3.2.1. Data Collection
According to the online survey, we have a preliminary understanding of the economic development of each county. From July to August 2021, our research group arranged 20 students to be divided into 5 groups to conduct investigations in 8 cities and 10 counties (cities) under their jurisdiction in Anhui Province. They collected data related to the treatment of rural water pollution, including the relationship between the level of economic development and the progress of water pollution treatment. In order to make the surveyed counties as representative as possible, we sampled regions with different levels of economic development. The main contents and basic route of the survey are shown in Figure 2
. The survey method mainly adopts interviews and questionnaires, and the main data obtained are as follows.
Overall situation of rural sewage treatment
All villages had been connected to tap water, and at least 98% of households had used tap water (only a few households were unwilling to pay the opening fee). Among the 10 sample counties, except Linquan County, the sewage treatment rate of all the county towns had reached more than 90%, and the effluent from the sewage treatment plant in the county seat adopted the Level I B standard in GB18918-2002. Many organic towns had combined with nearby township enterprises and some surrounding villages to use large-scale sewage treatment plants to treat sewage. The corresponding standards in DB343527-2019 were adopted for the effluent of township enterprises, rural hospitals, rural towns and villages and the sewage treatment facilities below the village level. Sewage from rural hospitals was generally subject to professional medical disinfection treatment before entering sewage treatment facilities.
Large livestock and poultry farms were far away from residential areas and important water sources according to regulations, and had independent sewage treatment facilities, mainly using biogas digesters and other biochemical equipment. Many villages with scattered residents, such as Linquan County and Jing County, where most of the villages were located in the mountains, try to use buried sewage treatment facilities. All counties attached great importance to the control of agricultural non-point source sewage, and mainly took two measures: (1) Establish an ecological agricultural park, gradually promote the use of organic fertilizer instead of chemical fertilizer and experimental biological pest control technology and reduce the use of chemical fertilizers and pesticides. (2) Constructed wetlands will be built downstream of farmland to prevent farmland sewage from flowing directly into the water source. Effluent water shall meet the Grade 2 standard in DB343527-2019. In addition, in each sample county, in some township streets, township enterprises, livestock and poultry farms and hospitals that have not yet established standardized sewage treatment facilities, simple sewage treatment facilities have been established as required to disinfect and filter the harmful substances in the generated sewage before discharge. The standard rate of tailwater is generally 30–55%.
Disparities in sewage treatment in different regions with different economic development levels
In economically developed counties, the urbanization rate is high, township enterprises are relatively concentrated and the implementation of sewage treatment is progressing smoothly. For example, the comprehensive sewage treatment in Fanchang County and Feixi County has been promoted rapidly. In underdeveloped counties, only a few villages and towns with well-developed township enterprises have taken the lead in establishing sewage treatment facilities with some surrounding villages and towns under the leadership of township enterprises. It is difficult to promote comprehensive sewage treatment in economically underdeveloped villages, especially those “hollow villages” that appear somewhat depressed. For example, Zongyang County is the first batch of poverty-stricken counties in China, and the progress of various sewage treatment processes is relatively slow. There is a special case in underdeveloped areas. Shou County has just removed the hat of a poor county, but the progress of all kinds of sewage treatment is only second to that of developed counties. All villages and towns in the county have completed the domestic sewage treatment plan, and it is proposed to adopt the PPP (Public Private Partnership) mode for operation. The main reason is that the tap water intake of Shou County cannot avoid the seriously polluted Huaihe River, and the county government attaches great importance to promoting rural domestic sewage treatment.
Linquan County is located in the northwest border of Anhui Province, where there are 6 rivers in vertical and horizontal directions, and the waterway transportation is developed, but it is difficult to control water pollution. At present, it is a provincial key support county in Anhui Province. In 2019, Fuyang Municipal Government gave Linquan County a one-time compensation of CNY 7.5 million to promote sewage treatment. Due to the scattered residential areas, many rural households adopted underground and other small sewage treatment facilities. In addition, 33 rural hospitals had adopted small- and medium-sized sewage treatment equipment, with an average sewage treatment capacity of 50 m3/d. Hefei, the provincial capital, had invested about CNY 1.7 billion in the construction, transformation, operation and maintenance of rural domestic sewage treatment facilities. A total of 65 resident sewage treatment plants of township governments and 491 village-level sewage treatment facilities were inspected, covering all township governments and 833 central villages in the city. The treatment modes such as centralized collection of pipe networks and combined decentralized treatment were adopted, and the integrated treatment of “manure + water” was realized.
In order to speed up the promotion of domestic sewage treatment and ensure the normal operation of existing sewage treatment facilities, all counties had begun to charge sewage charges for two categories of residents: first, for households who join the public sewage treatment and, second, for households that have not participated in sewage treatment and directly discharge sewage. The charging standard is generally CNY 0.85 per ton according to the consumption of tap water. The overall planning of domestic sewage treatment in all counties has been basically completed and is planned to be implemented over many years. On average, about 10% of sewage treatment facilities are under construction.
From relevant government departments, we have collected all the quantitative data needed, which are listed in Table 3
. See Section 3.3.4
for the operation analysis of sewage treatment facilities.
are used to represent the “up to standard operation rate”, “operation rate” and “tailwater up to standard rate” of Class
sewage treatment facilities, respectively.
. Since most counties do not have complete statistical data on indicators
, we estimate the values of these two indicators based on the reference data provided by relevant government departments, combined with the information obtained by visiting some sewage treatment facilities and interviewing villagers. We also visited 8–10 villages and towns in each sample county and visited some rural sewage treatment facilities. As there is no publicly available data on the compliance of rural tap water and the quality of surface water and groundwater, we chose to conduct a questionnaire survey on the quality of tap water, groundwater and surface water. Surface water quality includes (1) water quality of rural small rivers, (2) pond reservoir water quality and (3) water quality of paddy fields and aquaculture ponds. In each county, 200 questionnaires were distributed to villagers, which introduced the five classification standards of surface water. Three options were set for tap water: normal, obvious sediment, peculiar smell or discoloration. Three options were set for the quality of groundwater (mainly well water): normal, peculiar smell and discoloration. Four options were set for each of the three surface water quality indicators: Class I–III, class IV, class V, inferior class V. There were 18 options in total. Each respondent was required to give an interval [a, b] estimate of the probability of each option, b–a as small as possible or only give an estimate. At least 176 valid questionnaires were collected by each county, and the maximum was 191.
3.2.2. Data Sorting
The quantitative data obtained from the survey are sorted out and calculated and listed in Table 3
. The “average” in the last column is the weighted average calculated based on the population proportion of each county. In addition, based on the experience data provided by the environmental protection department, the average proportion of harmful substances in domestic garbage is 26.25%. Based on this, we assume that if the harmless treatment rate of domestic garbage is increased by 1%, the pollution in the rainwater used for washing garbage can be reduced by 0.2%. Agricultural wastes mainly include chemical fertilizers and pesticide packaging materials. Local governments have encouraged and forced farmers to send these wastes to professional recycling departments for disinfection, but the amount of discarded wastes is still large every year. It is estimated that when the recovery rate is increased by 1%, 0.16% of the pollution in the rainwater washing these wastes can be reduced. The harmless transformation of toilets is being promoted in rural areas. According to government personnel, the transformation rate is increased by 1%, which can reduce the pollution of surface water around toilets by 0.09%. Therefore, we take
Because the 18 options of the five indicators in the questionnaire are fuzzy, it is suitable to use the convex membership function method to sort out the collected data. We take 10 cells of equal length,
, and record the 10 cells as
. Suppose that a county takes back m
valid questionnaires, and for the i
, the m
intervals given in the questionnaire are
, respectively. In these intervals, there are
not empty intersected with
, and there are
not empty intersected with
, and so on. There are
not empty finally intersected with
to represent the i
-th option, we can obtain the convex membership number of
and we have
the standardized convex membership number of
. By direct calculation, we obtain
expected value and variance
We set the value of as , and use to judge the reliability of the questionnaire results. For example, the three options of tap water quality in Fanchang County are sorted as: (0.891, 0.056, 0.022), and then united as (0.920, 0.058, 0.022).