Adsorption and biodegradation of sulfamethoxazole and ofloxacin on zeolite: Influence of particle diameter and redox potential

Zeolite played an important role in the removal of antibiotics in constructed wetlands (CWs) due to the high pollution adsorption capacity and tremendous amount of microorganism attachment sites. However, the contribution of adsorption and microbial degradation of this substrates on antibiotic removal, and the degradation difference and mechanism in different redox conditions are still unclear. The adsorption and biodegradation of antibiotics on zeolites with two particle sizes were compared under aerobic, anoxic and anaerobic conditions. The results showed the competitive adsorption strength on powder zeolite was higher than that on mass zeolite. However, the maximum adsorption capacity of sulfamethoxazole (SMX) on powered zeolite was lower than that on massive zeolite, which was mainly due to the destruction of pore structure in powder zeolite. The adsorption effect and mechanism of zeolite to antibiotics can be disrupted by different particle size. Adsorption contributed more than 50% of the total ofloxacin (OFLO) removal, while biodegradation contributed more than 60% of the total SMX removal in our antibiotic removal experiments. In addition, redox conditions can obviously affect removal of antibiotics with the highest removal efficiency for SMX (75%) occurred in aerobic and for OFLO (99.5%) occurred in anaerobic conditions. This phenomenon probably resulted from the different microbial community structures on substrates in anaerobic, aerobic or anoxic under different antibiotic stress. This study can provide strong support for defuzzification of removal mechanism of different antibiotics in CW systems.