Abstract
In this study, actual swage waste activated sludge in batch reactors was employed to assess the synergistic effect of free nitrous acid and Fenton pre-treatments on enhancing methane production in the anaerobic digestion process. In addition to methane enhancement, the mechanisms driving the enhancement were also investigated via measuring enzymes activity and solubilisation of organic matter. This study revealed that the combined pre-treatments solubilised organic matter significantly more than the bioreactors pre-treated with individual FNA and Fenton. For understanding the influence of pre-treatments on solubilisation of organic matter, soluble protein, soluble polysaccharide and soluble chemical oxygen demand (SCOD) were measured before and after the treatments and it was shown that they respectively increased by 973%, 33% and 353% after the treatments. Protease and cellulase activity, as the key constituents of the microbial community in activated sludge, decreased considerably after the combined pre-treatments 42% and 32% respectively, which resulted in considerable methane enhancement. The results corroborate the synergy of the combined FNA and Fenton pre-treatment in degrading the organic and microbial constituents in waste activated sludge, paving the way for the big-scale implementation of these technologies.
Highlights
In this study, actual swage waste activated sludge in batch reactors was employed to assess the synergistic effect of free nitrous acid and Fenton pre-treatments on enhancing methane production in the anaerobic digestion process
This study revealed that combined FNA and Fenton pre-treatments significantly enhance solubilisation of organic matter, microbial degradation, methane production, and organic degradation of waste activated sludge during anaerobic digestion, compared with these pre-treatments individually
Methane production enhanced by 69% in the bioreactors pre-treated with combined FNA2 + Fenton[2], which is attributable to the synergistic effect of the pre-treatments and higher solubilisation of organic matter caused in these
Summary
Actual swage waste activated sludge in batch reactors was employed to assess the synergistic effect of free nitrous acid and Fenton pre-treatments on enhancing methane production in the anaerobic digestion process. Svensson et al.[12] and Campo et al.[13] propounded methods of post and intermediate treatments of sludge with the intent of enhancing www.nature.com/scientificreports anaerobic digestion of sludge, dewaterability and quality of sludge These treatments disrupt cell walls and extracellular polymeric substances (EPS), which improve the solubilisation of organic matter and methane production [14]. When it comes to oxidation-reduction potential, Fenton reagent produces stronger radicals (+2.33 V) than hydrogen peroxide alone (+1.36 V) and ozone (+2.07 V), and it disrupts cell walls and EPS in sludge[18] It has good potential for enhancing methane production and degradation of organic matter in anaerobic digestion of sludge[20]. Erden and Filibeli[21] demonstrated that 4 g Fe+2/kg TS and 60 g H2O2/ kg TS with 60 minutes exposure time increased methane production by 19.4% in anaerobic digestion of waste activated sludge
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