What is the principle of treating heavy metals in wastewater?

Heavy metals in wastewater can't be decomposed and destroyed by various common methods, but can only transfer their existing positions and change their physical and chemical forms. For example, after chemical precipitation treatment, heavy metals in wastewater are transformed from dissolved ions into insoluble compounds and precipitated, and transferred from water to sludge; After ion exchange treatment, metal ions in wastewater are transferred to ion exchange resin; After regeneration, it is transferred from ion exchange resin to regeneration waste liquid. In a word, after treatment, heavy metal wastewater forms two products, one is the treated water from which heavy metals are basically removed, and the other is the concentrated product of heavy metals. The treated water with heavy metal concentration lower than the discharge standard can be discharged; If it meets the requirements of production process water, it is best to reuse it. Most of the heavy metals in concentrated products have utilization value and should be recycled as much as possible; Those without recycling value should be treated harmlessly.

Comprehensive measures must be taken to treat heavy metal wastewater. First of all, the most fundamental thing is to reform the production process and not use or use less toxic heavy metals; Second, in the production process of using heavy metals, reasonable technological process and perfect production equipment are adopted, and scientific production management and operation are carried out to reduce the consumption of heavy metals and their loss with wastewater; On this basis, a small amount of low concentration wastewater was effectively treated. Heavy metal wastewater should be treated where it is produced and should not be mixed with other wastewater to avoid complicating the treatment. It should not be directly discharged into urban sewers without treatment, nor should it be mixed with urban sewage to enter sewage treatment plants. If sludge and wastewater containing heavy metals are used as fertilizers and irrigated farmland, the soil will be polluted and heavy metals will accumulate in crops. The heavy metals with the highest enrichment coefficient in crops are cadmium, nickel and zinc, while the heavy metals with the highest enrichment coefficient in aquatic organisms are mercury and zinc.