen waste covered leak proof and lockable containers are used Catering waste and category 3 animal by products that are destined for processing in the factory will be processed within 24hrs of delivery Housekeeping and hygiene procedures Preventative maintenance system to reduce CCN Micro AD Phase 2 Report 23 August 2010 be within an acceptable level specified in site operating procedures for customer deliveries CCP 5 Catering will be processed within 24hrs of delivery CCP 6 All catering waste to be stored inside the building CCP 7 Pest control system in place at all times CCP 8 Preventative maintenance schedule in place and emergency repair and maintenance support available CCP 5 C
51. tection tubes are available for analyzing for several gasses e g CO5 concentration but not for methane With the CO measurement indirectly the percentage of methane gas can be calculated assuming biogas comprises for almost 100 of these two gasses Also H2S can be measured with gas detection tubes Portable gas analysers are available for multiple gasses such as carbon dioxide CO2 methane CH4 and hydrogen sulfide H2S for example from Geotech UK or from BW Technologies If needed biogas sample can also be sent to a commercial laboratory for measurement of the biogas composition 5 2 6 Dry matter and organic matter Analysis of the dry matter and organic matter content of the digestate gives information on the solids content of the reactor the mixer will be designed for a maximum solids and can also be used for estimation of the amount of viable biomass The ash content the non organic fraction of the dry matter indicates the amount of inert material in the digester In laboratories the dry matter and organic matter are determined by placing samples in a drying oven at 105 C and then in an ash oven at 550 C Small compact systems for dry matter determination are commercially available e g Halogen Moisture Analyzer 5 2 7 Pathogens According to the guidance on ABPR Defra 2008 in the phase of plant validation samples have to tested for Salmonella Testing for Enterobacteriaceae is not required when food waste is digested
52. tems can often be easily accessed e g because the top is connected to the body by means of a flange This should be taken into account during construction When opening the digester inhalation of biogas should be avoided and careful ventilation is needed before entering the tank CCN Micro AD Phase 2 Report 23 August 2010 27 478 9 LeAF 6 HACCP outline This chapter gives a Hazard Analysis and Critical Control Point Plan HACCP outline for anaerobic digestion of kitchen waste based on the delivered HACCP by CCN It will support the preparation of a HACCP for a specific situation Table 6 1 HACCP outline for kitchen waste digesters of CCN where there is an assumption that the group which is responsible for processing food waste collects the material itself Step Collection of Product Instructions given to householders about CCP 1 Levelof X Constant 1 Sticker placed on bin Refused bins Analysis of end domestic contaminated with what wastes are acceptable in the bins contamination to monitoring by indicating reasons for no recorded by product for Catering waste other materials not 2 Collection crews to inspect catering waste pe within an collection crew of Collection collection staff if contaminants by by Company suitable for bins prior to loading acceptable level _ bins as they 2 Visit to householder if possible to identify approved laboratory staff digestion such as chant cele ted Vibe removed specified i
53. the contents calibrated every 3 will not be pumped into the Records of Daily inspection of digester If the digester may be contaminated with non pasteurized material then the effluent from the Full batch digester will be stored and ccountability due batch pasteurized a second to numbering months calibration checks temp log by project manager CCN Micro AD Phase 2 Report 23 August 2010 32 Testing for Salmonella Final product moved off site Review of HACCP plan Final product fails log reduction testing for required bacteria due to cross contamination or failure to reach temp barrier resulting in failure of batch Cross contamination of final product by untreated material Failure of any of the CCP s to prevent system failure 1 Temperature monitoring 2 Time monitoring Final Product will leave from the clean area doors which are separate from waste reception Loading shovel to be washed go through wheel wash and use designated final product bucket if material being loaded to go off site Flow of material through the site does not allow for cross over of materials Signage Staff training During first run through the system will be monitored continually to assess for performance All breakdowns in process will be recorded in site diary and the necessary people informed All staff will continue with Professional Development Training and pass down all relevant chan
54. this document Measurement of organic acids with Dr Lange kits may give a good indication of the VFA concentration and is relative easy to perform 5 2 5 Biogas First of all an indication of biogas production can be made based on the contents of gas collection bags or system which indicate the amount of biogas produced although this is only applicable for biogas storage units that will expand when the biogas amount increases However for the pilot plant and perhaps as well for the other anaerobic digesters more insight in the biogas production is required For this purpose gas flow meters able to measure gas flows in the order of 3 m d would be suitable The biogas composition depends on the performance of the anaerobic digester If the process runs well about 60 methane is present and about 40 CO and for minor percentages moisture and other components However when acidification processes occur in the digester initially the biogas production may continue but the composition changes to lower amounts of methane and higher amounts of CO Therefore it is important to analyse the biogas composition next to biogas production This can be measured in several ways a very low tech way is the use of diluted sodium hydroxide solution A method to determine the biogas composition with sodium hydroxide solution is given in the appendix Another more accurate way is to use gas analysers or gas detection tubes e g from Drager Gas de
55. tness of the system should be checked This can be performed by filling the reactor with water and verify the system e g loading sampling and discharging works correctly Gas lines should be checked to ensure they are gas tight This can be done by filing the digester with water to the point that it would normally be filled with slurry and increase the gas pressure by blowing into a pipe then leaving the system for 24 hours to see if there is a loss of pressure Using good quality inoculum Inoculum seed sludge should be taken from successfully operating biogas plants for example digested manure or digested sewage sludge Ideally digested kitchen waste would be used as then the microorganisms responsible for biogas production are already adapted to the substrate Digested manure generally has a relatively high buffer capacity which is an advantage when starting up a digester with quickly acidifying materials such as food waste If no digested materials are available fresh cow manure could be used but then start up will be slower The presence of methane producing bacteria is vital for start up and the higher its methanogenic activity the more suitable an inoculum is Biomass originating from other types of processes non methanogenic such as compost are not suitable as an inoculum as they do not contain the right groups of microorganisms 4 2 Start up procedure During start up optimal conditions for growth of methane producing micro
56. tralised Micro Anaerobic Digestion project by the Community Composting Network CCN The overall aim of the project is defining a suitable anaerobic digester AD to be able to utilise anaerobic digestion as a technology in the decentralised treatment and utilisation of bio wastes The system should be simple and robust comply with regulations and produce sanitised effluent or digestate suitable for use in horticulture The overall project is divided in three phases In phase 1 suitable decentralized AD systems for CCN members in the UK within the scope specified by the Steering Group of CCN are identified and described Phase 2 comprises of the development of a suitable decentralized AD system for the scope specified by the CCN Steering Group and providing a commercial component guide and operational manual for this system In phase 3 the construction and testing of at least one pilot plant is foreseen LeAF was contracted to work on phase 1 and phase 2 Phase 1 report has been delivered to CCN and precedes this report For a good understanding of the scope and aim of the overall project as well as the anaerobic technology identified systems required auxiliaries and proposed design of the AD this phase 1 report is referred to and we would recommend to people new to AD that you read the Phase 1 report first The phase 2 report presented here has a summary of the proposed AD design with key information from the phase 1 report In chapte
57. ure analyzer Halogen Moisture Analyzer Mettler Toledo Biogas Gas flow meter TXB Digital Gas Meters BELL Flow 780 excl vat lt 0 05 30 m h Systems DFM Variable Area Gas Flow Meters BELL Flow 70 excl vat minimum flow 0 2 m h Systems Transco Standard Domestic Meter BELL Flow 70 excl vat 0 12 6 m h Systems CO H2S Drager sampling device Fischer Scientific 350 Test tubes 60 80 10x Portable landfill Model GFM416 CH4 CO H2S Gas Data Ltd gas analyser Model GFM430 Flow CH4 CO2 H2S Portable biogas Biogas Check CH4 CO optional H2S Geotech analyser CH 3 NaOH solution plus bottles large NaOH method syringes etc see annex 2 Pathogens Pathogen test kit DelAgua Water Testing Kit DelAgua Thermotolerant faecal coliform count Information from Fischer Scientific catalogue 2008 2009 http www hach nl http www mt com http www gasdata co uk http www draeger co uk http www geotech co uk http www bellflowsystems co uk own laboratory Similar spectrophotometer from WTW would cost 2500 5000 euro plus 70 100 euro per box of 25 cuvettes Fischer Scientific catalogue However it appears they do not provide the organic acids determination CCN Micro AD Phase 2 Report 23 August 2010 24 9 LeAF Laboratory analyses can be expensive because of the high precision instruments accessories and chemicals involved Costs can be reduced by using second hand equipment On the
58. w by site supervisor Weekly review by project manager Batch numbering records will be maintained Final product analysis 9 Storage of final Cross Storage takes place in a separate closed CCP 21 Nocross Daily site In the event of untreated Details of all non Final product contamination with vessel This vessel is dedicated a clean contamination of inspections and material contaminating final conformances analysis material not at the vessel treated product findings recorded product the material will be recorded in site Daily inspections by Only treated material brought in to the with untreated in site diary processed again diary along with the site supervisor storage vessel material records of actions Vessel is separated from dirty area by faken Weekly inspection by concrete walling Signage in place the project manager Staff training Cleaning and Waste reception and processing area to be CCP 22 All items Daily site Any areas that have not been A non Daily inspections by hygiene contamination with swept daily and litter and debris cleared by of the cleaning and inspections cleaned or area causing a conformance to be the site supervisor material caused by the end of the working day This will prevent hygiene plan to be recorded in site problem will be cleaned raised in the event movement of solids Material being tracked around or outside the carried out as diary immediately or before t
59. y all site staff On verification of site HACCP will be reviewed 4 monthly 9 LeAF Annex 1 Determination of VFA with titration method Principle This method is to determine the lower fatty acids in aqueous solutions as an indicator for the volatile fatty acid content The pH of a clear sample is reduced to pH 3 with standard 0 1 N HCI During this process the hydrogen carbonate is transformed into CO and the lower fatty acids are transformed into their non dissociated form After boiling out of the CO by reflux distillation the solution is titrated to pH 6 5 with a standard solution of 0 1 N NaOH The lower fatty acids and other weak acids present are transformed into the dissociated form From the used amounts of HCI and NaOH the hydrogen carbonate alkalinity and the concentration of lower fatty acids can be calculated Note that N is used to signify concentration N stands for Normal which is similar to M for Molar however Normal is used for acids and bases and denotes the concentration of H or OH For example a 3 molar M solution of HCI is 3 N whereas 3 M solution of H2SO is 6 N because there are two H ions for every single H2SO mole Materials Reagents Hydrochloric acid 0 1000 N Sodium hydroxide 0 1000 N Pumice Equipment 250 ml round bottom flask with tapered ground joint Reflux cooler Gas burner Centrifuge at 5000 rpm or folded paper filter pH meter with heat proof electrode Titration apparatus for acid a
60. y digester wall Price indication is for first mentioned equipment not for alternative Storage for 2 days and density of waste lower than water i Depending on exact properties of the shredded waste a larger diameter could be needed This could be tested first Exact mixer type and size should be chosen together with manufacturer when digester dimensions are known i sampling could be done on digestate only But it is useful to have sampling ports for checking e g mixing efficiency Safety valve on digester is optional as pressure release valve on gas holder functions as general safety valve In case biogas pipeline is blocked digester liquid will be forced out so inside pressure would not rise too much In case it is expected that also effluent line might get blocked a safety valve on the digester is useful Different types of activated carbon exist which would have different saturation periods Impossible to predict amount and price depends entirely on personal choice for carbon type and replacement period Chinese alternative Shenzhen Puxin Science amp Technology Co Ltd Size of biogas holder is determined by the number of days you foresee to run the digester without biogas use and possibly by local regulations e g fire brigade Also holder type could be subject to local regulations i pressure release valve is integrated with biogas holder so no separate safety valve needed 1 Direct information from supplier Thecogas cost estimati
61. y was produced with kitchen waste This will mean that the microbes are well suited for metabolizing kitchen waste and the digester can be completely filled As the feed is added to the CCN Micro AD Phase 2 Report 23 August 2010 13 Q WW b full digester it will be necessary to remove the same amount of the digestate Where an innoculum that is not adapted for example when starting the reactor on cow manure kitchen waste should be first added in small quantities and mixed with more cow manure to ensure the microbes are able to adapt to their new food gradually Starting at about 50 of total liquid volume the food waste is added during start up procedure with no corresponding removal of digestate so that liquid and solids contents in the digester increase until it is full 4 2 2 Start up protocol applying both VFA and pH analyses Firstly the start up protocol is described when both VFA and pH of the digester contents are analyzed A guideline for the applicable feeding rate for first start up is given in the decision support scheme presented below The scheme provides an iterative approach to evaluate the increments in feeding rate CCN Micro AD Phase 2 Report 23 August 2010 14 Apply currant feed for one week Na VFA Ye Increase feed by x 5I mag 5 kid Design feed reached Maintain design Fead Regularly check pH and VFA VFA lt 1000 mg Shop feeding Ada alkalinity 6 5 pH 7 5 Siop f

CCN Micro AD report - The Community Composting Network

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