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Zero Liquid Discharge: Treating Effluents as a Resource Stream might be the Way Forward

Zero Liquid Discharge (ZLD) is a series of processes (like membrane filtration, reverse osmosis, evaporation and crystallization) that extract pure water from industrial effluents, leaving behind sludge, dissolved solids, suspended particles and salt crystals. Even though the specifications of various membranes and chemicals used will vary depending on the manufacturing process, a typical Zero Liquid Discharge (ZLD) system consists of the following steps: 
  Figure 1: Zero Liquid Discharge Process Flow
Since ZLD means no liquids are to be discharged from a particular facility, Zero Liquid Discharge (ZLD) systems lead to 90- 92% water recovery, which reduces input water required by industrial processes by as much as 80%.
While the ZLD technology has been available and mandated in industries in Europe since the 1980s, it is still at a relatively nascent stage in India.  This is because ZLD systems are associated with prohibitive costs and are implemented usually as a result of legislation both in India and globally. A ZLD plant operating at 5 Million Liters per day will incur between Rs. 50-60 crores (USD 4-5mn) in CAPEX and spend Rs. 15,000-25,000 (USD 250-400) as OPEX per day.1,2 Thus, the treated and recycled water costs approximately Rs. 200/kl, while the cost of water extraction from the ground or from the municipality would be between Rs. 30- Rs. 60/kl.
More than 90% of this operating cost is incurred during evaporation, which is a very energy intensive process. This is because, after various stages of filtration, chemical treatment, and separation of water from chemicals following Reverse Osmosis (RO), the RO Reject is first evaporated and then condensed to recover the water.  

Drivers of ZLD implementation and adoption in India

The primary drivers of ZLD, both internationally and in India have been compliance regulations. Mandates are given by the court or regulations are formalized by the Pollution Control Boards (PCB) at the Centre and State level (e.g.: ZLD being a mandatory requirement for a renewing a factory’s License to Operate). Other policy interventions like subsidy schemes also increase uptake of ZLD.
ZLD in India has been successfully implemented in Tamil Nadu, where the High Court mandated that all dyeing and bleaching units, as well as tanneries and distilleries need to achieve zero discharge of industrial effluents in order to remain operational. Other states like Gujarat, Rajasthan, Andhra Pradesh and Punjab too have encouraged the uptake of ZLD by various mandates. (See Box 1 for details)
However, the impressive success of ZLD implementation in Tamil Nadu has been attributed not just to the presence of laws, but also their strict enforcement by the state PCB (Pollution Control Board). Real-time monitoring of input and output pipes through ultra-sonic water meters as well as frequent inspections by ‘flying squads’ have led to a very high level of compliance in Tamil Nadu. Nevertheless, even though the first Public Interest Litigation (PIL) against dyeing units in Tirupur was filed in 2003, it took 8 years for the manufacturing units to start taking concrete steps.

 Figure 2: Timeline of ZLD Legislation in Tirupur, Tamil Nadu

Assessment of the root cause for such mandates indicates that the actions taken by the state pollution control boards and courts was driven by increasing water scarcity and deteriorating water quality which led to protests by local farmer communities in various areas. This ultimately led to courts directing the most polluting industries to set up ZLD systems. In other cases (like in parts of Andhra Pradesh), the polluting industries were asked to compensate farmers for the loss of productivity in their lands due to poor water quality. In such cases, many industries opted to implement ZLD rather than continue paying the farmers directly in the future. 
States that have so far promulgated legislation on ZLD are the ones where the ground-water level is considered to be either Over-Exploited or Critical or surface water is not replenished seasonally by the melting of snow and glaciers. This is primarily because in the case of rivers where surface water and consequently, ground water is seasonally replenished, the effect of toxic pollutants is significantly diluted and adverse environmental impacts take years to be revealed. 

Industries and Regions Most Likely to Require Mandatory ZLD in the Near Future

The regions that are most likely to be affected by Zero Liquid Discharge legislation in the near future would include the areas worst affected by industrial water pollution.

The Central Pollution Control Board (CPCB) surveyed 88 industrial clusters in the country and determined the level of air, surface water and land (ground water) pollution of those clusters in 2009.

As per the most recent CPCB Report (2013), 15 of these clusters have critical levels of surface water pollution, 5 have critical levels of ground water pollution and 3 have critical levels of both surface and ground water pollution (Figure 3). 

Out of these 23 clusters, 15 lie in regions where there is scarcity of ground water which indicates a greater need for water conservation and treatment in these 15 regions.


Figure 3: Clusters with 'Critical Levels of Surface and Ground Water Pollution' and level of ground water in the corresponding districts; Sources: CPCB 2013 Interim Report, Central Water Board’s Ground Water Assessment, 2013
ZLD and the Ganga Rejuvenation Plan

With India’s Ganga Clean-up Project, there is a very real possibility that ZLD may be mandated in factories in the Ganga Basin. The industries which release effluents with very high COD (Chemical Oxygen Demand) and TDS (Total Dissolved Solids) like Tanneries,Sugar Mills, Distilleries, Dyeing & Bleaching units, Pulp & Paper units and Food & Beverage plants  would be first in line to bear the brunt of new compliances regarding ZLD that may come into effect (Figure 4).  
An assessment of the 972 polluting units in the Ganga basin as per CPCB shows that tanneries in Uttar Pradesh, particularly near Agra and Kanpur are likely to be the initial target of ZLD regulation.  However, the government’s timelines for realizing these plans are still unclear.

The Way Forward for ZLD in India

Addressing cost Challenges with Existing ZLD systems

While going ahead with plans for implementation of ZLD in polluting industries, it might be beneficial to look at challenges currently being faced by existing ZLD systems in the country. 

Due to the high cost of ZLD systems, units often choose to implement some of the cheaper options available. However, this may have recurring adverse impacts on business. One of the most significant issues plaguing plants in Tirupur today is the maintenance of ZLD systems. If the ZLD system is underperforming or shut, factories have to operate at lower capacity or stop operations. 
Mr. Deepak Kachru, General Manager of Aquatech Systems Asia  (Indian subsidiary of Aquatech International Corp, a global provider of ZLD technologies), corroborates this sentiment. “There is a difference in the kind of ZLD systems that are popular in India and ones that are used globally. Cost is a big driver for ZLD in India. High Capex and operational costs, as well as high energy consumption influence Indian businesses towards less reliable low cost options. Globally, particularly in the more mature developed economies, ZLD systems are built to be robust and long-lasting, since they come without standby and the main plant has to be shut down if the ZLD plant isn’t working. ZLD systems are prone to rust attacks and this can be combated by using alloy metals, which are often much more expensive”, says Deepak Kachru. He believes that as the ZLD market in India matures and compliance becomes mandatory, we will be moving towards the more robust and reliable ZLD systems.
There is also the issue of dealing with the highly toxic rejects of a ZLD plant. Presently in Tamil Nadu, there are designated landfill zones (away from the industrial centers) for disposal of the salt. Not only does this increase the cost for the manufacturers because they have to store the salt (often for up to a year) before transporting it to far off locations, but this also does not resolve the issue of waste disposal. At best, this is a temporary solution until better methods of waste disposal are determined. Environmental experts suggest that it is perhaps time to move away from Zero Liquid Discharge to Zero Waste Discharge. 
Fiscal incentives to promote ZLD
A way to mitigate the high costs of ZLD would be to incentivize implementation through fiscal benefits. Government could play a key role to subsidize the initial capital expenditure of ZLD systems through various schemes. As per Mr. Kachru, Aquatech, the benefit from accelerated depreciation of effluent treatment and recycling systems, along with some other tax sops, will encourage ZLD implementation amongst Indian businesses. He also suggests the use of Green Stamps in products to encourage consumers to move towards sustainable consumption which would in turn give industries added incentive to take up such resource sustainability initiatives.
View Effluents as a Resource Stream, not a Waste Stream
Ms. Sandra D’Sa, General Manager, Marketing of Geist Research Private Limited says “the key is to change the mindset to view the effluent not as a waste stream, but as a resource stream. It is equally important to view the ZLD process as a part of the manufacturing activity rather than an ‘end-of-the-pipe’ process. The saving in the cost of treatment then actually adds to the profits”. Geist Research offers innovative technology platforms that enable recovery of a large number of chemicals in their pure form from a wide variety of industrial effluent streams which can be recycled or sold. The cost of recovery is typically 15-50% of the price of the chemicals recovered, and thus says Ms. D’Sa, "it is possible to convert ZLD into a profitable activity. The payback period varies between a few months to less than 2 years”. Geist’s solution is applicable to primarily chemical processing industries. Some of their clients include bulk chemicals, non-ferrous metallurgy, APIs, dyes and pigments, agrochemicals, tanneries, specialty and other chemicals, petrochemicals, etc. 
Simultaneously, efforts are also being made by researchers to recover the energy from the evaporation process (the energy cost for evaporation accounts for over 90% of the operational expenses of ZLD), which too would make ZLD much less expensive. 
Thus innovative technologies which give tangible short-term business benefits  coupled with strict enforcement of regulation is the need of the hour to promote the uptake of ZLD systems and enable businesses to adopt more environmentally sustainable waste management practices.


Author: Sustainability Outlook