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Performing experiments with mixed commercial waste, sampling is unavoidable for material analysis. Thus, the procedure of sampling needs to be defined in a way that guarantees sufficient accuracy regarding the estimation of the examined analytes. In this work, a sampling procedure for coarsely shredded mixed commercial waste, based on the Austrian Standard ÖNORM S 2127, the horizontal sampling standard DS 3077 and the theory of sampling, was established, described and examined through a replication experiment determining the relative sampling variability. The analytes are described through a matrix of nine (9) material classes and nine (9) particle size classes. It turns out that the typical threshold value of 20% can be reached for some fractions of the particle size-material matrix (for example, wood 20-40 mm and cardboard 60-80 mm) but gets as bad as 231% (wood 200-400 mm) for others. Furthermore, a decrease in the relative sampling variability with the mass share of a fraction is observed. Part of the observed variability is explainable through the fundamental sampling error, while contributions of other types of sampling errors are also evident. The results can be used for estimating confidence intervals for experimental outcomes as well as assessing required sample sizes for reaching a target precision when working with mixed commercial waste. Keywords Theory of sampling • Relative sampling variability • Commercial waste • Coarse shredder • Increment mass • Sample mass List of symbols v Binary matrix for combining adjacents of v particle size fractions [-] w Binary matrix for combining 1 to w material classes [-] c Constitutional parameter [kg/m 3 ] CV Coefficient of variance [-]

Mechanical processing using predominantly particle size and density as separation criteria is currently applied in the production of solid-recovered fuel or refuse-derived fuel. It does not sufficiently allow for the optimization of the quality of heterogeneous solid waste for subsequent energy recovery. Material-specific processing, in contrast, allows the separation criterion to be linked to specific chemical constituents. Therefore, the technical applicability of material-specific sorting of heterogeneous waste, in order to optimize its routing options, was evaluated. Two sorting steps were tested on a pilot and a large scale. Near infrared multiplexed sensor-based sorting devices were used (1) to reduce the chlorine (Cl) respectively pollutant content, in order to broaden the utilization options of SRF in industrial co-incineration, and (2) to increase the biogenic carbon (C(bio)) content, which is highly relevant in the light of the EU emission trading scheme on CO₂. It was found that the technology is generally applicable for the heterogeneous waste fractions looked at, if the sensor systems are appropriately adjusted for the sorting task. The first sorting step allowed for the removal of up to 40% of the Cl freight by separating only 3 to 5% of the material mass. Very low Cl concentrations were achieved in the output stream to be used as solid-recovered fuel stream and additionally, the cadmium (Cd) and lead (Pb) concentration was decreased. A two- to four-fold enriched C(bio) content was achieved by the second sorting step. Due to lower yields in the large-scale test further challenges need to be addressed.

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