Recycled water refers to the water that can be beneficially used after the wastewater has been properly treated to meet certain water quality indicators and meet certain usage requirements.Compared with seawater desalination and cross-basin water transfer,recycled water has obvious advantages.From an economic point of view,the cost of recycled water is the lowest.From an environmental point of view, sewage recycling can help improve the ecological environment and achieve a virtuous circle of water ecology.
Recycled water is a very valuable water resource because of its large quantity,stable water quality,and little influence by season and climate.There are many ways of using recycled water.According to the relationship with users, it can be divided into direct use and indirect use, and direct use can be divided into local use and centralized use.In most countries,the recycled water is mainly used for farmland irrigation, mainly for indirect use.In a few countries such as Japan, the recycled water is mainly used for urban non-drinking water,and it is mainly used on-site. The new trend is environmental water for urban environmental water landscapes.
The advantages of recycled water reuse in agricultural production:
(1) Alleviate the problem of agricultural water stress. The spatial and temporal distribution of water resources is uneven, and agricultural production requires a large amount of water resources. However, severe droughts have caused large-scale disasters to crops, restricting the development of agriculture. The domestic sewage produced in large quantities every year has a stable water source. Such sewage has been properly treated to reach the corresponding use standard and then irrigated the farmland, which not only improves the reuse rate of water resources, but also alleviates the shortage of agricultural water resources to a large extent.
With the continuous increase of sewage treatment volume, recycled water has gradually become a stable source of water for agricultural irrigation.
(2) Improve the safety of agricultural water Recycled water reuse in agriculture has higher safety than sewage irrigation. First of all, the effluent of the sewage treatment plant can only be discharged if it meets the relevant water quality requirements of the "Urban Sewage Treatment Plant Pollutant Discharge Standard" issued by the environmental protection department. Biological comprehensive toxicology test can be used for agricultural irrigation.
Therefore,the recycled water is reused, and the safety of agriculture is guaranteed. Secondly, the reuse of recycled water in line with agricultural production, agriculture can effectively reduce forced sewage irrigation caused by water shortage, reduce the pollution caused by active sewage irrigation in pursuit of sewage water and fertilizer resources to the production area of agricultural products, and ensure the environmental quality of the production area and agricultural products. safety and maintaining the health of the people.
(3) Good environmental and economic benefits From the sewage treatment side,sewage contains a large amount of nitrogen and phosphorus nutrients,organic matter and trace elements required by crops,and the soil has the ability to adsorb and filter suspended solids and bacteria in the recycled water.Therefore,compared with industrial and other water use,the quality requirements of agricultural irrigation water are relatively low, and no advanced treatment such as dephosphorization, denitrification,flocculation and disinfection is required, which can not only simplify the process,reduce the infrastructure cost of sewage treatment plants,but also reduce The running cost of sewage treatment.
In terms of agricultural use,recycled water is reused in agriculture,supplementing agricultural irrigation water sources, saving agricultural input costs,and increasing farmers'income.Recycled water is reused for agricultural irrigation,and the benefits obtained vary from place to place, but among all water sources,recycled water is the best choice for agricultural irrigation. Recycled water is a sustainable,safe and nutritious source of water.Using recycled water for irrigation not only saves agricultural production costs,but is also a way of protecting water resources.
Recycled water treatment process
(1) Process 1 (coagulation, sedimentation and filtration): secondary effluent → coagulation → ozone decolorization → mechanically accelerated clarifier → V-type filter → ultraviolet disinfection → effluent.
(2) Process 2 (MBR process): urban sewage → aeration grit chamber → MBR → ozone decolorization → chlorine dioxide disinfection → effluent.
(3) Process 3 (MBR+RO process): urban sewage → aeration grit chamber → MBR RO → chlorine dioxide disinfection → effluent.
(4) Process 4 (secondary RO process): secondary effluent → filter → ultraviolet disinfection → microfiltration „ → primary RO → pH adjustment → secondary RO → chlorination disinfection → effluent.
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