Chemical-free water purification

Researchers at Siemens are developing a process that can turn waste water into drinking water without the need for chemicals.

The process will ensure that germs cannot develop a resistance to the treatment, and will also do away with the need to transport or store large amounts of disinfectant chemicals.

The first commercial system should be available in two to four years’ time, while the process will grow to play an increasingly important role in water treatment within 15 years.

Pulsed electrical fields are used to kill bacteria, viruses, algae and even mussel larvae. If left, mussels can grow to clog piping or spoil water passing through it after they die.

During purification, untreated water flows through a chamber containing two electrodes positioned a few centimetres apart. A pulsed voltage of around 100 kilovolts with a pulse length of less than a microsecond is applied, producing very high electric field strengths between the electrodes. The field sets two processes in motion.

The first causes cell walls to become more porous, eventually destroying them. The second creates free radicals such as ozone, which have a germicidal effect and break down chemical impurities such as hydrocarbons.

The process can also destroy hormones such as those from the contraceptive pill that are currently being investigated by the EU as a potential health threat.

‘We believe that pulsed electrical field technology is suitable for supplementation or replacement in current drinking water supply installations,’ said Dr Werner Hartmann, senior principal research scientist at Siemens’ Electromagnetic Systems & Plasma Technology division in Erlangen, Germany.

‘Installation and capital costs will be significant, but we also believe that overall costs should be lower than those of chemical systems.’ The treatment units will have a long service life and will be easy to maintain, making them more cost-effective than rival systems such as those using ultraviolet light.