Present situation and treatment of rural sewage treatment



1.1 Status of rural sewage collection and treatment: the collection and treatment rate is low and needs to be improved

(1) The overall collection and treatment rate of rural sewage is less than 10%. According to the "2016 Urban and Rural Construction Statistical Yearbook" data of the Ministry of Housing and Urban-Rural Development, China has 18,100 towns, 10,900 townships, and 190 million registered people; The village is 2.617 million, with 763 million registered residents. The amount of rural sewage is large, the points are many and scattered, and the collection and treatment is difficult. In 2016, 5,071 towns in China treated domestic sewage, accounting for 28.02%, and the sewage treatment capacity reached 34.64 million tons/day. 984 townships treated sewage, accounting for 9.04%, and the sewage treatment capacity reached 638,000 tons/day. The data of village sewage treatment was not fully disclosed. However, it must be far lower than the sewage treatment rate of towns and townships, so the overall collection and treatment rate of rural sewage should be less than 10%.

(2) The drainage network construction is imperfect and seriously lagging behind. The rural domestic sewage collection system (drainage network) consists of three parts: the farmer's courtyard sewage collection system, the village sewage collection system outside the courtyard, and the sewage treatment effluent discharge system. The drainage pipeline increased from 87,550 km in 2007 to 158,288 km in 2015, an increase of about 81%. It is found that the completion speed of the drainage network is lower than the completion speed of the sewage treatment plant, due to excessive investment (pipe network investment is about 2.5 times the investment of sewage treatment structures) and maintenance and management difficulties, taking into account the burden of government finance and operation and maintenance management, many sewage treatment facilities are "built without" sunshine.

1.2 Rural sewage treatment mode: It can be divided into three types, which need to be selected according to local conditions

(1) Household sewage treatment. The manner in which the sewage of single or multiple households is treated in situ. The domestic sewage of a household or several nearby households is collected in pieces and treated on the spot. Generally, small sewage treatment equipment or natural treatment modes such as septic tanks and ponds are used for treatment. This treatment mode has the characteristics of saving pipe network investment, simple operation and management, flexible application, etc., and is suitable for areas with scattered village distribution, low population density, and complex terrain that are not suitable for laying pipe network.

(2) Centralized sewage treatment in villages. The sewage of villages or farmers within a certain range is collected by pipe network and connected to nearby sewage treatment facilities. The domestic sewage of a village or a number of connected villages is to be centrally collected by laying sewage pipes, and unified treatment is carried out through the construction of unified sewage treatment facilities or sewage treatment stations, which generally adopts the conventional biological treatment and ecological treatment. This treatment mode has the advantages of stable operation, high treatment efficiency, small area, etc. It is suitable for areas with dense distribution of villages, large population density, large sewage discharge, and better economic conditions far from cities and towns.

(3) Into the urban sewage network. It refers to the way that the sewage of the villages located in and around the city is collected by the sewage branch pipe and directly incorporated into the main sewage pipe of the city, and is treated uniformly by the urban sewage treatment plant. That is, the domestic sewage of the village is collected by the sewage network and discharged into the nearby urban sewage treatment plant for treatment. This model has the advantages of convenient management, provincial investment and quick effect, and is suitable for villages with better economic conditions in the suburbs of cities and towns, or villages close to sewage treatment plants and municipal pipe networks.

1.3 Rural sewage treatment technology: there are many kinds, and the process technology with good effluent quality, low investment and operation cost, and easy maintenance and management should be selected

(1) Activated sludge method. Common processes include A2O process, A/O process, SBR process, oxidation ditch process, MBR process and improved processes based on the above processes, such as inverted A2O process, improved A2O process, UCT process, multistage AO process, step inlet process, CASS process, ICEAS process, MSBR process, Carcel and Aubel oxidation ditch.

The advantage of activated sludge method is that the effluent quality is good and the discharge standards can be reached, but the process is too complex and the operation and maintenance requirements are high, especially the need to reasonably control the aeration, sludge age and internal and external reflux, and the surplus sludge needs to be disposed of, which is suitable for medium-sized sewage treatment (tens of tons to hundreds of tons).

(2) Biofilm method (integrated equipment commonly used). Common anaerobic filter, biological contact oxidation process (BCO), biological aerated filter (BAF), denitrification filter, biological turntable, moving bed biofilm reactor (MBBR) and so on.

The advantage of biofilm method is that the operation and maintenance requirements are low, can be unmanned management, only a small number of biofilm fall off, most of the integrated equipment is used anaerobic filter + biological contact oxidation process, etc., but can not remove phosphorus, where there are phosphorus removal requirements need to add chemical phosphorus removal or electric phosphorus removal (iron and aluminum electrodes). The purification tank technology based on the biofilm method has been widely used in Japan, and in China, it is also the most widely used process technology for integrated equipment, which is suitable for small-scale sewage treatment (several tons to dozens of tons).

(3) Ecological treatment method. The common ones are constructed wetland, micro-ecological filter bed, artificial fast infiltration, land treatment and so on. The advantages are ecological sustainability and low energy consumption. It has a landscape effect, but the disadvantage is that the pollutant removal load is low and a large area of land is required.

(4) Other methods. Common septic tanks, stabilization ponds, biogas digesters and so on. This kind of method has limited pollutant removal ability and poor effect. It is generally used in remote areas with poor economy or as a pre-treatment measure.

1.4 Rural sewage treatment and discharge standards: there is no unified standard, resulting in a variety of problems in design, construction, operation and supervision

Because there is no unified emission standard, it causes difficulties in process and construction standards. There is also a lack of unified technical standards and specifications for the design, construction, evaluation, acceptance, operation and supervision of the project, and some places copy urban standards, resulting in high costs and problems such as abnormal operation.

The formulation of standards and norms should first consider the regional differences of villages and towns, and make corresponding design adjustments according to different regions, different terrain, different geographical and climatic conditions and economic development levels. Secondly, priority should be given to resource utilization. Due to the scarcity of water resources in our country, priority should be given to the treatment of sewage in villages and towns and the utilization of local resources, especially for the arid areas in the north and east of our country. Moreover, economic and efficient, the village sewage treatment system should invest in the province, low energy consumption, and adapt to the economic development level of the village and village and the economic affordability of the villagers. The process design is reliable and stable, and the effluent meets the discharge standard requirements.

Taking into account the economic capacity and operation and maintenance of rural areas, emission standards should not be too stringent. The formulation of rural sewage standards should first consider organic matter and SS, effectively control the black and odor of water, should not be excessively harsh TN and TP standards, in fact, many Western developed countries in rural sewage treatment and no nitrogen and phosphorus requirements, discharge standards should be formulated according to local conditions, to take into account the environmental capacity (self-purification capacity of receiving water) and discharge road. And the local social economy and other comprehensive consideration.

1.5 The operation and maintenance level of rural sewage treatment facilities is low

(1) Lack of operation and maintenance funds and management system, heavy construction and light operation. Due to the lack of operation and maintenance funds and effective operation management assessment system, supervision is absent, and there is still a lack of effective assessment means for the implementation of sewage treatment facilities, management effects, water quality testing and discharge, leading to some sewage treatment facilities idle or abnormal operation.

(2) Lack of operation and maintenance technology and personnel. At present, the operation technology of rural domestic sewage treatment facilities is lacking, and most of the management personnel are local villagers, who lack relevant knowledge of environmental protection and skills related to equipment operation and management. They can only be responsible for the daily care work of equipment, and are not qualified for professional system maintenance, which leads to problems such as fluctuating sewage treatment effect and substandard effluent water quality.

1.6 Construction and operating costs of rural sewage treatment: large investment and operating costs, and high electricity consumption per ton of water

According to the "Rural domestic sewage treatment Project construction and investment Guide" issued by the Ministry of Ecology and Environment, because the amount of water is small, under the same circumstances, the ton of water investment and power consumption of rural sewage and operating costs are slightly higher than that of municipal sewage plants. But the use of ecological treatment technology can reduce costs.

1.7 Business models need to be innovative: multiple models should be developed simultaneously, and the government, social capital and villagers should actively participate in solving investment, financing and operation and maintenance problems.

As a long-term project, sewage treatment needs to invest a lot of money, and the township governments in most areas can not afford the construction and operation costs, and there is no market-oriented financing channel. In addition, some areas rely only on government financial input, and there is a certain degree of heavy investment and light benefits.

We will give full play to the guiding and leveraging role of government investment, and support rural infrastructure construction through direct investment, investment subsidies, capital injection, financial interest discounts, subsidies instead of subsidies, construction before construction, and free provision of construction materials. Local governments and private capital will be encouraged to set up investment funds for rural infrastructure construction. Establish a standard local government debt financing mechanism, promote the transformation and reform of local financing platforms and market-oriented financing, standardize and promote the public-private partnership (PPP) model, attract social capital to participate in rural sewage treatment projects through franchising and other means, and pay operating fees through performance appraisal can greatly improve the governance effect.

We will accelerate the reform of the property rights system for rural sewage treatment facilities. For large-scale rural centralized water supply infrastructure mainly built with government input, the ownership of property rights shall be determined by the people's government at the county level or its authorized departments in accordance with the relevant provisions of the State; Small scale rural water supply infrastructure mainly built with government investment, and assets are owned by rural collective economic organizations or farmers' water cooperation organizations; For water supply infrastructure of single or joint household rural areas, the assets formed by the state subsidy funds shall be owned by the beneficiary households; The assets formed by the rural water supply infrastructure invested by social capital shall be owned by the investor, or the ownership of property rights shall be determined according to the will of the investor. The property right owner shall establish a management and protection system and implement the management and protection responsibility.

Actively explore and innovate the payment system, encourage the first trial, implement the payment system of sewage treatment farmers in areas where conditions permit, ensure that operating units obtain reasonable benefits, and establish a reasonable allocation mechanism between financial subsidies and farmers' payments.

1.8 Rural water quality and quantity fluctuate greatly

(1) Due to the improvement of drainage sanitation equipment, climate rainfall, water usage habits, economic conditions, etc., the per capita discharge of water varies greatly.

(2) Due to the villagers' living habits, there is a large difference in water volume between day and night, and the phenomenon of water cut off at night is obvious. Then there are seasonal, climatic and regional differences.

(3) Whether black water and gray water are collected separately leads to a big difference in water quality.

(4) Whether the separation of rain and pollution leads to water quality differences.