Decentralized Organics to Energy with Containerized Anaerobic Digestion
by John D. Forcier (Lee Enterprises Consulting, Inc./Biofuels Digest) Most trash and recycled waste materials are being processed on a regional basis to maximize the economy of scale. There have been various attempts to gather and process organic waste materials utilizing similar methods, but the challenges are far from resolved. As we transition to the bans on organic materials from landfills and even more organic materials will need to be processed, other organics reuse solutions will need to be deployed.
Organics Bans and Waste Recycling Laws
There are several States (including Vermont, Massachusetts, Connecticut, Rhode Island and California) and some municipalities (including New York City) that have passed new organic waste bans and recycling laws. Generally, they ban most or all organics (other than wastewater biosolids in most cases) from landfills by the years 2018 to 2020. There are intermediate deadlines that are based on thresholds (with less and less tons per year per producer) that are already in place. There are other intermediate deadlines until the final effective dates. In some States, there are exemptions, based on the distance to organics processing facilities, while in some cases there are no distance exemptions.
Current Organics Reuse Solutions
The two most popular beneficial reuse solutions for organic waste are:
- Composting- To date, most of the reused organic waste has been brought to compost facilities. However, there are significant amounts of land that would be needed for most composting solutions. Also, some of the organic waste products are not well suited for compost facilities. Most importantly, most compost facilities give off significant amounts of greenhouse gases in the form of CO2.
- Anaerobic Digestion- Many of the current anaerobic digester systems are not well suited for mixed substrates and can’t take full advantage of the energy from the organic feedstocks. Of those that are well suited for organic feedstocks, most of them are larger regional AD systems for economy of scale.
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Now, with newer containerized AD systems, they can scale down as low as 10 kW for economical decentralized solutions. That size will handle as little as 0.5 tons/day (180 tons/year) of food waste or as few as 50 milking cows, with other standard sizes up to 3 tons/day (1,100 tons/year) of food waste.
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By providing a local, decentralized solution, the cost of transportation, diesel consumption and carbon emissions are all reduced. There are many great applications at 10 kW – 100 kW for these containerized AD systems including: colleges, hospitals, hotels, grocery stores, small to medium farms, food processing facilities, etc. A simple dewatering/nutrient capture system can also be provided to produce valuable organic fertilizers for local use and/or sale.
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Some typical feedstocks (substrates) for containerized anaerobic digesters can include animal manures, pre-consumer and post-consumer food waste, food processing waste, certain farm crops, fats, oils and grease (FOG), source-separated-organics (SSO) and other organic byproducts. READ MORE and MORE (SEAB Energy)
