# Evaluation of Waste Blends with Sewage Sludge as a Potential Material Input for Pyrolysis
## 2 Materials and Methods
### Waste Blends Preparation  
Six waste materials were selected for experimental tests. The high and low heating values were measured for each waste blend (55 in total). These values were key parameters for the selection of suitable waste blends for the further study of thermochemical conversion processes. Information on the average dry matter or moisture and bulk density of selected waste materials is summarized in Table S1. Specifically, these were sewage sludge from a public wastewater treatment plant (SS), low-density polyethylene rejects (LDPE), non-specified thermoplastics (TP), solid residual fuel (RDF), polyester rejects from tire processing (PES), and paper rejects (PR). All the above parameters were measured according to the standards [33; 34; 35]. Except for SS, all materials were ground to a fraction <2 mm on a laboratory mill IKA MF 10 basic (IKA(r)-Werke GmbH & Co. KG, Staufen, Germany). From each of the individual materials, two and three mixtures were formed together with SS. In total, 55 waste blends in various volume ratios were prepared.  
Because SS has an average moisture content of about 72 wt. %, this moisture level was an advantage for mixing with other types of waste. SS served as a binder for individual components. The first \"binder tests\" were aimed at forming granular mixtures being prepared in volume and weight ratios, respectively. After weighing the individual components of the mixtures, the waste blends were then mixed on a laboratory mixer HOBART--HSM 10 (HOBART GmbH, Offenburg, Germany). The blends were then spread on the surface and freely dried in the laboratory at room temperature for 1 week.  
The dry matter or moisture of the blends were always measured after their preparation and after a week of drying. Then, gross and net calorific values and other parameters were determined. From 55 experimental blends, 8 blends were selected on the basis of the highest measured values of gross and net calorific values. In addition, 4 were double  
Figure 2: Consistency of 1—raw SS (moisture 72 wt. %) and visualization of waste inputs: 2—dry SS (sewage sludge), 3—LDPE (low-density polyethylene), 4—TP (thermoplastics (non-specified)), 5—RDF (residual derived fuel), 6—PES (polyester), 7—PR (paper rejects).  
blends and 4 were triple blends. The individual ratios, the combinations of waste materials, the moisture and dry matter, and the gross and net calorific values of selected mixtures are shown in Table S2.  
The description and physical appearance of waste blends are shown in Figure 3.  
1. The 3 RDF:SS:PR blend was light brown in color with a slight odor. The material was light.
2. The 3 PES:SS:PR blend was grey with a slight odor. The material was not compact. It consisted of separate pieces of rubber and fluffy PES fibers mixed with sludge.
3. The 4 LDPE:SS blend had a good structure. It was slightly damp. LDPE formed a compact mass with sewage sludge.
4. The 4 LDPE:2 SS:PR blend was well workable and was light black in color. It was slightly damp. Small pieces of LDPE can be seen in the mixture. LDPE formed a compact mass with sewage sludge.
5. The 6 LDPE:SS blend was rather dry and did not form a compact mass. Due to the large proportion of LDPE, small colored pieces were visible in the mixture. The mixture was blackish brown in color with a musty smell.
6. The 3 LDPE:SS:PR blend was rather dry and did not form a compact mass. The mixture was dark brown in color with a slight odor.
7. The RDF:SS blend was very moist with a strong odor. The mixture was hard to mix together. The individual grains stuck together and formed a lumpy structure.
8. The 3 TP:SS blend was very moist with a slight specific odor. The discrete grains stuck together and formed a lumpy structure.