Sludge treatment of water supply infrastructure in small towns

The production wastewater of the water plant mainly comes from sedimentation tank or clarification tank sludge water and filter backwash wastewater, which contains impurities in the raw water and chemical residues added in the water plant, and the sludge content in the sludge water reaches 1 to 3% . Due to the influence of technology, capital, habits, etc., for a long time, the sludge water produced by water plants in our country (mainly the sludge water of the tap water sedimentation tank and the flushing water of the filter) is usually discharged directly into the river without treatment. Although water plant sludge is not obviously toxic, it still contains certain pollutants, and long-term sludge siltation in the river will raise the river bed, requiring a lot of manpower and material resources to implement dredging; furthermore, if the sludge is discharged It belongs to the same place as the tap water source water intake, which will be detrimental to reducing the turbidity of the tap water, thus affecting the quality of the tap water.

Chongqing University recently released the “Environmental Infrastructure Technology for Small Towns in Western China” aimed at introducing the concepts, technologies and experience of sustainable development in the Netherlands and improving the development capabilities of water supply, sewage treatment and domestic waste in small towns in western China. The “Guide” clearly pointed out that the serious problem of sewage pollution from water plants in small towns with weak environmental protection awareness is more prominent. In order to meet the increasingly stringent environmental protection requirements and realize the sustainable development of resources, the treatment and resource utilization of sludge in water plants are particularly important and imperative. It will become the ultimate outlet for sludge from water plants in small towns.

Based on the status quo of sludge disposal at home and abroad, combined with field investigations in some small towns, three treatment ideas for water plant sludge are proposed: on-site treatment, combined treatment with sewage plant sludge, and joint treatment.

On-site treatment of sewage sludge

If funds and site permit, small town water plants can establish a separate sludge treatment system in the plant area to treat the sludge on-site. The treatment method can refer to the examples of domestic and foreign water plant sludge treatment projects, but it should not be copied blindly. As far as the actual situation of small towns in our country is concerned, consideration should be given to adopting a treatment process with low capital investment, low operation and management costs, and simple and efficient technology, with simple concentration, dehydration and drying as the mainstay. Considering the economic level of small towns and the abundant land resources around small towns in most areas, natural drying with lower treatment costs and maintenance and management costs can be used to dehydrate the sludge. The dewatered sludge can be filled nearby. Buried or sanitary landfill, etc. Due to humid weather and climate issues in small towns in Chongqing, Guizhou and other places, natural drying methods are not suitable, and mechanical drying or other methods can be used. For small western towns, due to cost and operational management issues, it is generally not recommended to set up separate on-site treatment facilities.

Combined treatment of sewage sludge and sewage sludge

Water plants in small towns are generally small in scale. When there is a sewage treatment plant nearby, if the treatment capacity of the sewage plant permits, the sludge of the water plant can be directly discharged into the sewer for treatment and disposal together with domestic sewage. The sewage and sludge treatment facilities inside can be omitted in whole or in part, which not only reduces the treatment cost, but the addition of sludge from the water plant can also promote sewage treatment to a certain extent. It should be noted that when sludge from the water plant is discharged, it must meet the pretreatment requirements of the sewage treatment plant, such as limiting the discharge time, discharge volume, maximum total suspended solids (TSS) of the sludge, and considering the potential of the sludge from the water plant. Corrosion and H2S production and other issues. This requires that water plants and sewage plants should be considered in the planning and construction.

Joint processing

Water plant sludge is much less than sewage sludge in terms of quantity. However, due to the small scale of water plants in small towns, the amount of sludge is relatively small, which makes it difficult for the construction and operation of treatment facilities to produce scale effects, and the project cost And the processing cost is higher. In response to this situation, we should break the traditional concept and take the road of intensive processing:

  1. In the suburban small towns within the planned area of ​​large and medium cities, the sludge treatment of their water plants can be incorporated into the urban water plant sludge treatment project planning for combined treatment.
  2. When the transportation is convenient among several small towns with concentrated or continuous distribution, the sludge treatment facilities can be jointly constructed based on the planning and optimization of the urban area.
  3. Establish a batch of sludge treatment and disposal centers that operate and manage in accordance with the laws of the market economy, and implement unified treatment and disposal of sludge from several nearby small towns and water plants. After the sludge is concentrated, conventional treatment is the main treatment method, and the dewatered sludge can be landfilled or used as building materials. The intensive treatment of sludge from water plants can not only alleviate the technical and economic pressure on water plants in small towns, but also ensure that the sludge can be treated and disposed of properly to avoid pollution to the surrounding environment. More importantly, the concentration of sludge in water plants provides good conditions for the realization of large-scale disposal and reuse of sludge.
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