They plan to try out nano-filtration, multi-effect evaporation techniques

A year after the Madras High Court directed the closure of over 720 dyeing units in Tirupur, the dyers have submitted fresh proposals with the promise of improved technology for achieving zero liquid discharge to be functional again.

“The closed dyeing units have submitted proposals for achieving zero discharge with new and proven techniques. Once all the proposals are in, the papers will be verified with assistance from professors of Indian Institute of Technology-Madras and Anna University-Chennai, over the next few months,” said an official at the Tamil Nadu Pollution Control Board (TNPCB).

If the proposals are found convincing, the dyeing units would be asked to submit a detailed project report and then allowed to operate in a phased manner, initially at 30 per cent of capacity and then at 50 per cent, to monitor if the zero liquid discharge as ordered by the High Court was adhered to, the official said. According to industry sources, the dyers had already invested Rs.800 crore on treating waste water and were paying huge sums as interest but could not achieve zero discharge. The new proposals are based on the governments’ grant of Rs.200 crore for the dyers, official sources said.

TNPCB officials in the know said the common effluent treatment plants (CETPS), to which over 500 dyeing units were linked, were able to treat 85 per cent of waste water but were struggling for want of technology to achieve zero liquid discharge.

“Now, the plan is to try out nano-filtration and multi-effect evaporation to achieve zero liquid discharge in three CETPs,” said a senior TNPCB official.

According to a Central Pollution Control Board (CPCB) report on waste water treatment, nano-filtration could be positioned between reverse osmosis (RO) and ultra-filtration. Nano-filtration can be operated on lower pressure than reverse osmosis and as such treatment cost is lower than for RO. For zero discharge, Tirupur dyeing industry has to look at a multi-effect evaporator instead of the mechanical vapour recompression used earlier, the official said.

In fact, the CPCB had specifically suggested nano-filtration and multi-effect evaporator as technologies to achieve zero discharge in Tirupur dyeing industry way back in 2005. However, the dyers refused to embrace the technology but came up with a marine discharge proposal. “We have rejected the marine discharge proposal asking the dyers to look at technological options to be functional again,” said a senior official.

Before the High Court order, the Noyyal river and ground water survey in Tirupur showed that the TDS (Totally Dissolved Solid) had grossly contaminated the water with levels ranging above 5,000 mg/l (milligram per litre) as against the standard 2,100 mg/l which was a gross violation of norms.

The TNPCB, after a study visit to dyeing units in Gujarat, has suggested nano-filtration membranes.

source: http://www.TheHindu.com / News> States> TamilNadu / by Special Correspondent / Chennai, February 13th, 2012