Renewable Energy Anaerobic Digester Feasibility Study
The University of California, Davis retained HDR to evaluate the feasibility of developing a Renewable Energy Anaerobic Digester (READ) facility to treat organic wastes from the campus, including agricultural and food waste. Other possible feedstock materials included waste paper towels, municipal solid waste (MSW), and biosolids from the wastewater treatment plant (WWTP). The goals of the READ facility are:
- Production of a renewable energy source
- Diversion of organic materials from being landfilled while retaining the highest and best use of recyclables
The feasibility study explores a variety of possible anaerobic digestion treatment technologies which include, but are not limited to:
- Traditional low solids digestion similar to municipal WWTP facilities
- Anaerobic phased solids (APS) process developed by Dr. Ruihong Zhang of UC Davis
- Dry fermentation using an enclosed bunker or using a flexible membrane liner
- High solids digestion for agricultural wastes similar to processes employed in Europe
Various anaerobic digestion technologies will be evaluated based on relative capital or operational cost, appropriateness to treat the feedstock, ability to contain odors, and proven track record.
In general, the facility will include enclosed unloading and handling operations to prevent the migration of fugitive odors, a phased digestion system with a hydrolysis/acidification phase where volatile solids would be converted into volatile organic acids. The acids from the hydrolysis/acidification phase would be converted to biogas containing methane and carbon dioxide in the methanogenic phase.
Biogas will be extracted from the digesters and could be used in a variety of energy production systems such as a fuel cell, microturbine or internal combustion engine. Other uses include supplementation of natural gas boiler fuel, or cleaning the gas for injection into the university's natural gas distribution system. Undigested solids will likely require stabilization using an aerobic process such as aerated static pile composting.