Removal of organic matter from food wastewater using anaerobic digestion at low temperatures enhanced by exogenous signaling molecule N-hexanoyl-homoserine lactone enhancement: Insight to extracellular polymeric substances and key functional genes.

This experiment aimed to study the effects of adding the exogenous signaling molecule N-hexanoyl-homoserine lactone (C6-HSL) on the anaerobic digestion of food wastewater at low temperature (15 °C). Daily addition of 0.4 μmol C6-HSL increased the average chemical oxygen demand removal from 45.98% to 94.92%, while intermittent addition (adding 2 μmol C6-HSL every five days) increased it from 45.98% to 72.44%. These two modes of C6-HSL addition increased protease and acetate kinase activity by 47.99%/8.04% and 123.26%/127.91% respectively, and increased coenzyme F concentrations by 15.79% and 63.16%, respectively. The regulation of loosely bound extracellular polymeric substances synthesis was influenced by C6-HSL, which increased protein and polysaccharide content in sludge. The relative abundance of Firmicutes and Bacteroidetes increased following addition of C6-HSL. After continuous addition of C6-HSL, the relative abundance of related functional genes such as amy, apgM, aceE, and accC increased, indicating that methanogens obtained sufficient substrate. The abundance of glycolysis-related functional genes such as glk, pfk, pgi, tpiA, gap, pgk, gpmA, eno, and pyk increased after the addition of C6-HSL, ensuring the efficient transformation and absorption of organic matter by anaerobic sludge at low temperatures. This study provides new comprehensive insights into the mechanism behind the enhancement of food wastewater anaerobic digestion by C6-HSL at low temperature.