Mechanisms of potassium permanganate pretreatment improving anaerobic fermentation performance of waste activated sludge

Potassium permanganate (KMnO4), one typical strong oxidant, is used extensively in various applications. However, its impact on anaerobic fermentation of waste activated sludge is unknown. This paper therefore aims to investigate its effect on generation of short-chain fatty acids (SCFAs) and qualities of fermentation liquor and fermented solid sludge. Experimental results showed that when KMnO4 increased from 0 to 0.1 g/TSS, the highest SCFAs production enhanced from 33.9 to 251.8 mg COD/g VSS. The mechanism analysis revealed that KMnO4 addition increased the disintegration of sludge cells and the degradation of substantial recalcitrant organics in sludge such as humus and lignocellulose, thereby provided more substances for SCFAs generation. Ultraviolet absorption spectroscopy analysis showed that KMnO4 addition destroyed unsaturated conjugated bonds and decreased organics aromaticity, thereby promoting humus and lignocellulose degradation. GC/MS analyses showed that several micro-molecular substances (e.g., acid-like, alkane-like, and alcohol-like organics) were generated from KMnO4 pretreated humus and lignocellulose, and some of them were demonstrated to serve as substrates to produce SCFAs. The enzyme activity and model-based analyses showed that although KMnO4 restrained all the microorganisms to some extends, the activities of SCFAs generators were much higher than those of SCFAs consumers. In addition, the sludge mixture was separated into liquid and solid fraction after anaerobic fermentation, and the components in fermentation liquid and solid sludge were tested. It was found that the addition of KMnO4 effectively reduced the categories and total detected frequency of refractory organic pollutants in fermentation liquid, which improved the quality of the produced SCFAs. KMnO4 addition also increased the inactivation of fecal coliforms and degradation of emerging contaminants in fermented sludge, which were helpful to its final disposal.