Diurnal and day to day variability in micropollutant concentrations in the influent and effluent at a wastewater treatment plant in south east Queensland
Environmental Monitoring
Williams, Mike ; Shareef, Ali ; Hodgers, Leonie ; Toze, Simon ; Kookana, Rai
The release of micropollutants, such as pharmaceuticals, personal care products and hormones, is expected to vary not only from day to day due to their domestic and industrial use pattern, but also diurnally, due to daily life patterns. Therefore, as a follow up of the previous routine sampling program (July 2008), a campaign of intensive sampling was undertaken to assess the extent of variability associated with concentrations of selected micropollutants in influent and effluent samples.Water samples were collected over a one-week period at Oxley Creek wastewater treatment plant (WWTP) from Wednesday 29th August until Tuesday 4th November 2008. Samples were collected on a daily basis at 9 am for seven days, while on Friday 31st August samples were collected every 2 h for a 24 h period. The concentrations of 11 pharmaceuticals and personal care products were monitored in collected water samples, including the cytotoxic surfactant benzalkonium chloride (BAC), the antiepileptic carbamazepine (CBZ) and the antidepressants fluoxetine (FLX), sertraline (SER) and venlafaxine (VEN). Some of these compounds have not been analysed in previous monitoring campaigns in the current project. In addition, the illicit drug methamphetamine (MAP) was included the suit of analyte as it may reflect a very different use pattern and therefore may serve as a good marker compound.Key Findings•Measured influent flow rates and water quality of both influent and effluent were reasonably stable over the seven day monitoring period. Also, the weather was stable over the monitoring period and no rain events occurred, with a subsequent hydraulic retention time (HRT) of ca. 33 h. Diurnally, there was a predictable peak (at 9 am), followed by a subsequent decline in flow rates until early the next morning before rising again to a mid-morning peak in the short term sampling. •The variability in micropollutant concentrations was not consistent with the measured influent flow rates. While CBZ (a little sorbed pharmaceutical) followed the pattern of flow rate, another pharmaceutical compound diphenylamine (substantially sorbed) lagged behind the flow rate and its concentration peaked either late afternoon (5 pm) or early hours of the morning (3 am). •All of the micropollutants analysed in this study were found to show the highest concentrations during the weekend instead of weekdays. Indeed the concentrations of several compounds (e.g. CBZ and VEN) were an order of magnitude lower during the week than during the weekend. •The effluent concentrations of the compounds were largely influenced by the treatment efficiency for a given compound. For example, while CBZ and DPH were hardly removed during the treatment process, the BAC and MAP were almost completely (99%) removed during the treatment. However, due to very high concentrations of BAC in the influent (as high as 42,750 ng/L), its effluent concentrations were still greater than other micropollutants studied.•The majority of other analytes were detected at low concentrations, generally at ng/L, particularly in the effluents. Based on relative concentrations in the influent and effluent, five of the analytes were likely to be readily removed during the treatment process, while the remainder had similar influent and effluent concentrations. The analytes which may have shown resistance to removal included CBZ, CHP, DPH, PCZ, SER and VEN. Although these findings were reflected in literature, a suitable Lagrangian sampling strategy would need to be implemented to properly determine removal rates. •Given the Oxley treatment plant is mainly capturing domestic wastewater, the pattern seems to reflect: (i) household activities (e.g. washing) which tend to concentrate over the weekend; and (ii) more people being at home over the weekend rather than at office (located in the catchments of other treatment plant), as reflected in the pharmaceutical concentrations.•The sampling in this study both over a short
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