Discussion on reclaimed water reuse
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It’s a mixed wastewater with a conductivity of 3000–4000, TDS of 2500, COD of 200, SS of 50, TN of 50, and pH of 8; all other parameters are within normal ranges. The flow rate is around 50 T/hr, and the wastewater is intended to be treated for reuse as make-up water in cooling systems. There are no restrictions on the budget for the treatment process – what suggestions do you have?
Personal opinion: 1. Add PAC and PAM (cationic) for coagulation and sedimentation, followed by treatment in a sand filter tank, to use as make-up water for circulating water； 2. It is directly used as make-up water for circulating water after sand filtration. Conduct experimental analyses in the laboratory to assess the quality of the treated water, and then choose a treatment method for greater certainty.
Since I have worked on a similar project related to recycled water reuse, the COD level of the water used for replenishing the recycled water should generally be below 60, ammonia nitrogen levels should be below 10, and TDS levels should be below 1000. Therefore, the three main challenges at present are reducing COD, ammonia nitrogen, and conductivity (TDS); everything else is relatively easy to handle.
The removal of ammonia nitrogen can be achieved by using sodium hypochlorite or nitrogen-removing agents； It’s more difficult in terms of TDS and COD; it’s hard to reduce COD from 200 mg/L to 60 mg/L using simple methods, which is similar to wastewater treatment ； To achieve this, biological treatment may be necessary, and an MBR membrane might also be required ； Or use a ultrafiltration membrane directly, and then treat the concentrated solution.
Reducing COD and ammonia nitrogen might be relatively easier, but when the conductivity is too high, and if it involves chlorides or sodium salts, there’s no good solution unless RO or anion/cation resins are used for treatment. The upper RO unit should be a good choice; although the water recovery rate is not very high, its operation is relatively easy to control. On the other hand, regenerating the resin bed is time-consuming and labor-intensive.
So, are there any simple and effective methods for removing COD and ammonia nitrogen in this case? Thank you!
The RO process can reduce COD and ammonia nitrogen.
In the PVC industry, many companies recycle mother liquor water and use it to replenish circulating water. If desalinated water is produced again (with very low COD/SS/conductivity control values), what is the application scenario in this regard? ?
Perhaps it is possible to reduce COD to 60; the subsequent desalination process needs to be carried out with a COD level of 60. It is estimated that dual-membrane systems are not the best choice due to operational costs and issues related to the concentrated brine. Take electroadsorption a look; it might be its strength.
Desalination methods mainly include RO, resins, and electrodialysis. There are also issues related to the treatment of concentrated water or reclaimed water.
This water quality is not very suitable for use in circulating water. However, after simple treatment such as coagulation plus sand filtration, it can be used in small amounts to replenish the circulating water supply, provided that the proportion added remains within the requirements for circulating water replenishment.