Experimental Study On The Operational Effects Of Biological Aerated Filter

BAF has many advantages, such as small volume, little covering earth and hydraulic retention time(HRT), high treatment efficiency and effluent water quality, low investment and running cost etc. BAF has been used widely for many years in the world and been used to treat several wastewater in our country.In this Paper, BAF was studied on the treatment of simulative low concentration rain and domestic sewage treatment with homemade expanded clay as the wad. The development process, characteristic of process, working principle, related factor of Biological Aerated Filter (BAF) and the technology flow of BAF are introduced here. And the effect and the law of the performance on the variation of temperature, height of media, hydraulic retention time (HRT) are studied here, too. Meanwhile, kinetic formulate is also obtained based on data collected in the experiment.The main results are summarized as follows:(1) BAF has good performance in treating wastewater, when the influent is 30 L/h, the ratio of gas to liquid is about 3: 1, the remove rate of COD,NH₄⁺-N and TP is probably 90%,80%,70%, respectively. And the optimum media height for the removal of COD,NH₄⁺-N and TP is 0～60 cm,30～90 cm,0～30 cm, respectively.(2) When the temperature is varied from 15℃to 25℃, it has less effect on the removal rate of COD. But to the nitrification of BAF, its effect will increase with the temperature growing. The experiment shows that when the temperature is lower than 19℃, the nitrification will get limited, meanwhile, the optimal temperature for the nitrification of BAF in this experiment is 24℃.(3) When the ratio of gas to liquid is about 3:1, the microorganisms will work better to get the contamination decreased if the HRT is prolonged. In this experiment, the removal rate of COD will over 90% when the HRT of BAF is over 1h (hydraulic load is less than 1．5 m³/(m²Â·h).Meanwhile, if the e HRT of BAF is over 1．5 h, the nitrification will better with the removal rate of NH₄⁺-N close to 78．62%.(4) The influent load will affect the performance of BAF directly. The results of the experiment show that the BAF has good capability to the impact of influent. When COD of the influent varied from 236 mg/L to 486 mg/L, the removal of which is above 85% steadily. Correspondingly, when NH₄⁺-N of the influent is varied from 12．07 mg/L to 5．12 mg/L, the removal of which is above 72% steadily.(5) When pH is between 6．9～7．7, the ratio of gas to liquid is about 3:1, the BAF will have its right condition to the biochemical reaction and the reactor will work well.(6) When the loss of the water head reached 0．4～0．5 m, get the reactor backwash. Take the method of firstly air scouring then air-water backwash, finally water-wash to backwash. In this experiment, 8 h after the backwash, the reactor will resume its ability in treating wastewater as usual.(7) When the BAF in its stabilization, the kinetic formulate of COD is C = C₀exp(-Kh) ,andthe relationship between K and HRT is K=2．8401×HRT-0．2614 (R²=0．9601) .When the temperature is reaching 20℃, KN is 0．7278 mg/L, the kinetic formulate of NH₄⁺-N is??, and the relationship between v_max and HRT is v_max=11．302×HRT+0．632 (R²=0．973) .The experiments of validation shows that the academic results of the kinetic formulate are very close to the values get from the test.