PHYSICAL AND CHEMICAL WASTEWATER TREATMENT METHODS

1. Wastewater treatment by physical (mechanical) methods

Used to separate insoluble substances and part of the colloidal substances from wastewater. Physical treatment units include:

• Bar screens and strainers: used to retain large debris (paper, plastic bags, vegetation, litter, etc.)
• Grit chambers: separate inorganic impurities with a high specific weight (such as coal slag and sand) from wastewater
• Settling tanks separate suspended solids whose specific weight differs from that of the wastewater. Heavy suspended solids slowly settle to the bottom, while light suspended solids float to the surface.
• Oil and grease skimming tanks: commonly used when treating wastewater that contains oil and grease
• Flotation is commonly used to remove suspended solids and to thicken biological sludge
• Equalisation tanks keep the flow and the concentration entering the treatment works stable, overcome operating problems caused by fluctuations in wastewater concentration and flow rate, and improve the efficiency of biological treatment processes.
• Filters separate small suspended waste by passing the water through a layer of filter media (used mainly for certain types of industrial wastewater)

Physical wastewater treatment can remove 60% of the insoluble impurities and 20% of the BOD from the water

2. Chemical treatment methods

This involves adding a reagent to the wastewater so that it reacts with the impurities, chemically transforms them and forms a settleable precipitate.

It is commonly applied to treat industrial wastewater. The methods include:

• Neutralisation: used to bring wastewater containing inorganic acids or alkalis to a neutral state (pH = 6.5–8.5)
• Coagulation: used to clarify and decolourise wastewater by using coagulants (alum, PACN, etc.) and flocculant aids to bind suspended solids and colloids in the water into large flocs.
• Ozonation: a method of treating wastewater that contains dissolved and colloidal organic substances using ozone.
• Electrochemical method: used to destroy toxic impurities in wastewater and to recover valuable substances (copper, lead, iron, silver, etc.) through electrochemical oxidation on electrodes.

Businesses interested in physical–chemical treatment solutions are welcome to contact NGO on +84 24 7300 0890 or by email at office@8ngo.com for direct consultation.

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