The effect of temperature on biochemical oxygen demand removal in a subsurface flow wetland

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 °C, whereas removal at wastewater temperature less than 20 °C exhibits a wider variation and lower mean. An exponential model relating splitter box temperature to effluent BOD concentration, R2 = 0.69, fits the data only slightly better than an Arrhenius type relationship R2 = 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 (R2 = 0.50).