Biogas Anaerobic Digester Considerations
Biogas Anaerobic Digester Considerations for Swine Farms in North Carolina
Collecting biogas from anaerobic digestion of swine manure can benefit the environment by reducing methane emissions (has potential value for equivalent carbon credits or greenhouse gas (GHG) credits), and by providing energy, as biogas is about 60 to 70 percent methane. Methane has an energy value of about 1,000 BTU/SCF1, so biogas can have an energy value of about 600 BTU/SCF.
Plug-flow or complete-mix anaerobic digesters using metal or concrete vessels have been used on dairy and other animal farms where the dry matter or total solids content in the wastewater is over 5 percent. These types of digesters are discussed in Barker (2001), Fulhage et al. (1993), Balsam (2006), and US EPA AgStar (2008a). However, as manure becomes more diluted, the volume of the vessel increases and this increases costs. Swine farms in N.C. typically use a flush system, either tank flush (several times daily) or shallow pit-recharge (about once per week), to transport manure from the barns. The resulting flushed wastewater is very dilute, about 98 to 99 percent water and 1 to 2 percent dry matter. The two types of digesters that are best suited for flushed wastes are: (1) In-ground ambient (or heated) covered digesters, and (2) Fixed-film digesters. Existing anaerobic lagoons can also be covered to collect biogas. able level. Loading rate of the lagoon is based on a design permanent treatment volume and is about 1 ft3 of treatment volume per pound of Live Animal Weight (LAW) for a feeder-to-finish operation, or about 5 to 6 pounds volatile solids (VS)/1,000 ft3 per day. Single-cell anaerobic lagoons have additional volume for manure and wastewater production for a period of time (usually 3 to 6 months), sludge accumulation (sometimes optional), temporary storage of excess rainfall (rainfall that exceeds evaporation), and runoff (if any), a 25-year, 24-hour storm rainfall and runoff amount, freeboard, and
Collecting biogas from anaerobic digestion of swine manure can benefit the environment by reducing methane emissions (has potential value for equivalent carbon credits or greenhouse gas (GHG) credits), and by providing energy, as biogas is about 60 to 70 percent methane. Methane has an energy value of about 1,000 BTU/SCF1, so biogas can have an energy value of about 600 BTU/SCF.
Plug-flow or complete-mix anaerobic digesters using metal or concrete vessels have been used on dairy and other animal farms where the dry matter or total solids content in the wastewater is over 5 percent. These types of digesters are discussed in Barker (2001), Fulhage et al. (1993), Balsam (2006), and US EPA AgStar (2008a). However, as manure becomes more diluted, the volume of the vessel increases and this increases costs. Swine farms in N.C. typically use a flush system, either tank flush (several times daily) or shallow pit-recharge (about once per week), to transport manure from the barns. The resulting flushed wastewater is very dilute, about 98 to 99 percent water and 1 to 2 percent dry matter. The two types of digesters that are best suited for flushed wastes are: (1) In-ground ambient (or heated) covered digesters, and (2) Fixed-film digesters. Existing anaerobic lagoons can also be covered to collect biogas. able level. Loading rate of the lagoon is based on a design permanent treatment volume and is about 1 ft3 of treatment volume per pound of Live Animal Weight (LAW) for a feeder-to-finish operation, or about 5 to 6 pounds volatile solids (VS)/1,000 ft3 per day. Single-cell anaerobic lagoons have additional volume for manure and wastewater production for a period of time (usually 3 to 6 months), sludge accumulation (sometimes optional), temporary storage of excess rainfall (rainfall that exceeds evaporation), and runoff (if any), a 25-year, 24-hour storm rainfall and runoff amount, freeboard, and