In the production of various catalysts, dyes and chemical intermediates, a large amount of acid-containing wastewater will be produced. Among all kinds of acid-containing wastewater, the treatment of mixed solutions containing organic acids and other organic substances is the most complicated. The organic acid waste liquid can be considered to be incinerated. However, the direct incineration of the waste liquid containing organic acid is more expensive, so the membrane is selected for concentration. After incineration, the COD of the supernatant liquid is reduced to a certain value and then subjected to biochemical treatment.
Due to the high acid content of the material, the composition of the acidic substance is more complex, and the material flocculates, resulting in a large amount of suspended solids. Directly passing through the organic membrane will cause irreversible damage to the organic membrane. Therefore, the ceramic membrane is used to remove the suspended solids, and then nanofiltration and multi-stage reverse osmosis for concentration. This research and development project is to concentrate the organic mixture through multi-stage membrane concentration.
First, the organic acid stock solution was directly processed by ceramic membrane to treat the flocs and then entered into the nanofiltration membrane, and then concentrated by the multi-stage reverse osmosis membrane to investigate the changes in the COD value and pH value of the deacidified solution. After one-stage nanofiltration and multi-stage reverse osmosis membranes are treated, the COD value is significantly reduced, and as the number of reverse osmosis membranes increases, the single-stage reverse osmosis membrane has a significant COD removal rate for organic acids. It is reduced but still unable to meet the requirements of biochemical treatment.
Therefore, on the basis of the above experiment, the organic acid tertiary reverse osmosis membrane clear liquid goes through adjusted pH value treatment. We can add calcium oxide powder and ammonia water to adjust the pH value. After calcium oxide is added, a large amount of solid precipitation is generated in the original solution, which is not conducive to the filtration and removal of impurities by the ceramic membrane. Although the addition of ammonia water will also cause a large amount of flocculation in the original solution, the flocculation is within the acceptable range of the ceramic membrane system, so the solution of adding ammonia water to adjust the pH value is selected.
After adding ammonia water to the three-stage reverse osmosis clear liquid to adjust the pH to be 7, the ceramic membrane, nanofiltration membrane and multi-stage reverse osmosis membrane are concentrated. The experimental results show that under the same operating conditions, the removal rate of COD is significantly higher than that when ammonia is not added. Therefore, experiments can be continued according to this idea to explore the effect of adjusting the pH on the concentration of the organic acid solution.