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

摘要

PURPOSErnConventional wastewater treatment systems are designed to treat readily biodegradable organicrnpollutants and settleable solids in municipal wastewater. The efficiency of the treatment systemrntypically is evaluated using parameters such as oxygen demand, total suspended solids, andrnnutrients such as phosphorus and nitrogen. Municipal wastewater treatment systems also arerndesigned based on the projected volume of wastewater generated in the community, includingrninflow and infiltration, e.g., shallow groundwater leakage into the system. Inflow and infiltrationrncan increase substantially the volume of water entering the wastewater treatment plant. Thisrnincrease in water to be treated may decrease the efficacy of the treatment system because itrnreduces the hydraulic residence time (HRT), the time available in the treatment plant to removernwaste products.rnEmerging contaminants such as pharmaceuticals and personal care products (PPCPs), pesticidesrnand PAHs are of concern because of their potential effects on the environment, especially aquaticrnorganisms such as amphibians and juvenile fish, and their general lack of information on sources,rneffects and treatability. These compounds are discharged to wastewaters and processed throughrnwastewater systems. However, conventional secondary treatment systems are not designed torntreat these complex synthetic compounds, and the treatment process is usually only partiallyrneffective for these compounds. Therefore, these compounds, either as unmetabolized parentrncompounds, or as intermediate degradation products, have been found have been found inrnsurface waters across the country.rnBENEFITrnThis research has been designed to determine if there is a significant difference in the treatabilityrnof these emerging contaminants in wastewater during dry weather conditions versus wet weatherrnconditions. Substantial differences between the dry weather and wet weather concentrations, plusrndifferences in the treatability of these compounds at the various stages of the treatment process,rnwould indicate the impact of additional flows due to stormwater infiltration and of reducedrnhydraulic residence time.rnCURRENT STATUS: Sampling and analysis to be completed in July 2012. 75% percent ofrnsampling and analysis currently completed.rnPreliminary data have been analyzed for acidic pharmaceuticals and PAHs. Pesticides and basicrnpharmaceuticals will also be included as analytes. Composite samples of dry and wet weatherrnflows were taken from the inlet of the plant, after the primary clarifier, after the secondaryrnclarifier and after disinfection by UV at the final discharge location. The pharmaceuticals werernextracted by solid phase extraction (SPE) and the PAHs and pesticides were extracted byrnseparation funnels with Kuderna-Danish (KD) concentrations. The analyses were done usingrnHPLC for the pharmaceuticals, GC-MS for the PAHs and GC-ECD for the pesticides.rnPreliminary data for some acidic pharmaceuticals are currently available: sulfamethoxazole,rnfluoxetine, carbamazepine, trimethoprim, ibuprofen, gemfibrozil and triclosan. Targeted PAHsrninclude naphthalene, acenaphthylene, acenaphthene, phenanthrene, fluorene, anthracene,rnflouranthene and pyrene.rnPreliminary data from the dry weather samples show a consistent reduction from effluent to thernfinal effluent for most of the PAHs and pharmaceuticals. During wet weather, there is not asrnclear of a treatment trend throughout the unit processes of the treatment plant and eachrnconstituent seems to behave differently. The additional data will allow for an improved statisticalrnanalysis of the trends in the individual compounds by treatment processes. These and the newrnresults also will be analyzed for impacts of hourly flows and retention times on treatmentrnperformance.rnWhile there was substantial variability between each of the seven events for wet weatherrnevaluated to date, most indicated that the concentrations of the pollutants were below therndetection limit and negligible after the biological treatment, similar to the results for dry-weatherrnflows. This indicates that the biological treatment processes were able to function as effectivelyrnat reduced HRTs as at the longer dry weather HRTs. These results indicate that, while dilutionrnmay be occurring in the plant during wet weather, it does not significantly affect therneffectiveness of the treatment plant for these compounds over the ranges of dilution seen in thesernresults.