In recent years, EDI technology has been widely used in power, chemical, medicine and other industries with high water quality requirements.
Long-term application research in the field of water treatment shows that EDI treatment technology has the following 6 characteristics:
1. High water quality and stable effluent
EDI technology synthesizes the advantages of electrodialysis continuous desalting and ion exchange deep desalting. Continuous scientific research and practice show that using EDI technology to desalting again can effectively remove ions in water, and the effluent purity is high.
2. Low installation conditions and small footprint
Compared with ion exchange bed, EDI device is small in size and light in weight, and does not need to set up acid and alkali storage tank, which can effectively save space.
Moreover, EDI device is an integrated structure with short construction period and small installation workload.
3. Simple design, convenient operation and maintenance
EDI processing device can be modular production, automatic continuous regeneration, do not need large, complex regeneration equipment, put into operation, easy to operate and maintain.
4. water purification process automatic control is simple
EDI device can connect multiple modules to the system in parallel, the module operation is safe and stable, the quality is reliable, so that the operation and management of the system is easy to realize program control, easy to operate.
5. no waste acid waste lye discharge, conducive to environmental protection
EDI device does not need acid, alkali chemical regeneration, basically no chemical waste discharge.
6. The water recovery rate is high, and the water utilization rate of EDI treatment technology is generally above 90%
To sum up, EDI technology has great advantages in water quality, operation stability, operation and maintenance difficulty, safety and environmental protection, etc.
However, it also has some shortcomings, EDI device has higher requirements on inlet water quality, and its one-time investment (capital construction and equipment costs) is high.
It should be noted in particular that, although the cost of construction and equipment of EDI is slightly higher than that of mixed-bed technology, EDI technology still has certain advantages after considering the cost of device operation comprehensively.
For example, a pure water station compared the investment and operation cost of the two processes, and EDI device could offset the investment difference with the mixed bed process after one year of normal operation.
02
Reverse osmosis +EDI VS traditional ion exchange
1. Comparison of initial project investment
In terms of the initial investment of the project, in the water treatment system with low water production flow, the huge regeneration system required by the traditional ion exchange process is cancelled due to the reverse osmosis +EDI process, especially the two acid storage tanks and alkali storage tanks respectively, which not only greatly reduces the equipment procurement cost, but also saves about 10% ~ 20% of the land area. Thus reducing the construction of plant construction costs and land acquisition costs.
Since the height of traditional ion exchange generation equipment is generally above 5m, and the height of reverse osmosis and EDI equipment is less than 2.5m, the height of water treatment workshop can be reduced by 2 ~ 3m, thus saving 10% ~ 20% of the investment in plant construction.
Considering the recovery rate of reverse osmosis and EDI, all the concentrated water of secondary reverse osmosis and EDI is recovered, but the concentrated water of primary reverse osmosis (about 25%) needs to be discharged, and the output of the pretreatment system needs to be increased correspondingly. When the pretreatment system adopts the traditional coagulation and filtration process, the initial investment needs to be increased by about 20% compared with the pretreatment system of ion exchange process.
Overall, the initial investment of reverse osmosis +EDI process in small water treatment system is similar to that of traditional ion exchange process.
2. Comparison of operating costs
It is well known that the operating cost of reverse osmosis processes (including reverse osmosis dosing, chemical cleaning, wastewater treatment, etc.) is lower than that of traditional ion exchange processes (including ion exchange resin regeneration, wastewater treatment, etc.) in terms of pharmaceutical consumption.
However, in terms of power consumption and replacement of spare parts, the reverse osmosis plus EDI process is much higher than the traditional ion exchange process.
According to statistics, the operation cost of reverse osmosis plus EDI process is slightly higher than that of traditional ion exchange process.
Overall, the overall operation and maintenance cost of reverse osmosis plus EDI process is 50% ~ 70% higher than that of traditional ion exchange process.
3. Reverse osmosis +EDI has strong adaptability, high degree of automation and little environmental pollution
Reverse osmosis + EDI process has strong adaptability to the salt content of raw water. The reverse osmosis process can be used in seawater, brackish water, mine drainage, groundwater and river water. However, the ion exchange process is uneconomical when the content of dissolved solids in the water is greater than 500 mg/L.
Reverse osmosis and EDI do not require acid and base regeneration, no large amount of acid and base consumption, nor produce a large amount of acid and base wastewater, only a small amount of acid, base, scale inhibitor and reducing agent dosing can be done.
In operation and maintenance, reverse osmosis and EDI also have the advantages of high degree of automation, easy to program control.
4. Reverse osmosis +EDI equipment is costly and difficult to repair, and it is difficult to deal with concentrated brine
Although reverse osmosis plus EDI process has many advantages, when the equipment fails, especially when the reverse osmosis membrane and EDI membrane reactor are damaged, it can only be replaced out of service. In most cases, professional and technical personnel are needed to replace it, and the outage time may be long.
Although reverse osmosis does not produce a large amount of acid and alkali wastewater, the recovery rate of primary reverse osmosis is generally only 75%, which will produce a large amount of concentrated water. The salt content of concentrated water is much higher than that of raw water. At present, there are no mature treatment measures for this part of concentrated water, and once discharged, it will pollute the environment.
At present, in domestic power plants for reverse osmosis of concentrated brine recovery and utilization of most used for coal transport washing, ash humidification; Some universities are conducting research on the process of evaporation, crystallization and purification of concentrated brine, but it is costly and difficult, and has not been widely used in industry.
The cost of reverse osmosis and EDI equipment is relatively high, but in some cases even lower than the initial engineering investment of traditional ion exchange processes.
The initial investment of reverse osmosis and EDI systems is much higher than that of traditional ion exchange processes in large water treatment systems.
In small scale water treatment system, reverse osmosis plus EDI process in small scale water treatment system and traditional ion exchange process in terms of initial investment is about the same.
In summary, when the output of the water treatment system is small, the reverse osmosis plus EDI treatment process can be given priority, which has low initial investment, high degree of automation and little pollution to the environment.
