Membrane technology for waste-water reuse is providing solutions to developers’ water needs.
With every new development creeping-up throughout Middle Eastern metropolises, more strain is being placed upon central sewage systems. Such systems are quickly reaching their breaking-point, so where will all the waste go?
This is precisely the question that all new developers are asking themselves; their waste products have to go somewhere, after all. In recent years, treating such waste ‘in-house’ and reusing it has become an increasingly common occurrence.
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Not only is it practical, it is also environmentally friendly and cost-effective in numerous ways.
Accordingly, the membrane technology (MBR) industry has witnessed unprecedented demand for its services.
“Three or four years ago in the UAE there was only one small MBR plant processing around 200m3 per day. Now there are probably 30 or 40 plants either running or under construction.
This year alone around 10-15 have already been awarded; the industry is certainly taking-off,” explains Chris Jeffery, commercial developer of GE Water and Process Technologies.
The past, to present
MBR technology has been around since the late 1960s, but only in the last ten years has it become truly economically viable.
Conventional water treatment technology has traditionally been employed using an activated sludge bioreactor that harnesses naturally occurring microorganisms to break-down waste products.
If developers are to reuse their waste, however, then such biological methods are wholly inadequate. Hence the increasing focus on MBR.
“Conventional technology is fine if you just want to treat your waste and then dispose of it,” says Majd Hamadallah, operations manager at Eagle Electromechanical.
“If a company wants to harness its waste and reuse it for things such as cooling towers or water features, then MBR must be used. The major difference between MBR and conventional technology is the purity of the water – the former being significantly cleaner.”
MBR now combines traditional use of biological processes with a membrane that is generally submerged into the bioreactor.
The membrane fibres have billions of microscopic pores on their surface that form a barrier to impurities, while allowing pure water molecules to pass. Water is drawn through the pores using a gentle suction.
While the water produced is incredibly clean and removed of any suspended solids, it is not sufficiently removed of impurities to be used as drinking water. If the water is to be drunk then it must go through an additional reverse osmosis membrane – the same used in desalination.
Why MBR?
MBR technology is certainly being utilised in the Middle East – GE alone now has 35 MBR plants in the region. The drivers behind such expansion are considerable in number.
“The primary reason that people use MBR technology in the Middle East is because of the space saving,” says Jeffery. “MBR plants take-up about half of the space of traditional water treatment plants allowing the developer to optimise their land. Economically, this can make a huge difference in the Middle East since land is so expensive.”
“MBR does present much higher capital costs – at least 10-20% higher than conventional plants and the membranes themselves comprise about 15-20% of the total cost. In the end though, building an MBR plant is much more cost-effective since your footprint is reduced and you do not have to desalinate sea-water, which is even more costly. I would say within five to six years you would have recovered your initial outlay,” adds Hamadallah.
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Octal manufactures APET sheet and PET resins for the packaging industry. The company is commissioning 300000 tons of resin capacity in October 2008 to be followed by 500000 tons of additional capacity in 2010, so demand for water is vast.
“Being in Salalah we had only two choices – either employ a very elaborate and expensive process of desalinating sea water or, as we found out, take Salalah’s municipal waste, pipe it to the plant and treat it ourselves,” explains Brij Malhotra, Octal’s group director of operations.
“It was more cost effective for us to reuse Salalah’s waste water, with the additional benefit of such reuse being environmentally friendly. Salalah Ministry did not know how to dispose of the waste anyway, so we took the problem out of their hands.”
Conventional waste-water treatment technology was not appropriate since the effluent Octal receives contains a high percentage of suspended and dissolved solids. MBR had to be employed if the water was to be clean enough for Octal to use.
The 6.5 km pipeline to transport the effluent from Salalah municipality to Octal’s plant has already been constructed and from September reuse will begin, providing cooling and process water. Initially around 2500m3 of waste will be processed and reused per day; this is expected to rise to 4200m3 by 2010. By 2012, 7000m3 per day may potentially be reused.
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The other important factor that is shifting focus to MBR in the Middle East is district cooling. This consumes huge amounts of water – you could now use treated sewage water instead of using drinking water that is much in demand. There is huge potential for this in Dubai and other areas,” explains Hamadallah.
Problem solving
A major hindrance to the earlier expansion of MBR plants, and a problem that engineers still face to today, is fouling of membranes.
The major difference between MBR and conventional technology is the purity of the water – the former being significantly cleaner. – Majd Hamadallah, operations manager, Eagle Electromechanical.
MBR filtration performance inevitably decreases with filtration time due to the deposition of sludge components into, and onto, the membrane. Such fouling is the most significant factor affecting MBR system performance.
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Various measures have been employed to lessen the effects of fouling. Intermittent permeation is often used, whereby filtration is stopped at regular time intervals to prevent particles settling on the membrane.
Membrane backwashing may also be employed where permeate water is pumped back to the membrane and through the pores, dislodging any internal and external foulants. Complimentarily, additional chemical cleaning may take place.
The importance of adequate cleaning is understandably critical to MBR operators since it has a marked effect on the longevity of the membrane.
“Seven to ten years is probably the best estimate of life-span, but it all depends on how well the membranes are maintained. They are useless if they are not cleaned,” says Jeffery.
Still, membrane design and manufacture can make a significant difference to MBR performance.
“The real evolution of MBR comes in the quality of the membrane and the ability to produce more flux through the membrane, so you can get more out of the membrane in terms of cubic metres in comparison to the others. Membranes can now survive stronger chemicals and have greater longevity and more competitive costing,” declares Sady Juez, managing director of Metito.
Limits to reuse
MBR technology is taking-off in the Middle East, much as a result of water scarcity and the region’s rapidly expanding number of property developments. MBR technology allows developers to address all such issues while, most critically, reducing the land devoted to plant instead of saleable property.
Quite how far waste-water reuse will progress is, as yet, unknown. Through the use of MBR and reverse osmosis membranes, it is now technically possible to recycle waste water and use it as drinking water. The city-state of Singapore has been a leader in this area.
Still, the major impediment to reuse is psychological. The extent to which public perception can be overcome will ultimately determine the limits of reuse.
MBR history
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- Waste-water treatment revolved around the use of an activated sludge bioreactor process harnessing natural microorganisms.
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- Late 1960s – MBR process introduced to water treatment industry as soon as ultrafiltration (UF) and microfiltration (MF) membranes available on a commercial scale.
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- High cost of membranes, the low monetary value of the effluent recovered and the rapid loss of performance due to membrane fouling, limits MBR usage.
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- 1989 – Major breakthrough with the idea to submerge the membranes into the bioreactor.
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- 1990s – Lower operating costs, decreased amount of membrane fouling and reduced cost of membranes increases demand.
The district cooling system used on The Palm requires vast quantities of water. Rather than desalinate the sea-water that surrounds them, reuse of waste water was selected as the best source of the necessary liquid.
Land costs on the man-made island are understandably staggering, so any footprint saving is critical. MBR technology was, therefore, the most appropriate water treatment option since MBR plants are considerably smaller than conventional ones.
“Aesthetic considerations were also a decisive factor in deciding to use MBR. The Palm is a beautiful island so no one wants to see huge waste water treatment tanks going up ten metres into the sky,” says Sady Juez, managing director of Metito, the company that designed and will manage the Palm’s MBR plant.
“Through the use of compact MBR technology, we were able to develop the system nine metres underground – saving valuable space and avoiding any unnecessary eyesore.”
The MBR plant is yet to be commissioned, but once completed it will provide around 22000m3 of water per day.
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