The effect of electrocoagulation (EC) on total arsenic, arsenite (As3+) and arsenate (As5+) species removal from model groundwater investigating toxicity and sludge characteristic

Abstract

This study showed that the model groundwater containing As3+ and As5+ species was successfully treated with electrocoagulation (EC) first time in the literature investigating toxicity reduction, inorganic arsenic species and detailed sludge characterization. The arsenic removal from model groundwater with 1000 µg/l total arsenic containing equal arsenite (As3+) and arsenate (As5+) concentration was examined by the EC treatment optimized with following parameters; current density (5.0, 7.5 and 10.0 mA/cm2) supporting sodium sulfate electrolyte amount (10, 20 and 30 mM Na2SO4) and initial water pH (3, 6 and 9). In EC treatment, the 99.87% arsenic removal was obtained with 10 mA/cm2, 10 mM Na2SO4 at pH 3 after 40 min supplying 1.44 μg/l effluent As concentration lower than the WHO limit for drinking water. Through transformation mechanisms of more toxic As3+ to less toxic and easily settled As5+ according to As speciation analysis, the toxicity of the model groundwater was successfully decreased in parallel with total arsenic, As3+ and As5+ removal during EC. The precipitated Al(OH)3 and Al2O3 coagulants were the main peaks in the FTIR-ATR spectrum as well as As(III)–O vibration observed between 717 and 721 cm−1 peaks and As(V)–O vibration dominated 899 and 972 cm−1 peaks were detected in the produced sludge after the EC. The SEM–EDS morphological analysis was demonstrated that the sludge was consisted of mostly amorphous structure aggregated size range of 200 μm–2 mm, relatively uniform cake including O, Al, As, Na, and S.