Treatment of sanitary sewer overflow using fixed media bioreactors
Sanitary sewer overflow (SSO) has characteristics of high flow rate, low and varying pollutant concentrations, and low frequency of events. Fixed media bioreactor (biofilter) is a proven technology used for wastewater treatment in unsewered rural areas. No previous research has been published on SSO treatment with fixed media bioreactors. This study expands the application of fixed media bioreactor technology by testing its feasibility in the treatment of SSO wastewater at high hydraulic loading rates. Five types of fixed media bioreactors – sand, textile peat, textile/sand, and peat/sand – were set up in the laboratory and used to treat SSO once a month. Wastewater from a simulated 25-year peak flow was loaded to the surface of bioreactors at 0.2 m/hr for 6 hr. Biochemical oxygen demand (BOD5), total suspended solids (TSS), ammonia nitrogen (NH4-N) and total phosphorus (TP) were measured as waster quality characteristics. Sand bioreactors showed the best system performance for treating SSO with effluent concentration of 14 mg BOD5/L, which met 7-day effluent limit for stream discharge from conventional treatment technologies in Ohio's antidegradation rule (3745-1-05). Linear regression and Bayesian models were applied for the factor analysis of organic matter removal. The results showed that the type of bioreactor media was the most significant factor. All bioreactors had the effluent concentrations of TSS < 18 mg/L, the discharge standard of the Ohio antidegradation rule. The bioreactors had the highest efficiency in the NH4-N and TP removal for a relatively short SSO event of 2 hr. The treatment capacity decreased with higher influent concentration during 4 hr and 6 hr loadings. The treatment efficiency was also evaluated in sand bioreactors with different resting period between two SSO events and different dosing strategies. The low frequency of SSO (1, 2, 3 and 6 months resting between events) did not show significant impact on the treatment performance. The performance declined with high levels of organic matter at extremely high hydraulic loading rates. Ponding on the top and slow drainage were noted as operational problems and were resolved by distributing the SSO in small frequent doses in pilot-scale experiments.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:sanitary sewer overflow fixed media bioreactor biochemical oxygen demand total suspended solids ammonia nitrogen phosphorus statistical model
Date of Publication:01/01/2008