Bottlenecks of anaerobic degradation of proteins in sewage sludge and the potential targeted enhancing strategies

Abstract

Proteins degradation plays a decisive role in the biogas production and subsequent dehydration of sewage sludge. And the anaerobic degradation of proteins in sewage sludge is limited by enzymatic hydrolysis barrier during hydrolysis process, selectivity and underutilization during amino acids fermentation, as well as molecular toxicity effects of metabolic products. Traditional pretreatments could solely improve the hydrolysis and even brought inhibition on the latter metabolism processes. In order to overcome the above bottlenecks, regulating microorganisms, secretion and activity of key enzymes, as well as interspecies electron transfer are proposed to be potential strategies of targeted enhancement of proteins degradation in sewage sludge. Since complex organic matters restricted the domestication of microorganisms and key enzymes that targeted degrade refractory proteins in sewage sludge, more profound investigations on regulating methods based on ORP control, bio-stimulation and AD-MEC etc. are needed to screen and domesticate the targeting microorganisms and enzymes related to refractory proteins degradation in AD systems. Moreover, more research should also be focused on the components and physical-chemical characteristics of refractory proteins in sludge and also their isolation strategies, especially which are remained in anaerobic digestate of sewage sludge after traditional pretreatments.