## Materials and Methods
### Methods  
For the conversion of raw human excrement and other organic matter collected through the sewerage system into Class-A biosolids, a bio-drying process was used. In this process, the weight of biodegradable waste was reduced through heating in the initial stages of composting. The process was sustainable since biological heat generated by aerobic degradation was used in heating to dry the sludge. As a second step, pyrolysis was used to turn the biosolids into biochar. Pyrolysis involved the heating of organic matter in the absence of oxygen, at 650\({}^{\circ}\)C with a residence time of 20 min. This process was sustainable and eco-friendly since no extra carbon and other harmful gases were left in the environment. The pyrolyzed biochar acquired from Bioforcetech Corporation was further thermally treated using a vertical furnace and a quartz reactor, at a heating rate of 15 \({}^{\circ}\)C/min and kept at 1000 \({}^{\circ}\)C for 30 min in an argon atmosphere. A Raman analysis was performed on the non-thermally treated and thermally treated biochar with a Renishaw spectrometer with excitation energy of 532 nm. A 50\(\times\) objective was used for the characterization. The spectral resolution of the spectrometer was 2-3 cm\({}^{-1}\) and laser power was kept well below 1 mW to avoid damage. Spectra were processed by removing fluorescence and normalized on I\({}_{\mathrm{G}}\) peak of carbon. The morphology of biochars were investigated using a Field Emission Scanning Electrical Microscopy (FESEM, Zeis SupraTM 40). Energy Dispersive X-Ray analysis (EDX, Oxford Inca Energy 450) was used to study the elements present in the biochars under study. A measurement setup previously validated in [22; 23; 25] for DC powders' characterization was used, which is similar to the setup adopted in [26; 27; 28; 29; 30; 31; 32; 33; 34]. As shown in Figure 1, the instrument is comprised of two solid copper cylinders, 30 mm in diameter and 5 cm in length, and encapsulated in a hollow Plexiglas cylinder with a nominal inner diameter of 30 mm in the case of powders' electrical characterization. In this configuration, the inner diameter is slightly larger so that it is possible to force the copper rods inside the Plexiglas cavity and the upper rod can slide inside the hollow cylinder during measurement. This arrangement creates an internal chamber between the two cylinders where the carbon powder can be inserted. The values obtained with this setup provide an estimated conductivity with a margin of error ranging from 15% to 20%. The electrical resistance of the powders was measured at increasing loads (up to 1000 bar) applied by a hydraulic press (Specac Atlas Manual Hydraulic Press 15T). Electrically insulating sheets were placed between the conductive cylinders and the load surfaces in order to ensure that the electrical signal passed through the sample. The resistance of the carbon fillers was measured using an Agilent 34401A multimeter. From the values of the resistance, R, the conductivity, \(\sigma\), can be calculated by:\[\sigma=\frac{L}{RA} \tag{1}\]  
where \(L\) is the length of the cylinder and \(A\) is the section. The shielding effectiveness, which is a measure of the reduction of the electromagnetic field propagating in a medium, can be obtained in several ways: for example, from the measured permittivity of the medium [35] or from the measured scattering parameter in a waveguide [36]. There are two main contributions to the shielding effectiveness, namely, dissipation loss, \(L_{D}\), and mismatch loss, \(L_{M}\)[37]:  
\[SE=L_{D}+L_{M} \tag{2}\]  
where \(L_{M}\) and \(L_{D}\) can be calculated from the scattering parameters as:  
\[L_{M}=-10\ log_{10}\left(1-\left|S_{11}\right|^{2}\right) \tag{3}\]  
\[L_{D}=-10 log_{10}\left(\frac{\left|S_{21}\right|^{2}}{1-\left|S_{11}\right|^{2 }}\right) \tag{4}\]  
The composite samples were measured in a rectangular waveguide structure, as shown in Figure 2. Samples of specified dimensions needed to be fabricated to fit in the waveguide structure.