Research on sewage pollution control technology an

Research on technology and policy of urban sewage pollution control

Keywords: urban sewage, sewage treatment, industrialization, technology and policy

I. urban sewage pollution has become the primary problem of water pollution control

1. Current situation of urban sewage pollution and treatment

since 1985, the total annual discharge of wastewater in China has been maintained at about 35 ~ 40 billion m3/A. In 1996, 532 of the 666 cities in China had no sewage treatment plants, and 309 sewage treatment plants were built in 134 cities. The total amount of urban sewage treatment was only 4.46 billion m3, of which only 6.9% were treated by secondary biochemical treatment, and 77.4% were directly discharged into water bodies without any treatment. In 1997, the wastewater discharge reached the highest value of 41.6 billion m3, including 22.7 billion tons of industrial wastewater and 18.9 billion tons of municipal wastewater. In 1999, the urban sewage pollution load exceeded the industrial wastewater pollution load for the first time. The focus of water pollution in China has gradually changed from industrial point source control to urban sewage pollution control. According to the estimate of the Ministry of construction, the wastewater discharge in 2000 was 48billion m3

2. Prediction of urban sewage discharge

at present, there are more than 640 cities, more than 16000 towns, and a population of about 270Million. Since the 1990s, China's gross national product has been growing at a high rate of 8 ~ 11%. It is expected that China's economic growth will remain at a high and medium rate of 6 ~ 9% in the first 20 years of the new century. Considering the above factors, the sewage volume shall be increased at a rate of 5%. By 2010, the sewage volume will increase by 30billion m3

according to the small town development plan newly formulated by the relevant departments of the Chinese government, the focus of the development of new small towns in the future will be small towns along the road, along rivers, along the coast, along the border and other geographical locations and transportation conditions, rich resources, township enterprises have a certain foundation or rural wholesale and professional markets are beginning to take shape; The construction goal is to build a new small town with a population of about 30000, with reasonable layout, supporting facilities, convenient transportation, beautiful environment, prosperous economy and unique characteristics. By 2010, the national urban population will reach about 560million, and the urbanization level will reach about 40%. In 2010, there were about 1200 cities and 25000-30000 towns nationwide. By 2010, the penetration rate of tap water in villages and towns across the country will reach 65%, and the per capita daily water consumption in small towns will be 180 liters and villages 110 liters. Based on this calculation, the annual waste water volume of villages and towns may reach 27 billion tons

3. Sewage treatment rate and investment estimation

considering the current sewage volume, sewage increment and sewage volume of built-up towns, the total sewage discharge will be 105 billion m3/a by 2010. To sum up, considering the current sewage volume, sewage increment and sewage volume of built-up towns, the total urban sewage discharge will be 105 billion m3 by 2010. According to the requirements of the Ninth Five Year Plan for national economic and social development and the 2010 long-term goal outline, to achieve 50% of the urban sewage treatment rate by 2010, it is necessary to increase the treatment scale by 50 billion m3/a (140 million m3/D). See Table 1 for the prediction of urban sewage volume and investment according to the growth rate. If the sewage treatment rate reaches 50%, the investment per cubic meter of sewage treated according to the static investment (considering the supporting pipe) is yuan, then it needs to invest billion yuan. According to the growth of sewage treatment degree and sewage volume, the market share analysis of main technical equipment (especially secondary treatment related equipment) of urban sewage treatment plant is shown in Table 2. In order to expand domestic demand and drive economic development, the state has increased investment in infrastructure since 1998, and urban infrastructure has become an important part of it. 30billion of the 100billion national debt currently issued will be used for urban infrastructure construction. Among the water supply and drainage construction projects reported by local governments to the Ministry of construction, there are 322 water supply projects and 208 sewage projects, with a total investment of 110billion yuan. In 1999, the state issued an additional 65billion yuan, some of which were mainly used for projects under construction and some new projects in 1998. Such a huge investment and market share are both opportunities and challenges for the development of China's water industry. Table 1 sewage volume forecast and investment forecast of reaching 50% treatment capacity in 2010

year 2000 2010 (5% growth) urban sewage volume (100 million m3/a) 480780 static investment (100 million yuan) - 2500 urban sewage volume (100 million m3/a) - 270 static investment (100 million yuan) - 1500 total urban sewage investment (100 million yuan)

Table 2 water pollution control investment composition, Including the proportion of each part

project consulting services Civil Engineering General equipment special equipment automatic control instruments other investment proportion%%%%%% investment amount (100 million yuan)

in the above shares, traditional industries such as mechanical processing (mechanical and electrical products: such as water pumps, fans, etc.) account for about% of the share, and the construction industry accounts for% of the share. The sum of the two accounts for more than 60% of the total investment, and there will be a market share of about 20billion per year in the next 10 years. The main bodies engaged in the above industries are national large and medium-sized enterprises. It can be seen that for large-scale infrastructure projects such as urban sewage and urban water supply, national investment will drive the development of a large number of traditional industries such as Electromechanical industry, machinery manufacturing and processing industry and construction industry. Thus, it can drive the development of related industries and the increase of total consumption, which is conducive to the reform and economic development of large and medium-sized enterprises, which is also consistent with the current national policy of invigorating large and medium-sized enterprises. Although the proportion of automatic control, instrumentation and technical services in water pollution control is not high at about%, the relative output value is relatively high. This part of the market is rated at about 100 million yuan/year. In addition, the operation and management cost of general sewage treatment accounts for about 10% of the investment, and the share of operation service industry is about 4 billion 2. The maximum experimental force (KN): 10/year

facing such a huge market for environmental pollution control in China, foreign companies have begun to enter. At present, many urban pollution treatment plants are constructed with foreign capital. For example, in, dozens of foreign-funded loan projects were built to build large-scale urban sewage treatment plants, many of which key equipment and supporting products were imported from abroad. Due to the mature technology, good quality and excellent service of foreign water treatment products, it poses a severe challenge to China's water treatment industry

II. Development of urban sewage treatment technology

1. Urban sewage treatment process

China's urban sewage treatment technology has been gradually studied since the national scientific and technological research in the Seventh Five Year Plan. There are many studies on natural treatment technologies such as oxidation ponds, land treatment and complex ecosystems in the "Seventh Five Year Plan" and "Eighth Five Year Plan" key projects, which are based on these achievements. Some oxidation ponds and land treatment demonstration projects for urban sewage have been established. In terms of manual treatment technology, the "Eighth Five Year Plan" has conducted in-depth research on sludge, high load biofilm and integrated oxidation ditch technology of high load activated sewage within the same functional range, and introduced and developed a/b, a/a/o, a/o, b/c, SBR and other treatment processes. The research results have been applied to a large number of sewage treatment plants; The problem of sludge disposal in urban sewage plants has been paid attention to in the scientific and technological breakthrough of the ninth five year plan, and a complete set of sludge treatment has been developed. During the "Ninth Five Year Plan" period, the research on process technology focused on the practical complete set of technologies for simple and efficient sewage treatment in small and medium-sized cities and towns to solve the problems of high energy consumption in manual treatment and large land occupation in natural treatment

through the efforts during the seventh, eighth and ninth five year plans, China has made great achievements in urban sewage treatment technology and achieved fruitful results in tackling key problems. In terms of the breadth of technology, the gap with the international community has narrowed. At present, in terms of water pollution control technology, the process parameters of the following technologies can be provided. Traditional activated sludge technology includes traditional method, time delay method, adsorption regeneration method and various new activated sludge processes, such as SBR, AB method and oxidation ditch technology, etc; A-O method and a2-o technology; Acidification (hydrolysis) - aerobic technology; Various types of stabilization pond technology; Land treatment technology, etc. This can already meet the requirements of most urban sewage treatment

2. Discussion on urban sewage treatment technology

from the 1920s, oxidation ditch and SBR process have developed rapidly and become the dominant process of urban sewage treatment plants in China in recent years. Biological aerated filter (BAF) and primary enhanced process are high-efficiency urban sewage treatment processes with development potential, which were newly developed in the late 1980s and early 1990s. Hydrolysis aerobic biological treatment process, a new process for urban sewage treatment, is a process with independent intellectual property rights in China. In recent years, China has introduced many foreign new processes and established a considerable number of projects. These works are valuable wealth in the field of urban sewage in China, which should be systematically summarized. However, the research on sewage treatment technology in China is mainly single research, and focuses on process research, lacking enough systematicness and integrity, as well as comprehensive comparative research and technical and economic evaluation system. This is also the reason why AB process is popular first, then three ditch oxidation ditch and other forms of oxidation ditch are popular in recent years, and SBR process is popular at present. Lack of comprehensive and comprehensive comparison ability, foreign new technologies and new products continue to impact the domestic market for a long time, and domestic technologies are always unable to occupy a place in the market

on the other hand, at present, the commonly used processes in China's urban sewage treatment plants are ordinary activated sludge process, oxidation ditch process, SBR (intermittent activated sludge) process, AB process, etc., which is almost at the same level as the technology and process adopted by the United States, Germany and other developed countries, while China's GDP is far lower than the above countries. The above technologies are proved to be effective in water pollution control abroad. However, the above technologies are not necessarily advanced technologies, especially not necessarily fully suitable for China's national conditions

for example, at present, the oxidation ditch and SBR with delayed aeration introduced from abroad are mostly used in China. Delayed aeration is a low load process. For a developing country with insufficient resources and a large population, it is worth considering whether it is suitable to promote this low load activated sludge process. First, the tank capacity and equipment of low load aeration tank are several times that of medium and high load activated sludge process, so the corresponding investment is several times higher; Secondly, the aerobic stabilization method is adopted for sludge by delayed aeration, and its energy consumption is about 40 ~ 50% higher than that of medium and high load activated sludge; The increase in energy consumption has not only brought about the increase in direct operating costs, but also increased indirect investment. It is reported that at present, 1000 US dollars is needed for desulfurization per kW of power generation capacity, and 700000 yuan is needed for desulfurization investment per 10000 tons of sewage. If the desulfurization investment is 10% of the power plant investment, the increased power plant investment is 7million yuan, which is close to 50% of the sewage treatment unit investment. From the perspective of sustainable development, low load processes with delayed aeration, such as oxidation ditch process, are not suitable for China's national conditions

in terms of urban sewage sludge treatment and disposal, it is still in its infancy in China, and there is still a large gap compared with foreign advanced countries. With the commissioning of a large number of sewage treatment plants, sludge production will increase significantly. The investment of sludge anaerobic digestion is high, and the sludge treatment cost accounts for about% of the investment and operation cost of sewage treatment plant. And the sludge anaerobic digestion treatment technology is more complex. Among the only dozen sludge digesters in China, few can operate normally, and some of them are not operating at all. This is also the reason why oxidation ditches with delayed aeration function have been widely used in China in recent years. Therefore, the key to adopt efficient (high load) and low consumption sewage treatment process