Activation of persulfate by biochar from spent malt rootlets for the degradation of trimethoprim in the presence of inorganic ions

BACKGROUND Antibiotics such as trimethoprim (TMP) are used in large quantities and recent studies show that TMP is not eliminated completely in wastewater from municipal treatment plants. Advanced oxidation processes (AOPs), especially sulfate radical-based AOPs, are highly reactive in the presence of a catalyst. Biochar, a green and low-cost carbon material, is an excellent catalyst to degrade persistent pollutants. In this work, the degradation of TMP is studied using biochar from spent malt rootlets. RESULTS The biochar has a specific surface area of 62 m(2)g(-1), point of zero charge 6.8, contains aromatics and is rich in -OH surface groups. The effect of sodium persulfate (SPS) (100-500 mg L-1), TMP (150-500 mu g L-1), biochar (BC) concentration (45-180 mg L-1), solution pH (4-9) and water quality on degradation was investigated. The degradation rate increased with increasing SPS and BC concentration, decreasing TMP concentration and water matrix complexity, but remained insensitive to pH changes. Seven transformation products were identified and quantified, including hydroxylated and oxidized keto derivatives, and reaction pathways/mechanisms are proposed. The BC activation was coupled with low-frequency ultrasound (20 kHz), which plays a synergistic role in degradation, but not when coupled with simulated solar irradiation. CONCLUSION The occurrence of various ions in bottle water (BW) impact negatively TMP degradation and so does the existence of organic matter in treated wastewaters. The studied reaction seems to be a surface process where the biochar serves as a platform to generate sulfate and -OH radicals, as well as an electron transfer mediator. (c) 2020 Society of Chemical Industry