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Previous work with agricultural anaerobic digesters shows existing system designs must be improved in two key areas: 1) energy consumption must be minimized and 2) the system must be designed to accept a range of co-feedstocks. Current anaerobic digester systems usually require a significant fraction of their self-generated energy to heat the digester and power pumps, mixers and motors, leaving only small fraction of the energy produced to be put to profitable uses. Maintaining a stable thermal profile is particularly challenging for digesters operating in northern states such as Michigan during wintertime. The system under development by Quantalux and MSU will demonstrate thermal and electrical energy minimization, including the use of renewable energy, and also energy recovery techniques.

The addition of co-feedstocks to manure-based digesters offers the potential for significantly higher biogas production, but many co-feedstocks are available only on an irregular basis. This calls for an improved approach for supplying and integrating various organic waste material into the digester while maintaining high biogas production. Co-feedstocks are organic waste materials can be sourced from local food processors (peels, spoilage), pre/post-consumer sources or from byproducts in the food production process (off specification or nonedible products). Adding co-feedstocks can substantially increase biogas production for a given digester, but this process requires pre-planned mixing, high-level control of feed-rates and enhanced process monitoring.

Quantalux and MSU have developed an innovative design for an anaerobic digester that is both energy efficient and that will readily accept various co-feedstocks for digestion. The system is sized for 5-7 cows (tank size 10 m3) and is designed to be scaled-up to 100-300 cow size. Testing will show that the combination of energy and feedstock management will increase revenue generated per dollar of investment. The design for the pilot system can be readily scaled-up to deliver a turn-key anaerobic digester for small to mid-sized dairy farmers in Michigan and elsewhere. This work is part of a USDA-sponsored SBIR Phase II awarded to Quantalux in 2010.