Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH(4)(+) (2069 ± 103 mg·L(−1)), chemical oxygen demand (COD) (3608 ± 123 mg·L(−1)), high salinity (2690 ± 70 mg Cl(−)·L(−1), 1353 ± 70 mg SO(4)(2−)·L(−1)), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm(−2) was the most effective amongst those tested (C(8h)/C(0): COD = 0.09 ± 0.14 mg·L(−1), N-NH(4)(+) = 0.39 ± 0.05 mg·L(−1)). COD removal fits the model of pseudo-first-order reactions and N-NH(4)(+) removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm(−2)) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m(−3) (BDD 0.5 k, j = 100 mA·cm(−2)).