Characteristics of dissolved organic matter and their role in membrane fouling during simultaneous sludge thickening and reduction using flat-sheet membranes

Four parallel simultaneous sludge thickening and reduction reactors using flat-sheet membranes were employed for the aerobic digestion of sludge to explore the characteristics of dissolved organic matter and its membrane fouling effect. During the initial 8 days of using flat-sheet membranes for simultaneous sludge thickening and reduction (MSTR), a notable increase was observed in the concentrations of humic acids and compounds that resemble soluble microbial by-products in the effluent. Subsequently, a fluctuating trend in humic acid levels ensued, accompanied by a gradual decline in soluble microbial by-product-like substances. Post the initial 8-day period, the capillary suction time (CST) rose from approximately 400 s to over 800 s, the viscosity increased from 20 mPa s to 38 mPa s, and the membrane resistance increased from roughly 6.0e+ 11 m⁻¹ to approximately 9.0e+11 m⁻¹. This phenomenon can be attributed to the clogging of pores by foulants whose size is similar to that of the membrane pores leading to the accumulation and deposition of macromolecules and larger particulates forming gel layers and cake layers. The interplay among diverse microorganisms engenders functional modules, collectively influencing the distribution and characteristics of dissolved organic matter within the MSTR. These microorganisms exert their metabolic effects individually and interact reciprocally, creating synergistic and inhibitory mechanisms. Notably, the synergistic interactions among microorganisms predominated, culminating in an enhanced effluent quality within the system.