Process Optimization of Waste Activated Sludge in Anaerobic Digestion and Biogas Production by Electrochemical Pre-Treatment Using Ruthenium Oxide Coated Titanium Electrodes

Abstract

Anaerobic digestion (AD) appears to be a popular unit operation in wastewater treatment plant to treat waste activated sludge (WAS) and the produced methane gas can be harvested as renewable energy. However, WAS could inhibit hydrolysis stage during AD and hence pre-treatment is required to overcome the issue. This paper aimed to study the effect of electrochemical pre-treatment (EP) towards efficiency of AD using titanium coated with ruthenium oxide (Ti/RuO2) electrodes. The investigation has been carried out using in-house laboratory batch-scale mesophilic anaerobic digester, mixed under manipulation of important operating parameters. Optimization was performed on EP using response surface methodology and central composite design to maximize sludge disintegration and dewaterability. By operating at optimal conditions (pH 11.65, total solids 22,000 mg/L, electrolysis time 35 min, current density 6 mA/cm2, and 1000 mg/L of sodium chloride), the pre-treated WAS in terms of mixed liquor volatile suspended solids (MLVSS) removal, soluble chemical oxygen demand (sCOD), capillary suction time (CST) reduction, and extracellular polymeric substance (EPS) were 38%, 4800 mg/L (increased from 935 mg/L), 33%, and 218 mg/L, respectively. Following AD, the volatile solids (VS) removal and chemical oxygen demand (COD) removal by EP were enhanced from 40.7% and 54.7% to 47.2% and 61.5%, respectively, at steady-state. The biogas produced from control and electrochemical pre-treated WAS were in the ranges of 0.12 to 0.17 and 0.2 to 0.24 m3/kg VSfed, respectively, and the volume of biogas produced was 44–67% over the control. Based on the results obtained, suitability of EP for WAS prior to AD was confirmed.

Electrochemical oxidation process on palm oil mill effluent waste activated sludge: optimization by response surface methodology

“…From the results, a slight drop in sCOD occurred as the NaCl concentration increased, as well as the EPS concentrations. This could be due to the presence of negative charges at the bacteria surfaces that generate a high electrostatic repulsive force that leads to the occurrence of sludge disintegration (Heng et al 2021). MLVSS removal and CST reduction rate showed no effect on the increase in NaCl concentration.…”

“…Mechanical, thermal, chemical or biological treatments are a few common types of pre-treatment that serve the same purpose, which is to increase the solubility or reduce the size of organic compounds, so that the sludge can be degraded easily and further improve its dewatering properties (Heng et al 2021). Among the pre-treatment methods, the advance oxidation process (AOP) is easily implemented and considered as a comprehensive technology in terms of its competence on degrading contaminants and its ability to conquer the shortcoming of conventional methods (Iskurt et al 2021;Jiang et al 2021).…”

“…The mechanisms of EO start with oxidation of water molecules to form •OH radicals and induce a reaction with metal oxides that generates a high oxidizing power electrode. Following that, redox reactions of RuO 3 /RuO 2 oxidize the pollutants (P); decomposition of the oxidized electrode by the oxygen evolution by-reaction is shown in the following equations (Equations ( 1)-( 4)) (Heng et al 2021):…”

A Review of the State of the Art of Biomethane Production: Recent Advancements and Integration of Renewable Energies

“…The optimal value for the cavitation process was found at 5 min in laboratory and the results showed that this treatment can be economically applied to plant scale for this application. Electrochemical pretreatment was recently investigated by Heng et al [67], who applied titanium coated with a ruthenium oxide electrode for the disintegration of waste activated sludge used for the AD process. Experimental analyses were carried out in a batch-scale reactor operating under mesophilic conditions, whose main parameters were varied, aiming at optimize sludge disintegration and dewaterability.…”

“…At the end of 2017, at least 542 biomethane production plants were active in Europe: the great majority of such plants inject biomethane directly into the natural gas network. Germany has 203 biomethane plants, followed by the United Kingdom (85) and Sweden (67). Sweden represents a particular case in the European scenario, since most of the produced biomethane is used for transport [82].…”