The Characterization of Sulfur Flows in Farm Digesters
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Ludington, David; Weeks, Stanley
The flow of sulfur through eight dairy farms in New York State, inputs to animals, digester influent and effluent and biogas, were studied from January 2007 to March 2008. Digesters on five farms were traditional plug flow, two were horizontal and mixed and one was vertical with a mixer. Food waste was added to the digester at two dairy farms and there was pre-separation of solids at two farms. On the farms that did not use food waste, 88 percent of the sulfur entering the digester came from the total mixed ration (TMR), 5 percent from drinking water and 7percent from bedding. Where food waste was used 73 percent came from the TMR, 10 percent from food waste, 13 percent from water and 4 percent from bedding. One farm using food waste had a high sulfur content drinking water which shifted these percentages. The concentration of hydrogen sulfide in the biogas ranged from 1,020 to 6,730 ppm. Digesters with no pretreatment of influent averaged 11.1 pounds of sulfur entering the digester for each 100 cow-days, those with pretreatment averaged 4.8 while those with food waste averaged 13.8. On average, 25 percent of the sulfur entering the digester was removed in the biogas.
Anaerobic Digestion; Dairy Manure; Biogas; Sulfur Flows