Study On City Daily Sewage Treated By Composite Vertical Flow Artificial Wetland Technology

By theoretical analysis and practical investigation in Yaoni Ditch, composite vertical flow (upflow and downflow) artificial wetland system in a small scale was established. This paper mainly studied some contents which included plant selection, filling choice, hydraulic characteristics,influence factors and purification results in the wetland system, in order to strengthen and popularize the technology.In autumn and winter, daily wastewater was regarded as study object and the operation characters of artificial wetland system were studied in experiment. The study results showed that:1) Experimental start-phasea CODin(CODcr concentration in the influent)=190.8 — 346.2mg/l, CODou(CODcr concentration in the effluent)=106.6—157.6mg/l and the CODcr removal efficiency was 44.1—54.5%. BODin(BODs concentration in the influent)= 95.8—176.4mg/l, BODou(BOD₅ concentration in the effluent)= 48.5—79.6mg/l and the BOD₅ removal efficiency was 48.2—55%.b In the phase, the change of the NH3-N removal efficiency was the most unsteady in all pollutants. NH₃-Nin(NH₃-N concentration in the influent)= 37.4— 62.1mg/l, NH₃-Nou(NH₃-N concentration in the effluent)=14.6—23.6mg/l and the NH3-N removal efficiency was 46—66%. TPin(TP concentration in the influent)= 3.3 —5.1mg/l, TPou(TP concentration in the effluent)=0.41—0.96mg/l and the TP removal efficiency was 76.6—91.6%. It was shown that the function of fillings was obvious in the experiment.c The SS removal efficiency was higher than other pollutants' in the system. SSin(SS concentration in the influent)= 82.1—216.2mg/l , SSou(SS concentration in the effluent)= 5.6—12.5mg/l and the average removal efficiency was more than 90%.d By observation, the growth of reeds was fit for the circumstance of high pollution load . And sweet flag was fit for the circumstance where water submerged fillings.2) Analysis-phase of influence factorsIn the phase, the paper mainly studied influence led by hydraulic load , pH value and temperature in the system. By analysis , the choices of operation condition were better when the range of hydraulic load was chosen among 0.6—0.8m3/m2.d, the range of pH value was chosen among 7.5—8.5, and the range of temperature was chosen among 16 °C—18 °C.According to analysis of the orthogonal experiment , the results showed that:Affected order of influence factors was that hydraulic load > temperature >pH value. As far as removal efficiency of pollutants were concerned , the optimization condition was that hydraulic Ioad-0.7m3/m2.d, temperature=16°C and pH value=8.5.3) Experiment-phase in optimization conditionWith change of time, purification results of pollutants were analyzed, and the growth of plants was observed in the system. The study results showed that:a The system ran 22 days in the optimization condition. By analysis, SSin=85.8—249.7mg/l, SSou=10.3—20.5mg/l and the average removal efficiency was more than 90%. And purification results were very obvious.b In the phase, organic pollutants were treated in the system, and the purification function of system was powerful to organic pollutants. The CODin=144.7 —341.7mg/l, CODou=45.8—97.8mg/l and the average removal efficiency of CODcr was 67.6%. BODin= 74.7— 195.8mg/l, BODou= 19.4—51.9mg/l and the average removal efficiency of BOD5 was 71.3%. By comparison, the purification results of BOD5 were better than CODcr's.c In the phase, NH3-Nin= 33.1—61 .lmg/1, NH3-Nou=10.3—19.8mg/l and the average removal efficiency of NH3-N was 68%. TPin= 3.7—6.7mg/l, TPou=0.8— 1.3mg/l and the average removal efficiency of TP was 79%. It was shown that selection and arrangement were fit for the system, and that the function of fillings was obvious in the experiment.d By cultivation of plants in 4 month, the average height of reeds amounted to 60cm , and sweet flag amounted to 55cm. According to observation to root of plants , root of reed had extended 60cm from surface of filling to root of reed, and root of reed had yet grown to 45cm. As far as branch of plants was concerned, plants grew 4 budsin the upflow system, and plants grew 3 buds in the downflow system.In addition, the study indicated that the purification results were not affected in the system though root of plant might decrease hydraulic retention time.