Harry Istepanian

Although water efficiency and recycling wastewater are the primary reasons driving the feasibility of using TSE, Istepanian adds that the opex and capex of district cooling plants using TSE is also lower compared to when using desalinated water. “Desalination costs, due to the needs of water-cooled chillers, comprise 24% of the cost factors for district cooling plants in the GCC region,” he says. “For example, the price of TSE water in Dubai is one-tenth of potable water, and using TSE for district cooling is more viable than for irrigation, as district cooling’s contribution to the country’s GDP is 10 times higher than if used for irrigation.” He adds that while there is increased demand for TSE for district cooling during summer, the excess TSE during wintertime can be diverted for irrigation. “Therefore, the extended reuse of TSE for district cooling and irrigation should be carefully managed to reduce the use of distillate water as part of an integrated water resources management approach,” he says. “We expect the demand for district cooling will continue to increase along with growing infrastructure spending across GCC region countries, with more emphasis on optimisation of energy efficiency increasing the share of district cooling in the energy mix, fostered by government norms toward development of sustainable energy.” Istepanian adds that the goal set by the Government of Dubai to achieve 40% of the cooling demand through district cooling by 2030 is achievable, subject to the availability of water.

Weighing in, Kingson Jebaraj, General Manager, Innovative Water and Energy Technology, in the UAE, highlights key considerations affecting water use in the context of district cooling. Firstly, he points out that water used for cooling towers has to be purified or polished. While there is an option to use TSE directly in the cooling tower without polishing or purification, as water treatment service companies have evolved in their use of higher levels of chemicals and inspections, doing so opens the plant to a certain amount of risk, he says. “If control goes off or if management of chemical treatment conditioning goes down by a small margin, the entire plant could be exposed to fouling,” he says.

“Mineral-based fouling affects the DCP operation. That is a big risk for any district cooling company. In a matter of few days, the fouling can increase so high the whole DCP can be tripped.” Although the use of unpolished TSE leads to lower capex, Jebaraj says the risks associated are too high for district cooling companies, following a thorough evaluation of their respective legal, financial and contractual obligations. “Though it is for comfort cooling, it’s not a small plant,” he says. “They are a utility company, and they have a contract with clients to supply chilled water. They don’t want to put any operation at risk.”

Kingson Jebaraj

To avoid these risks, Jebaraj says the second option is to construct a TSE-polishing plant, which will produce TSE water at a higher quality, similar to desalinated water, for the cooling tower. However, Jebaraj points out that there are still challenges associated with managing the TSE polishing plant. Considering the polishing plant will include pre-filtration, Ultra Filtration and then Reverse Osmosis as well as disinfection, it would need to be operated by trained personnel. “Also, this means for DCP the initial cost is higher, because there is a capital equipment going into TSE polishing plant,” he says.

Another challenge associated with constructing a TSE plant is space, Jebaraj says, adding that this is perhaps an even bigger challenge than initial cost. “Most plants will have limited space, and this requires a substantial amount of space,” he says. “So, operation, maintenance and higher capital cost – these are the issues when it comes to TSE polishing, but the advantage is no-risk operation to district cooling plants, because all the risks are eliminated or controlled. By doing this, we also adhere to government policy of using TSE.”

While weighing the cost and benefit on the quality of TSE is an issue in itself, Jebaraj says a larger and encompassing challenge that applies to both is the quantity of TSE in the first place, adding that availability is a big issue. “It depends on the district cooling plant’s locality, whether you have a TSE supply line,” he says.

As district cooling plants are capital intensive and the district cooling companies are financially prudent, Jebaraj says companies have redirected their overall strategy towards more modular plants. “Before, district cooling companies used to go for an area with really big plants,” he says, “So, now the strategy followed by many district cooling companies is towards smaller and modular plants, which will be 1/10th or 1/20th of the size of the original plant. The capex is lower, cash flow is better and the plant is operateshifted tod in full-load capacity.” Jebaraj says that small modular plants also allow for expansion, once capacity comes in, based on real estate and client development. “These modular plants can be  other areas, and when you go with many modular plants, the idea is to develop a permanent plant at a later stage, when you have higher capacity,” he says.

DEALING WITH REJECT WATER

Although availability of water poses a challenge in itself, the ultimate impact of the water that is used cannot be ignored, especially in the context of long-term sustainability. Istepanian
says that currently, in the GCC region states, for every one cubic metre of fresh water produced, two cubic metres of brine is generated and discharged into the Arabian Gulf sea. “As a consequence, intensive desalination processes constantly decrease the quality of seawater for desalination and continuously impact the marine life,” he says. “The usual way of dealing with brine effluent from desalination plants in the Gulf region is disposing direct to the sea. But, direct discharge of the brine is causing the most pronounced effects on receiving waters, such as eutrophication, pH value variations, and accumulation of heavy metals, which have short- and long-term environmental impacts.”

As such, Istepanian highlights the potential of zero liquid discharge (ZLD) for wastewater management to eliminate liquid waste, which, he says, maximises water usage efficiency. “The ZLD method is the most promising technique, because it resolves two severe environmental issues of the desalination plants by reusing the concentrated brine effluent and producing fresh water and salt,” he says.

Jebaraj also touts the value of ZLD as an alternative option. “However, there are several levels of filtration and water treatment, like evaporation and crystallisation, which is more complex and capital-cost intensive,” he says. In agreement is Istepanian, who says that although ZLD decreases water pollution and enhances water supply, the technology is costly and has intensive energy consumption. “The ZLD market is expected to grow from USD 5.4 billion in 2018 to USD 8.1 billion by 2023,” he adds. “Major drivers in the market include the implementation of stringent environmental regulations. In addition, rising concerns over the disposal of brine concentrates into water bodies is expected to drive the zero-liquid-discharge systems market.”