Vermont Tech Community Anaerobic Digester! Harvesting renewable energy & recycling nutrients for a more sustainable community!"#$%& '(%)*+&,-$).%($#& www.digester.!
VTCAD 3 April!
It takes a village! Major funding: U.S. Department of Energy Vermont State Colleges Invaluable help and funding also from: U.S. Senator Patrick Leahy Vermont Sustainable Jobs Fund Vermont s Clean Energy Development Fund Vermont Agency of Agriculture, Food and Markets Vermont s Agency of Natural Resources Vermont s Department of Public Service Vermont s SPEED program Natural Resource Conservation Service Kresge Foundation Town of Randolph Tri-Town Alliance Vermont Environmental Consortium Project founder Central Vermont Solid Waste District Project founder This material is based upon work supported by the U.S. Department of Energy under award number DE-FG36-08GO88182.
Community AD! Community (or cooperative) AD is common in Europe but we not yet in the US. An AD facility owned cooperatively, municipally or privately recycles organics produced by a community. Organics producers or collectors benefit. Renewable energy is produced & offsets some cost of organics recycling. Nutrients are recovered and distributed to farmers and others in the food chain. Advantages?! Allows small farms and communities to use an technology that requires capital and Significant regulated operation, maintenance, record keeping & nutrient tracking.
Geeky technical pre-tour tour! The big components:! 1.! Reception pit 2.! Hydrolysis tank 3.! Anaerobic digestion tank 4.! Genset 5.! Solids separator bay 6.! Digestate storage tank!"#$%&'()( *+,%-+#%+.( &" %"!" '" N #" $"
Feedstock: 51% on-farm / 49% off-farm! manure & crops processing residuals
Feedstock to date! Initially filled with ~450,000 gallons of conditioned cow manure: manure that had been stored in the manure pits since mid-summer. Over the last month we ve added small amounts of: Heady Topper brewing waste from the Alchemist Long Trail yeast waste Glycerol fraction from Nava Bioenergy s biodiesel production Our short-term plans are to: slowly & deliberately add a variety of food processing residuals like whey &FOG while maintaining homeostasis; collecting data; working through logistics; and then adding food residuals collected here at the college.
Feedstock planning: phase 3! '%!!!" '$!!!" '#!!!" '!!!!" Meal volume near maximum Biogas ()**+,-./)0" within 24% of max FOG 12./)0" could increase biogas &!!!" %!!!" $!!!" #!!!"!" 51%! Vermont Tech Osha/ Dutton RTF Ayers crops 49%! whey diary DAF buttermilk brewery!"#$% &'()*+",(% -./",%,-../0123-4" 5(23-4"
Feedstock planning: phase 4! '%!!!" '$!!!" '#!!!" '!!!!" Meal volume maximum Biogas ()**+,-./)0" maximized Focus 12./)0" on local residuals &!!!" 51%! 49%! %!!!" $!!!" #!!!"!" Vermont Tech Osha/ Dutton RTF Ayers crops whey buttermilk & local residuals!"#$% &'()*+",(% -./",%,-../0123-4",-../0123-4" 5(23-4" 5(23-4"
Feedstock partners! Feedstock: strong & local partnerships Vermont Creamery Ayers Brook Goat Dairy Recycled Organics Grow Compost Nava Bioenergy Nutrients: up to nine local farm partners Cow dairies Goat dairies Horse farm
1. Feedstock reception storage & mixing! Daily meal: 15,840 gallons of feedstock @ 51/49% Delivered directly to the preparation pit or to one of three stainless steel storage tanks in the reception bay. &" Meals are assembled by pumping volumes of each feedstock into the preparation pit and mixing them with a chopper pump and propeller mixer. The goal is to create consistent meals with neutral ph, % solids, buffering capacity, etc. Pasteurizer can be used to heat and pasteurize feedstock. %"!" '" Ferric chloride may be added to reduce formation of H2S if needed. Storage capacity of the hydrolyzer allows 5-day feeding. #" $"
2. Hydrolysis! Meals are pumped to the 135,000-gallon hydrolysis tank designed to hold 106,000 gallons of feedstock. Bacterial fermentation uses up oxygen, creating anaerobic conditions over a period for 3-6 days. Fermentation breaks food particles and macromolecules down into amino acids, fatty acids and sugars, and then into small organic acids. Some gases, carbon dioxide and a small amount of methane, are produced. &" %"!" '" #" $"
Complete-mix tanks! Feedstock is mixed both vertically & horizontally to increase efficiency. Roughly 10 mixing / hour. Undigested material can be purged during operations.
3. Anaerobic digestion! After 3-6 days of hydrolysis, organics are are pumped to the 410,000-gallon anaerobic digestion tank designed to hold 317,000 gallons of feedstock. The AD tank is topped by a 93,000-gallon balloon that passively captures biogas: a mixture of 50-60% methane, carbon dioxide, hydrogen gas, water vapor and hydrogen sulfide. In the absence of oxygen, methanogenic bacteria turn small organic acids like acetate into methane-rich biogas. &" %"!" '" The anaerobic digestion process takes about 20 days and harvests over 90% of the methane potential of the feedstock. #" $"
4. Combustion and co-generation! Biogas travels from the gas balloon to the generating engine (aka genset). As the biogas travels underground water condenses and is removed. The 375-kW 2G engine combusts the biogas, creating electricity and heat. The electricity is transmitted to GMP via a pole on Furnace Road and sold for $0.14/kWh under a 20-year SPEED contract. At maximal capacity VTCAD can produce 2.8 million kwh of electricity per year. &" %"!" '" Cooling jacket water heats the hydrolysis & AD tanks. Over the next three years, high-temperature engine exhaust heat will be captured and used to heat four campus buildings: Green, Nutting, Facilities and SHAPE. #" $"
5. Solids-separation! Digested organics (digestate) is pumped to a screw-press auger solids separator and separated into liquid and solid fractions. The separated solids have about 35% moisture content and are somewhat phosphate-enriched. Dairy bedding &" %" Field amendment Compost feedstock!" '" #" $"
6. Liquid digestate! Liquid digestate is enriched is pumped to a 115,000- gallon storage tank that holds one week s worth of digestate. Nitrogen-enriched digestate is either spread directly on fields or is moved to a 3-million-gallon storage pond and held until needed. &" %"!" '" #" $"
Community Nutrient Management Planning! Vermont Tech is regulated as an MFO and must implement: new best management practices a nutrient management plan (NMP) We ve worked with ACS to create a NMP featuring: 5.8 million gallons of digestate 409,118 pounds of N 45,834 pounds of P 609,966 pounds of K 5 farms 730 acres 0 5 miles of transportation
Community NMP! Vermont Tech:! Develops plans; Oversees implementation; Keeps & shares records 5 miles toward Randolph Village
Applied Research Questions! Soil & water quality studies Nutrient levels & soil structure ph, hardness, dissolved oxygen, macroinvertebrates Crop productivity following fertilization with digestate Reduction in synthetic fertilizer use Pathogen levels in separated solids Effects of Pasteurization on pathogens & microbes Simple diet formulation Development of simple metrics for highest & best use of organics Nutrient separation and / or dewatering Effective administration, record keeping & data collection Operational costs and benefits We are all about data collection & dissemination!
What do you want to know?! Send us questions and find contact info @ digester.!
Some thoughts about highest & best use! Each organics recycling technology has a place in helping Vermont implement Act 148. Composting in windrows or containers AD: plug-flow vs. complete mix vs. dry Other? Why not harvest the energy of high-energy feedstock in addition to harvesting its nutrients? In Europe, AD and composting are being used together (sequentially) to recycle large volumes of organics on relatively small sites while creating energy. Metric? energy / nutrient ratio + a structural factor?