results

[questionary]    [recovery rates]    ["impurities" in biobin]    [processing]    [BDP composts]

Processing in the composting plant

The impact of BDPs on the source separation during processing was studied by adding defined quantities of BDP packaging to the organic waste. This provided information as to whether BDPs can be detected during manual source separation, how much of them are mistakenly removed and how they influence the efficiency with which impurities are removed. Impurities are removed from organic wastes at the Göttingen composting facility by a manual source separation process on a conveyor belt before entering the composting section. This practice differs from that in other facilities where the impurities are removed mechanically by screening aggregates before or after composting process.

The results of the studies varied according to belt speed, the amount of impurities and the BDP fraction. Impurities were removed effectively if they were present in only moderate levels and if the BDP fraction was not to high. In such cases, the quantity of BDPs removed mistakenly was relatively small. Where the organic waste was highly contaminated (percentage of impurities higher than five percent) and the BDP fraction was high, the success rate decreased - the workers had quickly to evaluate which objects were impurities and which not. Due to the similarity of BDP with conventional plastic packaging the quantity of impurities removed decreased, and more and more BDPs were mistakenly removed.

Nevertheless, comparisons cannot be made with other composting facilities, since they employ different methods to remove impurities, such as mechanical upstream and downstream screening, in which the packaging size is the determining factor.
The results do, however, afford insights into how the method might be optimised. Plants that employ manual source separation would likely also benefit from mechanical pre-processing (generally screening) of the incoming organic waste stream and slower throughput. This would increase efficiency and ensure that the BDP products reach the composting section without being mistakenly removed to any significant degree.

The BDP packaging itself did not impair the composting process. Machines as e.g. turning units were not damaged or negatively influenced by the BDP packagings. The property of compostability itself was not investigated since only certified products were employed that meet the standards of DIN V 54 900 or EN 13432.