THE RISING INDUSTRIAL ADOPTION OF ZERO LIQUID DISCHARGE

Zero liquid discharge (ZLD) and similar solutions including minimized liquid discharge (MLD) are anticipated to play a more prominent future role in industrial water treatment across the globe. Ahead of the Industrial Water Solutions Forum in Singapore, this article looks at why a greater focus on environmental protection and water security is leading to a greater adoption of these technologies across multiple industries.

Booming megatrends in urbanisation and industrialisation are creating greater stress on the environment, including the world’s freshwater resources. In many areas globally - and particularly in fast-developing and emerging economies - rapid growth in manufacturing and industry presents a threat to water quality and puts tremendous strains on water supplies. Concerns related to water availability risks are heightened in regions prone to water scarcity.

As these trends escalate, industries that use vast amounts of water and generate significant quantities of wastewater are under mounting pressure to adopt more sustainable water management strategies that use less water, minimize impacts to receiving waters, and mitigate operational risks. This in turn is driving advancements that leverage technology in the global water treatment market.

ZLD and comparable approaches such as MLD are attracting greater interest as beneficial water treatment/water management solutions for difficult-to-treat industrial wastewater.Both strategies employ a sequence or “treatment train” of advanced treatment processes and technologies for maximizing water recycling and minimizing wastewater volumes. ZLD, however - by incorporating a final robust evaporation/crystallization stage - aims to completely eliminate all produced wastewater, reducing waste liabilities and decreasing discharge to the greatest extent allowable.

Drivers for adoption

In recent years, even as industrial economies continue to expand and produce greater volumes of contaminated wastewater, more agreement is being reached internationally in terms of the necessity to safeguard the environment from pollution. This mindset represents a major shift from historical views and is helping to build more support for programs and policies that encourage best practices and innovative solutions for protecting ecosystems, conserving water supplies, and improving water quality.

Based on a rapid evolution in the acceptance of advanced technologies and increasing recognition of the value of sustainable-focused approaches, greater momentum is emerging worldwide across the industrial landscape for water treatment solutions such as ZLD and MLD that minimise waste, recover resources, treat toxic industrial waste streams more effectively, and mitigate potential water quality impacts to receiving waters.

Water intense processes

Industrial ZLD and MLD adoption is also being driven by rising global water stress and mounting risks to industries that depend on consistent water supplies. Water-shortage risks are especially severe for operators located in water-stressed areas and for industries with water-intensive processes such as food and beverage, power, and pulp and paper.

By “closing the loop” and enabling for treated water to be recycled and reused in process operations - or in other industrial applications that require water - ZLD and MLD offer a proven technical water management strategy for mitigating water-shortage risks by boosting water efficiency and reducing water intake requirements. For industrial operators in water-restricted areas, this benefit can help insulate industrial operators from escalating source water costs.

ZLD in particular, with the capacity to treat the most challenging wastewater and virtually eliminate all discharge, is attracting rising interest as an effective and best available process for managing contaminated waste streams produced by industries such as power, chemical, steel, textile, electroplating and others as more regulatory focus is directed at the largest environmental polluters.

As an example, the U.S. Environmental Protection Agency (EPA) recently issued new Effluent Limit Guidelines (ELGs) for the steam electric power generating category, requiring ZLD for all pollutants associated with fly ash transport water, bottom ash transport water and flue gas mercury control (FGMC) wastewater in power plants that are 50 megawatts (MW) or higher.

Zero Liquid Discharge Benefits

1. To save costs and reduce the capacity needed, comprehensive water audits are usually performed which also ensure that the system deals only with the most polluting streams.
2. Installing ZLD technology is therefore often beneficial for the plant’s water management; encouraging close monitoring of water usage, avoiding wastage and promotes recycling by conventional and far less expensive solutions. 
3. High operating costs can be justified by high recovery of water (>90- 95%) and recovering of several by products from the salt. 
4. A more sustainable growth of the industry while meeting most stringent regulatory norms. 
5. Possibility of use of sewage for recovery of water, for Industrial and municipal use, using ZLD technologies.
6. Reduction in water demand from the Industry frees up water for Agriculture and Domestic demands.

Challenges of Zero Liquid Discharge

1. Zero Liquid discharge Is the Holy Grail of Industrial wastewater Treatment.
2. ZLD results in generation of hazardous solid wastes creating disposal challenges- need to think of Zero Waste Disposal (ZWD) Plants. 
3. Generate products/ by-products out of the waste.
4. Economic viability- cost and availability of water, regulatory pressure are the real driving force. 
5. High Carbon foot print- is this environmentally sustainable?
6. High Operating cost and financial impact on the industry and its Regional/ National/Global competitiveness. 
7. Technology shortcomings.

Zero Liquid Discharge Treatment Plants

There has been increased attention on ZLD technologies in the news over the past two years. New regulations and awareness of the water crisis have prompted businesses to adopt new technologies which treat waste water in ways that are more efficient and sustainable. ZLD, or Zero Liquid Discharge, are technologies which concentrate waste water until only solids and reusable “clean” water remains or, more broadly, which produce a “close to zero” amount of liquid waste.

Zero Liquid Discharge Plant by Austro Water Tech

Since ZLD technologies recover all, or almost all, of the waste water produced by an industrial process, they contribute to sustainable manufacturing practices and decrease the environmental impact of businesses. They also have economic advantages, such as:

• minimizing the cost of sourcing freshwater and disposing of waste,
• providing added value because valuable resources can be recovered from the “waste.”

ZLD technology maximizes the fresh water recovered and minimizes the volume of waste generated; however, there are trade offs. Conventional ZLD systems are based on thermal methods such as evaporators and crystallizes, which are expensive and use considerable energy. To increase the viability of ZLD technologies for both the environment and businesses, they must be further improved to minimize the amount of energy consumed by the treatment process.

One way to save energy is to reduce the amount of waste water which needs to be treated using heat. This can be done by using volume reduction technology. Another way to save energy is to operate the treatment system at a constant temperature throughout the process. Most of the traditional volume reduction technologies do not work at high temperatures, which means that the waste water has to be cooled and then reheated during the treatment process. However, some new technologies do work at high temperatures.

Nano scale ceramic membranes capable of de watering are an example of a volume reduction technology that can operate at high temperatures, unlike polymer membranes. Heat resistant ceramic filters make the use of heat ex changers for the final thermal concentration step unnecessary. This reduces the total energy use of the ZLD system.

It makes no sense to use ZLD technology if the advantages of the recoverable water and resources are offset by the disadvantage of the energy use necessary for the process. Emerging nano-ceramic technologies make ZLD more energy efficient and allow more businesses to take advantage of this cost-saving and sustainable process technology.