Bugs beat polyester pollution
15 Jan 2000
A new process developed by Japanese fibres producer Toray Industries uses a microbial process to decompose the wastes generated by the treatment of polyester textiles.
Caustic treatment is used to improve the surface appearance and flexibility of polyester; the fibres' surfaces are hydrolysed by heating them with sodium hydroxide. The waste water from this process contains terephthalic acid (the polyester monomer) and ethylene glycol at fairly high concentrations, which causes considerable problems for polyester plants; at some plants, according to Toray, waste from caustic treatment accounts for 90 per cent of the total waste water burden. Current treatments involve using activated sludges, either before or after removal of the terephthalic acid.
The Toray technique, developed in cooperation with sister company Toray Engineering, takes as its starting-point two naturally-occurring microorganisms capable of degrading terephthalate at the high temperatures and pH values (50 degrees C and pH9.0) of the waste water, which would kill off most other microorganisms. Further research uncovered another microorganism capable of breaking down ethylene glycol under the same conditions.
Over a five-hour residence time in a bioreactor, the microorganisms removed 99 per cent of the terephthalic acid and 70 per cent of the biological oxygen demand from the waste water. This performance - comparable to the conventional treatments - was achieved using 30 per cent less oxygen, leading to large potential energy savings. It also produced half the amount of sludge and, most importantly, used only 2.5 per cent of the space required for activated sludge processes.
