The role of new wastewater treatment technology in your ZLD strategy

Zero Liquid Discharge (ZLD) has always been the ‘holy grail’ of wastewater treatment. Now it’s becoming a reality for many industries, thanks to new technology.

Zero Liquid Discharge Water Treatment

It sounds like an impossible dream, doesn’t it? Like perpetual motion, or a week in England without rain, it’s just not possible. Or is it?

Well, ZLD (zero liquid discharge) is here and some companies are already starting to reap the benefits. For water highly polluted by some recalcitrant compounds it has been a technical challenge. However, a combination of maturing technology and rapidly increasing water prices is starting to make ZLD, or at least working towards it, a board room goal.

Before we look at the latest technology trends to assist companies in their quest for ZLD, let’s take a step back …

Water Conservation

Water poverty is on the increase. The fact is that water – something that we used to take for granted – isn’t as easily accessible as it used to be.

That’s because water is a finite resource and the combined factors of pollution, global warming, population growth and increased urbanisation in many parts of the world have now all come together to create water scarcity.

Global warming is upsetting weather trends with more droughts in some places and more floods in others, leading to ‘feast or famine’ conditions – often in places that can’t cope with either.

All this is leading to Water Poverty – currently at its worst in Southern Europe and Asia but becoming more prevalent in many other parts of the world.

And on top of the climate issues, the increased demand for water in industry and by a growing population has led to not only a more complex water profile for water companies to clean, but also more volume to deal with. Both issues have led to price rises, certainly in the UK.

Rising Costs of Water

But the UK is not alone – many other developed nations are in the same boat (figuratively) with water conservation issues, attempting to patch up legacy systems designed for half the amount of people and a lot less industry.

So today, it makes sense to recycle and reuse as much wastewater as possible, for two reasons:

1. Environmentally, we’ll all help the planet and earn favour with our customers and the public for being more environmentally responsible.
2. Financially, industries will have to eventually accept that fresh water will become a lot more expensive – and in some places supplies may become unreliable, potentially curtailing production capacity too. Additionally, regulations are likely to be just around the corner limiting even more what can and can’t be contained in discharged wastewater.

So there’s going to come a time when recycling more wastewater and potentially Zero Liquid Discharge becomes the obvious and responsible course of action – from everyone’s viewpoint.

The Problem with Current Water Treatment Technology

Historically, most wastewater ‘recycling’ was carried out by municipal water companies. This was a simple process incorporating first mechanical filters to remove debris (what the industry euphemistically called ‘logs and dogs’) and then settlement tanks and/or biological aeration to remove remaining solids. The water was then passed back into watercourses.

So for years – ever since the industrial revolution really – industrial and domestic wastewater containing all sorts of poisonous chemicals was essentially poured back into the sea.

But midway through the twentieth century it become obvious that a lot of dangerous chemicals were in the water but passing straight through municipal water treatment plants. So from the 50s and 60s, regulations have slowly evolved to limit the number of pollutants in water being discharged.

Nowadays, some municipal water treatment plants do rather more, but worldwide it’s been proven that antibiotics poured down the drain are causing AMR; endocrine disruptors from other medications in sewage are causing damage to marine life and PFAS are now a cause for concern and being banned in many countries. Only a small percentage of these and many other recalcitrant pollutants are currently removed by municipal treatments.

As a result of discharge regulations, many industries are now obliged to either tanker wastewater away for off-site incineration or treat their own wastewater on-site. 

Incineration creates even more pollution and merely kicks the can down the road, as the pollution simply becomes someone else’s problem.

On the other hand, on-site treatments can be fraught with COSHH issues due to the handling of harmful chemicals such as ozone. Water recovered may only be suitable for wash-downs or discharge to the sewers rather than being a valuable resource to be re-used.  

Also, in many cases, on-site treatments don’t go far enough. The really damaging pollutants are often not effectively removed by ‘legacy’ water treatments like anaerobic digestion, RO (reverse osmosis) or even ozone treatment. These traditional water treatments have been used for years but were never designed to remove the Persistent, Bioaccumulative and Toxic (PBT) chemicals which are the result of modern manufacturing.

Many recalcitrant compounds can only be effectively removed from wastewater using the next generation of water treatment technology.

Electrochemical Oxidation of Wastewater

Over the last ten years, the effectiveness of electrochemical oxidation has been proven to be extremely effective in removing many recalcitrant compounds and pollutants from wastewater.

Although electrochemical pollutant removal is not a new concept, scientists have found that careful tuning of electrical currents and of various component parts (including the materials and coatings of the electrodes) can combine to deliver outstanding results.

The technology is now being used in a wide variety of installations worldwide in the following sectors:

• Life Sciences
• Agrochemicals
• Speciality Chemicals
• Battery Recycling
• Waste Management
• Aquaculture
• Utilities

A further development of this, primarily to remove recalcitrant organic compounds in water has been introduced and patented by Arvia.

This hybrid system uses proprietary media inside the treatment reactor, trapping pollutants onto its surface by adsorption. Then as an electric current passes through this media, it destroys the pollutants, reducing them to harmless gases and water. At the same time, the media is renewed, ready to continue remediation without interruption.

In summary, the two related techniques of electrochemistry and adsorption with electrochemistry are both truly effective for the removal of many chemicals used in agriculture, aquaculture, battery recycling, chemical ingredients, corrosion inhibitors and pharmaceuticals.

In tests, concentrations below measurable levels have been recorded after treatment. 

Additional benefits of electrochemical water treatment systems include:

• No tip-ins: Dosing with hazardous chemicals is not required
• Can be placed upstream of existing processes, improving performance and reducing costs
• Low power consumption and instant-on operation
• Supplied in a variety of reactor sizes to treat at source
• Low maintenance
• Minimal staff intervention
• No sludge produced

Zero Liquid Discharge Water Treatment

Electrochemical or combined adsorption and oxidation systems as described above cannot normally be used as a standalone water treatment solution for ZLD. Essentially, these systems ‘polish’ the water after conventional water treatments have done the heavy lifting; or they are used in a sidechain to protect existing processes, to make them more efficient.

But as part of a treatment chain with an ambition to achieve Zero Liquid Discharge, an electrochemical treatment system is becoming vital.

Another aspect to consider is that electrochemical reactors are often small enough to place adjacent to specific industrial processes or even individual machines, so they can treat waste outflows at source.

So before the waste from one process is mixed up into a whole factory’s ‘pollutant soup’. it’s easier and more cost effective to remove specific pollutants early.

Benefits of Zero Liquid Discharge

ZLD – or at least an ambition to achieve it – requires a degree of culture shift in most companies.

When water – so long something that’s just available by turning on a tap – becomes more precious, people will have to treat it differently.

There are numerous advantages to ZLD, including:

• Water supply can be controlled; factories are no longer dependent on a continuous external supply.
• Cost of water can be planned for.
• Consistent, known quality of water.
• A far more environmentally responsible approach, benefitting the environment as well as staff, customers and stakeholders.

Zero Liquid Discharge is coming; because sooner or later, every industrial consumer of water will be affected by its cost and availability.

Only electrochemical treatment of industrial wastewater can efficiently purge it of so many recently-created pollutants that are harmful to life if left in wastewater. 

As the world heads towards increased water scarcity, it makes good financial sense to prepare now for a future when water may not be so readily accessible.