Using Fixed Media Bioreactors to Control the Environmental Impact of Sanitary Sewer Overflow

Sanitary sewer overflows (SSOs) containing raw sewage are sometimes discharged to the public land and can contribute to environmental and public health issues. This problem has attracted the attention of all levels of government and regulators but to date relatively little abatement research has been published. This study employed fixed media bioreactors, a proven on-site technology in rural areas, to treat SSO wastewater and reduce its impact on the receiving water environment. The results of this 32-month laboratory study showed that fixed media bioreactors, especially sand bioreactors, efficiently removed organic matter, solids and nutrients during 6-hr simulated SSO peak flows. Biochemical oxygen demand (BOD5) of the simulated SSO varied between 40 and 125 mg/L. The average effluent concentration of BOD5 at a high hydraulic loading rate of 20.4 cm/hr was 13 mg/L in sand bioreactors. In addition to high hydraulic loadings, SSO events occur at low frequencies, which require that treatment systems quickly start up and effectively treat wastewater after a period of no flow. The study demonstrated that a resting period of up to 6 months between two simulated SSO events did not affect the bioreactor performance. In conclusion, fixed media bioreactors have the potential to reduce the impact of SSOs on the water environment by following proper design parameters and operation strategies. The pollution loading about 18 g BOD5/m2/hr is recommended for the efficient performance of sand bioreactors in the SSO treatment.