Process optimization and effect of thermal, alkaline, H2O2 oxidation and combination pretreatment of sewage sludge on solubilization and anaerobic digestion.

BACKGROUND: This study investigated the feasibility of enhancing anaerobic digestion of sewage sludge with triple, dual, and individual pretreatment of waste activated sludge with heat, alkalinity, and hydrogen peroxide. These pretreatments disrupt sludge flocs, organisms' cell walls, extracellular polymeric substance, and intracellular organic matter, which increase biodegradability and hydrolysis rate of activate sludge. In addition, the influence of various variables on methane production was analyzed using the response surface methodology with the quadratic model. Eventually, an optimized temperature and chemical concentration for the highest methane production and lowest chemical usage is suggested. RESULTS: The highest amount of methane production was obtained from the sludge pretreated with triple pretreatment (heat (90 °C), alkaline (pH = 12), and hydrogen peroxide (30 mg H2O2/g TS)), which had better performance with 96% higher methane production than that of the control sample with temperature of 25 °C approximately and a pH = 8. Response surface methodology with a quadratic model was also used for analyzing the influence of temperature, pH, and hydrogen peroxide concentration on anaerobic digestion efficiency. It was revealed that the optimized temperature, pH, and hydrogen peroxide concentration for maximizing methane production and solubilization of sludge and minimizing thermal energy and chemical additives of the pretreatments are 83.2 °C, pH = 10.6 and 34.8 mg H2O2/g TS, respectively, has the desirability of 0.67. CONCLUSION: This study reveals that triple pretreatment of waste activated sludge performed better than dual and individual pretreatment, respectively, in all desirable output parameters including increasing methane production as the most important output, increasing in COD solubilization, protein and polysaccharide, and decreasing in VSS solubilization.

Synergy of combined free nitrous acid and Fenton technology in enhancing anaerobic digestion of actual sewage waste activated sludge.

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.