Experimental Study On The New Biological Filter Process Applying To Urban Sewage Treatment

This paper proposed ‘Downflow floating biofilter-upflow fluidized suspension biofilter-chemically enhanced phosphorus removal sand filtration’ technology is a new ceramsite biofilter process for urban sewage treatment developed on the basis of the suspended ceramisite biofilter technology.Suspended ceramsite aeration biological filter as the slightly polluted source water biological pretreatment process has been applied in many practical engineering projects,and shows the advantages of good treatment effect,covering an small area,low energy consumption,simple operation,the technology used in the field of urban wastewater treatment may become a new miniaturized sewage treatment technology with a good application prospect.The experiment study is to investigate the water purification effect and performance of this process,and also provide reliable technical parameters for engineering design.The experiment first studied on the biofilm culturing feature of the new technology,after the success of biofilm culturing,studied the water purification effect,and then carried out performance optimization of the process to understand the impact of filtration rate,gas-water ratio,reflux ratio on the purification effect,and preliminarily ascertained the process backwash method,and finally the phosphorus removal were studied,also ascertained the total phosphorus stable compliance standard method.The test results are as follows:（1）Test process used phase natural biofilm culturing method,started 23 days after,the process worked well,and water purification effect was good and stable.Under the experimental conditions,the process effluent NH₄⁺-N<0.5mg/L,could achieve ’Surface Water Environmental Quality Standard’（GB3838-2002）Class Ⅱ water NH₄⁺-N standard;effluent CODcr<30mg/L,could reach surface water class Ⅳ CODcr standard;effluent BOD5<3mg/L,the water could reach the surface water class Ⅱ BOD5 standard;effluent TN<15mg/L,could achieve ‘urban sewage treatment plant pollutant discharge standard’（GB18918-2002）first level of A standard.（2）Under the test conditions,the test process with the filtration rate increases,CODcr,NH₄⁺-N,TN removal efficiency decreased.Three kinds of upflow filter gas-water radio had little effect on CODcr,NH₄⁺-N,TN removal.three kinds of reflux ratio also had little effect on NH₄⁺-N,when a reflux ratio of 50% CODcr removal efficiency decreased significantly.Reflux ratio had a greater impact on total nitrogen removal,with reflux ratio decreasing,total nitrogen removal increased first and then decreased.（3）Two ceramsite filter of test process is suitable for a four days backwash cycle,sand filter’s backwash cycle is suitable for 8 hours.Test process backwash wastewater sludge volume estimate is the amount of dry sludge 81.4g/m³.（4）Under the test conditions,the experimental process itself effluent TP could achieve a B standard,but not reached the A standard.Test process needs to be chemically enhanced phosphorus removal,when the FeCl₃ dosage is 80 mg/L,the effluent TP can reach the A standard.Before upflow suspension ceramisite fluidized column dosing FeCl₃ had a better phosphorus removal than later adding,the average ratio of total phosphorus removal rate is 21.28% higher than later adding,before upflow filter adding the effluent TP could achieve the level of A standard.