Technical assistance: Seeking a wastewater desalination solution
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This post was last edited by cdpulin on 2012-12-28 at 15:38. We need to treat approximately 400 tons per day of chemical wastewater, and we are looking for treatment solutions that can remove salts. It would be ideal if the proposals include quotes, as well as information on the cost per ton of wastewater treated and the investment required. Water quality of the wastewater: COD
Does wastewater quality refer to the inlet water or the outlet water? How high is the salt content exactly? What level is required?
Treatment is carried out using conventional permeable membranes or seawater membranes.
That’s 400 tons per day, which amounts to about 150,000 tons per year. Assuming a salt content of 5%, the total amount of salt is around 7,500 tons. The salt content of these wastewater streams is only slightly higher than that of seawater; membrane methods are unlikely to be very effective in dealing with them, and multi-effect evaporation also requires significant energy consumption. If there is empty land near the enterprise and there are many sunny days in the area, it is most cost-effective to build two large shallow ponds and use the sun to produce salt; other methods are not cost-effective. Because the amount of salt recovered is not very large.
These are all water quality parameters that have already been processed; what we aim to do is further reduce their salt content through desalination processes. The current salt content is around 5–6%, and it would be ideal to bring it below 0.5%. While there are no specific requirements regarding salt content in wastewater discharge standards, we still want to remove the salt in order to improve the quality of the wastewater being discharged.
Your idea is good, but with such high salt levels, it’s difficult to remove them without spending a lot of money. Contact the manufacturers that specialize in pervaporation and ask; it might be cheaper than direct evaporation.
For this salinity level, multi-effect evaporation should be used. If the manufacturer is willing to invest, reverse osmosis can be employed first to produce concentrated brine; a concentration of 10% should be achievable. For this purpose, reverse osmosis membranes from Dow Chemical in the United States would be suitable. Given that the water quality seems to be fairly good, the lifespan of these reverse osmosis membranes should be around half a year. The concentrated brine can then be processed through multi-effect evaporation to achieve zero emissions. While the combination of reverse osmosis and evaporation results in higher investment costs, direct multi-effect evaporation requires less capital investment. If you need help designing the evaporator, you can contact me at hubeitianling@qq.com
Reverse osmosis requires a high initial investment and has a short service life, but it provides excellent treatment results. Evaporation requires a small initial investment but has high operating costs. This requires balance.
10% for reverse osmosis is the theoretical limit; how is it possible to achieve such a high percentage in reality? 5-6% is quite good; besides, this is wastewater – its salt content is already over 5%, so reverse osmosis is simply not feasible. The only option is evaporation
It is recommended to use evaporation for desalination; considering energy consumption, an MVR evaporator (mechanical vapor recompression evaporator) can be considered. I’m not sure what the main salts contained in LZ wastewater are; if they are relatively simple or easy to separate, evaporation crystallization could be considered as a method to recover those salts. If the salt content is complex, it may be advisable to adjust and optimize the entire wastewater treatment system: first, the wastewater is simply treated before being sent for evaporation; if the water obtained through evaporation does not meet the discharge standards, it is then sent to biological or other treatment systems.