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).