| The total amount of water resources in China accounted for about 6% of the world’s total water resources, but per-capita water resources was only 1/4 of the world average, and water shortage was seriously deficient. Recent years, due to people exploited groundwater at will, the level of groundwater had been severely decreased, especially in the North China, and had formed the largest groundwater funnel in the world; most municipal wastewater was collected through the pipe network and processed by the processing terminal. Lacking of rural financial and technical support, it was difficult to build sewage treatment system, sewage was spilled anywhere, and the impact of the application on the environment increased every year, the sewage treatment technology of alpine area was lack, which caused the pollution and waste of resources. In order to solve the problem of sewage pollution dispersion in alpine region, and to provide theoretical support and technical support for sewage treatment in cold area, the research group in Chongli area of Zhangjiakou through rural decentralized sewage discharge status and water quality, providing the basic parameters for the simulation test, and improved filler type and structure of underground infiltration system at low temperature(13±2)℃, adding different C/N poplar sawdust, studying the sewage purification effect, and to find the best C/N. In addition, the system ran in the actual, it would be unused for a period of time; after letting the system lie idle, which its function would be affected. By changing the water hydraulic load, the article studied its impact on the purification of wastewater, and providing technical support for the practical application. Results showed that:(1) The Chongli area of Zhangjiakou belonged to the alpine region, the rural decentralized sewage casual splash phenomenon was serious, and there were no sewage treatment facilities, sewage problem was more prominent. According to the investigation, local water supply facilities, centralized water supply in 100%; Aqua is serious, 98.98% were aqua, and only 1.02%were Flush toilets. 9L/d sewage emissions per head, and there was great difference in different villages of sewage discharges; in addition, 80.22% of residents spilled effluents casually, 19.78% household discharges from open drains.(2) The sewage water quality in Chongli area was fluctuant, and the average concentration of pollutants in sewage was far higher than the "Surface Water Quality Standards" V class standard, direct emissions could cause environmental pollution, and it need to be treated effectively. Sample analysis showed that sewage water quality index in the area was: chemical oxygen demand was 54 mg/L ~325 mg/L, total nitrogen was 13.23 mg/L ~31.65mg/L, ammonia nitrogen was 10.23 mg/L ~26.30 mg/L, nitrate nitrogen was 0.20 mg/L ~1.30 mg/L, and total phosphorus was 1.23~3.35 mg/L.(3) In the range of C/N, the best C/N of the sewage system was 20:1. Test was set 4 treatments which were recorded as R1(C/N=9:1)、R2(C/N=12:1)、R3(C/N=15:1)and R4(C/N=20:1) respectively, they added different sawdust to set the C/N, besides all the same. The system ran at low temperature(13±2)℃, and hydraulic load as 10cm/d, results showed that, all of the systems had a better removal effect on chemical oxygen demand, total nitrogen, ammonia nitrogen, nitrate nitrogen and total phosphorus. Effluent was stable, and the effluent concentration of each index almost reached primary standard municipal of the sewage treatment plant emission standards, integrated R1, R2, R3 and R4 effect of domestic sewage treatment knew that sawdust treatment of domestic sewage at low temperature optimum carbon to nitrogen ratio was 20:1. Analysis four groups of influent COD removal effect, we knew that R1 was better purifying effect, effluent concentrations of 24.0mg/L~60.3mg/L, and 43.1mg/L was the average effluent concentrations, average removal efficiency of COD removal rates for 76.6%; R4 processing system was relatively poor, effluent concentration fluctuation was 29.6mg/L~86.7mg/L, the average effluent concentration was 50.2mg/L, the average removal rate was 72.7%; the removal efficiency of R2 and R3 was between R1 and R4. There was no significant difference on COD removal efficiency among four groups. Total phosphorus removal efficiency of 4 groups system was nearly the same, the average effluent concentration was around 0.14mg/L, average removal rate was around 95%, adding sawdust was no impact on TP removal effect of the low temperature environment, no matter whether the system was idle, 4 groups had no significant effect on TP removal effect. The effect of nitrogen removal showed that, the ammonia nitrogen removal effect was almost the same, there was little relationship between the removal of ammonia nitrogen and C/N, adding sawdust was without impact on ammonia nitrogen removal. After the stability of the system, the effect of total nitrogen and nitrate nitrogen removal in 4 groups were R4>R3>R2>R1, the total nitrogen effluent concentration of R4 processing system ranged for 3.1mg/L~14.4mg/L, the average concentration of the effluent was 5.5 mg / L, the average removal rate was 74.7%; the total nitrogen effluent concentration of R1 treatment ranged for 4.9mg/L~12.9mg/L, the average concentration of the effluent was 8.4 mg / L, the average removal rate was 63.7%, the removal effect of R2 and R3 was between R1 and R4. The system nitrate nitrogen concentration of R4 processing in effluent was 2.13 mg/L~6.14mg/L, the average concentration of the effluent was 3.68mg/L; the nitrate nitrogen of R1 processing system in effluent concentration was between 3.62mg/L~11.47mg/L, the average concentration of the effluent was 6.95mg/L, nitrate nitrogen effluent concentrations of R2 and R3 ranged between R1 and R4.(4) After the groundwater infiltration system was unused, the hydraulic load of the influent could effectively reduce the recovery time and improve the purification ability of the pollutants. After the systems were idle, 4 groups system in hydraulic load was set 5cm/d(denoted as the treatment B), treatment B was recorded to SR1(C/N=9:1) SR2(C/N=12:1) SR3(C/N=15:1) and SR4(C/N=20:1), and after the effluent concentration of treatment B ran stability, restore the hydraulic load to 10cm/d. the remain still ran by 10cm/d(marked as treatment A) at room temperature(15±2) ℃ conditions. The result showed that processing system in groups 2 purification ability for cod were better than that of treatment A corresponding group, average strength of effluent of SR1 on COD was 16.7mg/L, average removal rate was 87.1%; average effluent of SR4 on COD was 29.2mg/L, and the average removal rate was about 76.9%; the removal efficiency of SR2 and SR3 was between SR1 and SR4. Each system of treatment B on phosphorus removal effects were better than that of a corresponding system in treatment A, illustrate the hydraulic loading can affect the system of phosphorus removal effect, it indicated that hydraulic loading could affect the removal efficiency of phosphorus.(5) After lowering water hydraulic loading, the best C/N for removaling the contaminants of treatment B was 20:1, the system could withstand the sudden increase in the influent hydraulic loading, compared each systems of treatment B showed that, the purification effect of total nitrogen and nitrate nitrogen was best by SR4. The difference of the removal of COD, ammonia nitrogen and total phosphorus between the 4 groups of the system was not significant. If the influent hydraulic load of treatment B restored to the 10cm/d, effluent concentration appeared transient increase and then restore stability, then the effluent of treatment B was better than treatment A. |
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