Pretreatment of palm oil-contaminated wastewater using fenton-like reaction for enhancing biogas production with spent coffee ground biochar as catalyst
Abstract:
This research investigated the pretreatment of wastewater contaminated with waste cooking oil using a Fenton reaction, employing spent coffee ground biochar as a catalyst to enhance the biodegradability of the waste cooking oil. Modification of the biochar surface with magnetite and calcium soap was also carried out to enhance its catalytic activity during the Fenton reaction and to increase oil adsorption and boost interfacial oxidation. Palm oil was used as a representative for waste cooking oil from household wastewater. The experiment can be divided into three parts. The first part involved studying oil adsorption using biochar of different sizes: 0.05-1.18 (S), 1.7-2.0 (M), and >2.8 (L) mm, and different pyrolysis temperatures: 300 (BC300), 500 (BC500) and 700 (BC700) °C. It was found that biochar BC300_L had the highest oil absorption efficiency, reaching up to 73 percent, with a tendency to absorb less oil as the biochar size decreased. The modification of biochar with magnetite (BCF) and calcium soap that attached the fatty acids to the biochar either before (BCFSCa) or after (BCFCaS) the addition of calcium. It was found that oil absorption in all biochar samples increased with higher oil concentrations (5, 10, and 15 g/L). Additionally, the adsorption efficiencies of each biochar, whether modified or unmodified, were comparable. The second experiment focused on the palm oil wastewater pretreatment using a Fenton reaction. It was discovered that in the BC and BCF experiments, higher COD levels than the initial palm oil value were detected after the reaction, likely due to the release of bio-oil produced during biochar pyrolysis. This incident was not observed in the BCFSCa and BCFCaS experiments, likely due to the coating of calcium soap on the biochar surface. During the Fenton reaction, the sequence of fatty acid and calcium embedment was found to affect palm oil oxidation, with embedding fatty acids before adding calcium appearing to enhance COD reduction. The third experiment involved incubating pretreated palm oil-containing wastewater, after the Fenton reaction, with anaerobic bacteria to study its effect on biogas production. It was found that a biochar to VSS ratio of 0.25 g biochar/g VSS produced the most biogas compared to ratios of 0.75, 1.5, and 2.5 g biochar/g VSS. According to COD analysis, smaller-sized biochar resulted in higher biogas production and greater COD removal. The study on the effects of different biochar surface modifications on microbial activity demonstrated that all pretreated wastewater with modified biochar produced more biogas than untreated palm oil wastewater. Specifically, BCFCaS700 applying 1,500 g/L H2O2 during the Fenton reaction produced the highest amount of biogas. This study highlights the importance of pretreating oily wastewater and the role of biochar in catalyzing the Fenton reaction and promoting microbial activity during anaerobic biogas production.