Waste Water Treatment process

The rain water as it passes through the atmosphere, picks up dissolve gases. When it comes in contact with the earth, picks up the suspended & dissolved matter. Thus the main impurities in the water can be broadly classified as under :

•  Undissolved suspended solids

•  Dissolved solids

•  Dissolved gases

•  Other impurities.

The water is used in industry or for drinking which requires certain specifications. The above mentioned impurities are removed through various processes and equipment's to give suitable water for each application.               

Filtration for removal of un-dissolved suspended solids :                

This is commonly known as turbidity. The turbidity in the water ranges very widely from as high as 5,000 to 10,000 PPM in rainy season in river water to almost 0 PPM in bore well water. The turbidity can deposit of heating surfaces, strainers, cooling tower fins and cause clogging.

The turbidity removal is achieved through settling, clarification & filtration.           

Micron Filters :

These filters are of various types and capacities. Generally these are used after the above coarse filters so that the life is increased. They come in 50, 25, 10, 5, 1, 0.5, 0.2 and 0.1 micron rating. They are either absolute or nominal type. Nominal means @ 90 – 95 % particulate matter is trapped and absolute means 100 % particles are trapped. They come in various materials like PP, RBC, Sintered, SS etc. The weaving is also different like spun, wound, pleated, grooved etc.

DM Plants :

When the dissolved solids in the water are to be removed, De mineralization is used many times. The DM plant essentially must have minimum two resin columns, Cation and Anion. The cation unit contains resins, which are in H form and Anion resins in service cycle are in OH form.

The filtered raw water, when passed through a two bed DM plant, cation resins exchange all cations in water and the salts are converted to respective acids. This acidic water is passed through the anion resins, which exchanges the anions and the pure water is achieved.

The water coming out of Anion unit generally has following treated water quality:

 Hardness : Nil

Conductivity : Less than 40 micro Siemens

pH : 7.5 to 9.0

The two bed DM plant generally consists of two pressure vessels for accommodating cation and anion resins, nest of valves or multiport valve, piping, chemical tanks, testing kit and conductivity meter.

Dealkaliser :

If the alkalinity in raw water is more, then the degasser tower is used to mechanically remove the alkalinity. This is done by passing the water after cation unit into the tower filled with media and the air is passed by using the blower, so that the water is scrubbed by air and the free carbon dioxide is removed through the vent resulting into alkalinity reduction at the outlet. This considerably reduces the ionic load on the DM plant. However, the cost of tower, sump and SS pump gets added into the system consuming more space & capital cost. The induction of this unit should be justified by the savings of NaOH used for the anion resins.

Mix bed Ion exchanger :

Some of the applications like pharma, high pressure boilers, electronic industry etc. require superior quality than above, in such cases, the mixed bed unit ( MB ) is used to further polish the water. The MB unit consists of two types of resins, cation & anion in the same column. The resins are separated by water during regeneration and mixed with air for service cycle.