Combining enzymatic membrane bioreactor and ultraviolet photolysis for enhanced removal of trace organic contaminants: Degradation efficiency and by-products formation

Abstract

Coupling of membrane distillation with bioreactors containing enzymes such as ‘laccase’ forms an enzymatic membrane bioreactor resulting in complete retention of both trace organic contaminants and enzyme, facilitating simultaneous trace organic contaminants degradation. Integration of enzymatic membrane bioreactor and ultraviolet photolysis may result in further improved degradation of trace organic contaminants in membrane-concentrate. We studied the degradation as well as by-products formation of five selected trace organic contaminants, namely, sulfamethoxazole, diclofenac, bisphenol A, oxybenzone, and carbamazepine by ‘membrane distillation — ultraviolet photolysis’ system and ‘enzymatic membrane bioreactor — ultraviolet photolysis’ system. In the former, the membrane effectively retained the trace organic contaminants and then ultraviolet photolysis of membrane-concentrate resulted in trace organic contaminant degradation in the following order: diclofenac (88 %) > sulfamethoxazole (71 %) > oxybenzone (35 %) > bisphenol A (33 %) > carbamazepine (27 %). By contrast, the enzymatic membrane bioreactor — ultraviolet photolysis system resulted in 100 % degradation of diclofenac, sulfamethoxazole, and bisphenol A and around 70 % degradation of oxybenzone and carbamazepine. This system also resulted in more than 50 % reduction in number of degradation products with 60–70 % lower abundance. Our results indicate that laccase degradation led to products that were more amenable to the post-treatment by ultraviolet photolysis. Overall, it can be concluded that for enzymatic membrane bioreactor — ultraviolet photolysis system, enzymatic pre-treatment not only helped in better degradation of the parent trace organic contaminants but also led to the formation of fewer by-products with lower abundance (i.e., more complete degradation).