Save water and pipes, and can also realize the pastoral cycle, how to change such a village toilet?
At present, the mainstream technical path for the treatment of rural human settlements is the standard discharge mode, the main symbol is to install conventional water flushing toilets, treat sewage at the end of the sewage pipe, and discharge it into the natural environment after reaching a certain technical standard.
However, there are two drawbacks to the compliance model. First, the direct economic costs of construction and operation are high, especially in rural areas where people live relatively scattered. The construction cost must be reduced to at least 1/3 of the current level, and the operating cost should be reduced to 1/5 or even 1/10, in order to meet the current economic affordability of most rural areas in China. Second, the cost of resources and environment is high, which is mainly manifested in the large consumption of water, materials and energy, the incomplete removal of pollutants, the high carbon emissions, and the difficulty of reusing resources. The reason for the above defects is not that the current technology, facilities and equipment technology are not advanced enough, but the difference in pollution control thinking.
Westerners invented toilets that were flushed with water and drained through pipes, and eventually discarded their own excrement to nature. In order to eliminate the resulting health and environmental hazards, the current model of re-discharge after standard treatment has gradually been formed. Different from other civilizations, the oriental civilization represented by China has long recognized the fertilizer utilization value of organic domestic wastes such as manure and urine, which has produced a pastoral cycle model that has lasted for thousands of years.
The author combs the development process of the pastoral cycle model and believes that this model can provide new ideas and new paths for the current rural toilet reform and sewage and garbage treatment.
Historically, China has been a pastoral recycling society with closed-loop management of organic waste. Before chemical fertilizers could be obtained cheaply, Chinese farmers regarded organic domestic waste as a resource with important economic value, which gave birth to related industries and objectively improved the level of municipal sanitation. In the traditional way of life, not only human excrement, but also almost all organic household waste, plant ash and dust are returned to the farmland through natural fertilizer. People's daily water consumption is also relatively limited, and a small amount of used water is splashed nearby, and purified through the natural cycle of the earth.
However, the main disadvantage of the traditional pastoral cycle is that the manure is not harmlessly treated, and there is a risk of disease transmission. In response to this problem, China's health department organized the development of multi-level storage toilet technology before the 80s of the 20th century, mainly including three-format toilets, double-urn toilets, double-pit alternating toilets, etc., and promoted them throughout the country, greatly reducing the incidence of intestinal infectious diseases. At present, there are at least 80 million multi-stage storage toilets installed in rural areas of China, serving more than 300 million people.
Multi-stage storage toilets are still aqua privies and toilets must be erected above the storage containers, so they are not suitable for installation in the room. The innovation of this technology lies in the transformation of the single-hole storage container below into a multi-stage storage container. In the process of long-term storage, complex physicochemical and biochemical reactions occur in the manure, which ferments and decays organic matter, and sanitizes pathogenic organisms at the same time. Graded storage prevents fresh manure from mixing into the matured manure and ensures that the final manure is harmless. This method is similar to the practice of traditional pastoral cycle in toilet and fertilizer use, so it belongs to the improved traditional pastoral cycle model.
With the development of social and economic development, rural households have a strong demand for modern toilets with water flushing + pipe sewage. The conventional technical solution is to install a gravity water flushing toilet. Since the water is completely dependent on its own gravity to provide the flushing force and the power of the pipes, the gravity water flushing toilet must use enough flushing water. The technical standard of water-saving toilets in China is 5 liters / time for toilets ≤ and 6 liters for squatting toilets ≤ times, and the volume of an adult's defecation is about 400 ml, which means that feces and urine should be diluted more than 10 times, not only losing the value of fertilizer utilization, but also directly used for irrigation has a risk of pollution to groundwater, and must be discharged through sewage treatment.
The key technical issue in modernizing the modified traditional pastoral cycle model was to reinvent toilets that could be cleaned with a small amount of water and drained through pipes. Taking into account factors such as fertilizer efficiency, harmless treatment of manure and the risk of secondary pollution to the environment by fertilization, the water consumption of low-water toilets should not exceed 1.5 liters per time. At present, there have been various forms of less water flushing toilet technology in the Chinese market, which can be comparable to gravity water flushing toilets in terms of toilet experience, cost and ease of use. The most common water flushing toilet technology is mainly based on the principle of vacuum pipeline sewage, and another is the air suction pipe sewage technology developed by Chinese scientific researchers, which integrates the pipe sewage technology of less water flushing with crushing technology, and can also be used to collect kitchen waste, further improve the sanitary conditions of family life, and break through the problem of garbage classification.
The modern pastoral recycling system process divides domestic waste into organic waste liquid (including manure and food waste), domestic miscellaneous drainage and inorganic waste. The high concentration of organic waste liquid is regenerated into liquid fertilizer and slag fertilizer by septic tank technology. The concentration of pollutants contained in other domestic miscellaneous drainage is low, and it is recommended to use ecological purification to treat it in rural areas, and discharge it after reaching the standard.
The treatment process involved in the modern pastoral cycle model does not rely on large-scale sewers, and is suitable for application in rural areas. The simplest way is a small system where farmers manage and use their own fertilizer, which minimizes installation and operating costs. In addition to being applied in each household, it can also carry out organized centralized operation and fertilizer services to adapt to different residential scenarios and user needs.
Compared with the standard emission mode, the modern pastoral cycle model can reduce the construction cost by more than 50% and the operation and maintenance cost by more than 60%, and reduce carbon dioxide emissions by 160 kg per person per year.
Looking forward to the future, based on the tradition of Chinese pastoral circulation, the use of low-water pipeline sewage technology to build a modern pastoral cycle model can reduce the cost of human settlements governance, and has the advantages of water saving, energy saving, consumption reduction, emission reduction and resource circulation, while improving the level of pollution control in China's rural life, it is also expected to contribute to the sustainable development of human settlements, which is worthy of support and promotion.
Fan Bin is a researcher at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, and Wang Bo is an associate researcher at the Chinese Academy of Environmental Planning, Ministry of Ecology and Environment
Original title: Exploring a new path for the governance of rural human settlements based on pastoral cycles
