Pretreatment of free nitrous acid combined with calcium hypochlorite for enhancement of hydrogen production in waste activated sludge

Abstract

A variety of variables limit the recovery of resources from anaerobic fermentation of waste activated sludge (WAS), hence pretreatment strategies are necessary to be investigated to increase its efficiency. A combination of free nitrous acid (FNA) and calcium hypochlorite [Ca(ClO)2] was employed in this investigation to significantly improve sludge fermentation performance. The yields of cumulative hydrogen for the blank and FNA treatment group were 1.09 ± 0.16 and 7.36 ± 0.21 mL/g VSS, respectively, and 6.59 ± 0.24 [0.03 g Ca(ClO)2/g TSS], 7.75 ± 0.20 (0.06), and 8.58 ± 0.22 (0.09) mL/g VSS for the Ca(ClO)2 groups. The co-treatment greatly boosted hydrogen generation, ranging from 39.97 ± 2.26 to 76.20 ± 4.78 % as compared to the solo treatment. Mechanism analysis demonstrated that the combined treatment disturbed sludge structure and cell membrane permeability even more, which released more organic substrates and enhanced biodegradability of fermentation broth. This paper describes a unique strategy to sludge pretreatment that expands the use of Ca(ClO)2 and FNA in anaerobic fermentation, with implications for sludge disposal and energy recovery.