Electrocoagulation as a stand-alone and hybrid strategy for medium-density fibreboard wastewater treatment: Performance, energy consumption and radical oxidant effects

Abstract

The aim of this study was to investigate the electrocoagulation (EC) treatment of medium density fibreboard (MDF) effluent and to improve its performance by integrating advanced oxidation processes (AOPs) using hydrogen peroxide (HP), peroxymonosulphate (PMS) and peroxydisulphate (PDS). Initially, different electrode materials and configurations were tested and the Fe-Al electrode pair demonstrated superior COD removal performance. Operating parameters including pH, current, electrolysis time, inter-electrode distance and electrolyte type/concentration were optimized. The optimum conditions were determined to be pH 7.4, 1.5 A current, 50 min electrolysis time, 0.02 M NaCl and 2 cm electrode spacing, resulting in 80.8 % COD, > 99 % colour and 93.4 % tannin/lignin removal. Subsequent experiments combining EC with HP, PMS and PDS at different dosages showed that EC-HP slightly improved COD removal (84.9 %) compared to EC alone, while EC-PMS (79.3 %) and EC-PDS (77.7 %) provided marginal or no improvement. All treatments achieved over 99 % colour removal, confirming the high efficiency of EC and EC-AOPs for the treatment of refractory organic pollutants in MDF effluents. The kinetics of COD removal for all treatment processes followed a pseudo-first-order model. The calculated rate constants were -0.0104 min(-)(1) for EC, -0.0204 min(-)(1) for EC-HP, -0.0082 min(-)(1) for EC-PMS and -0.0049 min(-)(1) for EC-PDS. The results also demonstrate the applicability of paper and pulp effluent studies for comparative evaluation due to the similar characteristics of these effluents. Among all the processes, the lowest specific energy consumption (SEC) was observed for EC-PMS treatment (38.75 kWh/m(3)), significantly lower than for EC alone (84.37 kWh/m(3)), EC-HP (80.00 kWh/m(3)) and EC-PDS (77.81 kWh/m(3)). This reduction was attributed to the increased conductivity caused by PMS (10.55 mS/cm), which allowed more efficient energy use compared to EC (4.09 mS/cm), EC-HP (3.69 mS/cm) and EC-PDS (4.85 mS/cm).