C   O   N   F   E     R   E   N   C   E     P   R     E   V   I    E   W                                                  ...
tem in order to minimize processing and one of the first 38 municipalities involved[contamination] disposal costs.”       ...
degrading at this point and are completely                                                                                ...
ferred to composting plants for stabilization prior to spread-ing in agriculture whereas the liquid is treated internally....
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2010 09 BioCycle Article on residential food waste in compostable bags going to anaerobic digestion

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2010 09 BioCycle Article on residential food waste in compostable bags going to anaerobic digestion

  1. 1. C O N F E R E N C E P R E V I E W Monday, October 18 Session: Organics Collection, Energy Production In Europe Presentation: Tools To Collect Organics, Diversion To Digestion And Composting Christian Garaffa, Novamont SpA EUROPEAN EXPERIENCE TOOLS TO COLLECT ORGANICS, DIVERSION TO DIGESTION S INCE the mid-1990s, food waste high water vapor transmission rates. This has been collected from house- enables the transpiration of wet foodSolid waste holds separately from yard trim- mings in Italy. The door-to-door waste, providing a weight and volume re- duction resulting in less waste to be col-management collection method allows for high capture and low contamination lected and treated. The water loss also re- duces initial fermentation, meaning lesscompany in rates. In recent years, some of these programs have implemented anaero- generation of unpleasant odors, a more hy- gienic bin, and overall reduced “yuck” fac-northeastern bic digestion (AD) as an initial processing stage, producing biogas from the organics tor (see “Intensive Source Separated Or- ganics,” April 2010).Italy operates and then composting the digestate. This article focuses on the case study of However, according to Walter Giacetti, environmental manager at ETRA, SSO di-two types of ETRA S.p.A., an Italian public company that manages the integrated water and mu-anaerobic nicipal solid waste collection and treatment service in an area of approximately 800digestion systems square miles in the northeastern region of Veneto. As of 2009, ETRA serves 63 munic-to process source ipalities with a population of 520,000 and collects 100,000 metric tons (110,000 tons)separated of organic waste annually. Within the boundaries of this territory,organics. organic waste is in a closed loop system, treated in a composting facility and two dif- ferent AD facilities operated by ETRA — a dry continuous flow system in Bassano del Christian Garaffa Grappa (Vicenza) and a wet two-stage sys- tem in Camposampiero (Padova). ETRA is constantly pursuing maximum recovery with minimal contaminants through the continuous monitoring of the collected feed- The anaerobic digestion facility in Bassano stocks, extensive information campaigns del Grappa treats separately collected and promotion of the use of compostable residential food waste using a dry bags for collecting organic waste. continuous flow process with three cylindrical digesters (center of photo). COLLECTION TOOLS, “CLEAN ORGANICS” The Italian system of intensive source version programs on their own do not de- separated organics (ISSO) involves fre- liver the expected purity and diversion quent food waste collection, allowing for rates. “The roll out of any residential pro- high capture of organics, and less frequent gram must be supported by extensive infor- residual waste collection, helping to opti- mation campaigns and tools which encour- mize the whole system. An important tool age participation,” he says. “We own and for ISSO is a 2-gallon vented kitchen pail operate the facilities where this material is used with compostable bags. Specific treated so not only do we want to reduce the grades of Mater-Bi ® compostable resin environmental impacts, we have a vested have a native starch content that allows for interest in optimizing all parts of the sys-BIOCYCLE SEPTEMBER 2010
  2. 2. tem in order to minimize processing and one of the first 38 municipalities involved[contamination] disposal costs.” in the initial phase of the “Clean Organ- ETRA constantly monitors the quali- ics” campaign, has about 44,000 inhabi-ty of collected materials to maintain op- tants and collects over 4,000 tons/year oftimum performance and allow for a organics. Its case is emblematic of how ittimely response to prob- was possible to reduce anlems should they arise. Figure 1. “Cleanup Organics” average rate of about 8Monitoring includes campaign flyer percent contaminationwaste analyses, looking through information andin particular at the total promotion of com-level of contaminants in postable bags. The datathe collected materials. in Figure 2 show how in Throughout the years, 2009, after the communi-ETRA has been manag- cation campaign, imple-ing an increasing num- mentation of a properber of municipal pro- monitoring system andgrams. While some involvement of local busi-municipalities didn’t al- nesses in promoting useways require com- of certified compostablepostable bags, others bags, contaminationhave had this require- dropped to less than 2.5ment since the creation percent, resulting inof the first organics col- avoided disposal of atlection programs in least 200 metric tons of1996. However, waste waste. The economic sav-analyses showed that ings for the city of Bas-about 15 percent of fam- sano were about €30,000ilies were still using con- (about $38,500).ventional polyethylene shopping bags Areas B, C, D (Figure 2) have curbsidefor collecting their kitchen scraps, prob- collection and showed the best results,ably because they were less expensive while the historic downtown area (A) re-and more readily available. The data sults are less striking because of the usewere further confirmed by waste analy- of centralized road containers (the his-ses at ETRA treatment facilities, which toric downtown accounts for about 10showed a worse quality compared to the percent of all kitchen organics collect-previous year. ed). Road containers commonly achieve To address the declining quali- lower capture rates and tend to have ty, an extensive campaign — higher contamination rates because of “Umido Pulito” or “Clean Organ- the lack of a direct link between house- ics” — was organized between holder and collection bin. Nevertheless, April and May 2008. The cam- in some specific situations due to space paign (Figure 1) was aimed at and logistical constraints, this option improving the quality of food can be preferred to curbside bins. waste collected by empowering citizens and therefore facilitat- BASSANO DEL GRAPPA DIGESTER ing the process of treatment and Opened in mid-2003, ETRA’s AD facil- recycling. ity in Bassano del Grappa treats sepa- Originally ”Clean Organics” rately collected residential food wastes was implemented in 38 of the 63 using a Valorga dry continuous flow pro- municipalities that ETRA serves cess. The resulting digestate is compost- and covered 71 percent of the ed with yard trimmings and minor 520,000 inhabitants. The cam- amounts of biosolids. The facility con- paign is still ongoing with more sists of preprocessing; three continuous municipalities joining. By the flow cylindrical digester reactors with aend of 2010, all municipalities in ETRA’s total volume of 7,200m3; a compostingservice area will have received the cam- plant for the digestate; a maturationpaign and monitoring pad; biogas clean upprogram. Figure 2. Waste analyses in (methane and carbon The campaign was Bassano del Grappa dioxide); three CHP en-partly funded by ETRA, gines (powered with theand partly by the munic- 16 15.5 Percent non-compostable biogas); and a dedicatedipalities themselves, 2007 2008 2009 sewer taking liquid fromwhich included a pro- 12 11.4 the dewatering processportion of total costs in 8.9 8.9 to a local treatment fa-the yearly financial 7.93 7.93 7.93 cility. 8plan. The campaign also 6.1 The Bassano plant was 5.4had the support of the 4 originally designed forItalian Composting 2.3 2.1 treatment of MSW. 1.3Consortium. 0 However, the later in- Bassano del Grappa, Area A Area B Area C Area D troduction of the curb-BIOCYCLE SEPTEMBER 2010
  3. 3. degrading at this point and are completely degraded during the postcomposting stage. CAMPOSAMPIERO DIGESTION PLANT The Camposampiero facility opened in mid-2005, treating separately collected mu- nicipal organic wastes, animal manure and biosolids. The integrated biotreatment cen- ter consists of a reception hall and pretreat- ment facility; an area for reception and pre- treatment of liquid waste; an anaerobic digester; and a treatment plant for wastew- ater. This plant utilizes a two-phase wet di- gestion process patented by Linde-KCA- Dresden GmbH that operates with low solids content under thermophilic conditions. Source separated food waste is loadedThe integrated biotreatment side collection of dry recyclables caused a into a bag opener with a front end loader,facility in Camposampiero, significant change in the composition of the passed through a grinder and magnetic sep-which processes separately MSW, leading to higher sedimentation arator and then goes into a hopper. Thecollected municipal organics, rates that clogged the digesters. This shredded and cleaned waste enters the hy-animal manure and biosolids, prompted a change to process just source dropulper, which after dilution with waterutilizes a two-phase wet separated food waste in the digesters. or industrial leachate, blends the putresci-digestion process. Food waste entering the facility is placed ble materials and, by sedimentation, sepa- in a bag splitter and then passed through a rates out the heavy solids (bones and shells, disc screen and magnetic separator. The spoons or any residual metal plugs, etc.). overs from screening are sent for disposal in The liquid is discharged from the pulper landfill or incineration with energy recov- into a drum screen that allows the separa- ery. The larger pieces of compostable bags tion of the pulp from plastics and other are captured in the overs; the smaller ones large fragments, which are washed and pass through the screen and enter the di- then pressed to remove excess water. The gester. ETRA is planning to introduce a me- compostable bags are removed via the drum chanical-biological treatment (MBT) step screen as well. ETRA is also planning to prior to sending the overs to disposal in or- add an MBT step at this facility to treat the der to have a further reduction of weight residues because of the high content of wet and disposal cost. organic materials. The bags would biode- Organic materials are steam-heated to grade during the MBT stage. reach the desired temperature (the walls of Screened overs (washed and pressed) and the digester are insulated but do not have the settling solids separated in the pulper any heating mechanisms) and loaded di- (and partly also in two traps in the sieve) rectly into three cylindrical digesters, each are sent to disposal. The pulped organics with a gross capacity of 2,400 m3. Solids fraction enters the hydrolysis tank where it content of feedstock entering the digester is remains for just over a day before being fed 29 to 33 percent. The average retention into the anaerobic digester. time is 35 days. The liquid waste stream consisting of an- After dewatering, digestate is mixed with imal manure is subject to screening and grit structural woody material and biosolids be- removal, then placed in storage tanks and fore a two-stage composting process. The fed to the digester. Biosolids are thickened first phase is conducted in a closed ware- and placed in storage tanks or the hydroly- house, using 18 windrows with forced aera- sis tank, prior to loading into the digester. tion. These are turned regularly for 18 to 30 The digester has a capacity of 3,300 m3 of days and then pass via conveyor belt to the which 3,000 are occupied by the liquid frac- refining process to remove any remaining tion. Mixing is ensured by recirculation of contaminants. The compost is further ma- biogas (gas lift) together with the input and tured for up to three months, with a total output flows of the liquids. Temperature is time to process each batch (AD plus aerobic maintained between 53° and 55°C by exter- composting) of never less than 90 days and nal heat exchanger tube bundles that use often more than four to five months. This heat emitted from diesel engines and heat produces high-quality compost (after recovered from the output gases. screening to 10 mm) used as fertilizer in Biogas passes through a gravel filter and agriculture. Air drawn from all parts of the is recycled or stored in the double skin premises is cleaned by an acid wash and 2,600 m3 gas tank at a pressure of 20 to 25 then routed to a 1,000 m2 biofilter. mbar. The plant was opened in 2006 and About 50 percent of all the contaminants since 2007, the production of electricity has removed from Bassano are generated dur- been constant leading to the generation of ing the refining step of the composted di- high levels of revenue. gestate. Increased use of compostable bags Average retention time in the digesters is is a benefit in terms of reducing the plastic about 22 days, after which the digestate is portion of the residues. The bits of com- dried by centrifugation with the addition of postable bags that enter the digester start polyelectrolyte. The solid fraction is trans-BIOCYCLE SEPTEMBER 2010
  4. 4. ferred to composting plants for stabilization prior to spread-ing in agriculture whereas the liquid is treated internally.HANDLING COLLECTION BAGS The systems used to handle bags of organic waste collectedfrom households are extremely important. This involves bothpre and post treatment steps to ensure operations run smooth-ly and produce a quality compost for agriculture. Pretreatment consists of a range of operations that preparea substrate for the biological process and depend on whethera dry or wet process is used. For dry processes, pretreatmentdoes not require additional dilution, whereas for wet process-es the selection phase typically involves the substrate beingmixed with water while simultaneously separating the light(plastics) and heavy (inert) fractions. In both facilities described, preprocessing technologies tendto separate bags and organics before the biological process.Bags are torn open mechanically followed by particle size re-duction (avoiding excessive grinding). Inert materials andplastics are then separated in order to reduce friction and po-tential blockages in the biological process. However, a signifi-cant portion of organics attached to the bags is lost during thisstage. One major benefit of a system using compostable bagsis that depending on the purity of the collected feedstock, theymay enter the facility with less intensive separation, subse-quently reducing the loss of organic material and reducing theamount of overs generated during the refining process andsent to disposal. Moreover, bags entering the facility have al-ready started degradation, are wet and not so easy to be sep-arated from the overall food waste mass, which has not beena detriment to the operation of either digester facility, and hashelped reduce the final residue stream. The choice of technology for post treatment varies depend-ing on the market for the final product and the level of con-tamination present. In a system where compostable bags en-ter the AD facility, the efficiency of this screening is lesscritical because remaining fragments have degraded in thepostdigestion composting phase. Overall, ETRA has foundthat its facilities need to keep a balance between the intensi-ty of the pretreatment screening process and relative purity ofthe screened material that is then fed into the digester. In oth-er words, the more intense the screening, the more energy isconsumed and the greater the amount of residues produced. And as noted earlier, these residues contain a significantamount of organics sticking to the noncompostable materials.This “drag effect” usually causes the weight of the overs todouble, i.e. one metric ton of organics lost and disposed of pereach metric ton of noncompostable materials separated dur-ing the screening process. Therefore, if the contamination ofthe input material is kept below 2 to 3 percent, it is possibleto have a less intensive screening because the digester sys-tems are able to cope with that contamination level. To keep impurities in the collected residential organic frac-tion well below 5 percent in ETRA’s service area, an appro-priate monitoring system has been implemented along withan extensive information and awareness campaign. Local re-tailers also have been engaged in providing certified com-postable bags at discounted prices. Last but not least, trainedcollection crews perform quality control while collecting theorganic waste and provide doorstep guidance and continuousinformation to the householders. The “Clean Organics” infor-mation and awareness campaign has significantly improvedboth the quality and quantity of residential organics collectedand reduced the amount of residues generated at ETRA’streatment facilities, resulting in an overall better environ-mental and economic performance.Christian Garaffa is Marketing Manager for source separationand recycling at Novamont SpA, producers of compostable poly-mers (christian.garaffa@novamont.com).BIOCYCLE SEPTEMBER 2010

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