By Peter Chawaga
Zero Liquid Discharge (ZLD) systems employ cutting-edge technologies to minimize water use within a given industrial facility and maximize the reuse of its processed wastewater. In the perfect ZLD system, no effluent ever leaves the factory, savings are immense, discharge and reuse requirements are met with ease, and the praise of conservation groups is bestowed fervently.
A cursory internet search reveals that ZLD solutions are plentiful. They are offered far and wide by a who’s who of industry leaders. GE, Veolia, Suez… they all claim the goods to maximize water use. So how to get in on the action?
Fit For All
The best place to start is to recognize that any manufacturer in any industry has the opportunity to approach ZLD. The only prerequisite is a desire to cut down on water waste.
“The question is less about type of industry and more about the economic and environmental issues affecting an industry at a specific place,” said Espen Mansfeldt, CEO of Thermal Purification Technologies.
Mansfeldt identified oil exploration and mining as industries that are particularly ripe for ZLD solutions. Factories operating in regions defined by water scarcity or strict governmental regulations would also be primed to seek liquid discharge savings.
Let’s Get Technical
As mentioned above, it’s not difficult to find a company offering a suite of ZLD technologies that promises to transform the way a factory uses water. But the specific technologies that would be installed in a particular plant can vary broadly.
“There is no such thing as the standardized ZLD process,” said Oliver Rappich, head of New Technologies and Markets at Hager+Elsaesser, an Aquarion Group company. “Every ZLD process needs to be adapted to the customer-specific production processes and wastewater composition. Therefore the ZLD process can contain various other treatment methods and need to be specifically engineered.”
That being said, there are five broad but universal categories of technology that are employed to achieve ZLD, per Devesh Sharma, managing director at Aquatech, and reproduced here in basic priority order:
- Minimizing technologies. “Within the industry’s manufacturing process, [identify] whatever technologies are available to minimize consumption of water and generation of wastewater. This is highly case and industry dependent.”
- Biological treatment technologies. “Once you generate wastewater, the first step is biological processes for the reduction of organic matter, such as oil, biological oxygen demand, and chemical oxygen demand. The specific technologies depend on the level of treatment needed.”
- Membrane technologies. “Once the biological treatment occurs, the dissolved solids need to be removed… Using membranes is the most cost-effective way to accomplish this as you can achieve high recoveries of pure reusable water. Reverse osmosis is the most common… and there are many emerging processes to try and address this further, such as forward osmosis and membrane distillation.”
- Evaporation technologies. “There comes a point where water is concentrated to a level where membranes will no longer be effective. This is when evaporative technologies are required to further concentrate the brine and eventually crystalize [it] to a solid.”
- Resource recovery technologies. “An important emerging issue in wastewater treatment, recycling, and ZLD is how to make it more economical with resource recovery. This could be utilizing the organics in wastewater to recover energy [or] finding ways to recover minerals from solids from the evaporation process.”
Now Is The Time
Given the crowded supply market for ZLD solutions, there is considerable optimism around its forthcoming demand. As available water supplies dwindle, government overseers tighten their grips, and industry decision-makers become savvier with their resources, suppliers see a ZLD revolution on the horizon.
“As water shortages and environmental constraints drive up the cost of water, many industries are also faced with increasing costs for disposal of various waste streams,” said Mansfeltd of Thermal Purification Technologies. “Thus, the time has never been better to make some real changes and use these available streams more efficiently.”