Unveiling the Mechanism of Urine Source Separation-Derived Pretreatment on Enhancing Short-Chain Fatty Acid Yields from Anaerobic Fermentation of Waste Activated Sludge

Abstract

A novel strategy employing urine wastewater derived from source separation technology, to pretreat waste activated sludge (WAS) for promoting yields of short-chain fatty acids (SCFAs), has been proposed in this study. It was found experimentally that SCFA production could ascend up to 305.4 mg COD/g VSS (volatile suspended solids) with a urine volumetric proportion of 1:2 to the whole reaction system, being 8.8 times that produced in the control. Exploration of the mechanism indicated that WAS disintegration was significantly enhanced due to the synergistic effect of urea and free ammonia (FA). Degradation rates of model organic substrates and measurements of critical enzymatic activities demonstrated that hydrolysis and acidogenesis were inhibited under high urine content (urine proportion of 1:2), while not significantly affected under low urine content (i.e., 1:4), which might be attributed to metal ions existing in urine wastes alleviating the inhibition induced by FA. In contrast, methanogenesis was negatively suppressed by any urine concentration owing to its higher sensitivity to the environmental variations. Shift of microbial population further elucidated the abundance of hydrolytic and acidogenic microbes were enriched in the fermenters with urine addition. The findings provide a new thought for recovering resources from wastes, potentially reducing the pressure of sewage and sludge treatment in wastewater treatment plants.

Optimizing anaerobic digestion: Benefits of mild temperature transition from thermophilic to mesophilic conditions

“…LB-EPS and TB-EPS were extracted to reveal the EPS variations and cell decomposition. EPS is a high-molecular polymer secreted by microbes as a protective barrier against microbial risks from environmental stressors [ 15 ]. The soluble PN concentrations in the LB-EPS and TB-EPS decreased significantly ( p < 0.05) in both ST and MT during phases 2 and 3 ( Fig.…”

“…The enzyme activities of α-glucosidase (α-Glu), protease (PT), butyrate kinase (BK), acetate kinase (AK), carbon monoxide dehydrogenase (CODH), and coenzyme F 420 were detected to elucidate the protein responses of the microbiome. To reveal the maintenance of microbial structural integrity, three layers of extracellular polymeric substances (EPS) — that is, slime EPS, loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) — were extracted using the modified heating method [ 15 ]. The composition and structure of the EPS fractions were characterized by three-dimensional excitation emission matrix spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy.…”

“…The physiological status of microbial cells can be damaged when exposed to inhibitors (e.g., capsaicin, microplastics, and antibiotics) and adverse metabolic conditions (e.g., temperature and pH changes) [ 2 , 14 ]. In these scenarios, cell membrane integrity and microbial viability would be reduced, intracellular substances would be released, and cell energy metabolism would be downregulated, resulting in poor biogas production [ 15 ]. Thus, identifying the cellular functional state, intracellular substance release, and energy metabolism level can reflect the physiological responses of microbial cells to environmental stressors.…”