Treatment Of Wastewater From Mountain Tunnel Construction By Coagulation In Chongqing

With the development of economy, more and more highways had been constructed in mountainous region of China, which resulted that a lot of tunnels were constructed in recent year. However, the tunnels mostly located in eco-environmental vulnerable area, such as drinking water source region, drinking water conservation region, water and soil erosion region, etc. At the same time, eco-environment could be contaminated by the tunnel construction wastewater that did not treated. Therefore, protection of the tunnel construction region well is of important meaning.At present, the study of the tunnel construction wastewater at home and abroad often focused on the sewage treatment, but little attended the bad impact of tunnel construction wastewater. Now, there were half tunnel construction and operation wastewater that were none of any treatment, directly into the ground or with the drain discharged to outside. The untreated wastewater not only would cause severe water pollution, vegetation withered, but also the corrosion of concrete tunnel lining, endangering the stability of the tunnel.The survey in two typical mountain construction tunnel wastewater found that the first pollution factor was the suspended solid, and COD, TP, pH also would be exceeded emissions standards. Construction wastewater was a type of inorganic wasterwater, causing eutrophication of water bodies were less likely. The concentration of SS in wastewater differed greatly, and it mattered correlation well between the concentration of suspended soild and TP, COD.Through the analysis of spatial variation in Pingyang tunnel, the exclusion of the influence of external factors, the concentration of suspended solid was gradually decreased, the concentration of other pollutants were also reduced along the road.Comparing with construction wastewater from the different tunnels, it was that wastewater of the Pingyang tunnel was a kind of large dispersion wastewater, and wastewater of the Bicheng tunnel was a kind of weak colloidal or colloidal dispersion wastewater. Through experiments that the best remaining time of Pingyang tunnel wastewater was 120min.Without considering other factors, for large dispersion wastewater, the best dosage range of sodium chloride was 10～25mg/L; the best dosage range of alum was 45-60mg/L; the best dosage range of sulfate was 15～30mg/L; the best dosage range of ferric chloride was 10-30mg/L; the best dosage of PAC was 20mg/L; the best dosage range of PFS was 40-60mg/L; the best dosage range of PFMS was 50-70mg/L; the best dosage range of CFPS was 100-140mg/L.Without considering other factors, for weak colloidal or colloidal dispersion wastewater, the best dosage range of sodium chloride was 25-45mg/L; the best dosage range of alum was 120～160mg/L; the best dosage range of sulfate was 70-90mg/L; the best dosage range of Ferric chloride was 55-65mg/L; the best dosage range of PAC was 180-220mg/L; the best dosage range of PFS was 140-200mg/L; the best dosage range of PFMS was 120-140mg/L; the best dosage range of CFPS was 180-240mg/L.In considering the other factors, the optimal combination of inorganic low-molecular coagulant was found by the orthogonal design experiment. For large dispersion wastewater, the optimal combination was at 15℃and high concentration, adding 40mg/L of alum, stirring 2min, depositting 40min. For weak colloidal or colloidal dispersion wastewater, the optimal combination was at 20℃and high concentration, adding 100mg/L of alum, stirring 2min, depositting 30min. Settling time and the dosage were the main influencing factors. For large dispersion wastewater, the optimal combination of PFS was at 20℃, adding 80mg/L, stirring lmin, depositting 20min. For weak colloidal or colloidal dispersion wastewater, the optimal combination of PFS was at 20℃, adding 200mg/L, stirring 2min. depositting 20min.The effect was poor, using PAM alone, but it was good to help coagulation, which can reduce the dosage of PAC and PFS. After hydrolysis of cement, it could be coagulation and coacervation, but the pH of wastewater was up to 11, used the cement, and the large amount of sludge generated, so cement could only be as a spare coagulation.In the dynamic case, setting the water flow of 2.4m3/h and the PAC dosage of 160mg/L could reach the emission standards of suspended solid, and proved that the result of static beaker experiment was reliable. At the same time, in this dosage, the residual aluminum content in wastewater could accord with the standards for drinking water quality.Finally, the paper pointed out that to treat the tunnel construction wastewater had not aroused people's attention. With the 12th Five-Year transportation Plan and the strategy for the development of the western regions implemented, the tunnel project would be more and more in the next ten years, so treating the tunnel construction wastewater could protect the water environment, and could prevent water pollution, particularly contamination of drinking water sources.The experiment only used part of the coagulant, so a future study play attention to find a more convenient, more economical and more environmentally friendly coagulant, particularly to further research into cement and other potential coagulant.At the same time, to evaluate the effect of coagulant treatment had only a single factor or apparent method to evaluate, so the hope that the future research could focus on the interaction effect of factors...