Development And Research Of Integrated Biological Fluidized Bed Equipment In Sewage Treatment

In Recent years,our country vigorously promoted the great strategic of “developing small town” and “building new social rural areas”,small town construction was developing rapidly,the number of small towns has grown dramatically,sewage discharged in these areas were also increasing.If the sewage can not be handled effectively,it will bring great harm to the environment of small towns.Small town sewage has the characteristics of small water quantity,large fluctuations in water quality and quantity,high nitrogen and phosphorus content and low concentration of organic matter.In addition,small towns also have fragile economic base,lack of technical personnel,weak public awareness of environmental protection,poor drainage systems and so on.Compared to conventional sewage treatment mode,integrated sewage treatment equipment integrate the functions of various process,has the advantages of compact structure,less land occupation,low investment and easy management,and thus more suitable for the small town sewage treatment.According to the characteristics of small town wastewater treatment,an integrated wastewater treatment equipment including biological fluidized bed and inclined plate sedimentation was designed.Fistly,the fast start-up capability and the operation performance under the design conditions were investigated,then the influences such as HRT,gas-water ratio and reflux ratio on the treatment effect were studied.The optimum operating conditions were also determined.The equipment started up with the method of fast discharging sludge and forming biofilm.Thin pale yellow biofilm appeared on the filler surface after 5 days,then the biofilm gradually thickening and the color gradually turned to brown.The removal rate of COD and NH +4-N reached 85% and 80% respectively after 15 days.The thickness of the biofilm on the inner surface and external surface were about 2mm and 0.5mm,the biofilm concentration was about 2700mg/L.The indicative microbes such as vorticella,rotifer were observed under electron microscope.Rich microbial species and complete biological systems were existed in the biofilm.The influent concentrations of COD,NH₄⁺-N,TN and TP were 78 to 244 mg/L,9.0 to 24.3 mg/L,22.7 to 55.7 mg/L and 3.4 to 6.4 mg/L respectively.Under the conditions of influent 3m3/d,gas-water ratio 5:1 and reflux ratio 200%,the average removal rates of COD,NH₄⁺-N,TN and TP were 88.6%,84.3%,46.7% and 52.0% respectively.The average concentrations of effluent were 18mg/L,2.7mg/L,17.1mg/L and 2.5mg/L respectively,the effluent quality reached level I B standard except for TP.During the experimental stage,the effluent quality was still stable though the influent quality fluctuated greatly.This indicates that the equipment has strong impact resistance to water quality fluctuation.The operation performances of different HRT,gas-water ratio and reflux ratio were contrasted,the result showed HRT of 8h,gas-water ratio 5:1 and reflux ratio 300% were the best operation conditions.The result of phosphorus removal experimental showed that when the dosage of PAC reached 50mg/L and 70mg/L respectively,the comprehensive removal rates of TP were 89.2% and 96.3% respectively,and the concentrations of TP in effluent can be controlled below 1.0mg/L and 0.5mg/L respectively.The integrated equipment that treatment scale was350 m / d covered an area of26.6m,one-time investment cost was 88140 yuan,treatment cost was30.32 yuan / m and operation cost was30.61 yuan / m.The equipment has more compact structure,lower investment,less land occupation,easier management and lower operating costs than conventional sewage treatment plants,so it is more suitable for the small town sewage treatment.