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

摘要

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 NFL), freezing (-5 degrees C) and combination of FNA and freezing (0.53-2.13 mg N/L, FNA at -5 degrees 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 NIL FNA + 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 co-pretreatment resulted in slight inhibition to hydrolysis and negligible inhibition to acidogenesis but severe inhibition to methanogenesis, maybe due to less endurance of methanogens. (C) 2019 Elsevier Ltd. All rights reserved.