Determination and improvement of the quality of separately collected bio-waste from households

The recycling of bio-waste from households is an essential factor in achieving the recycling quotas for municipal waste laid down by the EU. A major problem is posed by impurities in the bio-waste collected, such as plastics, metals and glass. It is virtually impossible for compost producers to produce quality-assured compost from bio-waste with an impurity content of more than 3 wt%_OS. The draft of the new Austrian Compost Ordinance stipulates a limit of 2 wt%_OS of interfering substances in accepted bio-waste. A rapid measurement method has been developed and comprehensively validated for the immediate on-site checking of contaminant content at the bio-waste bin or in a vehicles. Data on the type and amount of impurities collected in the course of sorting analyses carried out over several years in 10 selected areas in Styria, Austria showed an average impurity content of 2.1 wt%_OS. This impurity content can be considered representative for rural and urban communities in Austria. Among the interfering substances, plastics predominate, at 53%, of which pre-collection bags made of plastics form the highest proportion. A more detailed examination of pre-collection bags shows a higher proportion of use of biodegradable plastic bags, which have become more numerous in recent years in the more rural communities. In order to reduce mis-sorting, the effect of a wide variety of measures on citizens was tested in selected areas. Here, the distribution of paper bags as well as the threat of a cost increase due to special collections in combination with distribution of these bags were the methods with the greatest effect. Motivational letters and the threat of special collections, however, showed no significant result.