How to remove 70–100 mg/L of COD from large amounts of reverse osmosis concentrate?
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Refinery wastewater can meet discharge standards after multiple stages of treatment, including biological treatment. Now, fresh water is further recovered using ultrafiltration and reverse osmosis. Therefore, the wastewater that meets the standards undergoes flocculation, aerated biological filtration, sedimentation, and ultrafiltration before being fed into reverse osmosis for concentration by a factor of 4. This project started last year, but now the users want to make further use of the reverse osmosis concentrate. What we are doing now is to use multi-effect membrane evaporation to concentrate the reverse osmosis brine by a factor of 10 in order to recover fresh water; the resulting highly concentrated fluid (after secondary concentration, with a total concentration increase of over 40 times) is then subjected to two-stage evaporation-crystallization to produce solid waste salt. In our process, 0.1 ton of steam at atmospheric pressure is required to produce 1 ton of fresh water, so the energy consumption is very low. However, the problem is that if the reverse osmosis concentrate is concentrated further by more than 10 times, its color deepens (from colorless to brownish), and it acquires a taste. The resulting fresh water is colorless but has a slight taste. The measured COD value for fresh water was 40, which is clearly not within the acceptable range for reuse. Fortunately, even when the reverse osmosis concentrate is further concentrated by pervaporation using a pseudo-multistage membrane by a factor of nearly 20, the conductivity of the resulting fresh water drops to just 6 us/cm or less. Who helped remove COD from the reverse osmosis concentrate? Biochemical treatment is probably not feasible, as the wastewater has already undergone two rounds of biochemical treatment before reverse osmosis concentration. Use activated carbon for adsorption? Is it feasible? The daily reverse osmosis concentrate volume is 7,000 tons. How much is the investment, and what are the operating costs? How much is the cost to treat one ton of water? Electrochemical treatment? That expert, please give some advice! ! ! Oxidation method? That expert, please give some advice! ! ! Other technologies? Thank you!
It’s really troublesome to face these problems now; is it worth spending so much money? Is this truly energy conservation and emission reduction? To what extent should wastewater be treated to achieve optimal results?
Hehe, Dr. Qin, it’s great to see you again. There are several approaches to handle this. Abroad, it is ozone + biological filter. In your case, go with pure ozone; this way no other substances will be added to the fresh water.
3# *aoyu188 Should ozone oxidation be used for this COD concentration and water volume? How much do you need to invest in equipment?
This post was last edited by zfc318 on 2010-2-2 at 15:48. Due to the high COD level and large water volume, regenerating the activated carbon poses a significant problem; I think it’s not feasible. The electrochemical method is also unreliable; electrocoagulation finds it difficult to meet the required standards. For electrochemical oxidation on such a large scale, the power supply capacity needed is too high, making it costly to implement. Fenton is still the more reliable option – it requires less investment, and its operating costs are acceptable; based on this COD level, they should be within 1 yuan. (Process up to 20)
Is it worth making such a large investment and incurring such high treatment costs just to get that little amount of water? Since the COD of the reverse osmosis concentrate is not high, it is better to discharge it directly. Reusing reverse osmosis concentrate water is not suitable for large-scale application at least for now.
Activated carbon adsorption is costly; resin adsorption is an alternative as it can be reused. For more details, please contact 15951777817
Putting reverse osmosis aside for now, let’s talk about multi-effect falling-film evaporation. When it comes to treating wastewater, especially that with high levels of mixed salts and organic matter, few systems manage to operate properly; most of them are just for show. It’s really remarkable if your system can function correctly – keep up the good work