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

Abstract

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 H 2 O 2 /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 H 2 O 2 /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.

Agricultural and non-agricultural directions of bio-based sewage sludge valorization by chemical conditioning

“…In several cases, a multi-stage treatment is used to increase the efficiency of sludge solubilization. Siami et al ( 2020 ) present a three-stage process consisting of thermal treatment (75–90°C), alkaline treatment (sodium hydroxide (pH 12)) and oxidative conditions (hydrogen peroxide). The last one is used for anaerobic biomass decomposition.…”

“… n.a. 24h CODs 4.81(g/L) Protein 3.35 (g/L) Polysaccharide 0.46 (g/L) CODs 19.29 g/L Protein 3.55 (g/L) Polysaccharide 0.42 (g/L) 75–90°C (Siami et al 2020 ) Alkaline Oxidation NaOH H 2 O 2 5 M 30% m/m n.a. 2, 4, 6, 8, 24, 48 and 72h COD solubilization 10.5% COD solubilization 28% 28°C (Feki et al 2015 ) …”

“…The use of this type of sludge treatment significantly increases the solubility of organic fractions. The study also controlled the production of methane, which increased by about 90% compared to the control sample (Siami et al 2020) (Table 3).…”

Electrochemical valorization of waste activated sludge for short-chain fatty acids production

“…Anaerobic digestion is the conventional method for WAS treatment and energy recovery in the form of biogas (methane and carbon dioxide), however, methane is a low value product ($150 per ton) ( Xu et al, 2014 ; Liu et al, 2018 ; Chiappero et al, 2019 ; Li et al, 2019 ; Siami et al, 2020 ). The sluggish WAS hydrolysis is the rate limiting step in the AD and results in a low VFAs production rate (100 mg L −1 per day).…”

Selection of Iron-based Additives for Enhanced Anaerobic Digestion of Sludge using the Multicriteria Decision-Making Approach

“…Co-digestion of more than one substrate with complementary advantages aid maintenance of reaction pH, attainment of appropriate carbon-to-nitrogen (C/N) ratio and other nutrient range, reduction of possible toxicity and increase in organic loading rate of the bioreactor [4], [5]. Similarly, many substrate pretreatment types have been studied and reported to have enhanced substrate solubilization and hydrolysis rate via the alteration of intercellular structures of organic matter, disruption of sludge flocs, polyvalent ions, the cell wall of organisms and extracellular polymeric substances (EPS) [6]. Different pretreatment options, which are largely selected based on their cost-effectiveness and have been used for anaerobic digestion enhancement are categorized as physical (mechanical, hydrothermal, irradiation, etc.…”