This article introduces the types and application status of sewage treatment process of capillary percolation system, and summarizes domestic engineering examples. It is pointed out that the capillary percolation system is a sewage ecological treatment technology that is more suitable for my country's national conditions.
1 Introduction
With the development of economy and society, nature reserves with beautiful scenery have become a paradise for people to travel and vacation, and a large number of tourist attractions, villas and highways have been built. However, after solving the water supply problem, these facilities are far away from the urban area and do not have supporting municipal drainage systems. A large amount of domestic sewage is simply discharged directly into nearby rivers through septic tanks, causing serious water environment pollution and even threatening water sources. safety. Therefore, engineering measures must be taken to solve such water pollution problems. Most of the commonly used reclaimed water uses artificial physical and chemical treatment, which requires large investments and requires professional management and maintenance. Although the country strongly advocates it, it is difficult to promote it in the vast economically underdeveloped areas due to various reasons such as cost. In view of this, the author introduces an ecological treatment process that is low in cost, has good treatment effects, is simple and practical, easy to manage and maintain, and can be well integrated with landscape greening - the capillary infiltration soil purification system (referred to as the capillary infiltration system).
The capillary percolation system usually refers to a sewage treatment system composed of a septic tank and an underground percolation device. After the sewage is pre-treated by the septic tank, it is dosed into the percolation device in a controlled manner, and then Diffusion moves under the action of gravity and soil capillary force. During this migration process, sewage is purified through physical interception, physical and chemical adsorption, chemical precipitation, microbial degradation, animal and plant effects, etc. The underground infiltration system has the advantages of good effluent quality, low investment, simple management, the device is located underground without damaging the landscape, and has no odor. It has become an increasingly valued sewage treatment method at home and abroad.
The bathroom drainage is treated by the septic tank and the kitchen operation room drainage is treated by the grease trap and then merged. It is treated with capillary percolation technology to meet the water quality standards for landscape water.
2 Process and Principle
2.1 Process
A typical capillary percolation system can be composed of pretreatment, lifting transportation, and percolation field. When green space is targeted for reuse, sewage treatment and utilization are combined. The process flow is as follows:
If combined with greening, the process ends at the infiltration field, in which pretreatment is a more important process. Sewage contains a lot of solid feces, waste residue, etc., which can easily block pipelines and affect operation. There are several pretreatment processes available: sedimentation tank, septic tank, hydrolysis tank, fermentation tank, etc. In addition, cleaning measures should be taken for the water distribution pipe system in the infiltration field to prevent blockage.
A percolation field consists of a single or multiple underground percolation trenches. Generally, the width of the upper part of the percolation trench is 1m, the depth of the trench is 0.6m, and the center distance between trenches is 1.5m. The trench is composed from bottom to top: a plastic or clay anti-seepage layer, a gravel layer with water distribution pipes, a non-woven isolation layer, a special soil layer mixed with local soil, peat and slag in a certain proportion, and a more fertile tillage layer. The top layer of soil that makes up lawns and plant growth.
2.2 Principle
Capillary percolation technology uses a special plastic film to form a soil biological filter underground, and uses the water distribution system to introduce domestic sewage under the frozen layer of the lawn and evenly distribute it to the lawn. The anaerobic filter unit equipment penetrates; and under the action of surface tension, after crossing the outlet weir of the anaerobic filter unit equipment, it continuously penetrates into the lower aerobic filter bed through siphon and flows out of the soil biological filter. In the above process, water is separated from pollutants, and the water is filtered and collected through the water collection system as reclaimed water for reuse; pollutants are trapped in the soil through physical and chemical adsorption; C and N are trapped in the soil due to anaerobic and aerobic effects. Part of it is decomposed into inorganic substances C and N and remains in the soil, and part of it becomes N2 and CO2 and escapes in the air; P is mainly physically and chemically adsorbed by the soil, trapped in the soil, and used by lawns or other plants. The entire system is installed underground and has no direct contact with people, and has no impact on the environment, landscape and hygiene. The principle of capillary percolation treatment process is shown in (Figure 1), and the structure of the soil capillary percolation system is shown in (Figure 2).
3 Comparative Advantages
The difference between the soil capillary percolation system and the traditional underground percolation system is that there is an impermeable anaerobic tank (i.e. Nimi) under the water distribution pipe. trough), filled with sand or other filler, the water distribution pipe is surrounded by gravel wrapped in synthetic fiber fabric, and the top layer of gravel is covered with soil.
When sewage comes out of the water distribution pipe, it first enters the anaerobic tank. After accumulating to a certain extent, it diffuses into the soil above and around the anaerobic tank under the action of sand and soil capillary force. The solid suspended matter in the sewage is large. Most of it is trapped by sand and stays in the anaerobic tank and gradually liquefies and acidifies in the tank. This can reduce the possibility of soil being blocked and improve the quality of effluent. The existence of anaerobic tank can also play a role in impact resistance.
Compared with other sewage treatment systems, the capillary percolation system has the following advantages:
1) The entire system is installed under the surface and does not come into direct contact with people. It has no impact on the environment, landscape, Not only does it not affect health and safety, but it can also keep the vegetation evergreen in winter and extend the greening period;
2) It is not affected by the outside temperature, or has little effect, and the purified water quality is good and stable;
3) It can remove nitrogen and phosphorus while removing biological oxygen demand;
4) Easy construction, simple maintenance, low infrastructure investment and low operating costs;
5 ) combines sewage treatment with greening and sewage resource utilization, greening the environment and saving water resources while treating sewage.
4 Conclusion
Capillary percolation systems are widely used abroad. In the 1960s, Japan began to adopt underground soil sewage purification technology, and finally developed a soil capillary infiltration ditch sewage purification process. The system's treatment of effluent is better than secondary treatment, and even achieves the effect of tertiary treatment. It has been patented in Japan and more than 20,000 units have been built so far. In the United States, about 36% of rural and scattered family houses have adopted capillary percolation systems, which have achieved satisfactory results. In my country, it has just started and has broad development prospects.
The capillary percolation system makes full use of nature's natural purification ability, so it has the advantages of low infrastructure costs, low operating costs, and simple operation. This system can not only treat sewage and reduce pollution, but also make full use of its water and fertilizer resources, combine sewage treatment with greening, and beautify and transform the ecological environment. This system has special promotion significance in water-scarce areas in the north.
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