Study On Chlorination Disinfection Way In A Constructed Wetlands For Advanced Treatment Of Municipal Sewage Plant Effluent

Our study is aim at two uncertain timing and site problems of chlorination artificial wetland deeply treat urban sewage plant tail water. We choose a urban sewage plant tail water which is secondary treatment effluent concentration could achieve the A in first grade discharge standard of GB18918-2002 at the central South region of China.We assembled vertical flow constructed wetland treatment units with sodium hypochlorite disinfection as advanced treatment technology. In order to fully understand three problems: the purification effect and the influence of substrate enzyme activity of the artificial wetland after the influent water was chlorination. Further more, to know the stress response of submerged plant after the wetland water chlorination. The main research contents and results are as follows:1 As the hydraulic retention time HRT extension, the removal rates of CODcr, TN, NH4 +-N and TP are rising in the first stage, then falling or stable in vertical flow constructed wetland system. When all the pollution indicators are in the highest removal rate, the corresponding hydraulic residence time, respectively, 4 days, 2 days, 3 days, and 4 days.2 Vertical flow constructed wetland is used to treat tail water which is disinfection. Its influent concentration respectively as follows. CODcr is 47.5 mg/L, TP is 1.2 mg/L, TN is 27.1 mg/L, and NH4+-N is 16.7 mg/L. The treated effluent concentration of the disinfection tail water as follows, respectively, CODcr 27.8 mg/L, TP 0.5 mg/L, TN 2.1 mg/L, and NH4+-N 1.3 mg/L. The quality of the effluent water can meet the landscape water reclaimed water quality standard(GB/T 18921-2002). When sodium hypochlorite dosing quantity is less than 6.0 mg/L, the constructed wetland is less affected by chlorination, and the removal effects of nutrients and organic matter at C2 is similar to the control group C1. When sodium hypochlorite dosing quantity is 12.0 mg/L, the substrate enzyme activity in artificial wetland is decreased, which will drop the decontamination, even appeared negative removal rate, mainly showed in the release of phosphorus and the accumulation of nitrite.3 Treated with the artificial wetland, the UV254, DOC and E4 / E6 values of tail water which without disinfection treatment, will be significantly lower, while the UV253 / UV203 and SUVA values rising. After adding the sodium hypochlorite, the removal effects of SUVA and UV253 / UV203 values are improved. At the same time, the aromatic organic matter in the water is decreased.4 Considering the change of exterior characterization and physiological indexes, when Vallisneria spiralls and Ceratophyllum Demersum Linn are treated with sodium hypochlorite, the death threshold concentration is 1.0 mg/L. When the concentration of Na Cl O is greater than 1.0 mg/L, the photosynthesis of Vallisneria spiralls is restrained, metabolic is disturbed, and plant antioxidant enzyme system is destroyed. So the chlorine disinfection of water should control the residual chlorine content which must not exceed 1.0 mg/L before into the landscape of lakes.