Zero Liquid Discharge – A Real Solution?
By China Water Risk 12 January, 2012
With more companies in China moving towards ZLD, China Water Risk takes a closer look.
Businesses operating in China are increasingly concerned about water use and pollution reduction. A potential solution that a number of organizations have employed, is not just to improve water use efficiency and reduce liquid effluents, but to discharge no water at all, that is Zero Liquid Discharge (ZLD). While most industrial processes generate a waste water stream, the objective of a ZLD system is to recover and reuse all water, thereby avoiding any emissions The concept at first seems counterintuitive; surely water ‘in’ must lead to the discharge of at least some liquid effluent?
Introduction to the Zero Liquid Discharge System
Technically, a ZLD system involves a range of advanced water treatment technologies, whereby the water stream is managed according to the following steps:
| Pre-treatment: where the waste water is filtered using membranes technologies such as ultra-filtration1. The water stream is directed through porous membranes separating the water into a permeate (clean water) that is reused and a concentrate (polluted stream) which is further treated.
Evaporation: The concentrate then enters a brine concentrator which is a mechanical evaporator using a combination of heat and vapor compression to evaporate the brine solution, resulting in a wet sludge. Crystallization: The crystallizer then converts the sludge to solid waste using high pressure steam which further evaporates the water and facilitates formation of crystals. Any remaining water should be clean enough for reuse. Source: Desalination and Water Purification Research and Development2 |
| The solid content known as ‘salt cake’ can then be disposed of according to its constituents, which in turn depends on the nature of the original industrial processes.
For the most toxic type of wastes such as biocide concentrate from the pesticide industry for example, incineration is usually the safest mode of disposal. Less hazardous waste from power plants on the other hand can be disposed of to landfill. In rare cases, the waste is homogeneous enough to be considered as a byproduct and can be reused directly e.g. as industrial salt. But ZLD does not always rely on high tech, capital intensive systems such as those described above. ZLD can also refer to processes where waste water is treated to a level where it is clean enough to be reused for example for cleaning or watering. |
Figure 1: The ZLD process: key steps
Source: Suez Environment, Degremont Technologies |
ZLD Technology moves East
| Going back to the seventies, increased salinity of the United States Colorado River, due to power plant discharges, created the regulatory context to push for ZLD in the US. For new industrial projects, where gaining an approval for a discharge agreement might traditionally take five years, with ZLD it could be a matter of 12 months. As a result, ZLD technology effectively evolved in the US and later grew globally.
According to a December 2009 study by Global Water Intelligence (GWI)3, today there are thousands of evaporator/concentrator systems around the world in a large range of industries. Worldwide construction of ZLD equipment represents an average of 100 to 200 million USD of investment annually. Generally ZLD systems are employed where there are environmental constraints such as water scarcity and/or where strong environmental regulations are enforced; either because an industry’s activity is highly polluting such as coal processing, petrochemical and pesticide production, or because water resources are scarce. Coal rich, but dry North West China for example, is an ideal environment for ZLD systems. While many regional players supply technologies to the ZLD sector; three key players provide the important evaporator and crystallizers technologies: Veolia Water, GE and Aquatec. Veolia Water: As part of the Veolia Water group of companies, HPD Veolia Water Solutions and Technologies is a leader in the design and development of ZLD equipment having built more than 700 ZLD systems to date. HPD has 85 years of experience in ZLD technology and has in recent years widened its American base with projects worldwide, albeit excluding China. GE: has a track record of 35 years in the design and development of ZLD systems It’s design usually combines GE membranes and ultra-filtration systems to improve water recovery efficiency. Aquatech: the water technology provider has also developed a ZLD technology specifically for shale gas water, which is more complex given the high suspended solid content of the waste water discharges. Its technology has recently been chosen for the Yunnan Yuntianhua’s flagship project in inner Mongolia (see below). |
Eraring Power Station, Waste Water Reclamation and ZLD discharge – Australia
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ZLD technology has been mostly developed in Western countries for power plants, but is spreading widely to drought stricken regions such as the Middle East and to highly pollution sensitive environments. Indeed, countries such as China where water is scarce and the industrial water recovery ratio4 is relatively low are potential candidates for the development of ZLD solutions.
At the end of 2010, Aquatech was awarded a ZLD contract by chemical company Yunnan Yuntianhua5 (ticker: 600096) for a coal-to-chemicals plant in an environmentally sensitive location, one of the largest grasslands in China.
The project which includes a High Efficiency Reverse Osmosis Unit and Thermal Concentrator is described as “the solution to reinforce the delicate balance between industrial development and environmental conservation in the biggest grasslands in China”6. Yunnan Yuntianhua is paving the way for more environmental protection projects in the water intensive and polluting chemical sector.
Still some hurdles overcome
While the benefits of ZLD are significant, adoption of the technology has two key ‘environmental’ considerations: firstly, energy consumption for the evaporation process and secondly disposal of the solid waste.
As regards energy consumption, ZLD is energy intensive, however perhaps surprisingly, the process is actually relatively energy efficient. It seems that evaporating a quantity of water with mechanical vapour recompression, would use only 3% of the energy needed to evaporate the same quantity of water by boiling it on a stove.
Moreover 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. Installing ZLD technology is therefore often beneficial for the plant’s water management; encouraging operating departments to detail water usage, avoid wastage and spur recycling by conventional and far less expensive solutions.
Secondly, management of the solid waste needs consideration due to its potentially hazardous nature. If the waste is non-hazardous solid waste or non-hazardous sludge it can usually be disposed of to landfill. However, if the waste is hazardous it should be treated in a specific waste treatment unit such as a hazardous waste treatment plant. Unfortunately these types of units are not widespread in China and eventually the hazardous waste may be disposed of to landfill.
Notably not all landfills are equal. While some meet world class standards such as the North East New Territories (NENT) Landfill in Hong Kong, which has been designed with a durable liner to contain the toxic leachate prior to its collection and treatment. This contrasts to the reality of some landfills in China where poor design and management lead to the release of contaminants to the environment.
Finally, when considering ZLD, the capital cost necessary for installing an evaporator and crystallizer can be prohibitive. Global Water Intelligence in a recent publication7 notes that for a 20 million USD water treatment system which recovers 80% of the waste water stream, CAPEX costs will be doubled to treat the remaining 20% using ZLD equipment.
Zero Liquid Discharge – a less technology intensive approach
As noted above, while achieving zero liquid discharge can be a technology and capital intensive exercise, notably when employing ZLD evaporator and crystallizer systems, some simple solutions can also be used to achieve the same objective. For example when the industrial waste water can be relatively easily treated in a conventional waste water treatment plant some interesting and inexpensive approaches to zero liquid discharge can be adopted.
| Figure 2: Street cleaning in Xian using treated wastewater (Swire Beverage 2010 Sustainability Report)
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For example Swire Beverages, a joint venture between Swire Pacific and the Coca-Cola company, operates seven bottling plants across China and aims to reduce its impact on water resources.
In 2010, Swire beverages plant in Zhengzhou, Henan province in China became the company’s first plant to attain Zero Liquid Discharge by delivering its treated waste water to the municipality urban cleaning services. By reusing its treated waste water and not releasing it to the sewer, 220 million liters of fresh water are saved every year. |
In 2011 Greenpeace’s “Dirty Laundry Campaign”8 targeted several global sportswear brands urging them to eliminate all releases of hazardous chemicals from their supply chains and their products, after research revealed toxic water pollution from key textile suppliers in China.
In response Puma, Nike and Adidas pledged to improve the management of waste water pollution drastically and to achieve zero discharge of hazardous chemicals associated with their supply chains. Waste water streams discharged by this industry are indeed significant and to guarantee zero toxic contaminant release will indeed be a technical challenge. According to Mr. Ma Tian Jie, head of Greenpeace’s toxic campaign based in Beijing, the textile companies are investigating which technical solutions to apply. ZLD allowing total pollution removal could be one solution to achieve this ambitious objective. (Read more on this in “Can Fashion be Green?“)
Looking forward
ZLD will most probably find more applications in China in the drought stricken regions and in environmentally sensitive areas.
- The central government has already decided that any new desalination project bordering the Bohai Sea should integrate a ZLD design. We can expect that mineral rich region of Qinghai and Inner Mongolia to face the same constraints.
- In urban areas, communities are more and more aware of the environmental risks. Greenfield projects may also have to consider the ZLD options to obtain approval .Recently Fujia Dahua Petrochemicals operation in Dalian9 has been threatened to be closed under public pressure over the risk their effluents can cause to the environment.
ZLD projects are still relatively rare in China, however the recent example of Yunnan Yuntianhua’s coal to chemical project shows that under specific circumstances this solution can address a number of environmental issues. But before expecting that this expensive and energy intensive technology would be largely employed, businesses will more likely favor better water management, higher recycling rates and effluents discharge control.
1 Ultrafiltration (UF) is a pressure-driven process that removes emulsified oils, metal hydroxides, colloids, emulsions, dispersed material, suspended solids, and other large molecular weight materials from water and other solutions. UF membranes are characterized by their molecular weight cut-off, source: Koch Membranes Systems Website.
2Program Report No. 149Evaluation and Selection of Available Processes for a Zero-Liquid Discharge System for the Perris, California, Ground Water Basinlination
3 Ref: From Zero to Hero – the Rise of ZLD,GWI, Dec 2009
4 The ratio of industrial water reuse in China is currently 0.55, when most advanced countries are reaching ratio between 0.75 to 0.85 according to the Chinese Ministry of Water Resources.
5 A former state owned enterprise, listed in Shanghai
6Aquatech wins Mongolian ZLD Job, The International Desalination & Water Reuse Quarterly industry website https://www.desalination.biz/news/news_story.asp?id=5657&channel=0
7 Ref: From Zero to Hero – the Rise of ZLD,GWI, Dec 2009
8 Dirty Laundry 1: Dirty Laundry 2: Hung Out to Dry , Unraveling the toxic trail from pipes to products Greenpeace 2011, The Detox campaign
9Tens of thousands of residents in Dalian took to the streets in august 2011 and demanded the relocation of FujiaDahua Petrochemical Company, which threatened to spill toxins into the city last week when a typhoon breached a dike nearby.
As regards energy consumption, ZLD is energy intensive, however perhaps surprisingly, the process is actually relatively energy efficient. It seems that evaporating a quantity of water with mechanical vapour recompression, would use only 3% of the energy needed to evaporate the same quantity of water by boiling it on a stove.
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