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First, agricultural water
Agricultural water is a large user of urban wastewater reuse, mainly including irrigation of field crops, flowers and woodland. When sewage is used for farmland irrigation, it not only provides a stable source of water for agricultural production, but also the nitrogen, phosphorus, potassium and other components in the sewage provide fertility for the soil, which reduces the amount of chemical fertilizer and increases the yield of crops. The self-purification ability of the soil can further purify the sewage, especially the reuse of sewage can control the uncontrolled extraction of groundwater in rural areas. However, if the sewage water quality does not meet the requirements, it will destroy the soil structure, accumulate pesticides and heavy metals in crops and soil, and reduce the quality and yield of agricultural products. The limits of pollutants used in reuse of sewage shall be based on the crop type and growth stage and hydrogeological conditions, and the water quality must comply with the Agricultural Irrigation Water Quality Standard.
Sewage irrigation is risky. Due to insufficient sewage treatment or insufficient estimation of long-term irrigation risk, there are many lessons learned in China's sewage irrigation. For example, after sewage treatment in Shenyang Zhangshi Irrigation District for more than 20 years, the contaminated cultivated land is 2500h m2, causing serious cadmium, cadmium paddy 5 - 7mg / Kg; suburbs of Tianjin lead 2 by irrigation water. H 30,000 square meters of farmland polluted; Guangzhou suburbs because of sewage pollution of farmland irrigated 2700h meters, sediment contamination due administration comprises about 13333h square meters of contaminated soil, contaminated area accounted for 46% of arable land; the mid-1980s, for A sample survey conducted in a sewage irrigation area in Beijing showed that about 60 % of the soil and 36 % of the brown rice were contaminated.
Second, the environmental water
Mainly used for urban water system supplementary water and green belts and garden irrigation water. There is no aura in a city without water. Replenishing the river and lake water system with medium water, replacing other water sources with one stone, achieving both water superiority and water conservation, and beautifying the environment. The lack of water resources is the key and difficult point of Beijing's ecological environment construction. Full development and utilization of water will provide sufficient water resources guarantee for urban water system supplementary water and green water. With the construction of ecological residential areas in Beijing, urban greening water will continue to increase, and Zhongshui will become the main source of urban greening water.
Third, industrial water
According to the survey, Beijing's industrial water accounts for about 25 % of the city's water use in various industries , and still has great potential in water conservation. Faced with the grim reality of fresh water shortage and rising water prices, industrial enterprises have paid more and more attention to the reuse of urban sewage, in addition to trying to recycle the wastewater of the factory to increase the reuse rate of water. Industrial water use varies greatly depending on the application. The higher the water quality requirements, the higher the cost of water treatment. The ideal recycling target should be cooling water and low-quality water ( washing, ashing, dust removal, direct cooling, etc. ) . When considering whether a process can utilize recycled sewage, it must meet the required water quality, and calculate the cost of recycled sewage and its treatment for maximum economic benefit.
Fourth, municipal miscellaneous water
Mainly used in construction, spraying roads, car washing and flushing. According to estimates, if more than 2 million vehicles in Beijing use car washes, they can save nearly 1 per day . 30,000 households use water for one month. In the reuse of water, special attention should be paid to hygiene so as not to endanger the health of consumers. In addition, the water should not contain pathogenic bacteria, should be clean, odorless, non-toxic, and the suspended matter content meets the application requirements.
5. Groundwater recharge
In recent decades, over-exploitation of groundwater caused by persistent drought, Beijing has formed a funnel area of more than 2500k m2, seriously affecting the safety of ground ecosystems and groundwater aquifers. After the urban sewage is treated twice, it is recharged underground. After flowing through a certain distance, the water is developed together with the original groundwater source as a new water source. This can not only prevent the ground subsidence caused by excessive exploitation of groundwater, but also use the self-purification of soil to improve the quality of the return water and directly supply water to industrial and domestic miscellaneous water. Sewage recharge groundwater requires high water quality . It must be biologically treated ( including nitrification and denitrification ) before recharging . It must also effectively remove toxic organic matter and heavy metals. Once the recharge water quality is not met, it will cause groundwater aquifers. Pollution.
This article was published by Yingnuo Instruments (Shanghai) Co., Ltd.
Introduction to pretreatment in paper industry wastewater treatment
At present, although there are many sewage treatment technologies, the basic principles mainly include separation, conversion and utilization. Separation refers to the use of various technical methods to separate suspended solids or colloidal particles in sewage, thereby purifying the sewage or minimizing pollutants in the sewage. Conversion refers to the conversion of pollutants dissolved in water into harmless substances by means of biochemical, chemical or electrochemical methods for pollutants that have been dissolved in water, cannot be "taken" or need to be "taken" out, or Converted into substances that are easily separated. In short, sewage treatment should make the pollutants in the water develop in a direction favorable to governance. After sewage treatment, it can be applied to agriculture, industry, construction, groundwater recharge, landscape, recreation, river ecological maintenance, etc. Different uses have different requirements for sewage treatment.