CONTENTS OF TABLES
Chapter 8. Conclusions
Chapter 8. Conclusions...8-1
With the continuous progress of economy and society, the single water supply mode has seriously hindered the development of Harbin City and the health of citizens. Therefore, this study studied the water quality differences, characteristic pollutants and sources of Mopanshan Reservoir and Songhuajiang River, two major water sources in Harbin. In order to deal with the current problems of water sources in Harbin, this paper takes a water treatment plant in Harbin as an example to upgrade the water purification process, and puts forward an effective measure to alleviate the risk of water supply in Harbin from the process transformation and the preliminary test of water quality of dual source water supply mode. The main experiments involved in this study include the water quality monitoring of Mopanshan Reservoir and Songhuajiang River, the enhanced treatment experiment of conventional water purification process, the ozone activated carbon experiment and the preliminary test of joint water supply of two water sources. The main conclusions are as follows.
In the chapter 1, background, previous research, objectives, and organization of the thesis are described.
In the chapter 2, an overview of the theory of urban safe water supply, the major reagents and experimental apparatus, methods of water quality assessment, and location map of the two drinking water sources.
In the chapter 3, we compared and analyzed the source water quality of Mopanshan Reservoir and Songhuajiang River in Harbin. The results show that most of the Mopanshan Reservoir basically meet the water quality standard above Case III, but some indicators exceed the Case III water quality standard, and the water quality has the trend of eutrophication. With the continuous deepening of Songhuajiang River treatment, the water quality of Songhuajiang River has been basically maintained at Case III water quality standard, reaching the water quality target requirements of drinking water functional zone, and the water quality has been improving year by year. The pH value of Mopanshan Reservoir raw water is less than 7.0, and that of Songhuajiang River is more than 7.0.
The total hardness of Mopanshan Reservoir raw water is lower than that of Songhuajiang River water, but the total phosphorus of Mopanshan Reservoir water exceeds the standard. The contents of dissolved oxygen, ammonia nitrogen, fluoride, sulfate, chloride, nitrate, iron and fecal coliform in raw water of Songhuajiang River were higher than those in Mopanshan Reservoir raw water. The potassium permanganate index and chemical oxygen demand of the raw water of Mopanshan Reservoir and Songhuajiang River decreased year by year, but the organic matter comprehensive index of Songhuajiang River was still higher than that of Mopanshan Reservoir raw water. In addition, the CCME WQI scores of Mopanshan Reservoir from 2016 to 2018 were 76, 68 and 64, respectively, indicating that the pollution situation has a rising trend year by year. After years of treatment, the water quality of Songhuajiang River has been improved. The CCME WQI score increased from 54 to 65, indicating that the water quality of Songhuajiang River has been significantly improved after years of treatment by the government.
In the chapter 4, based on the experimental data, we analyzed the main pollutants and the distribution of pollution sources in the two water sources in Harbin. At the same time, we compared and analyzed the effluent quality of the two water sources after regular water purification process.
The results showed that the characteristic pollutants of Mopanshan Reservoir water were permanganate index, total nitrogen and total phosphorus. Among them, the permanganate index showed the characteristics of seasonal over standard, the total nitrogen increased year by year, the water was slightly polluted, and there was a trend of eutrophication. The pollutants mainly come from agricultural non-point source pollution such as pesticides and chemical fertilizers, domestic sewage and surface runoff. The characteristic pollutants of Songhuajiang River raw water are permanganate index, chemical oxygen demand and ammonia nitrogen. Among them, permanganate index exceeded the standard in summer and ammonia nitrogen exceeded the standard in winter. The pollutants in Songhuajiang River Basin mainly come from the discharge of industrial wastewater and surface runoff. After the conventional treatment of raw water from the Mopanshan Reservoir, only the chloral could not meet the national standard, while all other water quality indices could reach the requirements of “Standards for drinking water quality” (GB5749-2006). For the Songhuajiang River, all the water quality indices and DBPs could meet the national standard after the conventional treatment, apart from the NH4+-N
in the
icebound season. Through contrast and analysis, the Songhuajiang River is more suitable for the drinking water at present.In the chapter 5, taking Songhuajiang River water as raw water, the operating parameters of enhanced conventional water purification process were determined through experiments. The results of enhanced coagulation test show that the effect of composite Al Fe is the best, and the optimal dosage is 60 mg/L. At this time, the removal rate of turbidity and chroma can reach 99% and 89%, respectively. The optimal parameters of enhanced filtration are as follows: influent flow rate 3.4 m3/h, backwash cycle 20 d, backwash intensity 12.5 L/(m2·s). Under these conditions, the removal rate of turbidity and chroma of sand filter is above 95%, the removal rate of CODMnis 80%, and the removal rate of ammonia nitrogen is about 40%.
In the chapter 6, we still take Songhuajiang River water as raw water, and determine the operation parameters of ozone activated carbon process through experiments. The water quality of the two water sources was studied. The results show that the average utilization rate of ozone is 87.30%, and it has a good coagulation aid effect. The optimum dosage of ozone is 1.0 mg/L, which can save about 12% coagulant. Main ozone biological activated carbon is the main process of the scheme.
The average utilization rate of ozone in the main ozonation process was 71%, which was lower than that of pre-ozonation, and the optimal dosage was 0.4 mg/L. Ammonia nitrogen can be reduced to less than 0.2 mg/L after chlorination at break point, which can meet the standard of drinking water.
And there is no big fluctuation during the stable operation of the system. The optimal chlorine dosage was 4.25 mg/L, and the free residual chlorine and ammonia nitrogen met the requirements,