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For rural sewage treatment

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High dispersion and difficult to collect uniformly. Due to the vast territory of our country, complex rural terrain and low economic development, sewage cannot be collected uniformly through municipal pipe networks. Farmers generally discharge it directly into ditches outside their houses or spill it onto the ground.

Current situation of rural domestic sewage

1. Characteristics of rural domestic sewage

1. High dispersion and difficult to collect uniformly. Due to the vast territory of our country, complex rural terrain and low economic development, sewage cannot be collected uniformly through municipal pipe networks. Farmers generally discharge it directly into ditches outside their houses or spill it onto the ground.

2. The water volume is small and the water volume fluctuates greatly. As rural areas are scattered and the permanent population is small, the domestic sewage produced is also very small. However, the water consumption habits of residents are basically similar every day. There is a peak period for water use in the morning, noon and evening, and there is very little water use at other times. The daily water consumption The coefficient of variation is generally 1.9 to 2.5. The seasonal characteristics are obvious, and the emissions in summer are larger than those in winter.

3. The concentration of organic matter is high. Domestic sewage contains COD, nitrogen, phosphorus and other elements, which are highly biodegradable. The average maximum concentration of COD can reach 500mg/L. However, domestic sewage does not contain harmful substances such as heavy metal elements, which is conducive to the use of biological treatment technology.

4. There are large regional differences in water quality and quantity. Due to the different development levels, topography, climate, and personal habits of various rural areas in my country, the amount and quality of rural domestic sewage vary in each place.

2. Sources of rural domestic sewage

1. Kitchen sewage. Kitchen sewage is the main source of organic matter in rural domestic sewage, and its discharge accounts for 20% of the total domestic sewage.

2. Washing sewage. Washing sewage accounts for more than 50% of the total domestic sewage and contains large amounts of ammonia nitrogen, phosphorus and other elements. It is the main cause of eutrophication of rural water bodies.

3. Toilet sewage. Toilet sewage is the main contributor to nitrogen, phosphorus, COD, bacteria, and viruses in rural domestic sewage.

1. Biological treatment technology

1. Biological contact oxidation method

Principle: The use of external aeration conditions can not only fully contact the biofilm formed by the sewage and microorganisms attached to the surface of the filler, but also enable aerobic microorganisms to decompose organic matter in the water, thereby achieving the purpose of purification.

Advantages and Disadvantages: Good effluent quality, small footprint, impact resistance, strong adaptability, no sludge expansion problem, and convenient operation and management. However, it has the disadvantages that the filler is easy to block and collapse, requires blast and aeration equipment, and has high infrastructure investment and operating costs.

2. Biological filter method

Principle: Using gravel and plastic as filter material, the sewage flows down evenly from the filter material to form a microbial film on the surface of the filter material. The microbial film decomposes organic matter to achieve the purpose of sewage purification.

Advantages and Disadvantages: No sedimentation tank is required during use, space saving, strong impact resistance, and low operating cost. In order to avoid the aeration process during operation and increase operating costs, natural ventilation biological trickling filters are currently used.

For example, when biological trickling filters are combined with constructed wetlands to treat rural domestic sewage, the average removal rates of CODcr, NH4-N, TN, and TP can reach 92.53%, 99.55%, 62.26%, and 63. 82%, the effluent meets the Class A standard of the "Pollutant Discharge Standard for Urban Sewage Treatment Plants" (GB18918-2002), and the effect is good.

However, this method has the disadvantages of mosquito and fly breeding, low treatment efficiency, easy clogging of the filler, and energy consumption for backwashing.

3. Earthworm biological filter technology.

Earthworms were innovatively introduced into the biological treatment system.

Due to the presence of earthworms, there are more types of microorganisms in the filler. Earthworms and microorganisms can cooperate with each other to degrade organic matter and achieve better treatment results. At the same time, due to the shuttle of earthworms foraging in the soil, the problems of easy clogging and biofilm renewal in traditional filters are solved.

However, in order to meet the growth requirements of earthworms, this method has strict requirements on environmental humidity and temperature, and the hydraulic load is low.

4. Anaerobic digester technology.

At present, anaerobic biogas digesters are widely used in rural areas of my country. They use anaerobic fermentation of microorganisms to turn organic matter in sewage into biogas and decompose organic matter in sewage to achieve purification purposes.

Advantages and Disadvantages: Low operating costs, the water can be used for farmland irrigation, it can be buried underground, and it can generate energy, and the resource utilization rate is high. It can be used for primary treatment of rural sewage in one household or joint households. For users who raise a certain number of poultry, the biogas residue and biogas slurry can be reused, but the effluent will have a foul smell.

5. Integrated sewage treatment technology.

Drawing on Japan's experience in implementing "johkasou", my country has also implemented integrated sewage treatment technology in treating rural domestic sewage. It can be buried underground or installed on the ground to combine the reaction, sedimentation and sludge return of traditional biological treatment processes. Concentrated in a reactor, sewage can be treated on site.

Advantages and Disadvantages: It integrates the advantages of strong impact resistance, low energy consumption, simple maintenance and management, and quick results. However, there are disadvantages such as high engineering construction requirements and excessive water treatment volume. It is suitable for areas that urgently need to solve the problem of domestic sewage pollution in rural areas and have less land and water resources.

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