Effects of free nitrous acid combined with alkyl polyglucoside on short-chain fatty acids production from waste activated sludge anaerobic fermentation and fermentation liquor for polyhydroxyalkanoates synthesis

Free nitrous acid (FNA) pretreatment and alkyl polyglucoside (APG) addition are environmentally-friendly methods for enhancing waste activated sludge (WAS) anaerobic fermentation (AF) performances. The short-chain fatty acids (SCFAs) produced are available substrates for polyhydroxyalkanoates (PHAs) synthesis to reduce the C-source cost. This study aims to investigate the optimal fermentation conditions of FNA + APG treatment and the performance of PHAs synthesis by the SCFAs from AF system. Through investigating the FNA + APG combined treatment effects, key enzyme activities, and microbial community variation, the AFL from optimal fermentation condition was utilized as a C-source for PHAs synthesis. Experimental results indicated that 0.653 mg/L FNA + 0.075 g/g VSS APG treatment could synergistically achieve the maximum total SCFAs yield of 324.94 mg COD/g VSS at day 5 of AF, which was much more than those of sole FNA or APG treatment. Mechanism analysis indicated that FNA + APG treatment could promote WAS solubilization, hydrolysis and acidogenesis, while severely inhibiting methanogenesis. Microbial community analysis results demonstrated that SCFA producers, including Enterococcus and Clostridium, became the dominant genera in the FNA + APG reactor. Finally, AF liquor after ammonia removal was applied for batch-mode PHAs synthesis, and PHA yields increased to a maximum of 44.44 % of biomass (w/w) after five operation periods.

Automated summary

Free nitrous acid (FNA) pretreatment and alkyl polyglucoside (APG) addition are environmentally-friendly methods for enhancing waste activated sludge (WAS) anaerobic fermentation (AF) performances and reducing the cost of polyhydroxyalkanoates (PHAs) synthesis. Through investigating the effects of FNA + APG treatment, key enzyme activities, and microbial community variation, optimal fermentation conditions were identified and the performance of PHAs synthesis using SCFAs from the AF system was evaluated. Results showed that the combination of 0.653 mg/L FNA and 0.075 g/g VSS APG treatment achieved the maximum total SCFAs yield of 324.94 mg COD/g VSS at day 5 of AF, promoting solubilization, hydrolysis, and acidogenesis while inhibiting methanogenesis. Furthermore, the dominant genera in the FNA + APG reactor were SCFA producers, Enterococcus and Clostridium. Batch-mode PHAs synthesis using AF liquor as a carbon source resulted in a maximum PHA yield of 44.44% of biomass (w/w) after five operation periods.