At an export centre housing several hundreds of textile bleaching & dyeing units producing hosiery and knitwear, water requirements were met by tanker water supplies from a cluster of open borewells in and around the area. The cost of the tanker water supplies was around Rs.50 to Rs.60/cu.m. Common Effluent Treatment Plants (CETPs) were constructed to treat effluent discharged from the individual dyeing units.
After primary treatment for colour removal, the treated effluent was being discharged into a river, polluting it and turning it unfit for agriculture and domestic uses. Discharge of the high TDS effluent into the river and subsequent percolation into the water system had also affected ground water quality. In view of this, the textile units were directed by the court to implement zero liquid discharge. Another problem they faced was disposal of the huge quantity of sludge produced due to the physico-chemical process used for colour removal.
Around 80 of these bleaching and dyeing units form part of this case study.
Ion Exchange carried out extensive pilot plant studies to identify the right solution to overcome the problems faced by the textile units. Based on trials, a treatment scheme was designed for a 10 MLD zero discharge plant. The plant was designed, engineered, constructed by Ion Exchange; we also undertook its comprehensive operation and maintenance.
Inlet and outlet characteristics were as follows.
|TDS - 8000 to 9000 ppm
||TDS - < 200 ppm
|Silica - 40 ppm pH - 7.5 to 9
||Suspended solids - Nil
|BOD - 100 – 200
||BOD - Nil
|COD - 300 – 800
||COD - < 5
|Colour - 3000 Hazen units
||Colour – Nil
FINAL SCHEME SUGGESTED FOR ULTIMATE CAPACITY PLANT
- The system uses advanced biological process of membrane bio-reactor to remove colour and organics, avoiding the use of chemicals like Lime/FeSo4 which are difficult to handle
- Capacity of the zero discharge effluent treatment plant is 10 MLD. 89% of the feed water is obtained as fresh water, of quality much better than raw water quality available. It has TDS of 200 ppm as against 1500 ppm of tanker water. This improves the quality of dyeing and also saves costs on fresh water
- Around 10% of the feed water is also obtained as pure brine solution as nano permeate which can be used for the dyeing process