Reduction of Organic Pollutants with Recovery of Value-Added Products From Soda Black Liquor of Agricultural Residues by Electrolysis

Batch electrolysis experiments were carried out on soda black liquors from agricultural residues at different interelectrode potentials. At low potential, the process was slow but energy-efficient, providing partial COD removal. It produced lignin at the anode with the exclusion of oxygen evolution. Hydrogen was produced at the cathode as a value-added product. At high interelectrode potential, the nascent oxygen produced at the anode led to oxidation of the organics. With prolonged electrolysis, complete removal of COD was possible, with a solution of sodium carbonate remaining. Low-potential electrolysis required about 2000 J of electricity per gram of COD removed, producing 180–190 mL hydrogen and approximately 0.55 g lignin. Electricity requirement per gram of COD removed in high-potential electrolysis varied from approximately 17,700 J at 1.5 V to approximately 149,000 J at 12 V. Approximately 1365 mL of hydrogen was produced for every gram of COD removed.