Nieuws - 17 januari 2002

Biorotor makes waste water usable

Biorotor makes waste water usable

In the sewage treatment plant, on the surface of the water, float large plastic discs. Half of the disc sticks out above the water, and the rest is below the surface. Bacteria attach themselves to the surface of the disc, forming a thin layer of slime. These bacteria break down the nitrogen compounds in pathogens in the sewage waste.

The system is called a biorotor. The biorotor is not new but a Wageningen researcher discovered a new application for it. When Egyptian PhD student Ahmed Tawfik Ibrahim attached the rotor to an anaerobic treatment plant the waste water became suitable for irrigation purposes as it contained fewer bacteria.

"Anaerobic treatment takes organic waste out of sewage water," explains Dr Ibrahim. "But waste water cleaned in this way still contains too many E.coli bacteria from human waste as well as other pathogens. It is however unsafe for reuse according to the WHO norms. The biorotor system solves this problem."


In an anaerobic treatment system the bacteria float around in clumps. "As the treated water flows out of the system the clumps float away with the water," explains Hardy Temmink from the sub-department of Environmental Technology. "This problem is overcome with the biorotor, as the bacteria are caught on the discs." Temmink was a colleague of Ibrahim and was also his 'paranymph' at his graduation.

Even water treated with the biorotor is perhaps not clean enough to use for irrigating food crops. "But crops such as cotton probably can be safely irrigated," according to Temmink. Ibrahim hopes that his innovation will make anaerobic treatment of waste water more attractive to countries like Egypt. "Anaerobic treatment has many advantages, for instance in providing energy. The process releases a lot of methane gas, which can be used for energy."

Ahmed Tawfik Ibrahim received his PhD on 8 January. He was supervised by Gatze Lettinga, Professor of anaerobic treatment technology, and Professor Fatma El-Gohary of the National Research Centre, Cairo, Egypt. Dr Ibrahim can be reached at National Research Centre, Water Pollution Control Department, Dokki, Cairo, Egypt. E-mail:

Willem Koert