By Utilities Middle East Staff Writer www.arabianbusiness.com
MBR technology is benefiting from the increasing reuse of wastewater in the region. But for MBR to supercede the conventional activated sludge process, membrane costs will have to come down, and the full potential of the technology needs to be realised.
The idea of reusing wastewater does not sit easily with everyone. It is, after all, not a pleasant thought that the grass your children are playing on, or the air that is cooling your apartment, has been subjected to water flushed down your toilet in the not too distant past.
The stigma attached to the reuse of treated wastewater is thus considered an obstacle by the advocates of membrane bioreactor (MBR) technology.
To add to this burden, MBR, which makes use of membranes as the final stage of the purification process, is also fighting for its place alongside the conventional approach, the activated sludge process.
There is, however, little doom and gloom about those who enthusiastically endorse the technology. This is partially because, in spite of all inhibitions, wastewater reuse has found its place in the region’s water supply chain.
“There is now widespread acceptance of the concept for a wide range of non-potable applications in most of the major economies including Saudi Arabia and the Gulf States,” says Jim Hotchkies, marketing manager at Toray Membrane Europe.
Moreover, MBR has a distinct advantage over the activated sludge process. “Can you reach the same quality of effluent with a conventional system? The answer is clearly yes – provided that you take the additional steps to reach the same quality,” says Murat Sarioglu, principal process engineer at MWH Europe. But when equipped with membrane filtration, the footprint of a plant is reduced significantly. The membranes make redundant some of the steps otherwise needed to purify the water, such as the final settlements tanks.
A smaller footprint is of a distinct advantage if you are struggling for space. This applies, for instance, to smaller, purpose built wastewater plants for developments in an urban setting. Consequently, MBR is a feature of water treatment facilities for landmark projects such as the Palm Jumeirah or the Burj Khalifa, where treated wastewater is used for the fountain display adjacent to the Dubai Mall.
While admitting that the technology is not feasible for the big sewage plants, such as the new 300,000 hectolitre plant in Jebel Ali in Dubai, Sarioglu believes that a more decentralised approach is the most intelligent approach going forward. By reducing the distances sewage has to travel to the plant, and treated effluent in turn has to travel to be reused, the cost of transportation could be slashed drastically.
“At the moment, wastewater is transported by sewers to intermediate pumping stations, and from one station to the other,” expands Sarioglu. “In Dubai, wastewater travels 60 kilometres to reach a sewage treatment plant outside the city. And because you need the water for irrigation, you end up taking the treated water all the way back again.”
A shift to a more decentralised approach could make MBR the preferred wastewater treatment technology. Plants using the membrane technology use less space, and can be built entirely underground, explains Sarioglu. “On a stretch of 60 kilometres, you could build three treatment plants, for example. You’d get rid of the pumping station costs, and the distribution back to the city. This should be looked into.”
Vikrant Sarin, business development manager at Aquatech, also believes in the benefits of a de-centralised approach. “If you look at the GCC countries, with some of the population in remote areas, it becomes difficult in connecting them in the first place, you have to tank wastewater and to supply water.” As potable water only makes up around 10 to 15 percent of consumption, it only makes sense to meet the non-potable needs of remote areas with locally treated effluent, argues Sarin.
The concept is starting to catch on, sometimes with a little outside help. In April, Hitachi Plant Technologies opened a wastewater treatment plant in the emirate of Ras al Khaima. The US$4.5 million project was financed by the New Energy and Industrial Technology Development Organisation (NEDO), a Japanese governmental organisation that promotes energy and water efficiency worldwide. The plant recycles 3,000 hectolitres of sewage into 2,000 hectolitres of water treated with MBR technology for agricultural use, and 1,000 hectolitres treated further with reverse osmosis (RO) technology for industrial use. Set up in the midst of a pristine desert landscape adjacent to an industrial site, with no access to a piping system, the plant is a showcase for a decentralised approach to wastewater treatment.
In a region in which power is almost as precious a commodity as water, the fact that MBR technology is generally perceived as more energy-intensive than the activated sludge process is clearly a drawback. However, there are some that believe that the focus on the energy costs of the aeration process needed for membrane scouring obscures the big picture. “MBR is more energy efficient in the overall perspective,” says Sarin. “You have to include the cost of sludge handling in the activated sludge processes, which includes sludge dewatering, and sludge drying. Plants with MBR technology only produce about 10 percent as much sludge as a conventional plant. People miss these points, they just talk about aeration.”
The energy requirements of the technology are likely to come down in future, as most MBR firms are looking for ways to increase efficiency, including the vertical stacking of membranes to extract more efficiency from the air scouring system, and higher efficiency aerators.
The biggest savings will not arise from improving the membrane, sums up Klaus Kallenberg, general manager at Toray Membrane. “The most dramatic developments in the area of MBR technology are expected to come from improved process efficiency rather than major improvements in the membrane itself.”
While process efficiency might be the buzz word when it comes to energy savings, membranes matter on the overall price equation. Equipping a plant with MBR is expensive, as the membranes represent a significant cost factor.
Sarioglu readily concedes that the membranes currently come with a heavy price tag. But he believes that this will change, and points to past experience. “I see that as the same story as with membrane diffusers which are an integral part of conventional systems,” he says. “These cost a fortune in the nineties, and now you can get them for one seventh, one eighth of the price of what it was back then. The same will happen in MBR technology, as more suppliers come into the picture, there will be more competition in the market and prices are going to come down. In my view, this is inevitable.”
In addition to achieving greater cost efficiency, MBR suppliers will stand to benefit from a greater understanding of the technology, and its uses. Not everyone in the water industry in the GCC as yet fully comprehends the potential for reuse, argues Kallenberg. “While the acceptance of wastewater reuse has grown considerably across the region, there remains some lack of understanding that such reuse water is safe in almost all non-potable applications.”
Yet it seems that this understanding is growing. Wastewater is increasingly used as the chilled water in district cooling, for example. To prevent scaling in the district cooling plants, the water will have to be further filtered in a reverse osmosis (RO) process. “Here, MBR has become very viable,” says Sarioglu. “You can put an RO system directly after a MBR plant, without having to use any additional steps.”
Sarioglu believes that as more research is done on the technology, the more it will grow in stature, and benefits previously unknown will come to light. “MBR has many sides to it that have not been discovered yet, and I always try and emphasise that in the conferences I attend. More and more additional features will come out that have not been investigated up to date. I think in the long term MBR will be the dominant process.”