Zero, Positive or Negative?




Most Pollution Control Boards in India are now insisting that industries meet the directive on Zero Liquid Discharge (ZLD). So is the judiciary.

The idea of ZLD is to not let polluting liquids be discharged into the environment.

ZLD is directed to industries in locations where there is no receiving water body for evacuating the effluents or the receiving water bodies are already severely polluted. We ask for ZLD here as we don’t want to burden these water bodies anymore!

ZLD implies that effluents are ‘contained’ within the plant itself and intake of freshwater for production is minimal or near zero. Hence ZLD is often imposed on industries at locations where there is poor water availability or the neighborhood is a water-stressed area. In most cases, ZLD leads to 90- 92% water recovery, which reduces input water required by industrial processes by as much as 80%.

Sometimes, ZLD is directed as a part of River Action Plans. For example, under the Clean  Ganga Action Plan, industries located in the critical stretches of the river have been asked to be ZLD compliant. All effluents must be recycled to 100%. But is this the right solution? We need to ask.

Normally one would expect that for a ZLD compliant industry, no liquid discharge will emanate from its premises. So if you walked around the compound wall of the industry or
viewed the industry on Google Earth then you should not ideally see any drain flowing out except the storm water drainage which cannot be intercepted. Essentially, the sewage and effluent generated at the industrial plot cannot be released if the industry wants to be ZLD
compliant. Can this be achieved by deep and secured injection of effluents underground? Some industries do that. Should this be permitted?

Unfortunately, there is no operational definition of what is meant by ZLD. If you know one, I will be keen to know.

I have been asking some of the industries in Gujarat about their experience with implementing ZLD systems. Most of them say that ZLD systems were very expensive to  invest in and operate. Accordingly to Sustainability Outlook, a ZLD plant operating at 5 Million Liters per day will incur between INR 500-600 million (USD 4-5mn) in CAPEX and spend INR 15,000-25,000 (USD 250- 400) as OPEX per day. Thus, the treated and recycled water costs will work out to approximately INR 200/kl, while the cost of water extractionfrom the ground or from the municipality would be between INR 30-60 per kiloliter. Consequently you will often see compromises being made in the material specs of the ZLD units to save capital costs. This results in problems of early corrosion, lower life of membranes etc. leading to poor performance, non-compliance and high operating  costs. For ZLD, short cuts on cutting costs don’t seem to work.

The technologies commonly used in ZLD systems such as Reverse Osmosis (RO) and Multiple Effect Evaporators (MEE) are the main energy guzzlers. If we accounted for the consumption of fossil fuels and air emissions arising from pumping, heating and combustion, then on a 3600 evaluation, the ZLD solutions may not be environmentally sound and in fact could lead to high carbon footprints. Further, we cannot forget the challenge of the management of residues (salt and sludges) – costs of residue management (destruction/transport) for a ZLD plant are exorbitantly high!

In this case, it will be interesting to carry out material and energy balance calculations for the ZLD plants. Such evaluations, I am sure must, have been done by industries internally but there is a need for these assessments to be conducted in the style of environmental accounting following a life cycle framework.

These independent assessments should ideally be sponsored by the Pollution Control Boards with outcomes discussed with industries in workshops. Indeed, there is a need to
demystify the ‘good and ugly’ part of the ZLD solutions (You may want to read article by Rajakumari, S.P. / Kanmani, S. titled Environmental life cycle assessment of zero liquid discharge treatment technologies for textile industries, Tirupur – A case study in Journal of Scientific and Industrial Research; 67, 6; 461-467)

Whether ZLD is applicable and relevant for Small and Medium Enterprises (SMEs) is a question. While on individual basis, ZLD for an SME may be almost impossible to achieve, but on a collective basis, SMEs could achieve ZLD. ZLD at the Common Effluent Treatment Plants (CETPs) of Tirupur in Tamil Nadu is an example where effluents are recycled from the CETP back to the member SMEs.

To develop an economical ZLD solution, key strategies are– segregation, chemical/material substitution, process optimization/change for reduction in effluent loads, followed by  selective reuse, recycling and recovery operations. It’s the ‘systems approach’ that is needed. If implemented in the right spirit and rigor, an imposition of ZLD could trigger cleaner production opportunities for the industry resulting into profitability and proactive compliance. In all of the above, the choice of technology (in process in particular) and economics (especially on chemical and water recovery) plays an important role.

Innovations are possible through ZLD. But then these possibilities are not commonly  observed and reported across industries for the purpose of guidance and inspiration. ZLD is often limited as an add-on or a ‘tertiary’ treatment unit. This perception must change  as ‘end of pipe’ driven ZLD systems are often seen as economically unviable over the long run. Unfortunately, most ZLD solution providers focus on the end of pipe approach and so does the industry. Process optimization and process changes followed by recovery &  recycling should be the focus of ZLD systems.

Many a times, we see that the economics of ZLD is not favorable because of the use of certain ‘dirty’ processes and chemicals (salts) and because of the ‘scale’ on which the industry operates. If ZLD is imposed on such industries then the industries would rather shut down instead of attempting implementation of ZLD. When backed by the judiciary, such closures do happen. Some argue that in this process, we achieve the goal of ‘ecological modernization’ to benefit the environment over the long term with the  negative of loss of jobs to the workers! So there is something to gain (positive) and something to lose (negative)

Should a central financing scheme be put in place for implementation of ZLD plants is therefore a question to ponder over. And should such a scheme have components of grants and subsidized loans, especially for SMEs? But will this not go against the ‘polluter pays’ principle?

We badly need a national workshop on ZLD to get all key stakeholders involved. We do see conferences where the focus is ZLD technologies but the policy, economics and the total cost (environmental) accounting perspective are rarely discussed. We need to know  whether in achieving the ‘zero’ in the ZLD, we are creating something negative or positive for the industry, environment and the society.

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For an insightful reading on ZLD visit



  1. In purely environmental terms, in a vast majority of cases ZLD is an oxymoron. The best it can achieve if prescribed selectively with good application of mind is to transfer the Environment impacts to a less sensitive locale.

  2. Prasad,

    Thought provoking blog on ZLD philosophy for industries.

    Needs number of workshops and ‘sharing info’ at places (where it is a legal and statutory requirement) bringing together all stakeholders to do some “Manthan”(churning) and chalk out a balanced way forward.

  3. People working in pollution control business know that pollution control department across the country is notoriously corrupt and industries don’t want to spend money for treating wastes and spending time and energy on effluent treatment research is waste and getting any business from client is very difficult given the fact that various compromises to be met . One gets business only when the unit closes and everyone knows that ETPs are run to get NOC & consent and not for treating effluent .It all sounds idealistic to have workshops and seminar on ZLD which is fashionable word now used and abused by both enforcing department .It is better to have clusters of small CEPTs and enforce regulations on its functioning rather than harassing individual industries who any day do not have skills, interests and money to run ETPs in Indian context .

  4. Dear Prasad,
    Your thought provoking views expressed in this blog are important.. In my view,.it t could be the pollution potential of the waste water which will be of great concern than ZLD.

    FYI: I remember to have witnessed fresh water from Pulp ad paper mill waste shown to us while I was in NEERI in Kolkata. Fresh water from cooling tower was released and that drain water was shown to us for sampling..With my little understanding, I told them this is impossible. Thy showed us State Pollution Board signed reports BOD as 12, 13,and 10 mg/l. I was to lead that team. Professor Nilay Chaudhuri CPCB visited CZL. I discussed with him in details. He was surprised. Later on I never worked on water pollution sampling.

    Coming back to ZLD..

    The concept of zero is absolute and rbased on perfect belief while we all work on partial belief.-the concept which has been brought out by my Guru -Professor Lotfi Zadeh ( 95) in his mathematical theory of fuzzy sets and fuzzy logic. You are correct in your statement that the views of all the stakeholders should be considered in this difficult but important issue. We call this type of exercise as Fuzzy Inference System.
    I congratulate you for a debate on a new debate.

    Ashok Deshpande
    On Visit to UC Berkeley.
    In the company of Professor Lotfi Zadeh in University of California Berkeley CA

  5. Dear Dr. Chaphekar Sir,
    I agree with Dr. Prasad Modak’s views and description.
    It is most essential to define the Zero Liquid Discharge from a particular activity.
    The Capital Cost as well as the Operating Cost for ZLD is very high.
    It is difficult to operate the high temperature Evaporator especially to separate high concentration dissolved salts from effluent.
    The high operating cost adds into the product cost making the sustainability questionable in todays competitive market.
    I have been telling the officials of MPCB, CPCB and also to industry that it is more feasible to optimise and control the resources at the manufacturing process and generate less and manageable waste rather than considering the end of the pipe expensive treatment.
    I have observed at many of the industries in different states that the ZLD is actually practiced by either emitting the water vapour from dryers to atmosphere which carries with it the contaminants or discharging the contaminated bleed from cooling tower to gardening area (cooling tower makeup is effected by using the rejects from RO plant or condensate from Evaporator or treated effluent).
    There is a big business these days to the manufacturing industry of ZLD systems and the authority is getting carried away by their presentations. Industry has to implement the conditions imposed by the authority.
    A very sad situation.
    Best regards,

  6. Dear Sir,

    Could not agree more on the need for 360 degree evaluation. ZLD is absolutely must and as you have pointed out the material and energy balance will more often than not will perhaps will prove that it is not that a promising solution as at appears to be. One technology which I had explored as a part of my assignment in Reliance Pharma was Mechanical Vapour Re-compression ( MVR) which is not very popular as MEE . Unlike MEE , MVR is very energy efficient . I had an opportunity to visit a 2000 KLD MVR system for a very reputed textile mill near Bangalore few years back. It was able to recycle as much as 97- 98 % water.

    In my opinion , instead of forcing ZLD on all and sundry, it should be prescribed judiciously to water intensive industries. One also has to see that the effluents there are lean streams ( like the ones in textiles ) In such cases the technology is feasible. MVR uses specialized polymeric heat exchangers which are susceptible especially to solvents.

    ZLD is kind of In Vouge and almost a fashion. Industrial sectors like synthetic organic chemicals, API , Agrochemicals etc. produce very complex effluents which even with ZLD are difficult to treat. Per kg effluent treatment costs are heavily stacked against the extremely competitive market, and if one forces ZLD down their throats, they sure are going to choke and die.

    I am totally for a national level conference ( or rather a workshop) and ready to pitch in whichever way I can.

    Maybe a joint forum of technocrats , enforcers and stake holders should deliberate and do a industry sector wise analysis ( along with material and energy balance) and come up with a report which will inform the pollution control boards about in which sectors ZLD can really add value.

    We all are grateful to you brining this topic on board.

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