Nitrification Performance Of A₂ N/BAF In Pilot System

Low carbon to nitrogen ratio was the characteristic of wastewater in Southern cities, leading to the lack of carbon source for nitrogen and phosphorus removal. A₂N (Anaerobic/Anoxic/Nitrification) technology based on the theory of denitrifying phosphorus removal exerted fine removal for low C/N sewage treatment, and hade draw extensive researches. BAF (Biological Aerated Filter) was a technology with high volume load and small footprint. According to the characteristics of the A₂N and BAF, the combind A₂N/BAF was proposed and researched in pilot scale. In this thesis, the efficiency of pilot scale operation and affecting factors of primary BAF and secondary BAF were systematically studied. At last, new types of BAF were designed and studied according to the ruuning charicteristics of BAF in the system.Results of A₂N/BAF running showed that COD in effluent was kept at 30mg/L or so , although TN might exceed the discharge standard. Primary BAF was the key of controlling TN and secondary BAF was the safeguard of effluent NH₄⁺-N.Primary BAF was critically important for TN control and results showed that COD in effluent of primary BAF was less than 50mg/L and NH₄⁺-N removal was about 20mg/L with suitable air to water ratio of 5:1. NH₄⁺-N removal was increased by 10mg/L when alkalinity was increased by 150mg/L. backwash cycle of primary BAF was 7 days and recovery was fairly fast. Increase of C/N had no significant effect on COD removal but effected the NH₄⁺-N removal greatly. NH₄⁺-N removal was decreased obviously when C/N was larger than 3.5. Running cycle could be prolonged from 2days to 8 days and consumed air and water could be reduced by one third, and recovery was achieved within 30min after the separation of carbon and nitrogen.Secondary BAF could provide the guarantee for NH₄⁺-N in effluent to reach the standard and results showed that average concentration of NH₄⁺-N, COD and SS in effluent were 4.0mg/L, 30mg/L and 5mg/L, respectively. Suitable gas-water ratio and HRT for secondary BAF were 2:1 and 0.3h. Heterotrophic bacteria in secondary BAF could be ignored with nitrifying bacteria dominating. Removal of NH₄⁺-N was achieved in 30min in secondary BAF after backwash.Research of new-type BAF showed that the effeciency of the combined BAF of fiber and ceramic particles was well. Running cycle could be prolonged by 3times through local backwash of fiber. SS and COD removal of fiber were 40mg/L and 50mg/L,while there was little removal of NH₄⁺-N. Nitrifying bacteria dominated in the ceramic layer of the combined fillers. Running effect of the combined BAF of raschig rings and ceramic particles was fine. Running cycle could be prolonged by more than 2 times and reaching 16 days. COD of raschig rings effluent was about 50mg/L and NH₄⁺- N was almost the same with influent. Moreover, SS of raschig rings effluent was 55mg/L on average. Flora distribution in the upper ceramic layer tended to alike the secondary BAF and the NH₄⁺-N was decomposed rapidly.