Study on anaerobic fermentation of waste activated sludge to produce volatile fatty acids by thermal-rhamnolipid treatment

BACKGROUND: The extracellular polymer and cell wall of waste activated sludge serve as chemical barriers for anaerobic fermentation, limiting the recycling and utilization of organic carbon contained in the sludge. To improve the efficiency of anaerobic fermentation, this paper proposes thermal-rhamnolipid (T-RL) pretreatment technology and systematically discusses the effect of T-RL treatment on the anaerobic fermentation of waste activated sludge for acid production from the perspective of organic matter dissolution characteristics, total volatile fatty acid (VFA) content, composition and microbial changes. RESULTS: T-RL treatment significantly promoted the dissolution of organic matter in sludge, with soluble chemical oxygen demand solubilizing to 6097.78-7375.56 mg L-1, soluble carbohydrates solubilizing to 207.38-274.74 mg L-1, and the dissolution of soluble proteins and DNA also at a high level. Both treatment factors significantly promoted the enrichment of acid-producing microorganisms, especially acetic acid-producing microorganisms. The best VFA production conditions of T-RL treatment were 60 mg g(-1) total solids and 70 degrees C, and the yield was 3294.96 mg L-1. Compared with thermal and RL treatments, the optimum yield of T-RL treatment increased by 33.16% and 22.06%, respectively. The VFA components in the T-RL group were mainly acetic acid and propionic acid. Under optimal conditions, the proportion of acetic acid and propionic acid reached 77%. CONCLUSION: T-RL treatment can promote sludge disintegration and organic matter conversion through the coupling effect of thermal and RL treatments, providing sufficient and high-quality substrate for acid-producing microorganisms, effectively enriching VFA producers, and thus improving the efficiency of anaerobic fermentation for VFA production. This treatment technology will provide some beneficial references for the future utilization of sludge resources. (c) 2023 Society of Chemical Industry (SCI).