What about True ZLD?

If you browse the internet or LinkedIn, you will find many reputable companies claiming to offer ZLD solutions using advanced membrane technologies.

If you go deeper into the process description, you will find that they mainly recover water using reverse osmosis or further concentrate using evaporators.

So in these cases these processes provide about 70% water recovery and a brine concentrate for about 30%.

The problem is that this 30% concentrated brine contains all the dissolved solids and waste impurities! And in most cases these are discharged back into rivers or aquifers.

So, from an environmental point of view, these solutions are not efficient at all, they only partially solve the problem of water recovery, some reduction in treatment costs, but they do not address the environmental and biodiversity issues at all...

Is there a false ZLD and a true ZLD?

Is there a bit of greenwashing in the way these solutions are marketed, what about the Zero?

Let us go into a little more detail about what a ZLD system is:

Zero Liquid Discharge (ZLD) is a water treatment process that aims to eliminate the discharge of liquid waste from a system, leaving zero residual liquid. In other words, it is a water management strategy that focuses on recovering and reusing all of the water from an industrial process, leaving no liquid waste to be discharged into the environment.

The ZLD process typically includes the following key steps

• Pretreatment: The first step involves the removal of large particles, suspended solids and other contaminants from the wastewater.
• Concentration: The treated water is then concentrated through processes such as reverse osmosis, which separates water from dissolved salts and other contaminants.This process has some limitations related to the amount of solids dissolved in the brine,Typically, about 6 to 20% of total dissolved solids limits water recovery to about 70%.To achieve true ZLD, the remaining 30% of concentrated brine must be further treated.
• Crystallisation: The 30% of concentrated brine is further treated by crystallisation, where salts are crystallised and separated from the water along with other impurities. This last step will recover water as a high quality distillate and a small salt cake to be collected for recycling or disposal.

So, without making any mistakes, we can say that we have two main types of liquid discharge:

Minimal Liquid Discharge (MLD): for the concentration step, it will help you to recover water but not to respect the strict environmental regulations about nitrates and phosphates and other rejects in mother nature.

Zero Liquid Discharge (ZLD): you need a crystalliser to properly solidify the dissolved solids to guarantee compliance with any discharge regulations that may be adopted in the future, as there is no liquid discharge to regulate.

Waiting for your comments !

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