Impact of external carbon dose on the removal of micropollutants using methanol and ethanol in post-denitrifying Moving Bed Biofilm Reactors

Abstract

Addition of external carbon sources to post-denitrification systems is frequently used in wastewater treatment plants to enhance nitrate removal. However, little is known about the fate of micropollutants in post-denitrification systems and the influence of external carbon dosing on their removal. In this study, we assessed the effects of two different types and availability of commonly used carbon sources -methanol and ethanol- on the removal of micropollutants in biofilm systems. Two laboratory-scale moving bed biofilm reactors (MBBRs), containing AnoxKaldnes K1 carriers with acclimated biofilm from full-scale systems, were operated in continuous-flow using wastewater dosed with methanol and ethanol, respectively. Batch experiments with 22 spiked pharmaceuticals were performed to assess removal kinetics. Acetyl-sulfadiazine, atenolol, citalopram, propranolol and trimethoprim were easily biotransformed in both MBBRs (biotransformations rate constants k between 1.2 and 12.9 L g d), 13 compounds were moderately biotransformed (rate constants between 0.2 and 2 L g d) and 4 compounds were recalcitrant. The methanol-dosed MBBR showed higher k (e.g., 1.5-2.5-fold) than in the ethanol-dosed MBBR for 9 out of the 22 studied compounds, equal k for 10 compounds, while 3 compounds (i.e., targeted sulfonamides) were biotransformed faster in the ethanol-dosed MBBR. While biotransformation of most of the targeted compounds followed first-order kinetics, removal of venlafaxine, carbamazepine, sulfamethoxazole and sulfamethizole could be described with a cometabolic model. Analyses of the microbial composition in the biofilms using 16S rRNA amplicon sequencing revealed that the methanol-dosed MBBR contained higher microbial richness than the one dosed with ethanol, suggesting that improved biotransformation of targeted compounds could be associated with higher microbial richness. During continuous-flow operation, at conditions representative of full-scale denitrification systems (hydraulic residence time = 2 h), the removal efficiencies of micropollutants were below 35% in both MBBRs, with the exception of atenolol and trimethoprim (>80%). Overall, this study demonstrated that MBBRs used for post-denitrification could be optimized to enhance the biotransformation of a number of micropollutants by accounting for optimal carbon sources and extended residence time.

Anammox and partial denitrification coupling: a review

“…The inhibition mechanisms are that methanol will be converted to aldehydes by methanol dehydrogenase, and ethanol will be converted to acetyl coenzyme before being oxidized to acetaldehyde. 79 As noted in previous research, there was no accumulation of NO 2 À in a reactor with added methanol; the contribution rate of anammox denitrication continuously decreased, and the coupling system was seriously inhibited. Peng et al 80 analyzed the methanol in the reactor experimentally; they found that anammox had no activity at 3 to 4 mmol methanol, and the inhibition was irreversible.…”

Reactor staging influences microbial community composition and diversity of denitrifying MBBRs- Implications on pharmaceutical removal

“…Hence, a number of engineering solutions are being explored to optimize the removal of micropollutants via biological wastewater treatment (Falås et al, 2016;Torresi et al, 2017Torresi et al, , 2016.…”

Biological Fixed Film

“…As previously discussed, Torresi et al (2017) investigated The influences of cerium dioxide nanoparticles (CeO2 NPs) on nitrogen removal in biofilm were investigated in an SBBR . When testing a progressive concentration of CeO2 NPs addition, the results showed that the removal efficiency could nearly stabilize at 67% with a continuous spike of 10 mg CeO2/L.…”