Enhanced reduction of polyethylene glycol concentrations in the effluent of a full-scale MBBR processes

Abstract Polyethylene glycols (PEGs) are increasingly found in wastewater due to their use in the production of non-ionic surfactants, pharmaceuticals, antifreeze agents, water soluble lubricants, and cosmetics. This has led to increased interest in determining the fate of this chemical species in wastewater treatment plants. For the first time, a detailed practical and theoretical study on the fate of PEG has been conducted at the Aoun sewage treatment plant (ASTP) and modeled using the TOXCHEM model. Data were collected and entered into the TOXCHEM model, after calibration and validation, and root mean square error (RMSE) and correlation coefficient (R) were 0.04 and 0.82, respectively, which is within acceptable limits. A sensitivity analysis showed that the most sensitive parameters were the wastewater influent flow rate, temperature, air flow rate, MBBR biofilm thickness, specific surface area of the MBBR media, and MBBR media fill fraction. The TOXCHEM model showed that emission of PEG varied according to the season. Emissions were greatest during the warmer months and summer and spring emissions were found to be 24% and 18.4%, respectively. During spring and summer 24% and results of the TOXCHEM model indicated that the fate of PEG during spring and summer (35°C) and autumn and winter (12°C) was that about 24 and 18.4%, 10 and 10%, 53.5 and 46.6%, and 12.5 and 25% was fated to be emitted into atmosphere, sorbed to sludge, biodegraded, and discharged with the outlet, respectively. The highest emission was 3.3 mg/m 3 during the summer season in the aeration basin. Excessive flow rate affects biodegradation and reduces treatment efficiency. Reducing air flow rate, and the effects of MBBR biofilm thickness, specific surface area of MBBR media, and MBBR media fill fraction all increase the biodegradation process, reduce emission rates, and improve the treatment process. Increasing temperatures increase biodegradation, but also increase emissions. Practically, air flow rate, MBBR media fill fraction, and return activated sludge (RAS) were chosen for their ease of application at ASTP. The practical enhancement contributed to the reduction of the concentrations of chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solid (TSS), nitrate (NO 3) , phosphate (PO 4 –P), ammonia (NH 4 ), hydrogen sulfide (H 2 S), PEG in summer, and PEG in winter, from 44, 35, 15, 35, 3, 0.15, 0.18, 0.8, and 1.9 to 20,11, 9, 8, 2, 0.12, 0.1, 0.35, and 0.6 mg/L, respectively. Overall improvements increased biodegradability from 47 to 75.4% and reduced emissions from 18 to 5.6%. The TOXCHEM model used in this study was found to be an excellent predictor of the enhancement process.