Dishwasher detergents


Why phosphates are a valuable
dishwasher detergent component

Phosphates do not have the same functions in dishwashers as in laundry cleaning. In dishwashers, phosphates improve rinse cleanliness, prevent "filming" of tableware and white incrustations on glassware, buffer pH (important for antimicrobial action and hygiene) and prevent deterioration of tableware surface and colours, in addition to counteracting hardness in water and in food waste minerals.

Furthermore, the principal chemicals used in P-free laundry detergents cannot be used in dishwashers because they are insoluble and would block the machine and be deposited onto tableware. In dishwashers, P-free formulations require more polymers and non-degradable ingredients[i].

Wash performance and hygiene

P-free dishwasher detergents do not provide the same quality of wash performance as phosphates, particularly in hard water or low-temperature economy wash programmes.

Wash performance is important in dishwashers, because microbe survival is known to be related to films or soils left on tableware[ii] and to used wash waters and deposits resting in the machine and in pipes between machine use cycles.

Energy and water consumption: CO2 and cost to consumers

If wash performance deteriorates, consumers are likely to pre-wash tableware by hand before using the dishwasher, add rinse and wash additives, or select more intensive wash cycles to ensure acceptable cleanliness and tableware hygiene safety.

A very approximate estimation for Europe suggests that if lower performance of P-free dishwasher detergents results in just 10% of households selecting a more intensive dishwasher wash programme, this would result in an increased consumption of electricity of more than 500 kwh/year, equivalent to around 35 000 tonnes/year of CO2 emissions and a cost to consumers of around 50 million €[iii].

Phosphates: the best solution

Phosphates are known to be safe, can be recovered and recycled, and their only environmental impact is eutrophication, which is specific to local situations and can be addressed by appropriate sewage treatment. Dishwasher detergents contribute <9% of phosphate in domestic sewage and <2.5% of phosphate to surface waters[iv].

Possible limits on phosphates in dishwasher detergents therefore need to be compared to the impacts summarised above: substitute chemicals, consumer cost and hygiene issues, performance impacts on household energy and water consumption.



[i] Chemical & Engineering News, vol. 89, n°4, 24th January 2011 "Struggling automatic dishwasher detergent manufacturers turn to chemical industry for help with phosphate-free formulations"

[ii] e.g. "Cross-contamination in dishwashers", E. Stahl Wernersson et al., Journal of Hospital Infection, 2004, 56, 312-317

[iii] * Calculation based on France figures, multiplied x5 for EU: (a) Electricity consumption per domestic dishwasher cycle at 55°C = 1,07 kwh, at 65°C = 1,44 kWh. (b) Level of dishwasher ownership in French households = 48%. (c) Number of French households = 26,4 millions. (d) Number of dishwasher use cycles per year = 220. (e) Electricity carbon emissions equivalent for France = 70g/kwh CO2

[iv] Derived from UK Impact Assessment 10/2009 and clarification 1/2010

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