Nitrogen Removal By One Stage Biological Aerated Filter With Floating Polystyrene Media

To achieve nitrogen removal for the low carbon: nitrogen （C/N） ratio sewage,concerning the complex control and high operation cost of multiple-stage BiologicalAerated Filters （BAFs）, the one stage BAF with floating polystyrene media is studied,which has two aeration modes: bottomed aeration and partial aeration. In this paperthe two aeration modes are compared in nitrification and nitrogen removal capacityand appropriate inflow requirements, meanwhile operation conditions are optimizedfor simultaneous nitrification and denitrification （SND） in the reactor.Firstly, the bottomed aerated BAF test was carried out for the operationparameters optimization, which included start-up, the best air-water ratio, the load ofpollutants, the distribution law of pollutants along the filter height, and the maxdenitrification load. Then it was compared with the partially aerated BAF with thesame operation conditions in repects: the removal of pollutants, the distribution ofDO along height, the degradation law of pollutants along height and the SNDcapacity.The test results demonstrated that one stage BAF can achieve nirification andnitrogen removal requirements, and compared with the traditonal two stage BAFs,have advantages of short flow, low operation cost and simple control.The bottomed aerated BAF had an average outflow NH₄⁺-N concentration lessthan5mg/L and TN less than15mg/L, when with the hydraulic retention time （HRT）3h，water temperature25-30℃, the air-water ratio4:1, and the reflux ratio100%, theinflow NH₄⁺-N concentration was less than30mg/L. To the partially aerated BAF,the NH₄⁺-N inflow concentration should be less than22mg/L. Compared withbottomed aeration mode, the partial aeration mode had a longer operation period anda larger TN removal capcity, but a lower ammonia removal load.The inflow sCOD concentration is a key factor in choosing the aeration mode.Provided the inflow sCOD more than120mg/L, the bottomed aeration mode ispreferred; If less than120mg/L, partial aeration mode is preferred.With the two aeration modes, the max SND removal took nearly50%in total TNremoval. The SND was negligible with the HRT3h, air to water ratio4:1and refluxratio0or100%, but very obvious when the air-water ratio was reduced to2:1or theHRT reduced to1.5h. The SND favors high pollutants load and relatively lowair-water ratio.