WTP typical sequence

Sedimentation

Filtration
 

Receiving waters may be:

• Rivers, lakes or sea
• Sewers, which convey the treated wastewater to a centralized unit, usually a biological type
• On the ground surface.

Discharge limits, set by appointed authorities, usually depend on the type of receptor and local restrictions.

A chemical-physical WTP removes pollutants through chemical reactions and physical separation processes.

Both for technical and economical reasons, not all pollutants may be treated in chemical-physical plants.

A chemical-physical plant’s main process is based on the precipitation of water pollutants as insoluble compounds.

There are several precipitation processes, such as:

Ø  Formation of metal hydroxides

Ø  Formation of metal sulfides

Ø  Formation of insoluble products of Calcium

The precipitation is related to the product solubility (Kps) of the specific substance.

Not all pollutants generate insoluble compounds, amongst which:

• Boron
• Chlorides
• Nitrates
• Nitrite
• Ammonia nitrogen
• Chromium VI
• Cyanide complexes
• Organic complexes

Untreatable pollutants, unaffectable by physical-chemical processes, should originally be kept within the limits of discharge or should be segregated from the main stream for separate treatment and disposal.

Precipitated pollutants produce a slurry (Sludge) which must be disposed of through specialized companies.

A chemical-physical treatment plant usually includes the following sections:

1 ) Individual pre-treatment of certain substances to make them suitable for the following common treatment with a Standard Chemical-Physical Treatment unit:

1. Chromium VI reduction,
2. Cyanide complexes oxidation,
3. Organic complexes specific treatment
4. Other

2 ) Coagulation

3)  Neutralization

3 ) Flocculation

4 ) Settlement (separation of the precipitate from the water)

5 ) Final purification of clarified water

6 ) Sludge treatment

CASE STUDY

   CYANIDE OXIDATION

   CHROME VI REDUCTION

   PRECIPITATION