Potential toxicity and implication of halogenated byproducts generated in MBR online‐cleaning with hypochlorite

Abstract

Online chemical cleaning of membrane bioreactor (MBR) with sodium hypochlorite (NaClO) has been extensively applied for membrane fouling mitigation. However, it was recently revealed that residual NaClO from the online cleaning of MBR caused serious microbial lysis with the subsequent formation of dissolved organic matter (DOM), in which a substantial level of halogenated byproducts was detected. Different from those generated in potable water chlorination, most of the halogenated byproducts generated during MBR online cleaning with hypochlorite belonged to the haloaromatic family, which were apparently more toxic than aliphatic compounds. It was shown that a substantial amount of the generated halogenated byproducts passed through the microfiltration membrane and entered the surface waters through the discharge of MBR permeate. As such, the concentration of halogenated byproducts might likely reach an alarming level via bioaccumulation in the aquatic environment. This emerging situation indeed poses serious concerns for the aquatic environment, water supply and public health due to significantly high toxicity of haloaromatic compounds produced. Unfortunately, the potential halogenated byproducts-associated environmental risks have not been carefully and systematically assessed towards the establishment of relevant regulations. Therefore, this review attempted to fill up such a gap by providing the insights into the potential environmental impacts of halogenated byproducts in the MBR permeate.A substantial amount of DOM and halogenated byproducts produced in the online MBR cleaning with NaClO could enter into surface waters (e.g. rivers, lakes, reservoirs, etc.) through the discharge J Chem Technol Biotechnol 2020; 95: 20-26

Formation of disinfection by-products during sodium hypochlorite cleaning of fouled membranes from membrane bioreactors

“…DBPs are generally refractory compounds with low molecular weight (MW), which are difficult to be biodegraded by activated sludge or hardly rejected by ultrafiltration/microfiltration membranes in MBR. It was reported that 62.4%-84.5% DBPs generated during online NaClO cleaning was found in MBR effluents (Cai et al, 2017), which will result in the deterioration of receiving water bodies and eventually affect the downstream drinking water quality (Zhang and Liu, 2020). To control the formation of halogenated DBPs, chlorine-free oxidants, like Fe 2+ activated PMS and ozone, were considered as alternative chemical cleaning agents for MBRs (Sun et al, 2018;Wang et al, 2020b).…”