The presence of microconstituents in effluents from municipal wastewater treatment plants (WWTPs) and their receiving waters has attracted considerable recent attention. This review summarizes the state of the science on the removal of bisphenol A (BPA) by WWTPs and presents evidence that the compound should be effectively removed in well-operated activated sludge systems. The biological treatment of BPA has been extensively studied in laboratory, pilot, and full-scale municipal WWTPs. Although removal efficiencies varied, the average of the reported removal efficiencies for BPA in full-scale facilities was 84%. Mass balance studies conducted in the laboratory with '"C-labeled BPA and studies of full-scale facilities show that biodégradation is the dominant removal process, consistent with the fact that BPA is readily degradable and able to support microbial growth. Many of the plants were able to reduce BPA concentrations in the wastewater effluent to significantly less than 1 |ig/L. This review examines operating parameters important for optimizing and sustaining the perfonnance of wastewater treatment systems including solids residence time (SRT), which proved to be the most critical. The weight of evidence suggests the optimum SRT needs to be approximately 10 days to ensure high treatment efficiencies. Other optimum operating conditions include maintaining dissolved oxygen concentrations of greater than or equal to 2.0 mg/L, elevating the SRT during periods of low temperature, and implementing step-feed control during storm-induced high flow conditions to avoid the washout of biomass. Water Environ. Res., 83, 650 (2011).

The fate of volatile organic compounds (VOCs) in municipal activated sludge plants was investigated at pilot and full scale. More than 80% of the mass flow of nonchlorinated compounds was observed to be biodegraded while less than 20% was removed by stripping. Conversely, 46% of the mass flow of chlorinated compounds was biodegraded and 47% was removed by stripping. Adsorption of VOCs onto waste sludge was not a significant removal mechanism. The pilot plant employed was found to effectively emulate the liquid‐gas phase partitioning and overall compound removals observed in a full‐scale plant. Little difference in liquid‐gas phase partitioning was observed for coarse and fine pore diffusers in spite of differing mass‐transfer characteristics as demonstrated by oxygen‐transfer measurements. This implies that equilibrium between the liquid and gas‐phase concentrations was achieved with both diffuser types. Stripping of VOCs was observed to increase with airflow; however, the extent of stripping increased at a declining rate.

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A three-facility, full-scale pilot program was undertaken at three small wastewater treatment plants in British Columbia, Canada. The project concludes several years of investigation and one year of plant evaluations for sludge treatment using autothermal thermophilic aerobic digestion (ATAD). Process effectiveness was shown by demonstration of pasteurization, stabilization, and odor acceptability. Control parameters were accessed by use of oxidation reduction potential (ORP), temperature, pH, air flow rates, and energy use. Dewaterability was also studied. The studies concluded that the ATAD process was suitable for use in small communities. The information presented is taken from the final project report and is supplemented with design suggestions for use when considering the ATAD process. Water Environ. Res., 65,849 (1993).Autothermal thermophilic aerobic digestion (ATAD) is a compact, fully enclosed digestion process which requires relatively small reactors, small volumes of air, adequate energy for complete mixing, and a concentration of biomass and organics sufficient to ensure the high temperature sludge digestion. Heat is produced from energy release due to organic decomposition. The process is described as autothermal; other than mixing energy, no other heat source is required. Thermophilic temperatures of 55° to 70°C can be obtained in the reactors. The reactors are normally operated on a semi-continuous or batch basis, and at these temperatures and with sufficient residence time, pasteurization and stabilization are assured. The small volume, low energy, and low instrumentation requirements make the process cost-competitive with other processes such as mesophilic aerobic digestion, anaerobic digestion, and composting. The potential benefits are a pasteurized stable sludge with low handling risk, and a process which can be used safely for sludge digestion in small to medium-size communities throughout North America.To investigate claims of the suitability of ATAD for domestic sludge treatment, a full-scale demonstration study was undertaken at three small wastewater treatment plants in British Columbia, Canada. Although previous work has been undertaken in Great Britain, Europe, and North America using high-temperature aerobic digestion, details of operation are either proprietary, give misinformation, or are often incomplete. Early attempts at the design of these facilities lacked information on process, design, and operating criteria to secure process stability and odor control. Investigations by many others (Kabrick

A field investigation was carried out at four Ontario municipal wastewater treatment plants to characterize stripping of volatile organic compounds (VOCs) from aerated process vessels. Concentrations of VOCs in the off-gas and wastewater at aerated grit chambers and aeration basins were measured. Thirty-two of 36 target VOCs were observed in at least one off-gas sample from the plants studied. The total emissions for the measured compounds ranged from 2 700 to 3 900 g/ d or 36 to 50 g/1000 m 3 of wastewater treated. Chlorinated VOCs tended to be stripped to a greater extent than nonchlorinated compounds. The data suggest that VOC stripping can be reduced by reducing aeration rates, and that operating and design parameters have an impact on the loss of VOCs.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res., 65, 708 (1993).