Energy Recovery from Poultry Manure in the Process of Semi-Continuous Anaerobic Co-Digestion with Sewage Sludge

Abstract

The possibility of co-digestion of poultry manure and sewage sludge and its effect on increasing biogas production compared to processing sludge alone was investigated. The process was performed in two continuously stirred-tank glass reactors at mesophilic conditions, with 20 days of hydraulic retention time. In the first stage, the batch assay with sewage sludge was applied to promote the development of an anaerobic community. The second stage involved feeding the reactors on a semi-continuous regime with sewage sludge for the control sample and a mixture with the gradual addition of poultry manure from 2.5-60%. During the experiment, the most important parameters affecting the process and the quantity and quality of the obtained products in the form of biogas and digestate were monitored. The study’s results indicated an advantage of the co-digestion process of poultry manure and sewage sludge over the digestion of sludge alone in terms of process efficiency. The highest biogas production was obtained with a co-substrate ratio of 42% manure to 58% sewage sludge (ratio based on volatile solids). Co-digestion had no significant effect on gas quality; in both cases, the methane content was more than 60%. Moreover, a digestate with fertilizer potential was obtained for each sample.

Keywords: anaerobic co-digestion, animal by-products, sewage sludge, biogas production, methane yield, GHG emissions