Converting gin and dairy wastes to methane

Alternatives to gin trash and manure disposal would benefit both the cotton ginning and dairy industries. Anaerobic digestion produces both methane gas and a class A soil amendment. Gin and dairy wastes were combined in the solid phase portion of a two-phase anaerobic system to determine the combinations of temperature, rewetting interval, and mixture ratio that maximize potential methane gas production and minimize process completion time. No significant volatile fatty acid formation occurred after leachate pH approached 7.0, indicating process completion. This took approximately three weeks when temperatures were above 32°C (90°F), mixture ratios were below 5:1 (gin to dairy waste, dry mass basis), and the solid phase was wetted twice daily. Ten percent of the mass was converted to soluble chemical oxygen demand (COD), which has potential for conversion to methane in the second phase.