Digester technology developed and evaluated at Washington State University. Photo courtesy of C. Kruger, with permission from the Journal of Soil and Water Conservation.
Anaerobic digesters provide the technology to convert animal manure into methane, which can then be converted to electricity, and odor-reduced effluent, which can be used for fertilizer.
Anaerobic digesters are an expensive technology but have been made available in many areas through cooperative arrangements and public subsidies.
Digester manufacturers have defined a wide range of benefits. Reduced emission of greenhouse gases is one of the global public benefits of the digesters. Some potential also exists for using digested dairy fiber as a substitute for peat in horticultural operations, according to one study (C. Kruger et al. 2008. High-quality fiber and fertilizer as co-products from anaerobic digestion. Journal of Soil and Water Conservation 63(1):12A-13A).
Because the resulting high nutrient concentrations, use of the digested influent as a fertilizer requires careful nutrient management to prevent nutrient overloading (also reported by Kruger et al. 2008).
Third-party evaluations to date have ranged widely—some supportive, some cautious, and some critical.
The combination of entities involved and impacted make this an interesting and important topic for discussion and debate. Do you have an experience with an anaerobic digester system in your area to share?