Experimental Studies On The Treatment Of Secondary Effluents By BAF

According to the technological process of reclaimed water factory, a series of experiments has been carried out using a down-flow BAF to treat the low concentration secondary effluent of municipal sewage plant.In order to quicken the culturing process of biofilm, the biofilter was inoculated with activated sludge from the secondary sedimentation tank. It take about 50 days to succeed in cultivating biofilm using the method of continuous flow adding some nutrient elements in the wastewater and the removal ratios of COD,NH3-N get to 30% and 60%.The experimental results show that the performance of down-flow BAF is excellent. Under the condition of the inflow COD is between 23.0-56.8mg/L , NH3-N is between 7.6 -20.5mg/L and turbidity is between 7.8-23.6NUT, the average removal ratio is 34.8%,71.8% and 75.9%. The quality of effluent reaches the reuse standard.The hydraulic loading rate and organic concentration of low-strength influent have little influence on COD removal ratio. When the organic loading rate is less 2.00kgCOD/(m3.d),the change of loading rate has less influence on the removal of NH3-N. But the hydraulic and NH3-N loading rates have some influence on NH3-N removal ratio. The optimal hydraulic loading rate is 2.5m3/(m2. h).The NH3-N removal ratio sets to decrease when the NH3-N loading rate is more than 0.37kg/(m3.d). As the NH3-N concentration is 67.9mg/L, the NH3-N removal ratio is below 50%. Gas-water ratio has more influence on the effect of NH3-N removal. The optimal gas-water ratio is 3.5. In the down-flow BAF, the optimum media height for the removal of COD is 0-80cm and the removal ratio is 79.1% of all. The great mass of ammonic nitrogen removal is concentrated in the nether regions of 80-200cm. And the NH3-N removal effect is increased along the filter column. When the influent COD is less than 50mg/L and NH3-N is less than 20 mg/L, it is 200cm height filter material that can meet the requirement.The backwash regimes of gas combined with water has a good backwash effect. First, the backwash, air scouring intensity is 10-12L/(m2.s); and second, mixing backwash, air-flow intensity is 10-12L/(m2.s) too, water-flow intensity is 4-5L/(m2.s);finally, water-wash intensity to backwash is 4-5L/(m2.s). The backwash interval is 7 days. In this experiment, it is the 4 hours after the backwash that the reactor will resume its ability in treating wastewater as usual.