To help achieve its goal of energy independence, the University of Wisconsin in Oshkosh invested in a high solids, dry fermentation anaerobic digester to process source separated organics.
BioCycle February 2012, Vol. 53, No. 2, p. 35
The university learned about the potential of generating energy via anaerobic digestion in late 2006 while attending an ACORE (American Council on Renewable Energy) Conference. Pursuit of the idea to install a biodigester continued throughout 2007, and in mid-2008, a delegation from UWO traveled to Germany to tour operating facilities. By this time, the university had zeroed in on the BIOFerm dry fermentation technology. “Originally, we were looking at only digestion of food waste, but then we met a representative from BIOFerm, who introduced us to the concept of processing additional feedstocks with the food waste, which led us to deciding on the dry fermentation system,” recalls Sonnleitner. “We received technical and financial assistance from Wisconsin’s Focus on Energy to proceed with the project.” UWO opted to build, own and operate the facility. The plant was designed and constructed by BIOFerm Energy Systems, based in Madison, Wisconsin.
Design began for a 8,000 tons/year dry fermentation plant to process separated food waste from the dining halls, commercial organics from area generators such as grocery stores, yard trimmings and silage and other farm biowaste. The plant was sited on university property adjacent to the city of Oshkosh’s wastewater treatment plant (and across the street from the municipal yard trimmings composting site). The university wrote a business plan to guide project development and help raise capital for the $4.7 million facility (includes all equipment, land and soil remediation). Grant funding for the biodgester came from the state of Wisconsin ($232,587), the U.S. Department of Energy ($500,000) and U.S. Treasury Section 1603 ($1.0 million) through the federal stimulus package. “We were strongly supported by the UW Oshkosh Foundation,” says Sonnleitner.
Construction of the biodigester was completed in July 2011 and commissioning began in August. The facility has four fermenters, each 70-ft long by 23-ft wide by 16.5ft high (volume of about 27,000 ft3). An 18,000 sq. ft. building houses the fermenters, mixing area, digestate storage, percolate tank and biogas collection and storage. A 370 kW combined heat and power (CHP) unit was supplied by 2G Energy. Installed on a skid, it uses a MAN engine block.) The unit has the capacity to generate 3.07 million kWh annually, however the complete system is expected to generate 2.3 million kWh annually. The 7,900 MMbtu of thermal energy eventually will be used to heat adjacent buildings.
Start-up of the plant began in mid-August. The facility has a solid waste permit from the Wisconsin Department of Natural Resources. Separated manure solids, combined with straw and food waste, were used as the starting materials. The CHP unit began operating the first week of October 2011. Electricity is purchased by Wisconsin Public Service for an average (of peak and off peak rates) of 8.8 cents/kWh. The utility receives the carbon credits.
Final transfer of plant operations from BIOFerm to UWO will happen in the spring of 2012. “We aren’t 100 percent turned over yet,” noted Brian Langolf, UWO’s plant manager, in early January. “We are at about 90 percent as BIOFerm is still doing some work on optimizing the computer software.”
Currently, the UWO biodigester is operating at about 55 percent of its capacity. It is receiving 40 to 60 tons/week of food waste from grocery stores and restaurants, collected and delivered by Sanimax. Some food processing residuals also are received. No tipping fee is being charged at this time, in order to procure an adequate quantity of feedstocks for plant operations. “We’ve wanted to ensure that we have enough material for plant optimization and biogas generation,” says Langolf. “We are just getting into the phase of understanding what mixes give the best optimization. We can easily double the quantity of food waste we are receiving now.”
Feedstocks currently being digested are food waste, yard trimmings and crop residues and livestock bedding. “It’s roughly 15 to 20 percent food waste and 40 percent or less bedding, with the remainder comprised of recycled digestate to inoculate the new material,” explains Langolf. “Yard trimmings average 5 to 10 percent of the mix, but there is less at this time of year.”
The system is designed to have upwards of 25 to 35 percent solids content in the starting mix. Incoming materials are unloaded on the tipping floor. A front-end loader is used to crush any large size items (pumpkins were evident when BioCycle toured the plant in late October), as well as blend feedstocks prior to loading the fermenters. Retention time in the units is currently 28 days. Start up of each fermenter was staggered; all four have been fully in use since September.
The facility has a 120,000-gallon percolate tank that is kept at a steady temperature using waste heat from the CHP. The percolate is liquid that is continually recirculated through the fermenters and contains requisite anaerobic microorganisms for methane production. Once a fermenter is filled, percolate is intermittently added via spray nozzles at the top of the digester, which gravity drains through the digesting material.
Biogas generated by the fermenters and percolate tank is captured and stored in a flexible, pillow shaped gas storage bag, constructed of the same material as typical wet digester roof domes. It is installed on the second level of the plant above the fermenters. The bag has enough capacity to allow for up to two to six hours of CHP downtime. Beyond that time, biogas is directed to a flare.
At the end of the 28-day retention time, a shut down sequence begins prior to unloading the fermenter. Percolate stops being added several days prior to unloading, so free liquid can drain from the material. Four to six hours prior to opening the fermenter, there are 10 air changes/hour, with all methane blown off in about three hours. That purge gas, a low quality biogas, is currently discharged over the roof, however the system is being redesigned to run this gas into the CHP. The plant software utilizes an automated gas quality measurement system to regularly check the gas quality in each fermenter, the percolate tank and the gas bag to make certain system decisions and/or allow the operator to open the fermenter doors.
Mixing area ventilation and fermenter exchange exhaust air are treated through a 12-ft high by 12-ft wide by 60-ft long biofilter located outside the main building. The media is comprised of 5-feet of lava rock.
After unloading, digestate is moved to a storage bunker. Material that isn’t retained for mixing with new feedstocks is taken on a back-haul by a farmer who land applies it (the farmer delivers livestock bedding to the plant), or goes to Zillges Materials, Inc. in Oshkosh for composting. Zillges just started receiving digestate this winter. “We expect to get about 2,000 cubic yards/year,” says Tim Zillges. His company, which sells landscape supplies, spas, outdoor furniture and other products, composts about 2,500 cy/year of yard trimmings. “We’ve built several windrows with the digestate, mixing it with either yard trimmings or horse manure,” he adds. “The material is pretty wet, so we are experimenting with the recipes.”
Zillges had to repermit the composting facility in order to take the digestate and animal waste. The company recently purchased a windrow turner from Midwest Bio-Systems. It already owns a McCloskey trommel, which is utilized for its topsoil operation. “We are excited about being involved with the University’s biodigester facility,” notes Zillges. “We are still on a learning curve.”
The CHP unit was sized for more than the quantity of biogas produced by the biodigester, as UWO formed a partnership with the neighboring wastewater treatment plant to receive its biogas, which is only utilized by the WWTP during the winter. “The UWO biodigester is currently producing 165 kW, and we think we can get that up to 225 to 230 kW when operations are optimized,” says Drew Tuchscherer with BIOFerm. “The remaining capacity of the 370 kW genset will be utilized by the WWTP’s biogas.”
The standard BIOFerm automated desulfurization system removes hydrogen sulfide. The system meters oxygen into the fermenters to scrub the H2S. An activated carbon filter was installed to scrub siloxane and H2S from the WWTP biogas. “We are getting H2S levels down to 0 to 10 ppm with the filter,” adds Tuchscherer.
Concurrent with development of the biodigester, UWO has invested $700,000 in renovation of a laboratory that will have full service analytical capabilities and on-site testing. The lab will be able to do methane evolution determinations, methanogen selection and optimization and air, water and solid matrix testing. It will also house bench-scale and pilot-scale bioreactors. “As the operator of a digester, we want to maximize biogas generation in order to maximize the payback of the facility,” says Gregory Kleinheinz, an Associate Dean at UWO.
Langolf, a microbiologist by training, also is overseeing work in the laboratory related to the biodigester. “Right now, we are mostly doing basic testing of ongoing operations of the biodigester, tracking daily, weekly and monthly parameters to monitor plant performance,” he says. “Next we will be focusing on how to increase biogas production, looking at the microecology of the digester, testing a variety of feedstocks and doing microbial and chemical analyses.” UWO students work both in the laboratory and at the biodigester, conducting research and in some cases, helping out with operations.
The university is also proceeding with a second digester, this one to be located at a dairy about 15 miles from the main campus. Groundbreaking for the wet digester is scheduled for spring of 2012, with a projected start up in 2013. The facility will be owned by the UW Oshkosh Foundation and led, managed and operated by UWO faculty, students and staff. A remote classroom and laboratory will be constructed. “The new facility will help UW Oshkosh continue to redirect financial resources previously spent on campus energy bills to the expansion of academic programs and classroom seats,” explains Sonnleitner. “That is the core of our institution’s mission.”
Ili kusaidia kufikia lengo lake la kujitegemea kwa nishati, Chuo Kikuu cha Wisconsin huko Oshkosh kiliwekeza katika digester ya anaerobic ya kuchaji kavu ya vimeng'enyaji vya vimeng'enyaji vya vimeng'enyaji vya vimeng'enyaji vya vimeng'enyaji vya vimeng'enyaji vya vimeng'enyaji. BioCycle Februari 2012, Vol. Hakuna, 53, "Mwaka 2006 chuo kikuu hicho kilijifunza juu ya uwezekano wa kuzalisha nishati kupitia ""anaerobic digestion"" wakati wa kuhudhuria mkutano wa ACORE (American Council on Renewable Energy)." Utafiti wa kuanzisha mfumo wa biodigester ulifanyika mwaka 2007 na katikati ya mwaka 2008 ujumbe wa UWO ulisafiri kwenda Ujerumani kutembelea vituo vya uendeshaji. Wakati huo, chuo kikuu hicho kilikuwa kimekazia fikira teknolojia ya kuchemshwa kwa maji kavu ya BIOFerm. "Hapo awali, tulikuwa tukitazama tu kumeng'enya taka za chakula, lakini kisha tukakutana na mwakilishi kutoka BIOFerm, ambaye alitujulisha dhana ya kusindika malighafi za ziada na taka za chakula, ambayo ilituongoza kuamua juu ya mfumo wa chachu kavu, "Sonnleitner anakumbuka." "Wakati huo huo, kampuni ya Wisconsin Focus on Energy ilitoa msaada wa kiufundi na kifedha kwa ajili ya mradi huo, na kampuni hiyo ilichagua kujenga, kumiliki na kuendesha kituo hicho.""" Kiwanda hicho kilibuniwa na kujengwa na BIOFerm Energy Systems, iliyoko Madison, Wisconsin. Mimea ya kuyeyusha ya tani 8,000 kwa mwaka iliundwa kwa ajili ya kutengeneza taka za chakula kutoka kwenye vyumba vya kulia chakula, viumbe vya kibiashara kutoka kwa viumbe vya eneo kama vile maduka ya vyakula, viungo vya bustani na silage na biofuels nyingine za shamba. Kiwanda hicho kilikuwa kwenye mali ya chuo kikuu karibu na kituo cha kusafisha maji machafu cha jiji la Oshkosh (na ng'ambo ya barabara kutoka eneo la uundaji wa mbolea ya bustani ya manispaa). Chuo Kikuu hicho kiliandika mpango wa biashara kuongoza maendeleo ya mradi na kusaidia kukusanya mtaji kwa ajili ya kituo cha $ 4.7 milioni (inajumuisha vifaa vyote, ardhi na udhibiti wa udongo). Ufadhili wa Biodegester ulitoka kwa Jimbo la Wisconsin (USD $ 232,587), Idara ya Nishati ya Marekani (USD $ 500,000) na Idara ya Hazina ya Marekani (USD $ 1.00 million) kupitia mfuko wa kichocheo wa shirikisho. "Tulikuwa na msaada mkubwa kutoka kwa UW Oshkosh Foundation", anasema Sonnleitner. Biodigester hiyo ilikamilika mnamo Julai 2011 na kuanzishwa kwa mradi huo kulianza mnamo Agosti. Mimea hii ina viwanda vinne vya kuyeyusha, kila kimoja kina urefu wa mita 70 kwa upana wa mita 23 na urefu wa mita 16.5 (kiasi cha karibu mita 27,000). 18,000 sq. Jengo la juu lina nyumba za fermenters, eneo la kuchanganya, kuhifadhi digestate, tank ya percolate na mkusanyiko na uhifadhi wa biogas. Kiwanda cha umeme na joto (CHP) cha kilowati 370 kilitengenezwa na kampuni ya 2G Energy. Imewekwa juu ya skid, inatumia MAN injini block.) Kituo hicho kina uwezo wa kuzalisha kilowatt saa milioni 3.07 kwa mwaka, lakini mfumo kamili unatarajiwa kuzalisha kilowatt saa milioni 2.3 kwa mwaka. Mimea hiyo 7,900 ya joto itatumiwa kupasha joto majengo ya karibu. Kuanza kwa kiwanda hicho kulianza katikati ya Agosti. Kituo hicho kina kibali cha taka thabiti kutoka Idara ya Rasilimali za Asili ya Wisconsin. Vitu vilivyojitenga vya mbolea, pamoja na nyasi na taka za chakula, vilitumiwa kama vifaa vya kuanzia. CHP unit ilianza kufanya kazi wiki ya kwanza ya Oktoba 2011. Kwa mfano, umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme. Huduma ya umma hupokea mikopo ya kaboni. Uhamisho wa mwisho wa shughuli za kiwanda kutoka BIOFERM hadi UWO utafanyika katika spring ya 2012. "Hatujawa na asilimia 100 bado", alisema Brian Langolf, meneja wa kiwanda cha UWO, mwanzoni mwa Januari. "Kama ilivyoelezwa hapo juu, ""BioFerm bado inafanya kazi ya kuboresha programu ya kompyuta, kwa sasa, biodigester ya UWO inafanya kazi kwa asilimia 55 ya uwezo wake.""" Kwa mfano, kampuni ya Sanimax inazalisha na kusafirisha takriban tani 40 hadi 60 za chakula kila wiki kutoka maduka ya vyakula na mikahawa. Baadhi ya mabaki ya usindikaji wa chakula pia hupokelewa. Hakuna ada ya tipping inayoshtakiwa kwa wakati huu, ili kupata kiasi cha kutosha cha malighafi kwa shughuli za kiwanda. "Tumetaka kuhakikisha kwamba tuna vifaa vya kutosha kwa ajili ya optimization ya kiwanda na uzalishaji wa biogas", anasema Langolf. <unk>Sisi ni tu kupata katika awamu ya kuelewa nini mchanganyiko kutoa optimization bora. Tunaweza kwa urahisi mara mbili kiasi cha taka ya chakula sisi ni kupokea sasa. <unk> feedstocks kwa sasa kuwa digested ni taka ya chakula, yard trimmings na mabaki ya mazao na malisho ya mifugo. "Ni takriban asilimia 15 hadi 20 ya taka za chakula na asilimia 40 au chini ya kitanda, na iliyobaki inajumuisha digestate iliyorudishwa ili kuingiza nyenzo mpya, "Langolf anaelezea." "Kama vile ""Yard Trimmings"" ni asilimia 5 hadi 10 ya mchanganyiko, lakini kuna chini wakati huu wa mwaka, mfumo huo umebuniwa kuwa na zaidi ya asilimia 25 hadi 35 ya maudhui ya imara katika mchanganyiko wa kuanza." Vifaa vinavyoingia hutolewa kwenye sakafu ya kugeuza. "Mchomaji wa mbele hutumiwa kuvunja vitu vyovyote vya ukubwa mkubwa (pumpkins zilikuwa dhahiri wakati BioCycle ilitembelea kiwanda mwishoni mwa Oktoba), pamoja na mchanganyiko wa malighafi kabla ya kupakia ""fermenters.""" Wakati wa kuhifadhi katika vitengo ni siku 28. Kuanza kwa kila fermenter ilikuwa staggered; wote wanne wamekuwa kikamilifu katika matumizi tangu Septemba. Kituo hicho kina tangi la percolate lenye lita 120,000 ambazo huhifadhiwa kwa joto la kawaida kwa kutumia joto la taka kutoka kwa CHP. Percolate ni kioevu kwamba ni daima recirculated kupitia fermenters na ina mahitaji anaerobic vijidudu kwa ajili ya uzalishaji wa methane. Mara baada ya fermenter kujazwa, percolate ni intermittently aliongeza kupitia nozzles kunyunyizia juu ya digester, ambayo mvuto drains kupitia digesting nyenzo. Biogas inayotokana na fermenters na tank percolator ni kukamatwa na kuhifadhiwa katika kubadilika, pillow-umbo gesi kuhifadhi mfuko, kujengwa ya nyenzo sawa na kawaida mvua digester paa domes. Ni imewekwa katika ngazi ya pili ya mmea juu ya fermenters. Mfuko huo una uwezo wa kutosha kuruhusu hadi saa mbili hadi sita za wakati wa kuzima kwa CHP. Baada ya wakati huo, gesi ya kibiolojia huelekezwa kwenye mwangaza. Baada ya muda wa siku 28 ya kuhifadhi, utaratibu wa kuzima huanza kabla ya kuondoa fermenter. Percolate huacha kuongezwa siku kadhaa kabla ya kupakua, hivyo kioevu huru inaweza kutiririka kutoka kwa nyenzo. Baada ya saa 4 hadi 6 kabla ya kufungua fermenter, kuna mabadiliko ya hewa 10 kwa saa, na methane yote imepepepuka kwa masaa matatu. Gesi ya kuondoa, biogas ya ubora wa chini, kwa sasa hutolewa juu ya paa, hata hivyo mfumo unaundwa upya ili kuendesha gesi hii katika CHP. Programu ya kiwanda hutumia mfumo wa kipimo cha ubora wa gesi ili kuangalia mara kwa mara ubora wa gesi katika kila fermenter, tank ya percolator na mfuko wa gesi ili kufanya maamuzi fulani ya mfumo na kuruhusu operator kufungua milango ya fermenter. Uingizaji hewa wa eneo la kuchanganya na hewa ya kubadilishana ya fermenter hutibiwa kupitia biofilter ya urefu wa 12 ft kwa urefu wa 12 ft na urefu wa 60 ft iliyo nje ya jengo kuu. Mwamba huo una urefu wa mita tano na una mwamba wa lava. Baada ya kupakiwa, digestate huhamishwa hadi kwenye hifadhi ya kuhifadhi. Vifaa ambavyo havijahifadhiwa kwa kuchanganya na malighafi mpya huchukuliwa kwa nyuma na mkulima ambaye ardhi hutumia (mkulima hutoa vitanda vya mifugo kwa mmea), au huenda kwa Zillges Materials, Inc. huko Oshkosh kwa ajili ya mbolea. Zillges alianza tu kupokea digestate majira ya baridi hii. "Tunatarajia kupata karibu mita 2,000 za kiunzi kwa mwaka", anasema Tim Zillges. Kampuni hiyo, ambayo inauza vifaa vya kutengeneza mandhari, spa, fanicha za nje na bidhaa nyingine, hutengeneza mbolea ya karibu maua 2,500 kwa mwaka. "Tumejenga vijito kadhaa vya upepo kwa kutumia mchanganyiko huo, tukichanganya na vipande vya shamba au chafu ya farasi", anaongeza. "Kama vile ilivyotangazwa, ""Zilges ilifanya kazi ya kuharibu vifaa vya kuyeyusha ili kuchukua magugu ya wanyama.""" Kampuni hiyo hivi karibuni ilinunua mashine ya kugeuza mizunguko kutoka kwa Midwest Bio-Systems. Tayari inamiliki trommel ya McCloskey, ambayo hutumiwa kwa operesheni yake ya udongo wa juu. "Tunafurahi sana kuhusika na kituo cha biodigester cha Chuo Kikuu", anasema Zillges. "Kama vile ilivyotangazwa, ""CHP unit ilikuwa na ukubwa wa zaidi ya kiasi cha biogas zinazozalishwa na biodigester, kama UWO iliunda ushirikiano na jirani ya maji taka matibabu ya kupokea biogas yake, ambayo ni tu kutumika na WTP wakati wa majira ya baridi." "U-Water biodigester kwa sasa inazalisha 165 kW, na tunafikiri tunaweza kupata kwamba hadi 225 hadi 230 kW wakati shughuli ni optimized, ""anasema Drew Tuchscherer na BioFerm." "Kama vile, ""kiwanda cha kuendesha gari"" cha BIOFERM, ambacho kina uwezo wa kuendesha gari kwa muda mrefu, kina uwezo wa kuendesha gari kwa muda mrefu, na kina uwezo wa kuendesha gari kwa muda mrefu." Mfumo wa oksijeni wa kisasa unafanya kazi kwa njia ya mtiririko wa oksijeni kwenye mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea ya mimea. Filter ya kaboni ya kazi iliwekwa ili kuondoa siloxane na H2S kutoka kwa biogas ya WTP. "Hii ni kwa sababu ya kiwango cha H2S cha chini cha 0 hadi 10 ppm, ""alisema Tuchscherer." Pamoja na maendeleo ya biodigester, UWO imewekeza $ 700,000 katika ukarabati wa maabara ambayo itakuwa na uwezo kamili wa uchambuzi na upimaji wa mahali. Maabara itakuwa na uwezo wa kufanya methane mageuzi maamuzi, methanogen uteuzi na uboreshaji na hewa, maji na imara matrix kupima. Pia itakuwa na bioreactors za kiwango cha benchi na kiwango cha majaribio. "Kama mwendeshaji wa digester, tunataka kuongeza uzalishaji wa biogas ili kuongeza faida ya kituo hicho, "anasema Gregory Kleinheinz, Mshirika wa Dean katika UWO. Langolf, ambaye ni mtaalamu wa vimelea, pia anasimamia kazi katika maabara inayohusiana na kichocheo cha viumbe hai. "Sasa, sisi ni hasa kufanya majaribio ya msingi ya shughuli za kuendelea ya biodigester, kufuatilia kila siku, kila wiki na kila mwezi vigezo kufuatilia utendaji wa mmea", anasema. "Kisha tutaweza kuelezea jinsi ya kuongeza uzalishaji wa biogas, kuangalia microecology ya digester, kupima aina mbalimbali za malighafi na kufanya uchambuzi wa microbial na kemikali. ""Wanafunzi wa UWO hufanya kazi katika maabara na katika biodigester, kufanya utafiti na katika baadhi ya kesi, kusaidia na shughuli." Chuo kikuu hicho pia kinaendelea na kazi ya kujenga digester ya pili, ambayo itawekwa katika kiwanda cha maziwa umbali wa maili 15 kutoka chuo kikuu. Ujenzi wa sehemu ya chini ya ardhi ya mto huo umepangwa kufanyika mwaka 2012 na mradi huo unatarajiwa kuanza mwaka 2013. Kituo hicho kitakuwa mali ya UW Oshkosh Foundation na kuongozwa, kusimamiwa na kuendeshwa na walimu, wanafunzi na wafanyikazi wa UW-Oshkosh. Darasa la mbali na maabara zitajengwa. "Kifaa kipya kitasaidia UW Oshkosh kuendelea kuelekeza rasilimali za kifedha zilizotumika hapo awali kwenye bili za nishati za chuo kikuu kwa upanuzi wa programu za kitaaluma na viti vya darasa, "anaelezea Sonnleitner. <unk>Hiyo ni kiini cha utume wa taasisi yetu.<unk>