Feasibility of EDI technology for treating high-salt organic wastewater
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At present, desalination technology represents a major challenge for chemical enterprises in China, and many are eager to know how to achieve efficient and cost-effective desalination. I hope everyone will feel free to share their thoughts here, discussing the problems and experiences they have encountered in desalination in their work. Exchange of ideas promotes progress, leading to mutual benefit through cooperation. It is said that membrane technology has many advantages in water treatment, but there is still much work to be done in this field. Fundamental research is important, yet in China, there is insufficient research on the underlying mechanisms of membrane technology, the production of membrane components, and the selection of membrane materials; efforts are mostly focused on the application of membranes. The available technologies are limited, and many of them are borrowed from abroad. As competition intensifies, those who focus on developing their own technologies will have difficulty surviving if they do not possess unique strengths. Speaking too much – this is the reality in China, and a major reason for this is **poor policy guidance, or perhaps short-sightedness**. Back to the topic, EDI technology has significant advantages in desalination, but what is its feasibility when it comes to treating high-salt organic wastewater? High power consumption is its fatal flaw; I wonder if there are any examples of this, and what the economic implications are
I’ve been looking at your post for a long time; I’ve wanted to reply many times but found it hard to do so. First, I am not familiar with EDI, and second, I do not have accurate data on the components and concentrations of the pollutants. If there are typical examples, please provide them so that everyone can analyze them more easily.
Currently, all EDI modules are imported from abroad; domestic manufacturers only handle assembly and debugging. The technical complexity lies in the application part, and there are basically just a few different combinations available. There are very few details. Moreover, each type of EDI has different requirements, making it difficult to conduct research on them. Actually, the best approach is to investigate whether your company has already purchased EDI equipment; you can start by learning about one particular brand. There are requirements regarding the water feed for EDI; for high-salt organic wastewater, many pre-treatment devices may be necessary, otherwise the lifespan of the EDI unit will be very short. Electricity consumption is not considered a problem, but controlling the current level is indeed a challenge. Also, relative to mixed-bed systems, they should be cheaper; at least there’s no need for regeneration, the stability of water quality is much better, and the amount of wastewater generated as well as the level of pollution are significantly lower compared to mixed-bed systems. Heh~~~~~~~~
For using EDI to treat high-salt organic wastewater, I think it is difficult to be competitive in terms of cost-effectiveness. As far as I remember, EDI is used only for further desalination after reverse osmosis, and its investment and operating costs are very high. I just checked out more information on EDI technology again; EDI is a combination of ion exchange and electrodialysis. Electrodialysis desalination is a technology that was invented quite early on; however, with the widespread adoption of ultrafiltration, nanofiltration, and reverse osmosis technologies, electrodialysis gradually fell out of use. The main reasons why electrodialysis desalination has been replaced by ultrafiltration, nanofiltration, and reverse osmosis are high operating electricity costs, high costs for dealing with scale formation in the equipment, and high investment costs for the installations (including the buildings). I know very little about EDI, but I believe its emergence was as a result of the use of reverse osmosis to produce desalinated water, replacing ion exchange as the method for this purpose. Considering EDI’s structure, investment costs, and operating expenses, it seems that it is only valuable and feasible when used in combination with reverse osmosis.
What was said upstairs makes some sense: electrodialysis lags far behind reverse osmosis technology in terms of pure water production and seawater desalination, but reverse osmosis cannot be used in wastewater with high salt concentrations. In recent years, nanofiltration technology has seen significant progress in wastewater treatment and concentration; concentrating wastewater to recover useful substances holds great economic value. However, nanofiltration does not retain monovalent ions such as chlorine and sodium ions, which greatly limits its ability to further concentrate high-salt wastewater. The common approach currently is to dilute it with large amounts of water, but this method does not reduce the volume of wastewater; instead, it increases it, thereby increasing the burden on subsequent treatment processes. Can’t we first use a two-stage electrodialysis membrane capable of retaining large molecular substances for desalination?
EDI is a continuous electrodesalination technology that combines the properties of electrodialysis and ion exchange resins; it was first developed around 1985 by E-CELL in Canada. The current EDI modules all have superior technology from North America. The water quality requirements for the feed water to EDI are quite high; it cannot be used directly. Therefore, a pre-treatment unit is necessary, which should include softening treatment followed by either single-stage or double-stage RO filtration. Before that, sand filtration and activated carbon filtration are required. Other devices such as precision filters and ultrafiltration systems are installed depending on the needs for deionized water and other usage requirements. EDI is generally used more in semiconductor-related industries, as well as in power plants and the pharmaceutical sector. Each industry has different requirements for water quality, which means that the setup of EDI systems varies as well, in order to meet those requirements. Strict control over pressure, current, and water quality is necessary; otherwise, the module is prone to damage or becoming unusable. Personally, I think EDI is not very suitable for wastewater treatment; it is only appropriate for the final purification step in producing pure water to achieve deionized water. EDI was developed to replace the previous mixed-bed exchange resins.
The chloride ion concentrations in the inlet and outlet water of our plant’s EDI system remain unchanged; why can’t the chloride ions be removed? Maybe there’s a problem with that place. How should it be dealt with? I would appreciate some guidance from those who are more experienced. (The first and second stage RO units ahead have already been cleaned; it seems they were cleaned with acid.)