Treatment Of Municipal Wastewater By Anoxic Activated Sludge-Biological Aerated Filter (A-BAF) Process

The biological aerated filter (BAF) process combined organic removal, solids filtration and nitrification in a singal unit, has the advantages of high volumetric reaction rates of the systems, resulting in small footprints. But most of the disadvantages of BAF are more or less negative consequence of its characteristics being a high rate biofilm process and being a filter unit: relatively high requirements for mechanical pretreatment and having a limited capacity of removing phosphorus. Developing anoxic activated sludge-biological aerated filter (A-BAF) process has offered a new thinking for solving these disadvantages of BAF. The A-BAF process is a combine innovation for A/O process, bio-flocculation process and biological aerated filter. The PAC dosing into the denitrification tank can not only remove phosphorus but also improve the settleability of the denitrification activated sludge. Through lab-scale experments the start-up, nitrogen removal efficiency and phosphorous removal efficiecy with the dosing of PAC in the denitrification tank were investigated. The results showed that:The new method which the BAF was started by inculation and was backwashed every 3 or 4 days quickly started the A-BAF in 17 days. In the seven days from start-up, the removal rate of COD, NH₄⁺-N and SS were above 80%, 90% and 85% separately. The backwashing sludge can act as the seeding sludge of the denitrification sludge in the anoxic tank.Through investigateing HRT (1 h, 1.5 h, 2 h) on the treatment efficiency, we make sure when the HRT of BAF was above 1.5h, the effluent NH₄⁺-N concentration of A-BAF can below 5mg/L, reaching the national discharage standard of first A level (China, GB 18918-2002). Also Through investigateing internal recycle ratio (100%, 150%, 200%) and air/water ratio (2:1, 3:1, 5:1, 7:1, 10:1) on the treatment efficiency, we make sure when the optimal internal recyle ratio and air/water ration was 200% and 5:1 separately.Under the optimal operation parameters, the performances of A-BAF during a filter run were investigated. The headloss of BAF generally increased in the operation time, and reached the maximum level at 84 h. There was no significant change in the effluent COD during the operation time, the average COD concentration of A-BAF effluent was about 34.7 mg/L. The removal rate of NH₄⁺-N in A-BAF decreased a little, and the NH₄⁺-N of the effluent increased gradually from 0.5 mg/L to 2 mg/L. The effluent SS concentration was often blew 10 mg/L, except at the beginning of the filter run. In the batch tests, with the PAC dosing into the influent, anoxic activated sludge and effluent, the current of phosphorus removal were similitude, when the dosage of 100 mg/L, the TP concentration were under 0.5 mg/L. In the long time operation with the dosage of 100 mg/L PAC, the TP concentration in effluent was under 0.5 mg/L, when the influent TP concentration was 3.5 m/L. The COD, NH₄⁺-N TN and SS removal rate were about 90%,95%,70% and 90% separately after the dosage of PAC. The addition of PAC had a positive effect on phosphorus removal by A-BAF, but it had no effect on the removal of organic matter nitrogen and suspened solids.