Effect of biomedia in wastewater treatment plants (WWTPs) on concentration of organophosphate flame retardants (OPFRs)

Abstract

Flame retardants are widely used as additives for preventing flammable products from burning in fire. Brominated flame retardants (BFRs) which account for 17% of global consumption of flame retardants in 2017 have been prohibited due to their risk for environments and human health. For this reason, production and consumption of OPFRs have been increased and substituted the BFRs. Recently, there were studies reported toxicity of OPFRs and behavior that easily released into environments. Thus, it is required to identifying emission of OPFRs, and wastewater treatment plants (WWTPs) are the best site for this objective because OPFRs occurred by anthropogenic activity. Moving bed biofilm reactor (MBBR) process which is one of the wastewater treatment process is used plastic carrier, called biocarrier or biomedia, to increasing their treatment efficiency. However, biomedia is also made up with plastic which is possible to contain the OPFRs as flame retardants or plasticizer. Therefore, this study was conducted to identify the effect of biomedia on concentration of OPFRs. Occurrence of OPFRs in WWTPs using reactors with biomedia and no biomedia were investigated, comparing removal efficiencies of OPFRs in both WWTPs. The result of comparison showed that removal efficiencies of OPFRs have same trends between both WWTP except TCEP. TCEP in WWTP applied MBBR process was increased through the process (87.1%), while concentration of TCEP in WWTP without MBBR process was almost maintained (-0.5%). Result of leaching test with methanol presented that only TCEP was leached out with 67.62 µg/L, and provided a basis for leaching of TCEP from biomedia. Leaching test with DI water also showed that only TCEP was detected, and concentrations of leached TCEP were fitted with three kinetic models. Among the three kinetic models, pseudo first-order model is the most suitable model with TCEP concentration (R2 = 0.981) with 55.26 ng/L of equilibrium concentration and 0.0204 h-1 of rate constant. From the result of fitting with kinetic model and information of WWTP, TCEP concentration leached out from biomedia calculated to 9.52 ng/L that cause the 5,712 mg/day of TCEP emission into aquatic environments. Therefore, TCEP leached out from biomedia is required to increase concerns, due to chronic toxicity of TCEP such as carcinogenicity and reproductive toxicity.