Anaerobic Digestion of Flushed Dairy Manure

In Florida, dairies use water extensively for barn flushing and waste collection, because it is sanitary and less labor-intensive. However, the practice of hydraulic flushing results in greatly increased volumes of dilute wastewater. In addition, many dairies have incorporated fan and sprinkler cooling systems for cow comfort in the warm Florida climate, which contributes even more water to the waste stream. The use of large volumes of flushwater for dairy manure collection, however, means that conventional anaerobic digestion using complete-mix or plugflow technologies is neither practical nor economical, since the dilute manure streams (typically less than 1% TS) would require excessively large digester volumes and higher heat inputs in order to achieve the hydraulic residence times and operating temperatures required for stable digestion (HRT > 15 days at 35C).