Decreased formation of disinfection by-products during electrochemical leachate oxidation and their post-removal by electro-adsorption

Abstract

Membrane electrochemical reactor (MER) is an effective treatment system to remove recalcitrant compounds in landfill leachate but harmful byproducts can be formed during the treatment. Herein, we have investigated the formation of total halogenated organics and the associated toxicity as a side effect of leachate treatment by the MER. Those byproducts are represented by the term “disinfection byproducts, or DBPs”, because of the similar formation mechanisms. Several DBP groups were detected during the leachate treatment; however, the amount of DBP generated in the MER only accounted for 19.1 ± 4.5% of that in a membrane-less electrooxidation system (control). Likewise, the total toxicity value in the MER effluent was 26.6 × 10−3, only 15.1% of that in the control system. While trihalomethanes dominated mass concentration by 84.1% in the MER, haloacetonitriles contributed to majority of the additive toxicity due to their higher toxicity index. Increasing the initial leachate pH from 9.5 to 13 could increase the DBP concentration by 2.18 times because of less removal of humic acids. A high initial ammonia concentration of 6000 mg L−1 resulted in the increased DBP formation by 146.8%, compared to that with 2500 mg L−1, due to the increased formation of nitrogenous DBPs. A higher current density of 30 mA cm−2 doubled the DBP formation because of a faster reaction rate and a higher solution temperature. The extended treatment time caused trihalomethanes to continue forming DBP and degradation of most DBPs to some extent. With removing 67.5% of DBP mass concentration and 74.4% of the additive toxicity, the GAC-electrode system was shown more effective than GAC adsorption alone in remediating DBP from the MER effluent.