Welcome to the Southwestern Cotton Ginning Research Laboratory/
New Mexico State University Bioenergy Experiment

Combining dairy and cotton gin wastes in a biphasic anaerobic reactor converts these resources into a biogas (50 to 70% methane gas) and a pathologically safe soil amendment. The compost can be spread on fields growing food crops (biosecurity). The methane can generate heat or electricity (distributed energy). Two liabilities become two assets (win-win). This technology is suitable for the arid climate of the Southwest and compliments our regional dairy culture.

The New Mexico State University prototype biphasic reactor has successfully demonstrated this technology on combinations of feed materials. Methane gas quality and production volume is high. Cycle time is short. This figure shows pumps and probes between the solid phase reactor and the methane phase columns. By courtesy of Dr. Zohrab Samani, NMSU.

Loading cotton gin trash and dairy manure in layers in the solid phase reactor (a steel trash dumpster that has been made air-tight). Cotton gin trash (7,600 BTU/lb.) provides necessary carbon while dairy manure (2,500 BTU/lb.) supplies nitrogen and cellulase (to break down cellulose).

Leachate from the bottom of the solid phase pile is recirculated to the top, extracting volatile fatty acids as cellulose degrading bacteria break down the gin trash and manure. The leachate is then fed to anaerobic columns where mesophilic bacteria convert the VFA to methane. By courtesy of Dr. Adrian Hanson, NMSU.

Cross section showing experimental reactors built by the USDA-ARS Southwestern Cotton Ginning Research Lab.
The USDA-ARS conducted experiments to optimize parameters for solid phase operation.

NMSU undergraduates assisted with reactor construction and operation at the SW Cotton Ginning Research Lab.

Dr. Adrian Hanson inspects solid phase reactors operating at SWCGRL. NMSU labs tested leachate samples for chemical oxygen demand (COD) and residue constituent concentrations (N, P, K, etc.).

Solid phase study results indicate Chemical Oxygen Demand (COD) of effluent fell when pH went up (lower pH is an indicator of volatile fatty acid content). Increasing manure to gin trash ratio and increasing temperature shortened the time to complete digestion. Leachate recirculation frequency was not as important provided it occurred daily.

This response surface shows the influence digester temperature and mixture ratio have on the time to reach process completion.

This plot (by courtesy of James T. Riordan, Graduate Student, NMSU Microbiology Dept.) shows the decline in Coliform Units per ml with days. The axenic Cotton Gin Waste had been triple autoclaved, ruling out microbial competitive exclusion. It appears that some chemical in cotton gin trash (that is not in cellulose) disinfects the manure, reducing pathogen populations to below detection in two weeks (the normal cycle time). The resulting soil amendment can be safely applied to food crops.

Current Collaborators Include:

Full Scale Prototype:

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Last updated 14 March 2005