[Hongjie Water Service] Basic Knowledge of Water Treatment Reverse Osmosis (RO) Concentrated Water Reuse

Whether it is the preparation of pure water or the reuse of industrial wastewater, the use of reverse osmosis (RO) technology will inevitably generate a certain proportion of concentrated water. Due to the working principle of reverse osmosis, the concentrated water in this section often has characteristics such as high salinity, high silicon dioxide, high organic matter, and high hardness. In response to such characteristics, we often need to take certain measures for concentrated water based on specific circumstances to avoid wasting water resources and achieve the goal of reducing costs and increasing efficiency.

1、 Common concentrated water treatment methods for pure water preparation:

① Direct discharge (all discharge): Commonly seen in small pure water equipment, tap water is used as raw water, and concentrated water is directly discharged in three stages.

Main reason: The raw water quality is good, and the indicators of concentrated water can meet the discharge standards; The flow rate is small and does not have the economic value of secondary pre-treatment and utilization (compared to the price of raw water)

Note: In some cases, concentrated water can be mixed with raw water with good water quality (reducing specific indicator concentrations) to meet the third level discharge standard. The system can also reduce the concentration of concentrated water indicators by reducing the recovery rate.

② Recycling (partial collection and treatment): It is commonly used in equipment or projects of medium or above level, with high system recovery requirements. After pre-treatment or ROR device, the concentrated water enters the main system for recycling and improves the overall recovery rate. Collect and treat a certain proportion of concentrated water (including all super concentrated water), and do not directly discharge it.

Main reason: The system recovery rate is relatively high, and the one-way recovery rate cannot meet the overall recovery rate requirements; High environmental requirements require a high proportion of water resource utilization. The circulation of concentrated water increases the concentration of indicators such as salinity infinitely, and it is necessary to regularly discharge stable concentrated water (ultra concentrated water) to achieve stable system operation. This part of concentrated water indicators often exceed the third level discharge standard and need to be collected and treated.

Concentrated water pretreatment: Based on the four major characteristics of concentrated water, mechanical filtration, softening and other measures are taken according to the actual situation to ensure that the pre treated concentrated water meets the basic water quality standards of the raw water, enters the raw water tank (pool), and is reused.

ROR device: For concentrated water, appropriate pre-treatment is carried out first, and then an additional RO device is used for treatment. The generated purified water (which may not necessarily meet the water quality standards for pure water) enters the raw water tank and is reused. The super concentrated water generated by the ROR device cannot be directly discharged and needs to be collected and treated.

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2、 Common concentrated water treatment methods for industrial wastewater reuse:

① Direct collection and treatment (including outsourced treatment): It is commonly used in situations where the wastewater treatment volume is small, the yield of concentrated water is small, or the treatment unit price is low.

Main reason: The concentrated water produced by the RO device has higher indicators than the concentrated water prepared by pure water, and further comprehensive collection and treatment are needed, or qualified units are entrusted for treatment. However, compared to further concentration (such as MVR evaporation) or crystallization processes, the equipment cost and comprehensive operating cost are lower.

② Concentration treatment: It is commonly used in situations where the production of concentrated water is high and environmental requirements are high. The DTRO device can directly follow the traditional RO device, and the low-temperature evaporator and MVR evaporator can directly treat industrial wastewater without passing through the RO device.

Main reason: By using DTRO devices or evaporators, the concentrated water output is further compressed to prepare for the next step of crystallization or zero discharge.

Note: When MVR is used to treat industrial wastewater, the recovery ratio is highly correlated with the salt content, COD, and other indicators of the wastewater raw water. Whether to first use UF, RO, and other devices for treatment depends on the actual situation.

③ Crystallization (zero discharge of liquid): Commonly seen in requirements for zero discharge of liquid (enterprise or local requirements), common crystallization equipment is multi effect evaporator (including single effect evaporator), MVR evaporation crystallization system, etc

Main reason: From a cost perspective, it has increased the initial investment and operating costs of crystallization equipment, but also reduced the treatment cost of high concentration wastewater. From a policy perspective, zero emissions is the trend, and it is not as good as morning at night, as there are rewards in the morning.

Compared to concentrated water prepared from pure water, the utilization method of concentrated water is often considered from a single perspective of comprehensive recovery rate. The treatment of concentrated water in the wastewater treatment process needs to simultaneously consider the economic benefits brought by water resource reuse and minimize the comprehensive cost of concentrated water treatment, and the latter is often the focus of attention for enterprises.

Briefly explain the advantages and disadvantages of various treatment methods in wastewater treatment

Reclaimed water reuse: ultrafiltration+reverse osmosis (UF+RO) process, with a comprehensive recovery rate of 50%. The remaining concentrated water needs further treatment.

Low temperature evaporator: Low temperature vacuum treatment method, with a small processing capacity, usually ranging from 200L/H to 3000L/H. Common mechanical processing waste liquids such as cleaning agents, electroplating wastewater, cutting fluid wastewater, etc., typically have a working temperature of around 30 ℃.

MVR evaporator: Combining low-temperature and low-pressure steam evaporation technology, the processing capacity is moderate, and generally the processing capacity is above 0.5T/H. Commonly used in fields such as chemical engineering, food, papermaking, medicine, seawater desalination, etc., with a general working temperature of 70-90 ℃.

Multi effect evaporator: Traditional high-temperature evaporators improve the comprehensive utilization efficiency of energy through multiple uses of steam. They have two parts: evaporator and condenser, stable system, high operating energy consumption, and need to be equipped with a steam system (with a separate steam generator equipment).

Outsourcing treatment: The composition of wastewater varies, and the treatment costs vary depending on the region. The unit price per ton ranges from several hundred to several thousand.

The purpose of cost reduction and efficiency increase can be achieved through a comprehensive selection of the above methods, either alone or in combination.

The above is the "Basic Knowledge of Water Treatment Reverse Osmosis (RO) Concentrated Water Reuse" introduced by Hongjie Water, hoping to be helpful to you.