Biodegradable dishwasher tablets

News from the future: Tuesday 19 December 2018

Boxes containing a three months’ supply of the new biodegradable dishwasher tablets, Clean-n-Green, will soon be on sale in supermarkets. They are made entirely from renewable resources produced in the UK, claims Chandra Murphy, head of research at India Chemical Industries (UK), located on Teesside. 

’Our most difficult challenge was to find an ingredient to neutralise the calcium of hard water,’ said O’Brien, ’but in the end we returned to using sodium tripolyphosphate. In the last century this was manufactured from mineral phosphate but for obvious reasons we were reluctant to use today’s reclaimed phosphate which comes from sewage works. Instead we developed a new process to produce it from animal bones.’ 

At the launch of Clean-n-Green, at Middlesbrough’s new Eco Center, Murphy gave further details of its ingredients. The surfactants are derived from sugar and rape seed oil, and the enzymes which break down food residues are extracted from bacteria. Other ingredients come from straw, thanks to new designer enzymes which act as multistage catalysts for processes carried out at normal temperatures. The sodium carbonate in the tablets is made from sea salt and the sodium percarbonate bleach is formed using hydrogen peroxide. Moreover, Clean-n-Green works well at 45?C, ten degrees lower than other dishwasher detergents, and uses a minimum volume of water. 

Murphy confirmed that the tablets were suitable for the new style dishwashers in which the final rinse water from the previous wash is sterilised in the machine and stored to be used as a pre-wash next time. He further claimed that washing-up is now as environmentally friendly as it is possible to be, and uses only 1 kWh of the average family’s daily ration of mains electricity. This is currently 15 kWh per household, but is to be reduced to 14 kWh next year, and then to 13 kWh in 2020. 

Our science correspondent writes:

Dishwasher tablets are some of the most sophisticated of household chemicals, with up to a dozen ingredients. They contain alkali and surfactants to remove grease; protease and amylase enzymes which dissolve protein and carbohydrate residues; and an oxidising agent to bleach tea and coffee stains. The surfactant is the non-ionic type which means it will wet all kinds of surfaces such as crockery, plastics, cutlery, and glass. The tablets also need a water softener, because most domestic water in the UK is hard and ion exchangers are no longer an integral part of dishwashers. A zinc salt is included to protect glass, which it does by replacing leached-out sodium ions. Finally there has to be a rinse aid so that the rinse water drains off completely and does not cause ’spotting’. Until a few years ago it seemed unlikely that all these ingredients could be made from renewables. Now they can.  

The chemistry is also complicated in that the new tablets contain ingredients that are chemically incompatible, so have been encapsulated in coatings which not only isolate and protect them but which ensure they dissolve and release their contents in a controlled fashion and at the right time. They are all sealed in the water-soluble polymer, polyvinyl alcohol, which is also produced enzymatically from plant crops.  

And how is the final rinse water sterilised? This is done by subjecting it briefly to pressures high enough to burst the membranes of any bacteria it contains.