| Based on the theory of Biological Aerated Filter. (BAF), this study built riverbed BAF in advanced treating the effluent of city sewage disposal plant to a reuse standard of landscape water body. It puts out the contents including: (1) Study on the treatment capability and the influence factors, analyse the mechanism of nitrogen removal by simultaneous nitrification and denitrification as well as the characteristic of biological film processes in riverbed BAF; (2) Determine the primary structures and design parameters of the riverbed BAF. Furthermore, this paper evaluated the corresponding economic benefits.1. Study on the performance and characteristic of riverbed BAF suggested:When the temperature is 15-30℃, the maxmium hydraulic loading rate of 0.708m3/m2·h, the ratio of gas to water is 3:1 and the low temperature is 4-10℃, under the maximum hydraulic loading rate of 0.18m3/m2·h, the ratio of gas to water is 5:1, the tail water treatment can meet the Scenic Water Quality Standard. The removal effects of A column filled with zeolite of 40cm-height above bottom and vermiculite and zeolite mixing in packed column of 40 cm-height at the top of the column was better than the B column which packed of 80 cm-height, mixing in vermiculite and zeolite mixture with ratio of 1 to 1.When the water temperature is about 15℃, the NH3-N influent varies between 11.16 and 13.95mg/l, the ratio of nitrite nitrogen of A and B reactors is over 50% in tail water treatment, both A and B columns achieve shortcut nitrification-denitrification.Study on biological film characteristic in reactor indicated that the difference of microorganism activities relates to microorganism quantities along the flowing direction. In other words, the more microbe biomass, the stronger the activities.2. Major design parameters are as follows:Under the normal temperature(15-30℃), the hydraulic loading rate of 0.708m/h, the ratio of gas to water is 3:1, the cycle of backwash is 5d.Under the low temperature(4-10℃), the hydraulic loading is 0.18m3/m2·h, the ratio of gas to water is 5:1, the tail water residence time is 3h. The cycle of backwash is 12d.Results addressed that the method is air-water backwash, firstly air scouring, then air-water backwash, finally water-wash has many advantages over other methods. Backwash parameters are summarized as: Single air scouring intensity is 10-13L/m2·s, last time is 3min; then air-water backwash, air is 10-13L/m2·s, water is 2-3L/m2·s, last time is 6min; finally water-wash intensity is 2-3L/m2·s, last time is 3min.In conclusion, the riverbed BAF showed significant predominance of both technique and cost in advancing treating the effluent of city sewage disposal plant. Application of this technique is worthy of widely extension in the process of advanced wastewater treatment for urban landscape water body. |
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