Forage, Biomass and Biogas Integrated Systems for Animal Waste Management
Alternative outlets for animal waste disposal and recycling must be developed to reduce the waste stream and result in sustainable use of nutrients. This project is studying an integrated biomass and biogas energy production system as a tool for managing animal wastes.
1.) Determine nutrient removal from the waste stream via energy production and nutrient fate when land-applied to switchgrass.
2.) Determine total energy production from an integrated biogas-biomass system.
3.) Examine the economics of the system and components including environmental impacts.
The biogas digester system components have been designed, installed, and tested. Biogas generation and utilization is anticipated in January 1998. Large plots of switchgrass were instrumented at the Texas A&M University Agricultural Research and Extension Center at Stephenville. Dairy waste was applied to the plots to determine nutrient removal in biomass, residual nutrients in the soil, movement of nitrate-nitrogen in soil water and nutrients in surface runoff water.
During 1996 and 1997 Alamo switchgrass biomass increased with increasing nitrogen rate to a maximum of seven tons per acre at 518 and 572 pounds effluent-source nitrogen per acre in respective years. Less than one-fourth of the applied nitrogen and one-third of the concurrently applied phosphorus was removed in the biomass during 1996 and 1997. At the highest effluent rate 0 to 6-inch soil test phosphorus increased from 25 pounds per acre initially to 87 pounds in 1996 and declined slightly in 1997. Soil phosphorus in the 0 to 6-inch depth of the untreated switchgrass filter strip remained at initial levels after application of up to 210 pounds phosphorus in the upslope treated area. Nitrate-nitrogen and phosphorus content of water collected at 39 inches soil depth in the treated area was greater after heavy rainfall and increased with increasing effluent rate to about 4 parts per million. Both the nitrate-nitrogen and phosphorus content of water collected at 18 and 36 inches on ten dates in 1997 averaged less than 1 part per million. Runoff nitrate, phosphorus, and chemical oxygen demand were significantly reduced by passing through the filter strip.
The most important findings of the first three years of this study are that using dairy waste for land application to switchgrass for biomass production can produce seven tons per acre of biomass and switchgrass filter strips can significantly reduce concentration of pollutants in the surface runoff water. Leaching of both nitrate-nitrogen and phosphorus is becoming a cause for concern and further soil water quality monitoring is indicated.