| When used in wastewater treatment, the constructed wetland own many advantages of good water quality of outlet,low cost of construction and daily operation, convenience of management and aesthetic value, especially is consistent with the latest environmental tendency of diminishing and spreading form innational wastewater treatment, and is worthy of popularizing in small and middling cities. However,the pollutant removal efficiency of constructed wetland is greatly affected by such factors as hydraulic loading rate, pollution load of influent, wetland types, wetland plants. These factors limit the further improving of purifying effect in wetland, now becoming the blocking bottleneck in extending application of wetland.Comprehensive investigate the key factors influence of nutrient removal, with a hybrid constructed wetlands of vertical subsurface wetland-horizontal subsurface wetland-surface wetland(VF-HF-SF); research the reinforcement performance of situ aeration for nutrient removal in wetland; at the same time, select the operation parameters optimized in biological methods combined with constructed wetland (A/BCO-CW). We can get the following results through the experiment:(1) There is a close relationship between purification performance and HLR in hybrid constructed wetlands. The concentration of TN in effluent weastwater can reach the Urban Sewage Treatment Plant Emissions Standards (GB 18918-2002) type I A standard(TN<15 mg/L) under the influent concentrationin is 17.9-30.8 mg/L in 0.25 m/d and 0.50 m/d. The effluent NH4-N can reach the GB 18918-2002 type I A standard (NH4-N<8 mg/L)under the influent concentrationin is 16.3-26.8 mg/L in 0.25 m/d; The effluent TP can reach the GB 18918-2002 type I B standard(TP<1.5 mg/L) under the influent concentrationin is 1.44-3.07 mg/L in 0.25 m/d.The higher HLR provided a lower nutrient removal rate. There are 49% removal of TN,59.6% removal of NH4-N and 35.8% removal rate of TP with the HLR of 0.25 m/d.(2) Pollution load test studies had shown that the removal load of TN,TP was increased with increasing the pollution load in wetland with plants, and both show a certain degree of linear relationship(R2>0.7). The mass removal of TN, TP can reach 5.19g/m2/d and 0.57g/m2/d, respectively. And there could be used to deal with a higher pollution load of sewage for more removal load on the premise of effluent can up to standard.(3) The removal effect under different type of CWs indicated that there was a direct correlation between mass removal and removal rate constants:When the HLR is less than 0.50 m/d, both VF and HF had a high k value regarding to TN removal, hence, in this condition, both of VF and HF can be first considered. When HLR is more than 0.50 m/d, VF can be chosen rather than HF. Another aspect, for the removal effect of TP, when the HLR is under the condition of intermediate and low level (eg.0.25-0.50 m/d), VF or SF technique can be first considered, while when the level of HLR is more than 1.0 m/d, only VS technique can be chosen.(4) Wetland plants have great significance on nitrogen removal. Nutrient mass removal rate is higher in planted system than unplanted system, especially in high HLR conditions. On the removal efficiencies of phosphorus, there is no significant difference in all our experiment hydraulic loading. Result indicated that the main mechanism of phosphorus removal in wetlands is adsorption by substrates.(5) The concentration of oxygen within wetlands will increase when aeration, what's more, the ability of anti-nitration was also enhanced through aeration in situ in the integrated constructed wetlands. At last, the high removal rate of NH4-N was archived. Comparing with the control section, i.e., without aeration, the removal rate of NH4-N was increased by the value of 26%. Under the condition of strong aeration in VF wetlands, the removal rate will enhance 5 times. Considering the same removal amount of NH4-N, the occupied land by the strong aeration wetlands is less than that the common wetlands occupied. The procession of aeration had a remarkable effect on TP removal. When aeration, the average of removal rate can reach more than 80%, with a clear difference to the average removal value of 0.03% under the condition of un-aeration.(6) When the variation of NH4-N contents was within 6.27-18.8 mg/L, the effluents could stably meet the typeⅣstandard, namely 1.5 mg/L, as specified in the Environmental Quality Standards for Surface Water (GB 3838-2002). A/BCO-CW was effective for NH4-N reduction, achieving annual average removal rates of 87.73%. The A/BCO pretreatment system removed NH4-N by 57.38%, full aeration at the aerobic section was conductive to nitrification, which helped address the problem of restriction on nitrification resulting from shortage of dissolved oxygen and with reduced the land occupation of follow-up constructed wetlands by 25%.The removal rate constants for TN NH4-N and TP were 39.8±21.1 m/yr,41.62±15.2m/yr and 23.2±12.4m/yr respectively, both ranging high among the k values recorded in the literature, provide design parameters and experience for the same or similar wetland technology in South China Region.Through the results of above:HLR 0.5 m/d was recommend for TN removal and 0.25 m/d for TP and NH4-N with the nutrient concentrations in this study (TN:17.9-30.8 mg/L; NH4-N: 16.3-26.8 mg/L; TP:1.44-3.07 mg/L). The water pollution load can be increased under the premise that meet the effluent standards in the pollution load range (TN:4.64-28.84 g/m2/d; TP: 0.36-3.07 g/m2/d). Using VF for treat nitrogen and phosphorus is the priority choice within the HLR (0.25-1.0 m/d), in the range of≤0.50 m/d HF was recommended to terat nitrogen; at 1.0 m/d or so, recommended HF phosphorus. Aeration to the average removal rate of NH4-N increased by 26% and average removal rate of phosphorus can reach 80%.Increase the pre-treatment system can save 25% of constructed wetland area for treat NH4-N. Key words:Constructed wetland; Nutrients; Sewage weastwater; Removal rate constants...
|
PDF Full Text Request