The drive towards ZLD

Zero Liquid Discharge (ZLD) is an ambitious goal for process manufacturers – achieving the target of eliminating liquid waste from industrial processes is currently expensive and requires a significant amount of energy - but it’s one that growing numbers are starting to prioritise.

We’re seeing interest around ZLD grow in the life sciences sector in particular but it’s also gaining traction in advanced manufacturing too.

The process industries in general, including food and beverage, and chemicals, have always been water intensive due to the amount of heating (including sterilisation), cooling, cleaning and dissolving that takes place. And this results in large amounts of sometimes hazardous water waste that needs to be disposed of in a responsible way.

Top benefits of ZLD

Before we look at how businesses could achieve ZLD, let’s look at some of the benefits.

ZLD promotes the transition to a circular economy by eliminating water waste. Instead of being discharged from the facility, water is purified for re-use, and what’s left is dried and evaporated to recover the solid waste. This solid waste, which includes salts and chemical compounds, which are typically disposed of safely, could open up opportunities to be reused, recycled or sold for other uses.

At a time of water scarcity, which has resulted in droughts around the world, ZLD could mitigate the impact of climate change and ensure the future of freshwater supplies. Another benefit, of course, is that it reduces contamination of our waterways, safeguarding the watersheds and ecosystems close to manufacturing sites. With public pressure growing, and regulation tightening, ZLD initiatives provide the ‘social license’ firms need to operate.

What does it involve?

As stated in our latest report, Water Stewardship: Trends and perspectives within the global process industry Water stewardship | Download the report here! - NIRAS, the processes involved in ZLD are very similar to the ultra-pure water treatment of treated wastewater effluents.

The difference is that ZLD plants include a water evaporation stage, so the final product isn’t just quality water that can be used again. It also includes solid waste, often known as ‘sludge’. This solid waste might be recycled – for example, as fertiliser in agriculture. However, where waste needs to be disposed of, a sanitary landfill is more environmentally friendly than discharging liquid waste into waterways.

Ultra-pure water production involves a number of treatments – including pretreatment, demineralisation and polishing. Pretreatments tend to include membrane filters and ion exchange, while demineralisation is often reverse osmosis, multi-stage flash distillation or cation/anion exchanger. Polishing removes the salts and dissolved substances.

Finally, there are the steps that make ZLD distinct from ultra-pure water production. Waterwater goes through a drying and evaporation process to produce the solid waste.

Overcoming the barriers

At first sight, ZLD seems like a win-win for businesses. It’s ethical and ensures the plentiful supply of water that process manufacturers depend on.

But despite the benefits, ZLD – like zero carbon – isn’t easy, and you have to be careful that it doesn’t impact other sustainability goals.

Like other types of processing, it’s often more energy-intensive to treat the water than it is to use fresh water. Changing your existing processes can be prohibitively expensive too, as can disposing of potentially toxic solid waste in sanitary landfills. While it may be  possible to recover at least some of these costs in the future by selling the byproducts, the ROI may not add up on paper.

Like any investment in sustainability, it’s important to look at the financial ROI of ZLD as well as the long-term social impact, including the social license to operate in the future.

There’s no doubt that, with innovation and optimisation across the industry, ZLD technologies and targets will become an increasingly attractive opportunity for businesses across process industries.

Until that becomes a reality, the starting point for any water stewardship initiative should be a full audit of your current water usage and waste to identify areas for optimisation.

Using the 4Rs – Reduce, Reuse, Recycle, Rethink – as a strategic framework allows you to first see whether you could reduce overall consumption by making processes more efficient, therefore reducing both costs and waste. Simple measures, like detecting and repairing leaks and implementing better practices, mean the volume of waste requiring treatment is lower.

With challenges around water scarcity increasing globally and rising regulatory and social pressure for corporations to reduce the risk of drought and contamination of waterways around manufacturing facilities, making ZLD an achievable and realistic approach for more businesses should be a focus for the entire sector.

Download our free guide, Water Stewardship: Trends and perspectives within the global process industry Water stewardship | Download the report here! - NIRAS, for expert insights and practical tips on how to get started.