Ecological treatment process for rural domestic sewage

With the rapid development of China's economy and society, sanitary ware, washing machines, shower facilities, etc. have entered ordinary households. The per capita daily water consumption and life in rural areas haveSewageThe emission volume has increased sharply, generating a large amount of domestic sewage. However, rural populations are dispersed and numerous, with no domestic sewage collection or treatment facilities. This makes rural domestic pollution sources an important factor affecting the water environment, especially in water sources and reservoir areas, where they have an undeniable impact on water quality. Moreover, it directly endangers the physical health of farmers and can easily lead to the occurrence and spread of some epidemic diseases.

Analyzing the characteristics of rural water quality, 1) Rural villages have smaller populations, are widely and dispersedly distributed, and most lack sewage discharge pipe networks; 2) Rural domestic sewage has a high concentration, with relatively high organic matter concentration, reaching an average maximum COD (chemical oxygen demand) of 500mg/L, with significant variations; 3) Most rural domestic sewage has similar properties, generally not containing heavy metals and toxic harmful substances (but with the improvement of living standards, some domestic sewage may contain heavy metals and toxic harmful substances), containing a certain amount of nitrogen and phosphorus, with large water quality fluctuations and strong biodegradability; 4) Water quality varies at different times; 5) Sewage discharged from toilets is of poorer quality but can be used as fertilizer after entering a septic tank; 6) Multiple sources: Unlike urban areas, rural water use generally combines river water, well water, and tap water. Tap water is used as drinking water, while river water and well water are used as auxiliary water for washing clothes, flushing floors, and raising poultry. In addition to sewage from human excrement and kitchens, there is also sewage generated from household cleaning and leachate from domestic waste piles.

Looking at the characteristics of rural water volume, 1) The volume of domestic sewage in general rural areas is relatively small. Except for small towns, rural populations are dispersed, resulting in relatively small water volumes and consequently smaller amounts of domestic sewage generated. Compared to urban areas, rural residents use and discharge less water, with a discharge volume generally around 100L/(person·d); 2) The variation coefficient is large. Similar living patterns among residents lead to higher rural domestic sewage discharge in the morning and evening compared to the daytime, with smaller discharge volumes at night, and even potential interruptions in flow. The water volume changes significantly, meaning the state of no water discharge is discontinuous and characterized by large fluctuations; 3) There are peak periods in the morning, noon, and afternoon.

Analyzing the engineering situation of rural domestic sewage treatment, the selection of sewage treatment processes should meet the requirements of treatment scale, sewage characteristics, effluent water quality, and discharge water bodies. At the same time, appropriate treatment processes should be selected with specific consideration for local sewage characteristics. To explore practical technologies suitable for small-scale rural sewage treatment, four aspects need to be considered. The first is the cost, with low initial investment and operating management costs. The second is simple operation and management, as limited rural conditions make simple operations and management suitable for farmers. The third is low energy consumption and high efficiency, with the reuse of nitrogen and phosphorus. The treatment of rural domestic sewage should refer to the actual engineering experience of rural sewage treatment in relevant domestic cities, combined with the specific situation of each resettlement site, and adopt processes with mature technology and good treatment effects. As for current domestic rural domestic sewage treatment processes, both artificial wetlands and stabilization ponds have been applied and are relatively mature in technology. However, these two processes have their own advantages and disadvantages and have certain applicability. In addition, the disadvantage of ecological engineering technology is its large land occupation and unstable treatment effect. Neither the experience of urban sewage treatment plants nor single ecological engineering technologies can solve the problem of small-scale rural domestic sewage treatment. By analyzing the differences between urban sewage treatment and rural sewage treatment, and combining with the current international research status, we believe that it is necessary to organically combine biological methods with ecological engineering to save costs and operating expenses while achieving stable phosphorus and nitrogen removal effects. To this end, in the research and application of new ecological treatment processes for rural domestic sewage, we have established and researched the "Five-Ring" (ACGMP) ecological and efficient rural domestic sewage treatment system, which was successfully operated on a small scale and then demonstrated and applied in the Three Gorges Reservoir area.

1. The "Five-Ring" (ACGMP) Ecological and High-Efficiency Rural Domestic Sewage Treatment System

Addressing the dispersed nature of rural areas, coupled with long-standing differences in living arrangements, habits, and economic conditions, this research has established the "Five-Ring" (ACGMP) treatment system. It employs anaerobic treatment + constructed wetland technology. On the basis of connecting sewage from individual households in natural villages, it constructs anaerobic reactors and constructed wetlands, plants vegetation that effectively absorbs major pollutants, introduces specialized highly efficient sewage-decomposing microorganisms, and utilizes natural ponds for further purification. Through 5 purification stages, the treated sewage meets the national discharge standards. It features a simple structure, low construction and operating costs, strong shock resistance, and stable effluent water quality, making it an optimized combined process for rural domestic sewage treatment. The "Five-Ring" represents the combination of 5 ecological and environmental protection concepts, which are: A: Anaerobic, C: Constructed Wetland, G: Genetically Modified Rice, M: Microorganism, P: Pond (see Figure 1). For specific details, please refer tohttp://www.dowater.comMore related technical documents.

2. Conclusion

The "Five-Ring" (ACGMP) rural domestic sewage treatment engineering system is mainly based on connecting domestic sewage from each household in rural areas. It constructs anaerobic reactors and artificial wetlands, plants vegetation with high adsorption capacity for major pollutants, introduces efficient specialized microorganisms for sewage decomposition, and utilizes natural ponds for further purification. Through these 5 stages, the treated sewage reaches the national emission standards.

Through the analysis of monitoring data and charts, it was found that after this process treated rural domestic sewage, COD decreased from about 360mg/L to about 110mg/L, total phosphorus decreased from about 2.1mg/L to about 1.1mg/L, SS decreased from about 97mg/L to about 22mg/L, and ammonia nitrogen decreased from about 27mg/L to about 13mg/L, all showing a significant decrease; total nitrogen slightly decreased (from about 32mg/L to about 17mg/L); hexavalent chromium adsorption slightly decreased (from 0.030mg/L to 0.024mg/L); the pH value remained almost unchanged, close to neutral; total lead, total cadmium, and total mercury were not detected. Rural domestic water, after treatment and then discharge, basically reached the national secondary emission standard. Through this engineering treatment, the environmental conditions in the village, such as mosquito and fly breeding and obvious odors caused by the indiscriminate discharge of sewage, have been completely changed, and the surrounding environment has been significantly improved. The "Five-Ring" (ACGMP) rural domestic sewage treatment engineering system is highly targeted and is an effective technology for rural sewage treatment. It has opened up a new path for water quality protection in the Three Gorges Reservoir area, achieved successful experience, and has important promotion value and broad application prospects.