Reference Type: Electronic Resource
Title: Anaerobic Digesters Control Odors, Reduce Pathogens, Improve Nutrient Manageability, Can be Cost Competitive with Lagoons, and Provide Energy Too!
Primary Authors: Moser, Mark A.
Published: Environmental Protection Agency
Abstract: There has been quite a bit of discussion and information published about energy production from anaerobic digesters. The basic design concepts proven by successful digesters built in the 1980's are applicable today. Additional benefits from anaerobic digestion have not been emphasized. Anaerobic digestion is more extensively used outside of the US where concern for treatment of animal waste has been a concern for a longer time. In todays world, odor and pathogen control are important. The first pig manure digester systems in the US were installed principally to control manure odors. The odor control goal was successfully met. It has been suggested that recent US episodes of surface water contamination with E. coli, cryptosporidia, and pfiesteria blooms are linked with manure discharges. It can be expected that future legislation will address pathogen control. Pathogen reduction using anaerobic digesters has been extensively studied in Denmark, where many centralized animal waste digesters with strict requirements for pathogen reduction are in place. Anaerobic digestion will eliminate >99% of most pathogens. Recent regulatory changes require significantly more investment in manure treatment and storage systems. A one cell anaerobic lagoon designed for treatment and storage of pig manure under Natural Resources Conservation Service (NRCS) or American Society of Agricultural Engineers (ASAE) standards can be a very large lagoon. A two cell lagoon designed for methane recovery from the first cell can reduce the total lagoon volume requirement by 10 - 25% per NRCS Conservation Practice Standard 360. A two part manure treatment system including a heated, mixed anaerobic digester preceding a storage structure reduces total volume requirements by 50 - 80%. The construction cost savings from reduced volumes can be significant and may pay for digester substitution in the manure system. Substituting a digester for a lagoon at the same planned investment level results in a very low cost supply of methane for use on the farm and biologically stabile and virtually odorless manure. During anaerobic digestion much of the manure organic N is converted to ammonia. Ammonia application for crop growth can be more accurately managed than organic N application. Methane recovery and use reduces the effect of direct methane release to the atmosphere, where it is considered a problem as a greenhouse gas. Full scale, long term operating digester systems are described. References and calculations supporting conclusions are included.
Ag Matters Catalog ID: 420