With economic development and population increase over the past decades, around 80% of sewage in the world has been directly discharged into the environment without treatment (Burket et al., 2018). The situation is even worse in rural areas because of limited investment, sanitation facilities, and research (Huang et al., 2021). Organic matter, nitrogen and phosphorus, coliforms, and pathogens are the main contaminants in rural domestic sewage (Latrach et al., 2018). A large amount of untreated rural domestic sewage discharged into surrounding ecosystems may not only lead to environmental problems such as water and soil pollution and affect agricultural production but also pose a potential threat to the health of rural residents and animals (Ye and Li, 2009; Lam et al., 2015; Wang et al., 2016; Elahi et al., 2017; Elahi et al., 2018).Currently, around 4.2 billion and 2.2 billion people are suffering from lack of safe drinking water and safe sanitation facilities worldwide, and about 47 and 70% of them live in rural areas, respectively (WHO/UNICEF, 2019). Consequently, rural domestic sewage treatment (RDST) is one of the crucial approaches to improve rural sanitation as well as to achieve the Sustainable Development Goals (SDGs) proposed by the United Nations.

In response to the challenge of SDG 6 “clean water and sanitation for all”, RDST has aroused worldwide concerns, particularly in developing countries (Ladu and Lü, 2014; Rout et al., 2016; Latrach et al., 2018). As for China, the Chinese government proposed a three-year action plan for rural living environment improvement in 2018, which took RDST as a priority and was difficult to be addressed (The State Council of the People’s Republic of China, 2018). The annual investment of the government in RDST has been gradually increasing each year, reaching 4.42 billion USD ¹ in 2019. As a consequence, by the end of 2020, even though 25.5% of the administrative villages implemented RDST (China Agricultural Green Development Research Association, 2021), they still lag far behind developed countries. This implies that more extensive RDST facilities are required in the future to ensure the well-being of farmers and further improve the rural living environment. However, owing to the high investment of RDST facilities, local budget constraints and fiscal deficit are proved to be the major impediments to improving RDST in developing countries (Massoud et al., 2009; An et al., 2015; Sbahi et al., 2020).

It is widely believed among scholars that both the centralized mode (CM) and decentralized mode (DM) of RDST were the predominant approaches (Hu et al., 2017; Yu and Yu, 2019). Previous studies determined that CM was applicable to rural areas with high population density and clustered households, while DM was recommended for mountainous and hilly areas with smaller villages, scattered households, and unavailability of sewerage collection networks (Wang et al., 2011; Song et al., 2020; Li et al., 2020). In reality, more than 60% of China’s rural population resides in the relatively flat eastern and central regions, which accounts for only 20% of the national territory area (National Bureau of Statistics of China, 2020). In addition, due to the characteristics of congregated residence developed over centuries, households in rural areas of China have a relatively high residential concentration, and congregated villages account for approximately 80% (Lu, 2013). Accordingly, the CM of RDST has a stronger applicability and broader coverage in the rural areas of China.

As a kind of rural public infrastructure with nonexclusive and nonrival characteristics, the CM of RDST is a typical public goods, and its primary beneficiaries are governments and rural residents. However, the centralized mode provision (CMP) of RDST as a kind of environmental improvement exercise demands massive investment with limited direct economic benefits and a long-term payoff period. Thus, environmental improvement has not always been the priority of local governments’ investment willingness under the government performance assessment system with economic development as the main indicator (Fu et al., 2018). Therefore, in areas with relatively low-economic development levels and insufficient financial resources of local governments, the local government may not be able to bear considerable investments in RDST. As the primary and most direct beneficiaries of RDST, rural residents are more prone to “free-riding” due to their large number of beneficiaries. Nevertheless, sociologists believe that under the influence of moral attitudes, social norms, and collective identity, people will participate in the provision of public goods and make the provision optimum (Qian and Ying, 2014). Furthermore, studies on public goods provision revealed that the phenomenon of non-zero-value voluntary provision was significant and robust, that meant even though not all would contribute, there was a significant number of contributors, who typically contribute 40–60% of the optimal amount of public goods (Ledyard, 1995). Therefore, while the phenomenon of “free-riding” does occur, the strong “free-riding” hypothesis that “no one will contribute” was not valid (Dawes and Thaler, 1988). Fischbacher et al. (2001) demonstrated that the social preferences of participants in public goods provision were heterogeneous, and exhibited different levels of willingness to provide public goods. Relevant studies on rural public infrastructure provision have concentrated on two aspects. First, it is aimed at different research fields, including agricultural water conservation facilities (Cai et al., 2016; Yang and Wang, 2020), rural environmental protection public goods (Wang et al., 2014; Han et al., 2019), rural disaster mitigation public goods (Luo and Levi, 2013), and rural public services (Shono et al., 2014; Dai and Du, 2017). Second, it is for diverse provision subjects, involving the government, cooperatives, farmers, and their collaborative provision (Zhang et al., 2004; Wang et al., 2021). Therefore, previous studies provide a theoretical basis and robust sustentation for this study regarding the farmers’ willingness to participate (WTPP) and WTP for the CMP of RDST.

Since farmers are the primary beneficiaries of rural public goods, their WTPP and WTP should be concerned when formulating relevant policies (Yi et al., 2011). Although studies on farmers’ WTPP and WTP in rural public goods provision have been extensively discussed in recent years, there are still some limitations. First, most of the previous literature on RDST focused on treatment technologies or processes (Gao et al., 2017; Matos et al., 2019; Nandakumar et al., 2019), and lack of research on farmers’ willingness for the CMP of RDST. Second, most studies focus on a specific area instead on a national scale (Gu et al., 2016; Wang et al., 2021). Additionally, the majority of existing studies analyzed farmers’ willingness to provide/pay for public goods but without estimating the payment level (van Hoang et al., 2013; Wang et al., 2019). Ultimately, and most importantly, most emphasis was devoted to the farmers’ socio-economic and demographic characteristics (Byambadorj and Lee, 2019; January 2021; Elahi et al., 2022a) when exploring the influencing factors on WTPP and WTP. In areas such as rural waste management, infrastructure development, etc., farmers’ individual perceptions, government effects, and distance between their house and towns/cities were shown to have significant effects on the farmers’ WTPP or WTP (Mukherji et al., 2016; Han et al., 2019; Rashid and Pandit, 2020; Su et al., 2020). Nonetheless, more influential factors should be included in this study, involving individual perceptions, government effects, and geographical factors.

As aforementioned, this study extended from two perspectives on the farmers’ WTPP and WTP for the CMP of RDST. First, farmers’ perceptions and government effects as significant influencing factors are incorporated in the analysis. Second, this study quantitatively analyzes farmers’ WTP regarding the CMP of RDST by employing an econometric model. The objectives of this study are 1) to explore the farmers’ WTPP and WTP for the CMP of RDST, 2) to determine the influencing factors of their WTPP and WTP, and 3) to provide insights for the policy formulation regarding RDST as well as to promote the realization of SDGs. For the objectives of this study, we proposed the following research hypotheses:

H1: Farmers’ WTPP and WTP for the CMP of RDST can be significantly and positively affected by their perception of the necessity of RDST.

In light of the estimation results by the Tobit model, the expected WTP for the CMP of RDST with total respondents and truncated respondents was 7.59 USD/year and 10.10 USD/year, respectively. Thereby, the aggregate value would be estimated at 179.05 million USD and 238.26 million USD for the total households and the households excluding the negative WTP proportion (18.13%) per year. Based on MOHURD (2020), the provincial governments of Shandong, Jilin, and Gansu invested 151.64, 25.55, and 29.66 million USD in RDST of 2019, respectively. It is evident that the farmers can also be potential contributors to financial access in RDST. However, depending on the estimation of the construction cost of the existing CM of RDST, the average construction cost is roughly calculated as 933.12 USD per household with a 20-year service life of the RDST facility. According to our results on the farmers’ WTP, the expected payments from households account for 16.28 and 21.65% of the total cost. This conclusion may be referred to policies formulating regarding RDST payment mechanism. In addition, it also reflects the fact that the contributions of farmers or government either cannot cover the cost of the CMP of RDST, and there is a significant funding deficit. Accordingly, in view of the actual situation, it is suggested that the financial investment at the national level should be effectively increased and establish relevant special funds. Since the expected value of the farmers’ WTP in three provinces varied significantly, it is also recommended that the government should take into account the socio-economic factors and demographic factors of different regions to formulate relevant policies according to local conditions. Recently, a multitude of studies focused on the influencing factors analysis of farm households’ WTPP of RDST (Fu et al., 2018; Liu and Feng, 2019; Su et al., 2020), as well as concentrating on the farmers’ WTP analysis of RDST without separating the provision phase and maintenance phase (Chen et al., 2017; Xie et al., 2018), but virtually few studies have measured WTP for the CMP of RDST by applying econometric models in China.

The descriptive statistics analysis of this study revealed that only 40% of the farmers in the study area are currently accessing the CM of RDST (Table 1), while nearly 80% (Figure 2) of the investigated farmers tend to adopt the CM of RDST. This indicates that a minimum of 40% of the farmers in the study area are expected to avail themselves of the CM of RDST, which implies that in order to meet the requirements of this portion of rural residents, about 8.8 billion USD will need to be invested. In consideration of the fact that rural households may only be willing to pay for their own households, the total value (for 20 consecutive years) for this proportion of farmers is about 1.43 billion USD. However, the governments of these three provinces invested a total of about 20.8 million USD in RDST in 2019 (MOHURD, 2020), which obviously reflects an enormous funding deficiency and intense pressure on government finances. If we assume that the annual investment amount of the government remains stable and rural households contribute at a rate of 16.28%, it will take 35.4 years to raise 8.8 billion USD, which is required for the demand of the CMP of RDST in the three provinces. According to Ledyard (1995), if rural households were able to contribute between 40 and 60%, the corresponding time for raising funds would be reduced to 16.9–25.4 years. Undoubtedly, the farmers contribute significantly to the CMP of RDST, while the government remains the tremendous source of funding. However, in reality, the process of improving rural living environment, particularly RDST, will be relatively delayed if it only relies on the investments by the government and farmers. Therefore, it is suggested that various funding sources should be introduced. Social organizations, enterprises, and individuals should be encouraged to actively participate in RDST by donations or other means.

Nowadays, people are becoming more concerned about the environment with the development of the era and the improvement of living standards. However, due to the limitation of education level and other factors in rural areas, the environmental awareness of the rural residents is relatively weaker than that of the urban residents. Interestingly, the effect of environmental awareness on the farmers’ WTP for the CMP of RDST in our study is positive but not significant. Therefore, the environmental awareness of the farmers should be further enhanced so as to increase the farmers’ WTPP and WTP for RDST. This recommendation is also consistent with that proposed by Uthes and Matzdorf (2016) and Su et al. (2018). Thus, it is recommended to promote the farmers’ self-awareness of environmental protection by means of propaganda and education, so as to form a “soft constraint” of moral concepts. In addition, it is necessary to strengthen the external restraint mechanism, such as legislation and village regulations and other “hard constraints” to reduce the farmers’ pollution behavior.

Although farmers currently have perceptions of rural domestic sewage and environmental awareness to some extent, it is identified in our study that there is a relative lack of health awareness among the farmers at this stage, and a significant proportion of the farmers consider that rural domestic sewage has no or minimal impact on human health. This may be due to the fact that, although farmers discharge domestic sewage directly into the nearby water bodies that would result in a certain level of pollution, this behavior does not affect the quality of domestic water in their daily lives. Therefore, they probably consider domestic sewage contaminating the environment, but not having much impact on their health. In fact, in order to guarantee the safe drinking water in rural areas, the Chinese government has invested in the construction of numerous drinking water supply projects since 2000 (Song et al., 2020). By the end of 2019, more than 78% of the villages in China had been supplied with piped water (MOHURD, 2020), which ensures the safety of drinking water for rural residents. According to Yang et al. (2018), urban residents demonstrated a stronger awareness of health, since health conditions considerably influenced both successful career and quality of life, urban residents were increasingly inclined to allocate a certain amount of money for their health. Therefore, we recommend further raising the health awareness of the rural residents, which would make them aware of the dangers of pollution to human health and contribute to the participation and willingness in environmental management.

As the initiator and promoter of RDST, the government performs an indispensable role in the whole process of RDST, particularly in terms of propaganda. For this reason, it is recommended that the government should incorporate propaganda as a priority in its subsequent efforts to improve the farmers’ environmental knowledge, perception, and awareness. Actually, since proposing the Three-Year Action Plan for Rural Living Environment Improvement, the central and local governments have formulated a series of policies, regulations, and institutions, and have gradually increased their efforts to propagate RDST with rural households which have demonstrated initial effectiveness. The propaganda approaches should also be broadened, a variety of propaganda methods should be promoted for various regions with heterogeneous farmers. In addition to traditional posters and brochures, new media platforms should also be promoted and introduced to diversify the propaganda about environmental protection and RDST.

In addition, the farmers’ socio-economic factors that affected their WTPP and WTP should not be ignored as for the farmers’ age significantly and negatively influenced their WTPP and WTP for the CMP of RDST. What is worrying is that the aging of the rural population in China continues to deepen, the aging rate in rural areas is predicted to reach 22.8% by 2030 (Fang et al., 2015; Li et al., 2020). Moreover, the population in rural areas of China has been reduced by 164.4 million and 14.21% in the last decade (National Bureau of Statistics of China, 2021). This phenomenon is attributed to the large number of rural laborers migrating to the cities (Xu and Zhang, 2021), of which mainly the young people are eager for employment and further education. Thus, the increasing aging population proportion and outmigration in rural areas of China imply that the farmers’ WTPP and WTP for the CMP of RDST might be diminished, which generates more pressure on government financial investments. The positive influences of the income on WTPP and WTP demonstrate not only the affordability of high-income farmers, but also shows that these farmers are more eager to improve their living environment than those with a relatively low-income. However, marginal effects reveal that when farmers’ income increases by 1,000 USD, their WTP only increases by 0.11 USD/year and 0.16 USD/year, respectively. Therefore, in the short term, it seems that there is a limit to improving the farmers’ WTP for the CMP of RDST by the increasing farmers’ income.

Interestingly, the distance from the farmers’ residence to the town had a significant adverse effect on their WTPP. This may be explained that the farmers who reside closer to the towns are more likely to be affected by the lifestyles of urban residents, and demonstrate a stronger desire for the living convenience of the town residents. In other words, this may also be due to the spillover effect of the improvement of urban public infrastructure on the surrounding rural areas. Therefore, villages and rural households that are close to the towns should be prioritized when formulating policies related to the CMP of RDST. In addition, villages that are located within a 5-km radius extension of the urban sewage network (Yu and Yu, 2019), the rural domestic sewage network that can be designed to connect with the municipal sewage network, and thereby to collaboratively treat domestic sewage with the town. Interestingly, distance did not have a significant effect on the WTP of rural households, which may be influenced by multiple factors such as age, education, and income.

According to the survey data of 761 farmers collected in Shandong, Jilin, and Gansu provinces, this study estimated the probability of the farmers’ WTPP and WTP for the CMP of RDST, as well as identified the influencing factors. Our research results show that more than 79% of the investigated farmers intend to participate in the CMP of RDST, and the expected WTP for the CMP of RDST for the total respondents and the respondents with a positive WTPP to be 7.59 USD/year and 10.10 USD/year, respectively. Accordingly, when the service life of RDST facilities is set to 20 years, the farmers’ payments can cover 16.28 and 21.65% of the construction costs, respectively. The present study explored and analyzed the factors influencing the farmers’ WTPP and WTP for the CMP of RDST in relation to the farmers’ perception, government propaganda, and individual and household characteristics. The results show that the farmers’ perception of the necessity of RDST has significantly and positively affected their WTPP and WTP for the CMP of RDST, which verified H1. As another variable that has significantly affected the farmers’ WTPP, farmers’ perception of the pollution of rural domestic sewage has no significant impact on their WTP, which partially verified H2. However, as indicated by the results of the regression models, although the farmers’ perception of healthiness positively affected their WTPP and WTP, it was not statistically significant, thus H3 was rejected. In addition to the farmers’ perceptions, we also found that the farmers exposed to the government propaganda about RDST showed relatively high levels of WTPP and WTP, which also confirmed H4. Interestingly, while rural households who resided closer to the towns demonstrated a stronger WTPP, they did not show a higher WTP, thus H5 was partially validated. Simultaneously, the study results demonstrated that age, education, village cadres, income, and centralized water supply have significant effects on WTPP, and age, education, and income have also significantly contributed to their WTP. Accordingly, H6 was partially corroborated, which means that not all the farmers’ individual and household characteristics have an impact on their WTPP and WTP.

Since most of the existing studies focus on the farmers’ WTPP of RDST and the willingness to maintain RDST, this study contributes significantly to the current academic literature by dividing the financial investment in RDST into a provisional phase and a maintenance phase, and reveals the influences of the farmers on the WTPP and WTP of the CMP of RDST, which complements the existing literature. In the areas with financial shortages for the provision of RDST, the results of this study provide a reference for broadening the funding sources and exploring the participation and payment mechanism of the farmers. However, due to the current WTP of the farmers for the CMP of RDST, the enhancement of environmental awareness of the farmers and strengthening of the government propaganda should be the next priority of the Chinese government. Ultimately, these recommendations may be effective in helping developing countries create a favorable rural environment and achieve the SDGs.

There are several inevitable limitations of this study that existed with most studies. First, eliciting a farmer’s WTP by open-ended questions is normally not the most appropriate approach. However, since there is little literature available to provide a reference for the farmers’ WTP for the CMP of RDST, and the economic development levels and geographic location vary from region to region, this study adopts open-ended questions as the first exploration in this study area. Therefore, more elicitation approaches are suggested to be employed in the subsequent studies. Secondly, the data analyzed in this study are only collected from China, so the results may not be applicable to all developing countries. Accordingly, performing relevant studies in the different developing countries with dissimilar conditions and socio-economic characteristics may enrich the results of this research field.