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ABSTRACT: Investigators have reported that seasonal variation in wastewater temperature has little or no effect on biochemical oxygen demand (BOD) removal in subsurface flow wetlands (also referred to as rock-plant filters). This study examined temperature and BOD data collected biweekly (every 2 weeks) over an 18-month period from a rock-plant filter treating high-strength wastewater (median pump station discharge BOD = 425 mg/L) at an interstate highway rest area in south central Louisiana. Results show a seasonal variation in effluent BOD with greater mean removal occurring when wastewater temperature in the splitter box is greater than 20 deg C, whereas removal at wastewater temperature less than 20 deg C exhibits a wider variation and lower mean. An exponential model relating splitter box temperature to effluent BOD concentration, R^sup 2^ = 0.69, fits the data only slightly better than an Arrhenius type relationship, R^sup 2^ = 0.67. Both models suggest that two cells in series may be required for this facility to meet its BOD permit limit in colder weather. A linear model relating percent of BOD removed to splitter box temperature did not fit data as well (R^sup 2^ = 0.50). Water Environ. Res., 71, 475 (1999).
KEYWORDS: temperature dependence, biochemical oxygen demand, removal efficiency, kinetics, wetlands.
Objectives
Unlike most biological treatment processes, investigators have reported little, if any, effect of wastewater temperature on treatment efficiency in subsurface flow (SSF) wetlands. This study examined whether such a relationship existed for a rock-plant filter at an interstate highway rest area in Louisiana. If a relationship was found to exist, a second objective was to fit data using an appropriate statistical model and assess its adequacy.
Previous Work
Kadlec and Knight (1996) reported the efforts of a number of researchers to assess the effect of temperature on biochemical oxygen demand (BOD) removal in SSF wetlands. They concluded that previous studies suggest little effect of temperature on BOD removal. Bavor et al. (1989) were unable to find any dependence on temperature of the first-order rate constant in five SSF systems operated with secondary effluent. Gumbricht (1992) studied a SSF wetland system treating secondary wastewater in Sweden for 3 years. He found no statistically significant relationship between temperature and BOD removal in the regression models he developed; observed BOD...