Bombarding clothes with soundwaves vibrates the dirt particles out of the fabric, allowing them to be washed away, according to scientists who have just completed a three-year study of the use of ultrasound for cleaning clothes.
The aim of the project was to find a less polluting way of doing the laundry. About 77 million washes are done every day in Europe, using between 100g and 150g of powder per operation. This creates a significant environmental problem as 11,500 tonnes of powder each day pollute waste water with detergents, enzymes and oxidising agents.
And in the same way as people are addicted to air-polluting cars, they are wedded to water-polluting washing machines. In 1992, about 42 million washing machines were manufactured worldwide. Of these, 6.5 million were made in the US where 75 per cent of households have a machine, 5.2 million in Japan where there is 99 per cent ownership, and 12.5 million in the European Union. Germany has 92 per cent ownership, France 90 per cent, Italy 96 per cent, and in the UK 91 per cent of households have a washing machine.
Just as car manufacturers are cleaning up exhaust emissions and reducing fuel consumption, washing-machine and soap-powder companies are cleaning up their environmental credentials. The latest machines use less than 80 litres of water per cycle compared to 100 litres five years ago, and soaps work at lower temperatures. Washing at 40 degrees centigrade uses 0.7 kilowatt hours of electricity per cycle, compared with 2 kilowatt hours per cycle for a 90 degrees wash.
The research programme, which brought together Unilever's Rotterdam Research Laboratory with the French washing machine manufacturer Ciapem and the Institute of Acoustics in Madrid, found that using ultrasound would speed up a washing cycle from 30-45 minutes to 5-10 minutes.
Ultrasound works well on grease and dust, and speeds up the removal of protein-based stains such as egg or blood, but it has no effect on pigments like red wine or coffee. So detergents would still be necessary.
But the main drawback is that for ultrasound to work properly, there has to be a high ratio of water to clothes. Ciapem says this means it is not commercially viable because it would involve redesigning washing machines.
'People have talked about using ultrasound to clean clothes for 50 years,' says Dr Simon Willemse of Unilever. 'Now we know it is possible but difficult to commercialise.'Reuse content