Textile industry and water treatment

The textile industry is very water intensive. Water is used for cleaning the raw material and for many flushing steps during the whole production. Produced waste water has to be cleaned from, fat, oil, color and other chemicals, which are used during the several production steps. The cleaning process is depending on the kind of waste water (not every plant use the same way of production) and also on the amount of used water. Also not all plants uses the same chemicals, especially companies with a special standard (environmental) try to keep water cleaned in all steps of production. So the concepts, to treat the water can differ from each other.

Water treatment with different kind of pollutants, is large-scale, because of many cleaning and removing steps involved.

The diagram above shows a general overview over the several steps in water treatment in the textile industry.

Screening, straining

This first step of treatment is to remove small particles from the process water. In this way the water will cleaned from fibres, fluff and cotton flock. Fore these filter steps drum- and bag filters are used.

Oil removal (if required)

If during the step of wool treatment, solvents like white spirit or others are used they have to be removed from the waste water. Membranes or oil removers are useful. Because of oil or other organic solvents in the water, microorganisms can be killed.

Homogenization

This step is useful to mix the water. With this step, the pollution is better distributed. That makes it more easy for microorganisms to treat the water. Result is a more effective biological cleaning step.

Neutralization

After homogenization, the solution has a pH of around 9 to 10. Neutralization of the water can be done by acid or air flow injector depending on the pH value.

Physical- chemical- treatment

If the concentration of dissolved solids is very high (sulfides, chromates, etc.) and/ or color is also in the water, the kind of treatment is various.

Possible are the following procedures:

catalyzed oxidation of sulfides
flocculation
decoloring with flotation

Biological purification

The type of biological treatment depends on the concentration and kind of pollutant. Two biological steps are used:

trickling filter

The construction is a great reservoir, which is filled with plastic “pieces”, crushed siliceous rocks or other materials which have a very large surface. The large surface gives microorganisms an easy chance to grow. The trickling apparatus sprinkles the waste water over the loaded material. Air is blowing into the pool from top or from below to give the aerobe bacteria the right living conditions. With the growing of the bacteria the biologic dismantlement particles in the waste water will be treated.

This easiest step of biological treatment is reducing the BOD₅ between 50 and 70%. A disadvantage is a very good filtrated water without particles which could clog the spray nozzles. Depending on this fact a flocculation process before trickling is necessary.

activated sludge

With this kind of procedure the waste water does not have to be flocculated because the bacteria live in the sludge. The principle is easy, waste water is filled into a pool where the bacteria are living. By a fan air is blowing into the water to give the aerobe bacteria the right growing conditions. The sludge, together with the bacteria are the activated sludge. BOD₅ removal rates reach 90 to 95%.

To dump the sludge, it has to be thicken. This can be done by different procedures, depending on the amounted sludge, which have to be dumped.

De-inking

If it is necessary this last step of treatment will remove the color by oxidation, adsorption or other procedures.

Find information about Water recycling in textile industry