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The Effects of Stormwater Infiltration on the Treatability of Emerging Contaminants in Conventional Wastewater Treatment Systems

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PURPOSE: Conventional wastewater treatment systems are designed to treat readily biodegradable organic pollutants and settleable solids in municipal wastewater. The efficiency of the treatment system typically is evaluated using parameters such as oxygen demand, total suspended solids, and nutrients such as phosphorus and nitrogen. Municipal wastewater treatment systems also are designed based on the projected volume of wastewater generated in the community, including inflow and infiltration, e.g., shallow groundwater leakage into the system. Inflow and infiltration can increase substantially the volume of water entering the wastewater treatment plant. This increase in water to be treated may decrease the efficacy of the treatment system because it reduces the hydraulic residence time (HRT), the time available in the treatment plant to remove waste products.

Emerging contaminants such as pharmaceuticals and personal care products (PPCPs), pesticides and PAHs are of concern because of their potential effects on the environment, especially aquatic organisms such as amphibians and juvenile fish, and their general lack of information on sources, effects and treatability. These compounds are discharged to wastewaters and processed through wastewater systems. However, conventional secondary treatment systems are not designed to treat these complex synthetic compounds, and the treatment process is usually only partially effective for these compounds. Therefore, these compounds, either as unmetabolized parent compounds, or as intermediate degradation products, have been found have been found in surface waters across the country.

BENEFIT: This research has been designed to determine if there is a significant difference in the treatability of these emerging contaminants in wastewater during dry weather conditions versus wet weather conditions. Substantial differences between the dry weather and wet weather concentrations, plus differences in the treatability of these compounds at the various stages of the treatment process, would indicate the impact of additional flows due to stormwater infiltration and of reduced hydraulic residence time.

CURRENT STATUS: Sampling and analysis to be completed in July 2012. 75% percent of sampling and analysis currently completed.

Preliminary data have been analyzed for acidic pharmaceuticals and PAHs. Pesticides and basic pharmaceuticals will also be included as analytes. Composite samples of dry and wet weather flows were taken from the inlet of the plant, after the primary clarifier, after the secondary clarifier and after disinfection by UV at the final discharge location. The pharmaceuticals were extracted by solid phase extraction (SPE) and the PAHs and pesticides were extracted by separation funnels with Kuderna-Danish (KD) concentrations. The analyses were done using HPLC for the pharmaceuticals, GC-MS for the PAHs and GC-ECD for the pesticides. Preliminary data for some acidic pharmaceuticals are currently available: sulfamethoxazole, fluoxetine, carbamazepine, trimethoprim, ibuprofen, gemfibrozil and triclosan. Targeted PAHs include naphthalene, acenaphthylene, acenaphthene, phenanthrene, fluorene, anthracene, flouranthene and pyrene.

Preliminary data from the dry weather samples show a consistent reduction from effluent to the final effluent for most of the PAHs and pharmaceuticals. During wet weather, there is not as clear of a treatment trend throughout the unit processes of the treatment plant and each constituent seems to behave differently. The additional data will allow for an improved statistical analysis of the trends in the individual compounds by treatment processes. These and the new results also will be analyzed for impacts of hourly flows and retention times on treatment performance.

While there was substantial variability between each of the seven events for wet weather evaluated to date, most indicated that the concentrations of the pollutants were below the detection limit and negligible after the biological treatment, similar to the results for dry-weather flows. This indicates that the biological treatment processes were able to function as effectively at reduced HRTs as at the longer dry weather HRTs. These results indicate that, while dilution may be occurring in the plant during wet weather, it does not significantly affect the effectiveness of the treatment plant for these compounds over the ranges of dilution seen in these results.
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Document Type: Research Article

Publication date: 2012-01-01

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