Studies of sludge collected from the anaerobic digester of a meat processing company

Abstract

Anaerobic digestion is commonly used as a wastewater treatment step where complex biological substrates are progressively degraded in the absence of oxygen to produce methane and carbon dioxide with hydrogen and volatile acids occurring as intermediate products. These intermediate products are more valuable commodities than methane so there is interest in optimizing their production and recovery from the anaerobic digestion process. In previous work, a sludge sample collected from a local meat processing company was reported to produce significant amounts of hydrogen at ambient temperatures.

In the present study, eleven sludge samples were collected from the same meat processing company and characterized in terms of their solids content, pH, as-collected gas production profiles and gas production profiles and gas production rates, when repetitively batch fed with glucose at their original pH and also at pHs successively lowered to pH 4.5. Similar studies were performed using cellulose as the substrate.

In these studies, no hydrogen was produced by the as-collected sludges, but hydrogen was produced by two of the sludges when batch fed with glucose. Detailed studies of the effect of pH on one of the sludges revealed that hydrogen was produced when the pH was lowered to between 5.2 and 5.4 and batch fed with glucose. No hydrogen was formed when the sludges were batch fed with cellulose under the conditions investigated. Acid conditions severely inhibited gas production rates when both glucose and cellulose were used as substrates. Gas production rates with cellulose substrate were systematically slower than when glucose was used as the substrate.