The hardware surface treatment process produces a wide variety of wastewater, including heavy metals such as copper, nickel, chromium, cadmium, zinc, and organic pollutants such as cyanide, brighteners, additives, etc. These pollutants are difficult to deal with, and reasonable wastewater treatment methods are required to ensure that they are harmless. Several wastewater treatment technologies are described in detail below, including their principles and application examples.
1. Chemical treatment
Chemical treatment technology converts harmful substances in wastewater into environmentally friendly or low-toxicity substances through chemical reactions.
1. Neutralization Law
Principle: By adding acid or alkali, adjust the pH value of the wastewater to the neutral range, so that the harmful substances can be precipitated and precipitated. It is usually used to treat acidic or alkaline wastewater.
Example: Pre-plating pickling wastewater in an electroplating plant is neutralized by adding alkaline substances, and then allowing the precipitated heavy metals to settle to the bottom of the wastewater in the form of hydroxides for subsequent separation.
2. Chemical oxidation
Principle: Oxidizing agents such as hydrogen peroxide are used to oxidize toxic organic substances or heavy metal ions in wastewater to a harmless or more manageable state.
Application: In cyanide-containing wastewater, cyanide is converted to carbon dioxide and nitrogen by oxidation to eliminate toxicity.
3. Chemical precipitation
Principle: Add precipitants, such as hydroxides and sulfides, to the wastewater, so that the metal ions react with the precipitant to form a water-insoluble precipitate to achieve the removal of heavy metals.
Example: In the chromium-containing wastewater of an electroplating plant, hexavalent chromium is reduced to trivalent chromium and then a precipitant such as sodium hydroxide is added to form a precipitate with trivalent chromium.
2. Physical treatment
Physical methods remove insoluble contaminants from wastewater through physical action.
1. Ion exchange method
Principle: Ion exchange resin is used to carry out reversible ion exchange with heavy metal ions in wastewater, so as to effectively remove heavy metals.
Application: Suitable for the treatment of heavy metal wastewater with low concentration and small treatment capacity.
2. Adsorption method
Principle: Use materials with high adsorption, such as activated carbon, diatomaceous earth, etc., to remove heavy metals in wastewater through physical adsorption.
Case: A hardware factory uses activated carbon to adsorb trace heavy metals in wastewater to effectively reduce the content of heavy metals in wastewater.
3. Membrane separation technology
Principle: Selective filtration of semi-permeable membranes is used to separate specific components in wastewater (such as heavy metal ions) from water.
Application: In electroplating wastewater, the heavy metal ions in the wastewater are effectively removed by reverse osmosis or ultrafiltration membranes.
4. Air flotation
Principle: Through the rising force of the bubbles, the suspended solids or oils in the wastewater are adsorbed onto the bubbles, so that they float to the surface of the water and are removed.
Example: For oily wastewater, oil droplets are floated to the surface by air flotation for easy recovery or separation.
3. Biological treatment method
The metabolic action of microorganisms is used to degrade organic matter and certain heavy metal ions in wastewater.
1. Bioadsorption
Principle: Some microorganisms have the ability to adsorb metal ions, which can be removed by binding to metal ions through their cell surface or secretions.
Application: Treatment of industrial wastewater containing small amounts of heavy metals, such as electroplating waste.
2. Bioflocculation
Principle: The flocculant produced by microorganisms is used to aggregate the suspended particles and heavy metals in the wastewater into a larger floc, which is convenient for precipitation or flotation.
Case: In the treatment of printing and dyeing wastewater, the wastewater treatment efficiency is improved by microbial flocculation.
3. Phytoremediation
Principle: Use plant roots to absorb and accumulate heavy metals, transfer heavy metals in wastewater to plants, and reduce water pollution.
Application: Suitable for wastewater treatment in small industrial areas or rural areas.
conclusion
The composition of the wastewater produced by the surface treatment of hardware is complex and usually requires a combination of technologies to be treated. Adopting appropriate chemical, physical and biological treatment methods can achieve effective treatment of wastewater and recycling of resources, and achieve the dual benefits of environmental protection and economy.