# Evaluation of Waste Blends with Sewage Sludge as a Potential Material Input for Pyrolysis
## 3 Results and Discussion
### Thermogravimetric Analysis of Wastes and Their Blends
#### 3.3.1 Input Materials  
For all samples, a typical weight loss up to approx. 100 \({}^{\circ}\)C is associated with the removal of water from the sample during its pyrolysis decomposition. The highest decrease is seen for the sample of sewage sludge and paper rejects, which is related to the high moisture content (Table S1). The results for the TGA/DTG of the input waste materials are shown in Table 1, and the TG curves of the input waste materials are shown in Figure 8. The temperatures of maximum weight loss in the TGA experiments for the input waste materials are shown in Figure S1.  
Figure 6: Combustible matter h\({}^{\text{d}}\) (%) and the ratio C\({}^{\text{d}}\)/H\({}^{\text{d}}\), d means in dry matter.  
Figure 7: The LHV\({}^{\text{d}}\) (MJ/kg) and ash\({}^{\text{d}}\) at 550 \({}^{\circ}\)C (%).  
For the sample of SS, (1) the first interval of decomposition was between 100 and 200 \({}^{\circ}\)C, which is related to the decomposition of sewage sludge components (biodegradable organic material and bacterial matter); (2) the second interval was between 200 and 520 \({}^{\circ}\)C, which related to the decomposition of organic matter (hydrocarbons between 200 and 390 \({}^{\circ}\)C, proteins, sugars, aliphatic compounds of SS between 390 and 520 \({}^{\circ}\)C); (3) at temperatures above 520 \({}^{\circ}\)C, the volatile matter evaporates from the carbon residue (secondary pyrolysis), and weight loss associated with organic matter may continue up to 600 \({}^{\circ}\)C; (4) at temperatures above 600 \({}^{\circ}\)C, inorganic material (e.g., CaCO3, ash in SS) decomposes [10; 49]. As described in a recent review [10], there is a difference in the pyrolysis product (tar and char) yields under fast and slow pyrolysis. Slow pyrolysis generally leads to higher char yield and lower tar yield than fast pyrolysis.  
Plastics  
For all samples containing plastics, a weight loss of up to 500 \({}^{\circ}\)C is typical, which is associated with the pyrolysis decomposition of a particular plastic. The thermal degradation of plastics takes place via a chain mechanism--fission reactions involving serial and parallel reactions (individual reactions overlap) [50]. The thermal decomposition of plastics takes place in several steps: chain radical mechanism \(\rightarrow\) initiation \(\rightarrow\) H-abstraction \(\rightarrow\) beta-scission \(\rightarrow\) radical recombination [51].  
Thermal decomposition is related to the chemical structure and complexity of the substance. PP decomposes at lower temperatures than HDPE due to tertiary carbons in the polymer structure, as described by [52]. In our experiments, the plastics decomposed in the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Inlet Material** & **Tmax** & **Mass Change at Tmax** & **T1** & **Weight Loss Rate at T1** \\ \hline  & \({}^{\circ}\)**C** & **\%** & \({}^{\circ}\)**C** & **\%/min** \\ \hline LDPE & 998.9 & 88.09 & 479.9 & 26.98 \\ RDF & 999.0 & 85.85 & 469.1 & 11.73 \\ TP & 998.8 & 85.13 & 429.3 & 13.77 \\ PR & 998.9 & 81.55 & 348.1 & 11.85 \\ PES & 998.8 & 72.66 & 378.6 & 6.16 \\ SS & 998.9 & 53.19 & 325.2 & 1.62 \\ \hline \hline \end{tabular} Note: T1 is the temperature of highest mass loss determined from the DTG curves.  
\end{table}
Table 1: Results of TGA/DTG for the input waste materials.  
Figure 8: TG curves of input waste materials.  
order PES > TP > LDPE, from lower to higher temperatures. LDPE and TP decomposed in a narrow temperature range. For pure plastics, there should be no carbon residue [53], which is not the case for our plastic materials.  
The PES sample is characterized by the TG decomposition curve of tires [54], which decomposes at two temperatures (361 and 410 \({}^{\circ}\)C). The first step is attributed to the presence of natural rubber, while the second step to a blend of butadiene rubber with styrene-butadiene rubber [55].