Kuwait’s 375,000 cubic metre a day Sulaibiya plant is expected to meet 26 per cent of the country’s overall water demand
The need to reduce reliance on expensive desalination is pushing the region to improve the quality of its wastewater. At present, the technical solutions employed to treat wastewater in the Mena region vary from simple septic tanks and waste stabilisation ponds to complex multi-stage biological membrane processes. As a result, the quality of effluent is similarly variable.
MBR reactors produce high quality effluent on a small footprint but cost more to implement than other methods
In technical terms it is possible to take sewage and treat it so thoroughly that it can be directly consumed. All pathogens, organic loading and heavy metals are removed. A good example of high quality effluent is Kuwait’s 375,000 cubic metre a day Sulaibiya plant, which uses reverse osmosis – more commonly found in desalination plants, and ultra filtration to produce an effluent that is good enough to drink.
Philosophically this is a step too far for water consumers. It is accepted that sewage can be re-used, but at this stage it is the industrial and agricultural sectors that are really embracing it. In Kuwait, for example, Sulaibiya effluent is used for aquifer recharge, irrigation and industrial applications and is expected to meet 26 per cent of the country’s overall water demand.
Getting sewage to a point that it can replace desalinated water, for example in a district cooling plant, requires a much higher standard of effluent than other applications, such as drip irrigation of crops. Water authorities are therefore considering and implementing a range of options for improving standards.
The primary sedimentation phase and the secondary biological treatment phase common to most major works can be followed with additional tertiary treatment processes and/or disinfection. Alternatively, whole new treatment packages such as mechanical biological reactors (MBR) can be employed, replacing the entire system. “There is not one single standard being used throughout the region. However most new plants are treating wastewater to a tertiary standard,” explains Dr Martin Currie, leader of consultant Atkins Middle East Water Group.
MBR reactors produce a high quality effluent on a small footprint but cost more to implement than other methods. “MBR is small and compact and produces high quality effluent, but it uses lots of energy. At the other end there are lagoons and wetlands which use lots of space,” explains Currie.
Energy use is a key factor for governments in choosing their treatment options and small scale, localised natural methods are also gaining momentum. German consultant Waagner Biro Gulf is promoting a natural form of wastewater treatment using reed beds and has 15 projects under way in the region. “There are wonderful possibilities for biological treatment in this hot climate,” says Peter Neuschaefer, the firm’s director of water energy and environment for the Middle East.
The approach promoted by Waagner Biro Gulf involves the use of natural reed beds to remove the biochemical oxygen demand from the sewage. Reed beds have been used in wastewater treatment for centuries but Neuschaefer is adapting it to modern applications and developments. In particular he says that a plant called Typha is well suited to removing heavy metals. “Working with the Unesco office in Qatar we found out that Typha have the best performance to eliminate the rest of the heavy metals after pre-treatment through reeds in the first stage,” says Neuschaefer.
“We found that the drying phases on the reed bed surface gives the same effect as the sludge dewatering process.” A key advantage of this approach is that there is no methane produced and no smell. This method has won the company a Green Innovation Award in Qatar for its application of the system on the Al-Khor housing project.
This effluent is also proving useful in other applications. By washing the treated water over photovoltaic (PV) panels the units are being cooled and cleaned by the water, increasing their efficiency. “The solar PV modules get cooled and washed with the cool effluent from reed beds. Our results are unbelievable, increasing the power up to 65 per cent,” says Neuschaefer. “What is more, this water can then be used for irrigation – making it doubly useful.”
Producing treated sewage effluent (TSE) using low energy intensive methods and then applying this to renewable energy is certainly likely to prove popular for clients looking carefully at their carbon footprint, particularly in a climate where demand for TSE is rising.
A typical treatment hierarchy
Screening – pre-treatment where grit is removed
De-greasing – removal of fats using skimmers
Primary treatment – sedimentation and removal of solids
Secondary treatment – removal of biological content
Tertiary treatment – further removal of nutrients, nitrates, phosphates and heavy metals
Disinfection – final removal of micro-organisms