Keypoints Of Process Design And Parameters Optimized In The Constructed Wetlands Dealt With Organic Matter

Sewage treatment system in CW(Constructed Wetland)have advantage in stable outflow water quality, strongly enduring impulsion load, the lower of capital construction cost and running cost, easily maintaining, and aesthetics value. CW has already abroad be applied in sewage treatment, agriculture point fountain pollution, surface fountain pollution and the treatment in eutrophication of the water bodies.However, a lot of deficiencies exist in constructed wetland for domestic wastewater treatment, for example, the ability of organic matter removal is sometimes relatively poor; the effluent can not be long-term stability meet standards. Common problems with clogging and improving water quality encountered in operation happened. As the wetland design parameters are not unified, it occupies much more ground than traditional treatment project.To overcome these deficiencies, we carried out the research on the key-points of process design and parameters optimized in the constructed wetlands dealt with organic matter. We use combined constructed wetland (CCW) (VF-HF-SF) as research object, study the affect of external conditions (HLR, wetland type, plant) on organic matter treatment in CCW. The effect of situ aeration in organic matter treatment in CCW was studied, too. At the same time, A/BCO (anaerobic/biological contact oxidation)-CCWS combined projects was used more than one year to study the organic matter remove ability of CW. The follow results were obtained:(1) The effects of CCW (VF-HF-SF) in CODcr, BOD5 purification had a close relationship with HLR, and the effluent concentrations of this system were increased with the increasing of HLR. Using k-C* model, we obtained CCWS k-value which was increased with the increasing of HLR. It explains why the removal load of CODcr, BOD5 in the CCW increased with the HLR. The constant k-value we obtained in our study was of great guide significance to the design of CW in subtropical regions of South China.(2) Research on treatment effect of CODcr and BOD5 under different HLR indicate that when HLR<0.50m/d, CODcr<250mg/l, and BOD5<100mg/l in influent, the CODcr and BOD5 of effluent could meet GB18918-2002 grade A standard. The most proper HLR recommended in our study was 0.50m/d.(3)CCW had high organic pollutants removal efficiency, the removal load were CODcr 14-83 g/(m2·d), BOD5 7-42 g/(m2·d), respectively. In CCW, VF had the best removal effect in treating CODcr and BOD5, and the second is HF. We obtained the k-value of CODcr and BOD5 in different wetland type using k-C* model, and the result indicate that:All the three type of wetland have high treatment rate in treating organic in low HLR (0.25 m/d); VF was recommended in medium and high HLR (0.50 m/d, 1.0m/d).(4) Situ aeration had significant impact on CODcr, BOD5 removal effect under the condition of HRT 3-6 h, gas 18 L/min respectively. The CODcr and BOD5 concentration in effluent was improved from GB 18918-2002 grade A to GB3838-2002 type IV standard. The removal rate increased nearly 20% which offers technology reference for improving the water quality in effluent.(5) Results from long runing showed that the effluents could stably meet the typeⅣstandard specified in the Environmental Quality Standards for Surface Water (GB 3838-2002), in the combined constructed wetland system of VF-SF-HF. The A/BCO system removal rates of CODcr,BOD5 and TSS reached 63.1%,67.7% and 66.2% respectively, under the condition of HRT 3-6 h, which helped avoid wetland jams and improve treatment efficiency, reducing land occupation by 44%.The average removal of CODcr, BOD5, TSS loading reached 9.4 g/(m2-d),5.1g/(m2·d),7.2g/(m2·d) respectively, under condition of HLR 0.30-0.59 m/d. The removal rate constants for COD and BOD5 were 74.6±12.1 and 166±30.5 (m/yr) respectively, all ranging high among the k-values recorded in the literature. It will offer the reference for designing constructed wetland in South China.