Co-digestion of sewage sludge and dewatered residues from enzymatic hydrolysis of sugar beet pulp.

Unlabelled: Sugar beet pulp residues (SBPR) from hydrolysis and dewatering of beet pulp were co-digested with municipal sewage sludge (MSS). The highest biogas yields of nearly 512 dm(3)/kg VSfed (volatile solids fed) were achieved for SBPR, treated both as the monosubstrate and as a mixture with MSS (1 : 1 by weight). Simultaneously, the highest methane production of 348 dm(3) CH4/kg VSfed was determined when the sewage sludge was co-digested with 35% SBPR. The analysis of digestate showed that neither ammonia nor volatile fatty acids destabilized the biogas production.

Implications: Processing of sugar beet pulp into bioethanol via enzymatic hydrolysis and microbial fermentation has become increasingly attractive. However, in this process, only the liquid fraction derived from hydrolysis is subjected into alcoholic fermentation, whereas the remaining solid fraction needs to be utilized. This study demonstrated that sugar beet pulp residues after bioethanol production can successfully be co-digested with sewage sludge to increase biogas productivity of anaerobic digesters located at wastewater treatment plants.