CBOD₅ treatment and nitrogen transformations of the marshland upwelling system in intermediate and saltwater marshes
Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
The marshland upwelling system (MUS) was designed to treat domestic wastewater from coastal dwellings where conventional methods are inadequate due to high water tables, poor hydraulic soil conditions, anaerobic soils, and saline groundwater. Currently there is no adequate treatment system available and coastal dwellings are contributing to water quality problems. This study focused on determining the treatment effectiveness of the MUS for organic matter and understanding the specific processes involved in nitrogen treatment.
The treatment of organic matter, measured as five-day carbonaceous biological oxygen demand (CBOD5), was effective in field tests for both saltwater and intermediate marshes. Global removal efficiencies were 95 and 99% and first-order removal constants were 0.80 and 1.30 m-1 for saltwater and intermediate marshes, respectively. A laboratory study confirmed effective treatment of organic matter. Wastewater nitrogen present as nitrate was removed very effectively (> 99%) during a laboratory simulation study. Ammonium removal was not as effective and dropped to 20% by the conclusion of this study. Removal of ammonium was dependent upon the sorption capacity of the soil under reducing conditions. While a field site would offer a much greater soil treatment volume and longer effective retention, ammonium would eventually saturate the soil sorption capacity which will be important in determining MUS longevity. As nitrogen is primarily present as ammonium in the wastewater, conversion of ammonium to nitrate, via nitrification, prior to injection would improve performance. A preliminary oxidation study yielded a 20% conversion of ammonium to nitrate. Further research should focus on improving nitrification rates prior to injection.
Additionally, a higher salinity (20‰, relative to 2‰) was found to have an initial, significantly negative impact on treatment of carbon, sorption of ammonium, and denitrification. Therefore, the impact of the native salinity should be considered in any future design modifications to the MUS.
In conclusion, the MUS has demonstrated great effectiveness in treating wastewater carbon and nitrate. This research showed additional work is required to enhance nitrification rates prior to injection to improve ammonium treatment. Thus, with modifications, the MUS stands to become the first, long-term, effective treatment system for coastal dwelling wastewater.
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Putnam, Lorna Anne, "CBOD₅ treatment and nitrogen transformations of the marshland upwelling system in intermediate and saltwater marshes" (2009). LSU Doctoral Dissertations. 3112.
Gambrell, Robert P.