A zero-discharge treatment method for reverse osmosis concentrated water

Abstract

The invention relates to a zero-discharge treatment method for reverse osmosis concentrated water. The method includes the following steps: firstly, removing substances, such as suspended matters and organic pollutants, in the reverse osmosis concentrated water by pretreatment; conducting low-retention nanofiltration process on the pretreated liquid materials, wherein the low-retention nanofiltration process has high retention rate of magnesium sulfate, sodium sulfate and magnesium chloride but low retention rate of calcium chloride, and obtaining nanofiltration concentrated liquid rich in SO4<2+> and Mg<2+> and nanofiltration penetrating liquid containing Na<+>, Cl<->, NO<3+>, K+ and Ca<2+> respectively; concentrating a plurality of inorganic salts in the nanofiltration concentrated liquid into a near-saturated state by the processes, such as medium-pressure reverse osmosis, multi-effect evaporation and multi-effect membrane distillation, and recycling fresh water resources; concentrating the nanofiltration concentrated water until CaSO4 is in a near-saturated state; then mixing the nanofiltration concentrated water after concentrating with nanofiltration penetrating liquid near-saturated solution obtained by concentration, so as to remove 70-90% of CaSO4 by precipitation; removing remaining Ca<2+> by concentrated CaSO4 in-line crystallization technology, and concentrating the liquid materials until the concentration of other inorganic salt is near saturated; preparing fresh water and solid salt, such as sodium chloride, sodium sulfate and magnesium salt through a crystallization process. The zero-discharge treatment method achieves zero discharge of waste water and completely eliminates the pollution of the reverse osmosis concentrated water, and the recovered fresh water and the solid salt can also bring significant economic benefits.

Description

technical field [0001] The invention relates to a zero-discharge treatment method for reverse osmosis concentrated water, belonging to the fields of industrial wastewater treatment, wastewater reuse, environmental protection and the like. Background technique [0002] In recent years, with the rapid development of my country's economy and science and technology, reverse osmosis technology has become an important technology in the fields of groundwater / surface water purification treatment, various wastewater treatment and wastewater reuse treatment due to its stable performance, small footprint, and low operating costs. dominant technology. However, the actual water yield of the general reverse osmosis process is less than 75%, while producing about 20-30% concentrated water. A large amount of salt and pollutants are enriched in the concentrated reverse osmosis water, and the direct discharge will cause secondary pollution of the environment, salinization of the land, and ser...

AI Technical Summary

Problems solved by technology

However, the actual water production of the general reverse osmosis process is less than 75%, while producing about 20-30% concentrated water

However, the content of calcium and magnesium ions in water in inland areas is very high (such as calcium ions in some surface waters in Northwest China account for about 35-45% of the total content of cations in water, and the concentration of magnesium ions can also reach 0.7-1.4 times the content of calcium ions) , which makes magnesium ions and calcium ions form a strong competitive relationship during the sodium carbonate precipitation decalcification treatment, which greatly increases the required chemical consumption and equipment volume, making the reverse osmosis concentrated water treatment economically unbearable

[0005] After eliminating the impact of COD and scaling salts, in order to achieve zero emissions, the conventional operation is to obtain solid mixed salts of no use value through evaporation and crystallization, and then landfill them, which results in huge investment and operating costs. The operating cost per ton of concentrated water is as high as tens of yuan, which brings a heavy burden to the enterprise

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