Mechanisms of free nitrous acid and freezing co-pretreatment enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation

Abstract

Free nitrous acid (FNA) or freezing has been recently utilized as an efficient pretreatment method to increase short-chain fatty acids (SCFAs) yield from waste activated sludge (WAS) anaerobic fermentation (AF). But until now, the performances and mechanisms of the co-pretreatment for SCFAs production are unknown. This research aimed to investigate the AF mechanisms through studying its influence on sludge solubilization and related bioprocesses. WAS was pretreated for 48 h with FNA (1.07 mg N/L), freezing (À5 C) and combination of FNA and freezing (0.53e2.13 mg N/L FNA at À5 C), respectively, then conducted batch AF. Experimental results indicated that the optimal total SCFAs yield of 391.19 ± 5.54 mg COD/g VSS was achieved after 1.07 mg N/L FNA þ freezing pretreatment at 9 days of AF, which was 2.2, 1.6 and 1.3-fold of the blank, freezing and FNA pretreated samples, respectively. The mechanisms analysis showed that co-pretreatment showed synergetic effects on sludge disintegration and solubilization, which could release more soluble substrates for SCFAs production. The copretreatment resulted in slight inhibition to hydrolysis and negligible inhibition to acidogenesis but severe inhibition to methanogenesis, maybe due to less endurance of methanogens.

Enhancing volatile fatty acids production from waste activated sludge: The role of pretreatment by N,N-bis(carboxymethyl)-l-glutamate (GLDA)

“…The potential net profit of GLDA-WAS fermentation was then calculated as positive. Compared with other WAS pretreatment methods, GLDA pretreatment has significantly higher net profits than K 2 FeO 4 [ 51 ], biosurfactant + microwave [ 52 ], CaO 2 + thermal [ 53 ], NaOH + ultrasound [ 54 ], and K 2 FeO 4 /NaNO 2 pretreatment, while slightly lower than NaNO 2 [ 51 ] and nitrous acid + freezing pretreatment [ 55 ]. Given the advantages of GLDA pretreatment in operation simplicity, high biodegradability, and low toxicity to organisms, it has broad application prospects in WAS pretreatment to improve the anaerobic VFAs production efficiency and the potential profit return.…”

Investigation of stable nitritation in a membrane bioreactor treating reject water

“…It should be noted that the applied FNA concentration did not break the cell membrane, which was different from FNA application of sludge pretreatment for anaerobic digestion (Wu et al, 2019;Zhang et al, 2020). In this study, the nitritation performance of MBRs under high FNA concentration was comparable or even better than that of control MBRs.…”