Electrochemical oxidation of landfill leachate using boron-doped diamond anodes: pollution degradation rate, energy efficiency and toxicity assessment.

Electrochemical oxidation (EO), due to high efficiency and small carbon footprint, is regarded as an attractive option for on-site treatment of highly contaminated wastewater. This work shows the effectiveness of EO using three boron-doped diamond electrodes (BDDs) in sustainable management of landfill leachate (LL). The effect of the applied current density (25-100 mA cm-2) and boron doping concentration (B/C ratio: 500 ppm, 10,000 ppm and 15,000 ppm) on the performance of EO was investigated. It was found that, of the electrodes used, the one most effective at COD, BOD20 and ammonia removal (97.1%, 98.8% and 62%, respectively) was the electrode with the lowest boron doping. Then, to better elucidate the ecological role of LLs, before and after EO, cultivation of faecal bacteria and microscopic analysis of total (prokaryotic) cell number, together with ecotoxicity assay (Daphnia magna, Thamnocephalus platyurus and Artemia salina) were combined for the two better-performing electrodes. The EO process was very effective at bacterial cell inactivation using each of the two anodes, even within 2 h of contact time. In a complex matrix of LLs, this is probably a combined effect of electrogenerated oxidants (hydroxyl radicals, active chlorine and sulphate radicals), which may penetrate into the bacterial cells and/or react with cellular components. The toxicity of EO-treated LLs proved to be lower than that of raw ones. Since toxicity drops with increased boron doping, it is believed that appropriate electrolysis parameters can diminish the toxicity effect without compromising the nutrient-removal and disinfection capability, although salinity of LLs and related multistep-oxidation pathways needs to be further elucidated.

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-NH4+ (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 SO42-·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 (C8h/C0: COD = 0.09 ± 0.14 mg·L-1, N-NH4+ = 0.39 ± 0.05 mg·L-1). COD removal fits the model of pseudo-first-order reactions and N-NH4+ 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).