There are three ways to treat reclaimed water for different purposes.
1. One is to treat it to the standard of drinking water and reuse it directly in daily life, that is, to realize the direct recycling of water resources. This treatment method is suitable for areas where water resources are extremely scarce, but the investment is high and the process is complicated.
2. The other is treated as non-drinking water, which is mainly used for water that does not directly contact with human body, such as flushing toilets, cleaning floors and cars, sprinkling water for greening, fire fighting and industrial common water. This is the usual way of reclaimed water treatment.
3. Industrially, the reclaimed water reuse technology can be used to reprocess the industrial sewage that meets the discharge standards. Generally, equipment such as softener, RO, EDI/ mixed bed will be added to make it reach the level of softened water, purified water and ultra-pure water, and it can be recycled in industry, which not only saves money but also protects the environment.
Second, according to the classification of processing methods
According to the treatment methods, reclaimed water treatment processes are generally divided into three types:
1. Physical treatment method:
Membrane filtration method is suitable for large water quality changes.
The process has the characteristics of compact equipment, simple operation and little influence by load change.
Membrane filtration method is that the separated solution flows along the surface of the filter membrane at a certain speed under the action of external force, and the solvent, low molecular weight substances and inorganic ions in the solution enter the low pressure side through the filter membrane from the high pressure side and are discharged as filtrate; The polymer, colloidal particles and microorganisms in the solution are intercepted by ultrafiltration membrane, and the solution is concentrated and discharged in the form of concentration.
2. Physical and chemical methods:
It is suitable for the situation that the sewage quality changes greatly. Commonly used methods are: sand filtration, activated carbon adsorption, flotation, coagulation and sedimentation, etc. The process adopts hollow fiber ultrafilter, which is advanced in technology, compact in structure, less in land occupation, intermittent in system operation and simple in management.
3. Biological treatment methods
Suitable for sewage with high organic content. Generally, biological treatment methods such as activated sludge method, contact oxidation method (pictured) and biological turntable are adopted. Alone or in combination with several biological treatment methods, such as contact oxidation+biological filter; Biological filter+activated carbon adsorption; Rotary table ten sand filtration and other processes. This process has the advantages of strong adaptability to the change of hydraulic load, less mud production and easy maintenance and management.
At present, some countries and regions are over-exploiting water resources in an uncontrolled way, and at the same time, the awareness of environmental protection is relatively poor, which makes surface water and groundwater polluted to varying degrees, and the supply of fresh water with good water quality is limited; Secondly, the fresh water source to be developed is far from the centralized water supply point, and the one-time investment cost is high, and some water-deficient areas are unable to expand the water supply capacity. To the extent of non-drinking, the concept of reclaimed water is introduced here. Reclaimed water is high-quality miscellaneous drainage (excluding feces and kitchen drainage), miscellaneous drainage (excluding feces and sewage) and domestic sewage (wastewater) used in people's life and production. After being collected and regenerated, it can be recycled as miscellaneous water that is not in direct contact with human body, such as floor cleaning, watering flowers, car washing, air conditioning cooling, toilet flushing and fire fighting. Because its water quality index is lower than the water quality standard of urban water supply and drinking water, but higher than the discharge standard of sewage allowed to be discharged into groundwater, that is, its water quality is between the quality standard of domestic drinking water and the quality standard of sewage allowed to be discharged, it is named "reclaimed water".
The technology of reclaimed water development and reuse has developed rapidly and has been widely used in the United States, Japan, India, Britain and other countries (especially Japan). According to the characteristics of their own countries and regions, these countries have determined the reclaimed water recycling technology suitable for their national conditions and national strength, which makes the reclaimed water recycling technology more and more perfect. In China, this technology has been paid attention by governments at all levels and relevant departments, and a lot of theoretical research and practical work have been done on the reuse of water in buildings. Many cities in China, such as Shenzhen, Beijing, Qingdao, Tianjin, Taiyuan, etc., have carried out the operation of reclaimed water projects and achieved remarkable results. China's state-owned industrial enterprises and some private enterprises, such as those with serious pollution and more water resources utilization, have built reclaimed water reuse projects, which have contributed to the country's call for low-carbon production, energy conservation and emission reduction.