| With the regional population growth and the rapid development of social economy, The water pollution of Erhai Lake and its river basin has been gradually increased, the eutrophication problem has become increasingly prominent. In recent years, The industrial and urban point source pollution in Erhai lake basin have been effectively controlled under the powerful treatment by local government, but the rural non-point source pollution controlling in northern eara of Erhai Lake has not yet achieved significant results, and the village mixed sewage which is constituted by rural domestic sewage and livestock manure has caused the most serious pollution to the water environment. Currently, with the accomplishment of the major projects in the Twelfth Five-Year Plan, the focus of pollution control in the Erhai Lake basin has shiftted from centralized treatment of inflow rivers and low pollution water to the improvement of rural ecological environment and the comprehensive treatment of village mixed sewage. This paper has discussed the pollutants source in the mixed sewage as well as all-day and seasonal variation rule of the sewage quality and quantity based on investigation and analysis of the sewage composition and discharge characteristics of the typical village sewage in northern area of Erhai Lake. According to the wastewater quality and the discharge characteristics, we used the internal circulation biological aerated filter to treat the mixed sewage of this aera. The processing efficency of reacter and optimization of processing way and the conditions have been investigated based on the research of properties of hydrodynamics and mass transfer; Eventually, the suitable new ideas and complete set of technology of village mixed sewage treatment in Erhai Lake basin have formed in order to provide theoretical reference and data support for the construction of rural sewage comprehensive treatment demonstration project. the main research results of this paper are as follows.⑴ In the pollutants discharge load of typical village mixed sewage, the main source of COD and SS are shed flushing sewage and washing/bathing wastewater, for which 64.55% of COD and 48.04% of SS come from the shed flushing sewage, 21.34% of the COD and 26.55% of SS come from washing/bathing wastewater. The main source of TN, ammonia nitrogen and TP are shed flushing sewage and toilet sewage, for which 68.26% of TN, 72.46% of ammonia nitrogen and 40.94% of TP come from the shed flushing sewage, 22.82% of TN, 21.85% of ammonia nitrogen and 42.04% of TP come from the toilet sewage.⑵ In summer, the typical village all-day sewage discharging mainly concentrated in four peak period, which are 8:00~9:00, 12:00~13:00, 16:00~18:00 and 21:00~22:00. The sewage discharge hour variation coefficient was 1.8. The concentration range of COD in the sewage was 662~1589mg/L,TN and ammonia nitrogen concentration range were 52~226.6mg/L and 14.8~136.4mg/L,The concentration range of TP was 4.5~15.8mg/L,the concentration range of SS was 40~108mg/L. For the sewage, its COD, TN, ammonia nitrogen, TP and SS had a higher concentration and less volatile in the period of 1:00~6:00, however, the concentration of these pollutants reached the peak in the period of 8:00~9:00 and 16:00~17:00 when the shed flushing in the village was relatively concentrated and the proportion of the shed flushing sewage increased significantly.⑶ In 2014, the monthly total sewage discharge amount of typical village was between 230m3 and 557.8m3. The monthly variation coefficient of the sewage discharge amount was 1.5. The overall trend of the sewage discharge amount showed a monthly rise from January to July and a monthly decline from July to December. The COD concentration range of annual sewage in this village was 602~1143mg/L, the TN concentration range was 109~175mg/L, the ammonia nitrogen concentration range was 45~107.2mg/L, the TP concentration range was 7.4~10.8mg/L, and the SS concentration range was 43~73mg/L. The concentration of COD, TN, ammonia nitrogen, TP and SS overall showed a monthly increase from January to June and a significant reduction from June to August. From September to December, the concerntration of COD, TN, ammonia nitrogen and SS have been monthly decreased, while TP concentration increased month by month. The pollutant load amount of village sewage ordered according to the seasons was Summer>Autumn>Spring>Winter.⑷ In this paper, the influences on internal circulation biological aerated filter performance of hydrodyanmics and mass transfer which were affected by the factors of the air flow rate and the cross-sectional area ratio of the draft tube to the teacter(Ar/Are) have been investigated. The results showed that gas holdup in riser(?), liquid circulation velocity, circulation water, volumetic mass transfer coefficient(KLa), and dimensionless variance of residence time distribution function(2) have increased with the increasing of air flow rate. These parameters showed a rapidly increase when the air flow rate was at a low level, but a slowly increase when the air flow rate was larger. In addition, The larger value of Ar/Are was, the less obvious slowly increase of these parameters became.⑸ Activated sludge inoculation has been used to start cultivating biofilm for internal circulation biological aerated filter. Under the conditons that influent was 6L/h, air flow rate was 240L/h, water temperature was 20.5~29.8℃, p H value was 7.2~8.0, inflow water COD was 740~843mg/L and the ammonia nitrogen was 49.36~68.28mg/L, it take about 23 days to succed in cultivating biofilm, and the removal rates of COD and ammonia nitrogen stably reached 85.8% and 62.3%.⑹ The influences on the treatment efficiency of internal circulation biological aerated filter which was affected by the factors of Ar/Are, HRT, gas-water ratio and organic loading etc have been studied. The results showed that the reactor whose Ar/Are was 0.10 get the largest amount of circulation water and the best treatment effect that the removal rates of COD, ammonia nitrogen and turbidity were 87.8%, 84% and 90.1% when influent was 6L/h, and the gas-water ratio was 40:1. With the increase of HRT and gas-water ratio, The removal rate of COD and ammonia nitrogen have also increased. However, The removal rate of turbidity reduced when the gas-water ratio was too large. The change of influent organic loading caused by changing the COD concentration had no significant effect on the treatment performance of the reactor, but the change of influent organic loading caused by changing HRT had a obvious impact on the treatment performance, which the removal rate of COD and ammonia nitrogen get reduced when the organic loading increased.⑺ The result of orthogonal experiment showed that the order of influencing factors affected on the processing performance of this reactor was air flow rate﹥HRT﹥Ar/Are﹥inflow water COD concentration. According to the test results, the optimum operating conditions that Ar/Are was 0.10, HRT was 12 h and air flow rate was 300L/h have been given out. The average removal rate of COD, ammonia nitrogen, TN, turbidity and TP respectively reached 91.4%, 90.6%, 53.5%, 88.4% and 34.7%. |
PDF Full Text Request