High Solids AnaerobicDigestion+Composting

In San Jose

RECYCLING MSW ORGANICS

AFACILITY that marries dryanaerobic digestion and com-posting under the same roofto process the organic frac-tion of municipal solid wasteopened for business late last

year at the south end of the San Fran-cisco Bay in San Jose, California. ZeroWaste Energy Development Company(ZWEDC) — developer and owner ofthe 90,000 tons/year facility — recog-nized the benefits of colocation to en-able extraction of the energy value ofthe food waste, followed by compostingof the digestate. The plant, comprisedof 16 high-solids dry fermentation di-gesters and four in-vessel compostingtunnels, began receiving organics fromthe commercial sector in San Jose inmid-December.

ZWEDC was formed in 2011 byGreen Waste Recovery, Inc. (Green-Waste) and Zanker Road Resource

Management (Zanker) to bolster or-ganics recovery infrastructure in SanJose. “We already operate the secondlargest composting facility in Califor-nia that processes a large portion of thecity’s organic waste stream,” explainsRich Cristina, president of Green-Waste and Zanker, referencing its Z-Best Composting Facility in Gilroy,about 30 miles away from San Jose.“Extracting and utilizing the energyvalue of the organic materials to powerour other resource recovery operationshere in San Jose was the next evolutionfor our family of companies.”

Biogas from the anaerobic digesterspowers a combined heat and power(CHP) plant that wheels electricity toZanker Road Resource Recovery Oper-ation and Landfill (ZRRROL), whichrecycles and processes wood waste, as-phalt shingles, sheet rock and othersegregated materials. Zanker under-

42 BIOCYCLE MARCH/APRIL 2014

Housed inside a100,000 sq. ft.building at thesouthern edge ofthe San FranciscoBay, a dryfermentationAD system withcomposting baysis processingcommercialorganics from theCity of San Jose.

Nora Goldstein

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AD In Action

Aerial photo highlights theprocessing building, biogas storagebladders (on left and right on roofsin center of photo) and the fourcircular biofilters (bottom of photo)treating building air. The outdoorwindrow composting curing pad ison far right.

went an electrification project atZRRROL, as well as its nearby ZankerMaterials Processing Facility. Olderdiesel-powered stationary processingplants were replaced with electric pow-ered equipment. ZRRROL is utilizingelectricity from the CHP for its electric-powered equipment. “We are able towheel power to ourselves without act-ing like a utility,” notes Emily Hanson,GreenWaste’s Director of Business De-velopment and Communications. “Theplan is for Zanker’s materials process-ing facilities to use 100 percent ofZWEDC’s peak power after theAD/composting plant covers its para-sitic load. When the Zanker plants arenot operating, the excess power will besold to the grid.”

PROJECT HISTORYOrigins of the ZWEDC anaerobic di-

gester (AD)/composting plant dateback to the City of San Jose adopting aGreen Vision goal in 2007 that includ-ed diversion of 100 percent of the city’swaste from landfill by 2022 and con-version of waste into renewable energy.At the time, one-third of the City’slandfilled waste stream came frombusinesses, and city officials recog-

nized that significant changes in thissector were necessary to improve thecommercial recycling rate of 22 percentat the time. San Jose had an open fran-chise commercial waste collection sys-tem; over 20 different haulers servicedthe more than 8,000 commercial, in-dustrial and institutional waste gener-

ators in the city. To help meet its GreenVision goal, the City Council voted toinstitute an exclusive franchise agree-ment and select processors for the ma-terials collected. A waste characteriza-tion study conducted in 2008 indicatedthat nearly 79 percent of the commer-cial solid waste could be divertedthrough recycling and composting.

Two Requests for Proposals were is-sued in 2010, one for commercial or-ganics processing and the other for com-mercial solid waste and recyclablematerial collection and processing.ZWEDC was awarded the organics pro-cessing contract, while Allied (now Re-public Services) was awarded the col-lection and recycling contract. (See“New Frontier For Commercial WasteIn San Jose,” May 2011 and “CreatingInfrastructure For Commercial WasteDiversion,” August 2011 for details onthe RFP process and final contracts ne-gotiated with ZWEDC and Republic). Itwas anticipated that the new contractswould increase the commercial diver-sion rate up to 80 percent by 2014,which is 5 percent higher than the city’sgoal of 75 percent diversion by 2013.

The official start date for the new col-lection and materials processing ser-

BIOCYCLE MARCH/APRIL 2014 43

Commercial organics that have beenprocessed by Republic Services at its

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MAI NTE NAN C E F R I E N D LY C O ST E F F E CT IVE H I G H P R O D U CT I O N

vices was July 1, 2012. Republic optedfor a wet/dry collection service, provid-ing customers with several options, e.g.,one container for wet material (organ-ics) and one container for dry materials(recyclables and everything else).Smaller businesses can use one con-tainer — they can either put organicwaste in loose in the container and bagthe dry trash and recyclables or theycan put dry trash and recyclables loosein the container and bag the organicwaste. “One of the most significant ben-efits of the wet/dry system is that allbusinesses in San Jose are in compli-ance with AB 341, a California mandaterequiring businesses that generate atleast four cubic yards of waste per weekto recycle,” explains Gil Cheso, GeneralManager of Republic Services of SantaClara County. “The only thing busi-nesses need to do is determine if mate-rial is wet (organics) or dry (recyclablesand everything else) and place it in thecorrect container.” Processing capacityat Republic’s Newby Island ResourceRecovery Facility was expanded to ac-commodate an organics sorting line forthe incoming wet fraction.

The contract negotiated by both Re-public and ZWEDC with the City of SanJose established four levels of contami-nation in the “Organic Material Deliv-ered by the Commercial CollectionFranchisee (CCF).” The tipping fee risesaccording to the level of contaminationin the “organics stream” (OS) loads de-

livered. Contamination levels (byweight) in the OS are divided as follows:OS 1: �5 percent; OS 2: �5 percent and�10 percent; OS 3: �10 percent and�20 percent; and OS 4: � 20 percentand �30 percent (similar to unpro-cessed MSW). The tipping fees rangefrom about $70/ton for OS 1 to the mid-$90s/ton for OS 4. These rates are verycompetitive in this region of California.

Because Republic launched itswet/dry collection service in July 2012,ZWEDC had to begin processing the or-ganics stream at the same time. Thecompany transferred the wet materialto its Z-Best Composting facility inGilroy, which already is composting amixed waste stream from Green-Waste’s materials recycling facility.Under its contract with the City, start-ing on January 1, 2013, ZWEDC wasrequired to achieve a diversion stan-dard for each Organic Stream pro-cessed. “The allowable residue per Or-ganic Stream category is based on themaximum allowable contamination in

the OS level, plus five percent,” ex-plains Hanson. “For example, OS1 al-lows 5 percent contamination byweight, so the allowable residue is 10percent by weight. This is calculated atthe end of the year.”

ZWEDC has the right to reject anyincoming load determined to containmore than 30 percent contamination,any load containing more than 30 per-cent paper and/or fiber materials, andany load containing more than 0.25percent glass.

DIGESTER/COMPOSTING FACILITYDEVELOPMENT

Once the contract was signed withthe City of San Jose, ZWEDC re-searched existing technologies and se-lected Zero Waste Energy, LLC (ZWE),a California-based project developmentcompany with the exclusive NorthAmerican license to the SMARTFERMhigh solids, dry fermentation anaerobicdigestion and in-vessel composting(IVC) technologies developed by Eg-gersmann, a German company. ZWEinstalled the Kompoferm technologiesin the San Jose facility, which is one ofthe technology options in its SMART-FERM portfolio. “We were seeking aprocessing system that was not only anet energy producer, but also requiredminimal processing, and little waterand energy to perform optimally,”notes Hanson. “ZWE’s KompofermPlus IVC technology fit that bill.”

The ZWEDC team successfully wad-ed through the local and state environ-mental review and land use permittingand entitlement processes (air, waterand solid waste), which covers the cur-rent Phase One (90,000 tons/year), aswell as planned expansions over the

44 BIOCYCLE MARCH/APRIL 2014

The four in-vessel composting tunnels(one shown on left in photo) are next toone of the banks of digesters (to theright). Content of two digesters fills onecomposting tunnel.

A portion of electricity generated by theCHP units is wheeled to the ZankerRoad Resource Recovery Operationsand Landfill — which processessegregated materials such as woodwaste and asphalt shingles — to powerstationary equipment such as thePeterson horizontal grinder on left ofphoto.

next few years (Phase 2 increases ca-pacity to 180,000 tons/year and Phase3 — a full build-out of the site — ex-pands to 270,000 tons/year). The pro-ject was financed through the Califor-nia Pollution Control FinancingAuthority, which issued bonds thatwere supported by a bank letter of cred-it, which in turn was supported by theguaranteed 15-year exclusive feed-stock contract with the city, and a pow-er purchase agreement with the localutility. “We needed to have these con-tracts in place to secure the financingand provide assurances that we couldservice our debt,” says Hanson.

ZWEDC’s organics processing facili-ty is sited on approximately 40 acres ofa city-owned former landfill site(known as Nine Par), adjacent to theSan Jose/Santa Clara Water PollutionControl Plant and directly between thetwo existing Zanker processing opera-tions. ZWEDC is leasing the site fromthe city. “This landfill was a privatelyowned 166-acre site that operated asan active landfill from 1938-1969,” ex-plains Jo Zientek, Deputy Director ofthe City of San Jose EnvironmentalServices Department. “The City pur-chased the property in 1982 to serve asbuffer lands for the Regional Wastewa-ter Facility. Changes to the require-

ments for the City’s wastewater facili-ty negated the need to keep the site forfuture expansion, and thus enabled de-velopment of the Nine Par site. Devel-oping on the site of an older landfillposed many challenges, and the Cityrecognized that it was not in the posi-tion to bring the site into a conditionwhere it could be leased for any pur-pose. The City gave ZWEDC credit to-wards its rent for the approximately$11 million that the company had tospend to bring the site into a conditionfrom which it could be useable by theCity, even if the ZWEDC project did notprogress to completion. This way theCity would benefit from the site im-provements.”

Zientek adds that infrastructure im-provements and preparations includedtopographical and landfill status inves-tigation, design and grading planning,geotechnical reports, wetland delin-eations, aerial surveys, drainage and ir-rigation planning, bringing utilities tothe site (potable and reclaimed water,power, sanitary sewer, etc.) importingfill and grading the site, installingstorm water and forebay protection sys-tems, onsite water treatments, and cre-ating roads and driveways.

Once the credit for site infrastruc-ture improvements is paid back to San

Jose, the City will receive about $4/tonof waste into the facility. “Therefore themore material ZWEDC is able to bringinto the facility for Phases 2 and 3, themore revenue is generated for the Cityof San Jose and the other jurisdictionsthat use the wastewater facility,” ex-plains Zientek.

The receiving area, digester bays,composting tunnels and related opera-tions are housed in an approximately100,000 sq. ft. fully enclosed building.

BIOCYCLE MARCH/APRIL 2014 45

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Each bank of eight digesters has itsown 425,000 gallon percolate tank inthe basement and 670 cubic meter gasstorage system on the roof (above).

There are two banks of digesters —eight on each side of the building. Eachbank has its own 425,000 gallon perco-late tank in the basement and 670 cu-bic meter (m3) gas storage system onthe roof. The building is constructed ona floating base, essentially “rafts” thatdisperse the weight and prevent thestructure itself from getting damageddue to differentiated settlement of theclosed landfill. Each digester bank hasits own raft, as does the receiving andoperations area. (The four compostingtunnels are next to one of the banks ofdigesters.) To allow for percolate tanksunder each bank of digesters, the sitehad to be built up. “Essentially we hadto raise everything so that we could digdown,” says Hanson.

The process of meeting the City ofSan Jose Fire Code was complicated bythe fact that dry anaerobic digestion isa new technology in North Americawith no code precedent. “An occupancyclassification of a building determinesthe construction type and allowablesquare footages, however since a largeportion of our square footage was pro-cessing area that would be minimallyoccupied, we had to come up with somecreative solutions to meet fire andbuilding codes without adding exorbi-tant costs, “explains Hanson. “Workinghand-in-hand with the regulatoryagencies, we created our own regulato-ry path by making a distinction be-tween processing areas and occupiedareas. The ultimate resolution is thatwhen the digester hatches are closed,the area is classified as ‘processing.’When the hatches are open, it is classi-fied as ‘occupied.’ To achieve this, theCity’s code enforcement officials re-quired additional sprinkler protectionin areas that are occupied at all timesof operation. Basically, through our ne-gotiations, we have created a modelregulatory path for any facility like thisin the United States!”

Construction of the facility was ac-celerated because much of the manu-facturing was done in the U.S. “Wework with Environmental SolutionsGroup’s Marathon Division to do ourfabrication,” says Dirk Dudgeon,ZWE’s Senior Vice President of Busi-ness Development. “In addition, allprocess controls were assembled inmodules and shipped, so it was ‘plugand play’ during installation at the fa-cility. Overall, these steps shavedmonths off the construction process.”

DESIGN AND OPERATIONSZWEDC receives and processes com-

mercial organics six days a week. Eachdigester tunnel — 18-feet wide by 16-feet high by 97-feet long — holds 350tons of organic material. OrganicStream 1 loads (�5% contamination)

that are hauled directly from collectionroutes to ZWEDC are visually inspect-ed for contaminants; some hand sort-ing is done. Loads that have been pro-cessed by Republic at its Newby IslandMRF arrive in walking floor trailers.Materials are directly loaded into thedigesters with front-end loaders.

Not long after Republic started upthe processing line for the wet streamat its MRF, it decided to add a finesscreen and a reducer. “The reducerhelps size the material and liberatesthe organics from the plastic bags,”says Cheso of Republic. “All materialfrom that line goes over the fines screenbefore it is sent to ZWEDC.” The pri-mary contaminants removed are plas-tic film, food service containers andother plastic items.

For the first six months of operations,Republic has employees on the tip floorworking with ZWEDC staff to monitorloads for contamination, and to helpgauge the quality of material arrivingand properly assign OS classification.In addition, representatives from theCity of San Jose visit on a monthly ba-sis to observe operations and monitormaterial quality. (The city does similarvisits to the Republic MRF.)

Because ZWEDC has been processingthe commercial organics since July 2012at the Z-Best Composting Facility, ithad a good idea of what to expect in thewet fraction of the commercial wasteonce the AD/composting plant opened.

What was less certain was the how thetonnages to be received would translateinto actual volume that would go intoeach digester. “The digestion tunnelsare designed for a volume throughputand a maximum material depth that al-low for adequate airspace for both per-colate distribution and methane pro-duction,” explains Hanson. “This is aprojected volume throughput, however,the exclusive feedstock agreement relieson tonnage. The density of the materialis going to determine whether the vol-ume throughput is higher or lower thananticipated. The higher the contamina-tion, the lower the density of the mate-rial and thus, the weight per unit of vol-ume decreases and the projectedtonnage throughput will be reduced. Ifthe material were too dense or wet, how-ever, then a structural/bulking materialwould need to be added. Currently, thematerial being delivered by Republic isaveraging 800 lbs/cubic yard and thecontamination is providing the struc-ture needed, so there is no need to addstructural material or bulking agent tothe organics going into the digesters.”

The Kompoferm digesters operate atthermophilic temperatures (125°F-131°F) with continuous recirculation ofthe percolate (liquid rich in anaerobicbacteria that acts as an inoculant tokick start biogas production). After thedigester door is sealed, the tunnel op-erates aerobically to reach the ther-mophilic range (the initial aerobic pro-cess takes roughly 1.5 days). Once atthat temperature, the oxygen is purgedand the 24/7 irrigation with percolatebegins. The percolate tanks are heatedwith thermal energy from the CHPunit. During commissioning of theplant, liquid manure was brought in asa percolate “starter.” The digesterfloors have a 1.5 percent slope thathelps drain the percolate.

Retention time in the digesters is

46 BIOCYCLE MARCH/APRIL 2014

ZWEDC installed two 2G Cenergy 800kW combined heat and power units.Thermal energy from the engines isused to maintain percolate atthermophilic temperatures.

“We were seeking aprocessing system that was

not only a net energyproducer, but also requiredminimal processing, andlittle water and energy toperform optimally,” says

Emily Hanson of ZWEDC.

about 21 days — essentially theamount of time for peak biogas produc-tion. Biogas from each tunnel is pushedinto the airspace of the percolate tank,combining biogas from each operatingdigester to yield a homogenous “rich”gas (higher methane content). In turn,the biogas goes to storage bladders onthe roof, which then feed two 2G Cener-gy 800 kW CHPs. “It is important tomaintain an optimal flow of ‘rich’ gas tothe CHPs, as that minimizes emissionsfrom the engine, which is critical forour air permit,” notes Hanson.

COMPOSTING AND CURINGAs biogas production decreases, oxy-

gen is introduced into the tunnel; theair is pushed up through the mass topurge all the methane from the mate-rial. Volume reduction after anaerobicdigestion is about 30 percent. A front-end loader removes the material fromthe tunnel and takes it to a BHS de-compactor designed to both loosen upthe digestate and mix in a bulkingagent if necessary. ZWEDC also in-stalled a BHS disc screener to removelarge contaminants before moving thedigestate into the in-vessel composters.

Roughly two tunnels’ worth of di-gestate fit into one in-vessel compost-ing tunnel. Material is composted inthe vessels for four to five days, pri-marily to remove ammonia and reduceodor compounds prior to curing out-side in windrows. The air pulledthrough the building for air exchanges(3/hour) is forced through the materi-al in the composting vessels to provideaeration before passing through twoacid scrubbers designed to treat

35,000 cubic feet per minute (CFM) ofexhaust air. The scrubbers use sulfu-ric acid to chemically react with am-monia from the compost tunnels toproduce ammonia sulfate, a liquid fer-tilizer. Over 90 percent of the ammo-nia is removed, along with particulatematter and odor compounds. In thelast step, air is distributed to one offour biofilters (each 52-feet in diame-ter) containing a mix of wood chipsand finished compost.

After in-vessel composting, materialis moved to an outdoor curing pad thatis built from crushed recycled rock fromthe adjacent Zanker resource recoveryfacility. Compost cures for four to fiveweeks after which it is screened tothree-eighth-inch minus with a Ver-meer trommel. All water draining fromthe site flows to a biotreatment con-tainment area.

INITIAL RESULTSAs of mid-February, all eight di-

gester tunnels in the initial phase werefilled and operating. (The second bankof eight digester tunnels was in the fi-nal stages of construction and testingat the time of publication.) RepublicServices continues to tweak its collec-tion routes to maximize the number ofloads that can be hauled directly to theAD/composting plant versus having tobe processed at its MRF. “Our recyclingcoordinators audit the wet and dry con-

tainers, and work with customers — es-pecially those with compactors — toimprove separation,” notes Cheso.

Of the incoming tonnages, 95 per-cent is comprised of about 70 percentorganic material and 30 percent nonor-ganic residuals/contamination. The re-maining 5 percent of incoming tonnageis 80 to 95 percent organics and 5 to 20percent nonorganic residuals/contami-nation. Currently, no yard trimmingsare added to the initial mix (e.g., forstructural material) beyond what iscontained in the organics receivedfrom Republic.

The facility is producing about 375 to425 m3/hour of biogas with a methanecontent at or above 60 percent. Ap-proximately 20 percent of the electrici-ty generated is used to operate all as-pects of the AD/composting plant,except for the rolling stock. Residue isdisposed at Republic’s landfill on New-by Island. “ZWEDC does not pay fordisposal,” says Hanson. “We are pro-vided vouchers based on the allowableresidue as determined by inbound ton-nage per Organic Stream.”

Over time, ZWEDC may be able toreceive organic wastes from othersources. Under its contract with theCity of San Jose, the company mustguarantee capacity for and anaerobi-cally digest the first 5,000 tons/monthof “Suitable Material” (i.e., suitablefor digestion) during the first year offacility operation, for a total of 60,000tons/year per year. Depending on howthat varies from year to year, ZWEDCcould take additional organic wastesto reach its 90,000 tons of annual ca-pacity (Phase One). “This was calcu-lated based on the total amount of or-ganic material delivered from SanJose’s commercial sector, less materi-al delivered that was not suitable fordigestion (residue and contamina-tion),” explains Hanson. �

BIOCYCLE MARCH/APRIL 2014 47

Material from the in-vessel compostersis moved to an outdoor curing pad. Allwater draining from the site flows to abiotreatment containment area(foreground).

The facility is producingabout 375 to 425 cubicmeters/hour of biogas

with a methane content ator above 60 percent.