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

Abstract

Biological-based treatment being the conventional treatment for palm oil mill effluent (POME) in open-ponding system faced a well-known rate-limiting step which is hydrolysis. In this study, electrochemical oxidation (EO) by ruthenium oxide coated titanium (Ti/RuO2) electrode was introduced as a pre-treatment for POME waste activated sludge (WAS). Surface morphology and elemental analysis were investigated by Field Emission Scanning Electron Microscopy and Energy Dispersive X-Ray, respectively. Response surface methodology type central composite design was used in this study to understand the relationship between the independent and dependent variables. Analysis of variance (ANOVA) was used to validate the model of the studied variables. The correlation coefficients (R2) indicated a close agreement between experimental results and predicted values, with high R2 values of 0.9044–0.9773. Multiple response optimization suggested that the range of current density (17–27 mA/cm2) and electrolysis time (55–75 min) at a fixed concentration of sodium chloride (10 g/L), resulting in mixed liquor volatile suspended solids (MLVSS) removal >20%, capillary suction timer (CST) reduction >43%, extracellular polymeric substances (EPS) increment <19% and soluble chemical oxygen demand (sCOD) increment >25%. EO appears to be an efficient pre-treatment as well as practical to improve the POME WAS disintegration and dewaterability.

Enhancement of Electrochemical–Anaerobic Digested Palm Oil Mill Effluent Waste Activated Sludge in Solids Minimization and Biogas Production: Bench–Scale Verification

“…The pre-treatment process aims to break down high-molecular-weight substances and the EPS layer protecting organic matter from being decomposed by AD microbes. The outcome showed promising results on cell lysis, in terms of sCOD and EPS increment as well as improvement on dewaterability through CST reduction [21]. EO showed a certain percentage of sludge reduction too whereby 23.1% MLVSS was removed after the EO pre-treatment.…”

“…After the sample collection, the collected WAS was left to be settled, and excessive water had been removed prior to any test. Pre-treated POME WAS was prepared according to the previous optimized condition generated through a Design Expert Software [21]. Both raw and pre-treated samples once prepared were stored in the refrigerator (4 • C) for better preservation and to prevent contamination of the samples physiochemically [28].…”

“…Figure 1 shows a schematic diagram of the EO pre-treatment system, where (1) is the DC power supply; (2), magnetic stirrer; (3), retort stand; (4), electric wires with clips; (5), electrodes; and (6), magnetic bar stirrer. In our previous study, EO pre-treatment on POME WAS had been optimized through a central composite design (CCD)-based response surface methodology (RSM) with the optimum conditions of 17-27 mA/cm 2 current density, 55-75 min of electrolysis time at a fixed electrolyte, sodium chloride (NaCl) concentration of 10 g/L, in achieving MLVSS removal (>20%), capillary suction time (CST) reduction (>43%), EPS increment (<19%) and sCOD increment (>25%) [21]. The pre-treatment process aims to break down high-molecular-weight substances and the EPS layer protecting organic matter from being decomposed by AD microbes.…”

“…An innovative pre-treatment-electrochemical oxidation (EO), a form of advanced oxidation process, has been showing its positive traits as a pre-treatment, to improve the biodegradability of waste activated sludge (WAS) [18][19][20][21]. EO is a clean technology that involves electrons by generating strong oxidizing agents in breaking down the EPS protecting layer of organic matter, which subsequently helps in dewatering and degrading the organic matters into simpler forms to help with the subsequent AD process [3,10,22].…”