Enhancing methane production during anaerobic digestion of sewage sludge using enzymes produced by autochthonous microbial consortia

Abstract

Sewage sludge represents a primary organic waste stream in wastewater treatment plants, where anaerobic digestion enables biomethane recovery; however, the initial digestion phase is frequently rate-limited by complex organic hydrolysis. This study evaluated the potential of enzymes produced by an autochthonous cellulolytic bacterial consortium isolated from digested sludge to enhance biomethane production, comparing free and activated carbon-immobilized forms against commercial cellulolytic enzymes (Cellic CTec2). Non-immobilized autochthonous enzymes increased biomethane yield by up to 21.7% relative to untreated sludge, achieving performance comparable to commercial preparations (p > 0.05). Mechanistically, free enzymes accelerated early-stage hydrolysis during the initial 3–5 days, whereas carrier-immobilized enzymes exhibited a controlled-release kinetic profile extending hydrolytic activity up to day 7 while offering protection against endogenous proteolytic degradation. Additionally, activated carbon carrier supplementation facilitated the adsorption of inhibitory extracellular polymeric substances (EPS) specifically protein (PN) and polysaccharide (PS) fractions, reducing mass transfer resistance and stabilizing digestion kinetics. Although net cellulose degradation remained unvaried across treatments due to rapid baseline microbial turnover, enzymatic addition shortened effective digestion lag times. Overall, autochthonous enzyme harvesting provides an effective, low-input strategy to enhance anaerobic digestion efficiency without relying on costly external enzyme inputs.