How to deal with excessive COD levels in wastewater discharge
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Our company discharges wastewater during production, which contains trace amounts of sodium thiosulfate, at levels of approximately <2 g/l. It also contains very small amounts of sodium sulfide and sodium hydroxide (trace amounts of sodium sulfide, and sodium hydroxide at levels of <0.5 g/l). This results in excessive COD levels in the wastewater, leading to shutdowns of the entire production process. Therefore, I would like to ask the experts what measures can be taken to reduce COD. Currently, **environmental regulations are becoming increasingly strict; on the other hand, we should also do our part in environmental protection. I have thought of some methods, but they are not easy to implement. I hope everyone can give me some advice. The manufacturing process should be simple, and the overall investment and processing costs shouldn’t be too high, otherwise it won’t be worth it. Thank you! !
Are your sodium thiosulfate, sodium sulfide, and sodium hydroxide the COD? May I ask what your COD is, OP? Are they polymers or small molecules? Should sodium thiosulfate, sodium sulfide, and sodium hydroxide be removed?
Based on the water quality you provided, as long as the COD is caused by sulfides, removing those sulfides will enable the COD to meet the standards. Chemical methods are used, along with the formation of sulfide precipitates, to remove it.
Let me talk about my actual situation. I have an oxidation roasting kiln for chromite, and at present temperature measurements are only taken at the rear end of the kiln, as opposed to the areas where the material is being roasted at higher temperatures or in other temperature zones. Due to the sintering of material on the inner walls of the kiln, it is necessary to remove this material mechanically on a daily basis. The kiln is located outdoors, and in such conditions I’m not sure which temperature measurement method would be more suitable for obtaining more accurate results.
There was a mistake in what was posted just now; two windows were opened simultaneously. It was supposed to be a reply regarding temperature measurement in rotary kilns, but it ended up related to COD treatment. Please ask the administrator to delete it.
It appears that the COD of this wastewater is still caused by inorganic reducing substances, mainly sodium thiosulfate and sodium sulfide; in addition, pH adjustment is required for discharge. For purification, air oxidation or physicochemical coagulation can be employed 1. Air oxidation requires a small low-pressure blower and perforated tubes; after aeration, sodium sulfide can be oxidized to elemental sulfur. It is possible to introduce flue gas (containing CO2 to neutralize part of the pH)2. The physicochemical method requires the installation of a chemical dosing unit and a sedimentation tank; wastewater is treated by adding chemicals to form coagulated suspensions, which are then separated through sedimentation. Ferric chloride is recommended for this purpose – liquid form can be used. Ferric chloride has strong acidic and oxidizing properties, and it can form good flocs in alkaline environments. After adding this chemical, the pH value is reduced, and elemental sulfur suspended in the water is separated. To maintain the sedimentation effect, PAM (anionic polyacrylamide) is also needed to assist in sedimentation. I’d like to share some personal opinions; to determine which methods are more effective, comparative experiments are needed. The operational costs of these methods are not high. In cases like yours, wastewater treatment is relatively straightforward, but the pollution level is high. It’s advisable to optimize the treatment process as much as possible given the available costs, as this will be beneficial both for controlling local water pollution and for the long-term development of the enterprise. Don’t wait until the environmental protection agency comes to investigate before looking for solutions.
Thank you to the friend on the 6th floor; I was wondering if you have any experience in this area! I can give it a try to see if this method is feasible and what the processing costs will be. If there are still any issues, I hope to be able to consult you further. Thank you once again!
Theoretically: S2O32- + 2O2 + 2OH- = 2SO42- + H2O; heating may be required (using steam or flue gas), as well as air aeration. A catalyst is needed – copper chloride and cobalt chloride are mentioned in the books, and manganese sulfate seems to work as well too
It depends on your processing volume; if it’s low, just use hydrogen peroxide or potassium permanganate directly! If the volume of treatment is high, aerate it; if the excess isn’t significant, it should work fine
Has that unit on the sixth floor been put into practice? What you’re using is a standard material processing procedure; it doesn’t address the specific issues at hand! Sigh, are there really any water treatment experts here? I’ve been away from this industry for a long time, and now I want to return