Treatment of wastewater with 5-6% salt content
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We have wastewater containing 5-6% sodium chloride; biochemical treatment alone is not feasible. While physicochemical treatment combined with biochemical methods can achieve the required standards, the costs are extremely high, with the cost per ton of water reaching 50 yuan. The concentrated brine obtained through evaporation has a very high COD value of around 30,000, and there are no effective ways to treat it. What do you think of using a vacuum salt production process to obtain solid salt, and then burning that solid salt to reduce the COD level so that the sodium chloride can be used in chemical manufacturing? Is this feasible?
You can dilute the saltwater to 1–2% before using biochemical treatment, but the biochemical bacteria require a cultivation process to develop salt tolerance. One issue with incineration treatment is temperature control as well as corrosion problems.
We have also tried the approach mentioned above; it meets the requirements. However, my amount of waste brine is quite large. By adding twice as much water, the current production volume reaches 1,500 cubic meters per day. If we were to increase production by four times, the volume would need to reach 6,000 cubic meters per day. In that case, the space required for biochemical treatment and the investment in related equipment would be substantial. Moreover, if there are restrictions on chloride ions in the wastewater, this treatment system would no longer be usable. We still hope to be able to reuse the salt – although its value isn’t high, it contributes significantly to environmental protection. I’m wondering if there are any good solutions.
Resin adsorption can be used for treatment, but the wastewater must meet the requirements for feeding it into the resin (free of oil, large molecular organic substances, and excessive solid content)
Vacuum evaporation can be used for salt production, but it’s not possible to achieve a high degree of purity by burning salts. The reason is that although burning removes organic substances, the inorganic salts that were originally present in the salts, as well as those formed as a result of the burning of organic substances, remain intact. Moreover, other harmful substances may also be generated. This approach is theoretically feasible, but it is not practical in practice. The treatment using membranes might be more ideal, but I don’t know what the COD level is
Our factory is basically in the same situation as what you described, except that it contains sodium sulfate. Our factory has installed a separate desalination unit that uses low-pressure condensate at 0.35 MPa for evaporation and crystallization. The effluent basically meets the requirements. (This device requires a relatively large initial investment.)
If biochemical testing is required, we have salt-tolerant strains that can be used for the experiment.
Our branch office has installed a desalination unit and an evaporation system. The cost is high
First, use multi-effect membrane evaporation; for processes similar to those in the chlor-alkali industry where salt crystallization is involved, the cost might be a bit lower
I’ve heard of membrane-based multi-stage multiple-effect evaporation; the manufacturer said they would conduct a pilot test, but after a long time they still didn’t show up. I’m not sure if this technology is mature yet, nor what the investment costs are; replacing the membrane is also very expensive.
It can be treated by electrodialysis; it’s completely achievable as long as the water quality meets the requirements!
The operating cost of using forward osmosis is relatively low; the steam consumption per ton of water is over 100 kilograms, and the operating cost per ton of water is generally around 20 yuan.
It seems that this water needs to be desalinated through electrodialysis and then subjected to biochemical treatment. It would be best if the extracted salt could be sold in the form of a by-product. Otherwise, it would be impossible to ship it out as hazardous waste. We also want to engage in waste recycling, but the process is slow. The key issue is not knowing the policies and extent of support provided by the department for upgrading waste treatment processes and reducing energy consumption in enterprises.
We can use physical and chemical treatment to remove sodium chloride and achieve the required biochemical standards; the cost is not high, at 2 yuan per ton of water. We are happy to discuss this further and welcome you to see our performance records. WeChat lcs8536