Zero Liquid Discharge (ZLD) in Industrial Wastewaters in India-Need for Sustainable Technologies and a Validated Case Study

ABSTRACT

Man needs Roti, Kapada and Makan (Food, clothing and shelter). The Kapada needs to be coloured else dirt shows up instantly and this results in residual colour and salt often in effluents. None of the individual effluent treatment plants (IETPs) or common effluent treatment plants (CETPs) in India have ever publicly staked a claim to their consistent ZLD achievement. It is all traceable to the famous Murphy’s Law which says “If a thing can go wrong, it will” The textile industries of world’s knitwear capital at Tiruppur in India are now languishing with only 30 % of installed production being permitted and that at Karur in India, another big capital of rugs having been totally closed down and the situation is other centers in Gujarat, Rajasthan, Maharashtra heading towards the similar fate. It is almost the same tale in the tannery sector. The bulk of CETPs are along the Palar River in the south of India. This monsoon dependant river has overland flows only for a couple of weeks in a whole year. The discharge of unsalted effluents all along has effectively closed down some of the intake wells in the river bed which were supplying drinking water to many towns. The UNIDO demonstrated a pilot plant for soak liquor evaporation by thin film spreading on roof top structures and spray systems finally culminating in solar ponds but then the USTDA which later on made a DPR for the ZLD of tannery CETPs and the PCB did not give weightage to this and perpetuated the thermal evaporators. The simple issue is while the pre-treatment of effluents by biological, chemical and membrane technologies for a true ZLD have been almost standardized it is the reject waters with salt concentrations and colours which are the problem. These are treated more in lapses or surreptitious discharges than concordant performances of salt-liquid separation and containment. A three phase mass transfer technology of falling film on drapes hung from a crib and cascading the reject effluents has been demonstrated by the Zuckerberg Institute for Water Research, Ben Gurion University and Middle East Desalination Research Center (MEDRC) as early as 2004 in Israel and the United Nations Industrial Development Organization (UNIDO) has demonstrated in field scale a non-mechanized nature based spray technology here in India way back in 2006 and, but still the thermal mechanized non-sustainable evaporators are being forced down on the industry by the Pollution Control Boards (PCBs) possibly driven by the marketing by the vendors. Written in this background, this article brings forth the validation of a modified falling film technology demonstrated on textile spent dye bath and another on reverse osmosis (R O) rejects. Whether this will pave the way for a renaissance and resurrect the industry or go the same way of the other earlier attempts is for the time to tell in the future. The author has the satisfaction that at least his Ph D work has resulted in this validated and sustainable option.

KEYWORDS: Closure of Textiles and Tanneries by Courts, ZLD, R O Rejects, Net Evaporator, Three phase mass transfer, Evaporation Index, O&M cost, Sustainable, MEDRC