Control of cyanides and sulfides in ammonia-vaporized wastewater
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The levels of cyanide and hydrogen sulfide in the ammonia-vaporized wastewater have been above the allowed limits, and the cause cannot be identified. The COD level in the wastewater is around 3500 mg/l, while the ammonia nitrogen level is between 260 and 290 mg/l. The pH value ranges from 9.5 to 9.9. Reducing the pH value leads to a decrease in cyanide levels, but the ammonia nitrogen level then exceeds the allowed limit (which should be below 300 mg/l). The sulfide level is around 500 mg/l. I hope the experts here can offer some guidance!
Reduce the pH value; look for the cause in the ammonia evaporation process.
The COD of the ammonia vaporization wastewater is not high, but the ammonia nitrogen level is high. Could this be due to issues with the control of the ammonia vaporization process – such as insufficient steam supply, or changes in the temperature and pressure at the top and bottom of the tower? How much cyanide do you have?
Cyanide and hydrogen sulfide should exit at the top of the tower; your ammonia nitrogen level is also high, which may be due to issues with the ammonia evaporation tower or the tower itself. Check whether the temperatures and pressures at the top and bottom of the tower are within the specified ranges. If that doesn’t work, open the tower to check for any damage or blockages in the trays (to determine whether this condition has been present since the equipment was put into operation or is a recent development; if it’s a recent issue, examine the temperature and pressure parameters before and after the change). If this continues, it might also be a problem with the design and manufacturing of the device).
If too much alkali is added, just lower the pH value
The COD level of the wastewater is not high; it’s necessary to check how much the control parameters and production metrics differ in the ammonia distillation tower – specifically, the temperature at the top of the tower, the amount of alkali added, and the pressure at the top of the tower
The pH value cannot be reduced; it’s better to find out the cause in the ammonia vaporization tower
Thank you all for your help; the problem has been resolved now. It is due to severe blockage of the trays in the ammonia vaporization tower; the top 2 layers have been severely corroded and can no longer be used. The outsourced construction team tried to clean the trays of the ammonia vaporization tower, but they were unable to do so; in the end, we had to remove them layer by layer, clean them, and reinstall them ourselves. Currently, the ammonia nitrogen level in wastewater is ≤100 mg/l, and sulfurides and cyanides are also under stable control. I hope my method can help everyone solve the problem of ammonia-containing wastewater. Thank you!
Lowering the pH and raising the top temperature of the tower will be effective