| In the process of rapid urbanization and industrialization, in Shenzhen, the current situation of heavy metal deposition in the rivers and coastal waters is not so optimistic.The contradictions between the heavy metal pollution and the development of economy is increasingly sharp, only controlling the discharge of heavy metal wastewater has not reached the requirements of environment on the pollutant total amount control any more. How to control the total discharge under ensuring the heavy metal wastewater emission on standard has become an urgent need. Flocculation process in heavy metal treatment has been occupied an important position, but the traditional neutralization precipitation flocculation technology in the treatment of electroplating wastewater has its big shortcomings, such as poor impact resistance, high sludge production,low processing efficiency, major heavy metal content fluctuation et al. In order to improve the traditional flocculation process, and considering the high cost of ballasted flocculation magnetic technic and sand loading process at the same time, this experiment uses the ballasted flocculation-sludge return process to treat the electroplating wastewater.Through the lab trials and pilot test, the ballasted flocculation process is proved to have better treatment effect than traditional flocculation process in the treatment of electroplating wastewater, besides, the turbidity and heavy metals contents are lower in ballasted flocculation process.The study adopts four kind of coagulant:aluminum sulfate, PAC, PFS and ferric chloride, and uses PAM as coagulant aid. From the angle of turbidity, heavy metal content and the sludge sedimentation performance, the experiment explores the factors’effect on the flocculation process respectively, which include pH, coagulant dosing quantity, coagulant aid dosing quantity, settling time, return flow influence factors.Finally, we find out the optimum coagulant in treating electroplating factory wastewater and then apply it to the pilot test on site. Based on the results of lab trials and pilot test, the two kinds of process can be compared on the treatment effect and the ability to adapt fluctuations in raw water. What’s more, we also make certain theoretical explanation aiming at experimental phenomena.From lab trials, we get some results:the optimal flocculation pH value of zinc is19.5-0, copper is9-9.5, while the mixtures’optimum pH is in the vicinity of9.5; Four kinds of coagulant dosing quantity decreases with the increase of heavy metal ion concentration in the solution, and different solution has different optimum coagulant dosing quantity; Along with the increase of the concentration of heavy metals,more colloids which is taken off the stability are formed after joining coagulant, therefore, it needs more coagulant aid to add the adsorption bridging role; Compared with aluminum salts, the floe sedimentation performance caused by joining iron salts is better, however, it plays a worse role on removal of turbidity; Under the best flocculation conditions of the chosen four kind of coagulants in lab trials, ferric chloride has wider coagulant dosing range and better treatment effect in the ballasted flocculation process than others, of the optimal treatment effect, for this reason, we chosen ferric chloride as the coagulant used in the pilot test.According to pilot test results, we can make some conclusions:the ballasted flocculation-sludge return process has better treatment effect compared with the conventional technology, the concentration of Cu and zinc in effluent was only47.8%and57.1%of the conventional process; even when the quality of inflow water is volatile, loading process still can guarantee good effluent quality with low turbidity and heavy metal content. It has stronger ability to adapt to fluctuations in inflow water quality. In pilot run, it is found that alkaline pool has its best alkaline pH, when the alkaline pH is near10, the treatment effect is the best. |
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