Studies On The Tertiary Treatment Of Domestic Wastewater By UBAF

It is well known that the shortage of water has restricted the continuable development of national economy of our country. Nevertheless, it is lucky enough that it has been found that a city's sewage recycle is one of the most effective methods that can be adopted to settle such problems as the shortage of water and the water pollution. Aimed at reclamation of sewage, a experiment was conducted to treat the effluent from the simulative secondary sedimentation tank by up-flow biological aerated filter and sand filtration process. The experiment studied the removal efficiency of pollutants, the characteristic of UBAF in different technical condition, and the bacteria in UBAF.The experiment show that UBAF add sandfiltration has high efficiency in the removal of pollutants .It can achieve 42.5% removal of COD_cr, 45.1% removal of NH₄⁺-N, 98.9% removal of SS, 89.1 % removal of colour and 86.3% for turbidity .The effluent form sandfiltration reactor has better water quality than standards of miscellaneous and landscaping water.It shows that several factors, such as temperature , the ratio ofgas to liquid, the media height, hydraulic load and organic load, can influence the efficiency of UBAF.The infulence of emperature is lighter than other and 2³:1 should be choosed for ratio of gas to liquid .For the up-flow biological aerated filter,when the media height is 800mm,the best media height for the removal of COD, NH₄⁺-N,SS and turbidty is at 30cm,60cm and 10cm form the bottom respectively .When hydraulic load or organic load increase ,the bset media height for removal of COD and NH₄⁺-N will rise as well The relation of hydraulic load and remove efficiency of pollutants is not linear,there is a optimum hydraulic load for the remove of COD and NH₄⁺-N. When the average concentration of COD in influent is 24.3 97.6mg/L, NH₄⁺-N is 0.98⁹.32mg/L, and the ratio of gas to liquid is 2:1, the best hydraulic load is 0.615m3/m2.h, average remove rate of COD is 39.8%,and the average concentration of COD in effluent is 33.8mg/L.The datas for NH₄⁺-N is 36.74% and 2.26mg/L .In addition, when the media hight is 800mm, the organic load that reactor can can stand against is 0.53 2.76Tcg/m³(filtrationmedia)-d .while,the NH4+-N load reactor can bear is 0.007⁰.56 kg/m3(filtration media).d .The reactor keep a constant the removal for COD(40%) andNH4+-N(33.3%⁶9.2%).The method, intensity, and period of backwash are all studied in experiment, results show that: the method of using air scouring firstly, then air-water backwashing, and adopting water-wash finally has many advantages over other methods. Backwash parameters summarized are: air scouring intensity is 1.36L/(m2.s), duration is 3min; air intensity, water intensity and duration of air-water backwashing is 1.36L/(m2.s), 1.42L/(m2.s) and 10min respectively ,at the end of the process, single water-washing intensity is 1.42 L/(m2.s), duration is 5min .Several validation showed the backwash as before is good enough.By microscope ,it can be found that there were many kinds of microorganism,which formed a complex biology chain form bacteria, algae to protozoan and metazoa in the UBAF reactor.The distributing of microorganism's kind and amount is relative to the media height .With the rising of media height, the amount of microorganism descends step by step. At the top of up-flow biological aerated filter reactor, the violence turbulence caused by the wallop of air bubble result in the rising of ss in efiulent .Therefore,sand filliter reactor must be added after the UBAF in order to increase the removal for COD, NH4+-N, SS , color and turbidty.