When you need to provide water to a herd of 25,000 cattle in the middle of the Saudi desert, finding sufficient supplies can be a struggle. Saudi dairy group Almarai, to which the herd belongs, uses an average of 2,500 cubic metres of water a day. This compares with domestic per capita consumption of water of 979 cubic metres a year in Saudi Arabia. Almarai, in line with other companies, is now under growing pressure from the government to curtail its water use. The need to conserve every last drop of water has become critical to its business.
The company is one of a growing number of businesses that have looked to technological solutions to reduce water usage.
The need to re-use water is becoming more pressing across the globe, as regulators insist that firms substantially reduce the amount of water that is wasted in the industrial process.
Levels of water re-use in the Gulf are improving. Some 70 per cent of wastewater is re-used in a number of countries, including Qatar, while Abu Dhabi is aiming for 100 per cent wastewater re-use in the emirate by 2015.
Zero liquid discharge (ZLD) is the term used for the latest and most high-tech development in water re-use. ZLD involves the use of evaporators and crystallisers to create solid waste from wastewater streams and reduce water waste to a minimum.
In North American and Europe, ZLD is a popular technology for large-scale industrial and commercial users. The goal of a well-designed ZLD system is to minimise the volume of liquid waste that requires treatment, while producing a clean stream suitable for use elsewhere.
Companies are able to reduce water discharge in a number of other ways, without having to opt for ZLD. “Before we get to using ZLD, there are a number of other major improvements that can be made on existing systems and infrastructure to efficiently re-use and conserve water, such as limiting pipeline leakages and evaporation losses on open tanks,” says Tawfiq Abu Soud, executive director of the UAE’s Drake & Scull International. “New technologies promise to free up power presently used by reverse osmosis plants.”
“New technologies promise to free up power presently used by reverse osmosis plants”
Tawfiq Abu Soud, executive director, DSI
Water required for irrigation, for example, can now be obtained by recycling wastewater at an energy consumption rate of 1-2 kWhrs/cubic metre, compared with seawater desalination, which at best only operates at just under 4 kWhrs/cubic metre and has the added disadvantage of high salt return to the environment, says Abu Soud.
With Qatar leading the way, ZLD is starting to make inroads in the Middle East – although the technology remains in its infancy, as regulatory pressure on industries to reduce their water usage still lags behind the pressure exerted by governments in the industrialised Western world.
“Regulations in Europe and North America are tough on the discharging of effluents. It is not permitted at all. But in the Middle East the regulations aren’t that stringent,” says Sushil Bajaj, business development manager at the US’ Aquatech, one of the three leading ZLD providers, along with France’s Veolia and the US’ GE.
The regulatory push is critical as ZLD equipment tends to be expensive. More work is needed to encourage uptake of wastewater re-use in the Middle East. Currently, the bulk of wastewater that is re-used in the Gulf is sewage water from cities, which is used to irrigate gardens, but there is more that could be done. In particular, industrial users could re-use far more within their own plant complexes.
ZLD has a number of benefits, not least in achieving the most effective reduction in plant water consumption of all available systems. While reverse osmosis and other membrane technologies can cut wastewater streams by 80 per cent or more, say experts, most industrial facilities still end up with a significant flow of concentrated liquid waste.
ZLD systems, in contrast, is far more efficient and can achieve a 90 per cent reduction in consumption. A further benefit of ZLD is that it produces high-quality distillate that can be recycled.
In areas of acute water shortages, using ZLD can also work out cheaper over the life of a plant, despite its higher initial set-up expense. And sites once considered unsuitable for industrial use, due to inadequate wastewater disposal facilities, may be made viable through the use of ZLD technology.
The need to manage the industrial water cycle is prompting greater interest in ZLD techniques. In the Middle East, it is Qatar that is leading the way. However, there are some disadvantages to ZLD, as with other technologies. Desalination process produces two streams: clean water and brine that must be disposed of. The Qatar government says it is concerned about potential brine-related problems and – supported by large oil and gas revenues – is seeking to develop better desalination methods, including ZLD.
On 1 February, Qatar’s Texas A&M University launched a new initiative, the Qatar Sustainable Water & Energy Utilisation Initiative, which will build on the expertise available at the university to include efficient re-use and ZLD systems. The university joined with Qatar Science & Technology Park to launch a project that would remove salt from groundwater via ZLD in 2008.
This innovation is intended to remove the salt chemically via a lime-aluminium process. If successful, the technology could be commercialised and exported.
The US’ GE Water already backs the use of ZLD technology to produce salt for commercial purposes – the firm has developed a ZLD seawater desalination system that produces fresh water and pure salt that is used to produce commercial-grade chlorine gas and caustic soda.
“GE Water considers the Middle East a key region for ZLD systems,” says a spokesman for GE. “As fresh water demand continues to grow and exceeds available supply, water recovery and re-use using ZLD will increase.”
“The first thing will be to make companies in the Gulf work towards water re-use and then slowly go over to ZLD”
Sushil Bajaj, Aquatech
Qatar is also in the vanguard on the regulatory front, encouraging state energy group Qatar Petroleum and its joint venture partners to install ZLD technology in new plant facilities. QP now specifies ZLD systems for all new industrial projects.
At the Shell-operated, Pearl gas-to-liquid (GTL) project, ZLD is already in use. France’s Veolia Water Solutions & Technologies was selected to provide an environmentally sound water treatment complex to treat effluents from the plant with the highest efficiency of water reuse, resulting in no discharge of water.
Veolia’s affiliate, HPD, provided the evaporation and crystallisation process design for the ZLD system, which concentrates the effluent stream to a solid residue. The plant will rely on the water recovered from this system as a major portion of its overall water demand. “We did a ZLD plan for them in which we re-use all the wastewater generated by the GTL complex, using evaporation and crystallisation. We did exactly the same thing in the US at a power plant in Arizona – an area of water scarcity,” says Philippe Valerio, deputy managing director at Veolia Water Solutions Oil & Gas.
Globally, companies in the automotive, mining and power industries have adopted ZLD as an economically viable method of treating liquid effluent, and the technology has potential in other sectors.
The Gulf’s oil and gas industry, and its petrochemicals sector, tend to use large volumes of water. Water produced by oil wells currently has to be injected back into the ground due to it being too polluted for other uses. ZLD technology opens up the possibility of treating this water and re-using it.
Among the projects where it could be used, a ZLD system may prove suitable for use in a enhanced oil recovery project in Oman, where the client, Occidental Petroleum, is seeking to raise production at a field at the south-central region from 10,000 barrels a day (b/d) to 150,000 b/d.
The water will treated be via Aquatech’s mechanical vapour compression (MVC) technology, producing 300,000 b/d of the water to the steam generators to generate brine stream. Brine from the MVC units is then placed in a settling pond and injected into a deep wells. At the Oman plant, about 90 per cent of produced water is purified through an MVC system, which Aquatech says lends itself well to a ZLD configuration at a later stage if limits are placed on water disposal at the facility.
ZLD can be built into most existing industrial processes. But the integration needs to be done on a case-by-case basis, and to be evaluated and implemented according to project and site constraints, says Abu Soud.
He predicts the greatest impact from ZLD will come in the more environmentally-sustainable use of waste from the desalination process, as it would boost the yield of drinking water, reduce the destruction of sea grass and other marine life, and reduce or eliminate the need for outfall structures. It will also produce salt for the chloro-alkali market and for human consumption.
“You can probably recover some useful salts for industry from the brine coming from the desalination plant,” says Bajaj.
Another potential application is in district cooling. Passavant-Roediger, a German wastewater treatment company acquired by Drake & Scull in late 2009, has developed an enhanced water recovery system for which it expects strong demand from Gulf clients in the field of district cooling.
Despite the usefulness of ZLD, the technology still faces challenges. According to Abu Soud, these include cost, space, legacy system integration, operability and additional energy consumption.
“One needs to understand that the electrical power supply system in the region has limitations. Industrial and commercial wastewater markets have fewer barriers than the desalination industry, as the volumes – and sometimes the salinities handled – are lower, so one can expect most of the early advances to be made here,” he says.
Cost is perhaps the key inhibiting factor and the search for more affordable technologies. ZLD technology is energy-intensive and its capital and operating costs are consequently high.
“If you put in ZLD, you add almost 30 per cent to the [capital and maintenance] cost,” says Valerio.
For cash-rich Qatar, this is perhaps less of a factor than for many other Middle Eastern states. Nonetheless, more regulatory initiatives to encourage ZLD would mitigate some of the cost concerns. Currently, there is no specific regulation for ZLD in the region. In time, more specific guidelines will emerge, predicts Abu Soud, as the lessons of effective governance are learned.
“One possible incentive to encourage improved water re-use systems and methods such as ZLD would be to apply a higher drainage fee to industrial discharges, because the current tariff structure treats the effluent from residential areas the same as that from industrial areas, which is not necessarily the case, given the difference in quality of the wastes. The fees and metering should reflect efficiency and be used to promote water re-use,” says Abu Soud.
Gradually promoting water re-use throughout industry, will deliver real benefits. Once regulatory and price incentives are in place, ZLD could emerge as a significant factor reducing the amount of stress on the Gulf’s limited water resources.
“I think the first thing will be to make companies in the Gulf work towards water re-use and then slowly go over to ZLD,” says Bajaj.
CAPTION – Gulf leader: Qatar is adopting ZLD technology
ZLD technology explained
Zero-liquid discharge (ZLD) uses one of two processes – membrane or thermal. The former includes microfiltration or reverse osmosis (RO). RO is a liquid filtration method for separating large molecules from smaller molecules – in this case salt and other impurities from water – by forcing the liquid at high pressure through a membrane with pores just big enough to allow only the small molecules to pass through.
The thermal processes in ZLD involve evaporators, crystallisers and/or dryers.
In both cases, water is reused as much as possible, but once it becomes too saline or impure, then RO and crystallisation processes begin.
The first stage of ZLD involves reusing water for the cooling tower (see chart, page 31).
“This doesn’t cost that much as you have to accept the salinity, say 300-500 milligrams, or you do a re-use for your process plant and boiler and then go further with RO,” says Philippe Vale-rio, deputy managing director at France’s Veolia Water Solutions Oil & Gas.
“Here the cost jumps higher because with RO you cannot fully re-use all the water. Depending on the technology, you go from 60 per cent to 85-90 per cent recovery. So you still lose some water in the RO process. The water that is lost in the RO process is put in an evaporator and that produces water that you can mix with the RO, which you can then re-use.”
At the outlet of the evaporator, a more concentrated brine is produced than from the RO. This is then put in a pool and crystallising technology is employed, resulting in zero discharge to get the solids.
“Generally, if you go for RO without an evaporator you increase the water reused by 20 per cent. If you put in the crystallisers, you get to 30-35 per cent,” says Valerio.