Observation versus self-perception: Effectiveness of measures to increase separate bio-waste collection from multi-storey residential buildings

Schemes for source separation of municipal bio-waste aim for maximum coverage and minimum contamination to enable high-quality recovery routes. To identify suitable approaches to improve the separate collection and quality of bio-waste in multi-storey residential buildings, which often exhibit poor source separation, this study evaluates the effectiveness of a set of measures aiming to sensitize residents and facilitate source separation at household level. Three buildings (181 residents) were selected in Kassel (Germany) using a purposive sampling approach. The measures implemented comprised verbal, written and visual communication as well as pre-sorting equipment. By conducting 8 waste characterization campaigns and 2 series of structured interviews (24 and 16 participants, respectively), the qualities and quantities of collected bio-waste were contrasted with the residents’ self-perceived level of information and participation in the source separation of bio-waste. Starting at 55%, 46% and 42%, separate collection rates for bio-waste increased to averages of 64%, 60% and 48%, respectively, after implementation of the measures. Impurity contents of separately collected bio-wastes were barely affected, averaging 2%, 8% and 4%, while peaking at 4%, 16% and 8%, respectively. Considering interview response patterns, the withdrawal of access to bio-waste bins from residents not interested in complying with source-separation guidelines seems necessary to achieve low contaminant levels. The residents’ perception of individual measures varied across the buildings, indicating a need for site-specific interventions to motivate people to participate in source separation. Further observations suggest that an intensified and sustained feeling of social responsibility and monitoring positively affects bio-waste separation behaviour.