The Need

Liquid phase anaerobic digestion (LAD) and solid state anaerobic digestion (SAD) traditionally exist as two separate processes often found in farming or food processing industries. Each independent method possesses distinct advantages and disadvantages. SAD requires larger amounts of inoculation materials and longer retention times than LAD processes. However, LAD effluent runoff is much more difficult to manage than SAD residues. Currently, composting is used to treat the LAD effluent which generates methane. A combined solid and liquid process would have the advantage of increasing methane output while effectively treating municipal or agricultural wastes.

The Technology

The Ohio State University researchers, led by Dr. Yebo Li, proposed an improvement on the anaerobic digestion processes. In this combined liquid and solid phase anaerobic digestion process, the effluent from an LAD reactor is mixed with organic solid waste and fed into a SAD reactor for digestion. With this design, there is no need to treat the wet effluent runoff from the LAD reactor because the effluent is a feed for the SAD reactor. The effluent feed circumvents the need for inoculation materials and retention time is also greatly reduced. When the SAD reactor runs under thermophylic conditions (50 - 60 degC), the pathogen in the residue is eliminated. The residue from the SAD reactor will hence be safe for use as an organic fertilizer. Compared to composting, this proposed two stage process will generate significant amounts of methane with an estimated 200% increase in production quantity over traditional composting techniques.

Commercial Applications

• Renewable energy
• Cleantech and Environmental
• Agriculture
• Biorefining/Bioproducts

Benefits/Advantages

• Elimination of required seed materials for solid anaerobic digestion
• Produce high yield of methane and compost like organic fertilizer
• Uses both wet and dry waste
• Increase the gas production
• No treatment for the liquid effluent