A practical open discussion for textile processing
Zero discharge system is meant treating effluent water in such a manner that water having no TDS (total dissolved solid) and free from any impurities. But practically this is not correct since some TDS (total dissolved solid) will be always available in waste water after effluent treatment process. Therefore, the main aim is to recover usable materials such as water and salt from effluent, and; minimize the generation of waste so that it can be safely stored on-site without the need for discharge into the environment it can be reused also. Due to industrial pollution environmental problem may arises in future. Hence this zero discharge concept is serious matter for discussion.
In a textile processing company maximum waste water will contain (In general it may be both dyeing and printing area):-
- Waste dye.
- Pretreatment / finishing chemical and auxiliaries.
- Printing gum, chemical/auxiliaries.
- Electrolytelike common salt/vacuum salt/gaubler salt.
- Other auxiliaries-fixer, soap, sequestering agent, leveling agent etc.
- Other chemical like caustic soda, hydrochloric acid, sulphuric acid --etc.
- Nitrogen and phosphorus related chemical/auxiliaries
Above all waste item maximum impurities we can be remove only- electrolyte (salt) cannot be completely removed. Water will still having some TDS (Total dissolved salt).
Maximum impurities from waste water can be removed by (In general if we are not thinking about cost):-
- By Aerobic and Anaerobic biological treatment plant
- Physico-chemical process like coagulation-precipitation, gravity separation (By treatment with chemical like alum etc).
- Chemical Oxidation using chlorine, peroxide, Ozone etc in the presence of suitable catalysts. In reactive dyeing /printing some unit in Erode (TamilNadu) is using bleaching liquor in waste waster to decolorized dye from waste water.
- Membrame Separation process (Ex-Ultra filtration and reverse osmosis process):-For removal or separation of dissolved salt from waste water.
- Thermal processes like evaporation, crystallization and incineration. For thermal destruction of concentrated streams or evaporator bleed to meet our PCB norms.
- Sludge Dewatering Systems like Centrifuge, filter press, belt press, etc.
- Biological nitrogen removal system.
- Softening plant:-For completely removing hardness from water to get pure water for reusing inside process house.
Selection of a Waste water treatment System operation, process or combination depends on the nature of the Treated effluent water and cost.
Now we are concentrating on dissolved salt in effluent water it can separated/collected by membrane separation system like-Reverse Osmosis systems, Ultrafiltration and Nano filtration systems.
Now Final link of a zero Discharge System is thermal process for thermal destruction of concentrated streams or evaporator bleed solid ex-evaporators, incinerators etc.
Above all discussion we have to select waste water treatment according to nature of our collected waste water to provide a well engineered cost-optimized Zero discharge system.
We have to get best possible combination of subsystems so that it should have low operating cost and simpler operation.