Determination and verification of posible resource savings in manual dishwashing

Many tests and consumer surveys have shown that manual dishwashing at home is done in very different ways, taking also different amounts of resources. Because almost every household, whether owning an automatic dishwasher or not still keeps on washing up a few items by hand, it seems necessary to investigate manual dishwashing regarding optimisation. Therefore, a project was run at the University of Bonn to find out an optimal way to clean the dishes by hand. Optimisation in this case means to reach a reasonably good cleaning performance with the minimum amount of resources, as water and energy for example. First, manual dishwashing was investigated experimentally: A repeatable method was developed for the sink washing process and with this method, several factorial studies were performed to find the factors in the process that influence the cleaning performance most. On the basis of the results of the experimental investigation and the knowledge – from previous studies on manual dishwashing – on how consumers wash up, Best Practice Tips were defined as an applicable guide for the consumer to save resources. In order to find out if it is possible to save resources when consumers apply the Best Practice Tips, several verification studies were run: three comparative laboratory studies, in which the test persons had to wash up different amounts of dishes, once with their usual behaviour and once by applying the Best Practice Tips. The results showed that especially with higher amounts of dishes, relevant resources of energy and water can be saved. However – possibly due to a different method existing for washing up of only a few items – no significant reduction was found when consumers were applying the Best Practice Tips with small amounts of dishes. As a next step, the possibility to save resources with the Best Practice Tips was verified in an in-home study in two countries (Germany and Spain). The findings of the previous studies could be confirmed in general. The savings of water and energy were especially high when persons usually washing up under running tap water changed their behaviour and washed up the dishes in a sink filled with water. However, the individual savings differed very much. This work delivers fundamental knowledge how resources can be saved in manual dishwashing. It is up to future studies to intensify the experimental investigation of manual dishwashing and the training with the Best Practice Tips.