Study On The Dark Colour Removal Technology Of Combined Sewer Overflow

In a combined sewer system, wastewater and storm water runoff are collected and carried in the same sewer line. When the capacity of the interception is reached in rain days, overflows, which are called "Combined Sewer Overflows" (CSOs), occur to the receiving waters. Based on the literature review of the pollution problems induced by CSOs and the relative control strategies, the reason as well as the quantitative indication and the removal technology of the dark color caused by CSOs was investigated in this report. This research covers the following points: 1. The quantitative indication of the dark color caused by CSOs was studied. 2. A model of assembly system for CSOs pollution control was designed. 3. The engineering practice research of CSOs pollution control in emergent situation was performed. 4. The optimized methods of the dark color removal technology were studied. 5. An air-blower system was designed for East Tianlin Road Pump Station. 6. Economic evaluations of the dark color removal engineering of the pump station were carried out. The result of the study showed that: 1. The luminous flux of transmitting beams can be applied for estimating the dosage of NaClO. It's applicable for engineering use. 2. Considering CIE's recommendation, the levels of dark color of CSOs can be compared and described under light source D₆₅. 3. The dark color of CSOs can be considered removed giving that the CIE1976 value of CSOs under light source D₆₅ is above 9.1. 4. The use of Ca(OH)₂ can greatly help Ca(ClO)₂ and NaClO to remove dark color. But simultaneously it will cause a high pH. With a same consumption of [Cl^-], Ca(ClO)₂ is more effective than NaClO in dark removal because of the flocculation and sedimentation effects of [Ca²⁺]. Ca(ClO)₂ performs the best because of it's both economical and applicable. In the laboratory, the feasible dosage of [Cl^-] is 140 mg/L. 5. Dark color removal effects can be highly improved by continuous air blow aeration, and finally be stable. The parameter of DO value can be applied for this process. In order to get the most cost effective substance of dark color removal, air blow aeration is needed, while in rainy days Ca(ClO)₂ should be adopted as well.