Sono-assisted electrocoagulation treatment of rice grain based distillery biodigester effluent: Performance and cost analysis

Abstract

Electrocoagulation process coupled with sonication is a type of advance oxidation process (AOP) to treat different type of waste waters. Biodigester effluent (BDE) generated from distillery industry contains very high chemical oxygen demand (COD=5500 mg/dm3) with high color (510 PCU) appearance. Organics reduction of biodigester effluent (BDE) in term of chemical oxygen demand (COD) and color have been investigated in a batch sono-electrocoagulation reactor with different electrode combinations such as Fe-Fe, Al-Al, Fe-Al, and Al-Fe at ultrasound frequency of 40 kHz. The impact of different operating parameters such as electrolyte concentration, electrode combination, pH and current density (CD) on COD and color removal are evaluated. The electrode combination of Fe-Fe has provided better results in sono-electrocoagulation process as compared to sonication and electrocoagulation alone. The maximum COD and color reduction efficiency of 99.1 % and 61.6 % was found at the electrode combination of Fe/Fe, CD 69.44 A/m2, pH 8, NaCl concentration 5 mg/dm3, and process time of 125 min. On the other hand the maximum COD and color removal efficiency of 98.3 % and 58.1 % was observed with the electrode combination of Al-Al at same operating conditions as described for Fe. Finally, sludge analysis and cost optimization are also incorporated in this article. It is found that at optimum condition (electrode combination of Fe/Fe, CD 69.44 A/m2, pH 8, NaCl concentration 5 mg/dm3, and process time of 125 min) the operating cost of the process is 1.39 $/m3. Sludge obtained after the treatment process contains anodic material (0.07 kg iron for the treatment 1 m3 of BDE) and also sludge had good heating value (5.5 MJ/kg). This work demonstrated that sono-electrocoagulation process is well applicable to treat BDE.