Nitrogen Removal Of BAF With Pre-denitrification For Treatment Of Wastewater At Low Carbon/Nitrogen Ratios

Cost-effective wastewater treatment processes are critical for the conservation and remediation of water environment. Biological aerated filters (BAFs) are such technology which is suitable for water treatment particularly in China. The major characteristic of BAF reactors is the biofim on the granular media which integrated solids separation as well as secondly or tertiary biological treatment in one unit. Thus the BAF reactors has the function of filtration, adsorption and biodegradation. It has been found that the BAF has advantages of less land occupied, high treatment efficiency, no requirement for srcondary settling tanks and the quality of effluent reaches the standards.In order to investigated the denitrification of the Pre-denitrification BAF, this paper focused on the experimental study on the Pre-denitrification BAF in treating artificial sewage with low carbon-to-ammonia (C/N) ratio using ceramisite as medium with particle size of 3-5 mm. The rule of the removal of pollutants was seeked and every effort was made to attain the optimal operational parameters, which aimed at providing both a reference for the research of treating high ammonia concentration wastewater with Pre-denitrification BAF and a theoretical basis for the promotion of the technology in the field of wastewater treatment.Compared to post-denitrification BAF process, the pre-denitrification BAF exhibited good performance on denitrification, and the reflux ratio and hydraulic load affect the nitrogen removal efficiency significently. In this paper, the removal efficiencies of COD, ammonia and total nitrogen (TN) were investigated under reflux ratios of 50%,100%,200% and 300%, respectively. Results showed the removal efficiecies of Pre-denitrification BAF increased till the reflux ratio was 200% and then decreased as the reflux ratio rose from 50% to 300%. However, apparent impact on TN removal was also noted. At the optimal reflux ratio of 200%, the average removal rates of COD, ammonia and TN were 92.67%,90.50% and 80.50%, respectively, with the everage concentrations were 16.38 mg/L,9.93 mg/L and 22.69 mg/L. While maintaining the reflux ratio of 100%, the removal efficiencies of Pre-denitrification BAF increased first and then decreased at the turning point of 2.08 m/h with the hydraulic load ranging from 1.52 m/h to 2.56 m/h, in which the average removal rates of COD, ammonia and TN were 91.72%,90.29% and 74.45%, respectively, with the everage concentrations were 25.44 mg/L,16.65 mg/L and 29.33 mg/L. COD, ammonia and TN were mainly removed in the anoxic part of BAF(DN) with average removal rates of 78.48%,68.02% and 58.21%, respectively. Results also showed obvious nitrite accumulation, as well as significant characteristics of shortcut nitrification and denitrification.Air-water backwashing is effective for Biological Aerated Filter. The effluent concentrations of COD and ammonia concentration recovered to normal in 5-6 hours. We can also see from the test, the removal of ammonia is less affected by backwash process.