# Moisture Measurement in Paper and Cardboard Packaging Waste Bales for Recycling
## 2 Materials and Methods
### Bale Analysis Methodology  
The methodology presented below was replicated 23 times in a total of 11 waste treatment facilities. In seven of the facilities, wastewater and cardboard came from selection bins, and they were sorted and baled. In the other four facilities operated by recycling companies, bales were produced from materials that had undergone more refined sorting.  
Forty-eight bales were analyzed in total. In each analysis, bales of recently produced paper and cardboard waste were selected, taking into consideration the condition of the bales' surficial characteristics. For example, the surfaces selected were as flat as possible, with a minimum number of empty spaces and not presenting evidence of significant contamination by fats or metals.  
The bales were weighed using a scale, and their dimensions were measured for weight and volume determination. The parameters of the medium (in this case, the bales of paper and cardboard packaging waste), such as the density and the content of cardboard packaging, needed be evaluated in order to study any interference with the moisture measurements with the tested equipment. The compression density, a parameter that is advanced by the manufacturer and calculated according to Equation (1), must also be evaluated for the same purpose:  
\[\text{Compression density}\left[\frac{\text{kg}}{\text{m}^{3}}\right]=\frac{ \text{Specific Weight}\left[\frac{\text{kg}}{\text{m}^{3}}\right]}{1+\frac{ \text{Moisture content}\left[\%\right]}{100\ \%}} \tag{1}\]  
After determining the bale dimensions, the \"front\" and \"back\" surfaces were defined as shown in Figure 2, and measurements were made with the equipment in volts (V). The number of measurements per face was variable, being at least five per face up to the maximum possible number of measurements according to the bale size. Then, the arithmetic average of these measurements was calculated, thus representing the moisture content of the measured bale.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Equipment Characteristics** & \\ \hline Resolution & 0.5\% \\ Operative temperature & 0–40 \({}^{\circ}\)C \\ Relative humidity of the ambient air & 30–70\% \\ Effective measurement depth & 30 cm \\ Maximum measurement depth & 50 cm \\ Detection limit (ww) & 1–50\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: EMCO® model AP 500-M3 operational characteristics, according to the manufacturer.  
Figure 2: **Sampling collection location**, front (F) and back (B) of the bales divided into the three sampling sections, plus the two samples collected in each center of a half-bale (C).  
Once measurements were performed, samples of paper and cardboard waste were collected, and the moisture content was determined using the conventional oven drying method, carried out according to the standard ISO 287 method [2]. For this purpose, eight samples were taken from each bale. Six of them came from the first 30 cm layer of each the front face (F1, F2 and F3) and from the back face (B1, B2 and B3) (Figure 2). The bottom and the top faces were discarded because they were not used for the measuring equipment due to contamination and the presence of metal straps. The other two samples were collected from the center of each half-bale (C1 and C2). This method allowed the sampling of a fair representation of the bale materials and moisture distribution and allowed determination of the moisture content from the oven drying method at the same location as the equipment measurements. Moisture content, on a wet basis, was determined by dividing the oven dry mass by the initial (wet) mass according to Equation (2):  
\[\text{Moisture content (MC), \%=}\frac{\text{Initial mass }-\text{ Owen dry mass}}{\text{Initial mass}}\times 100\% \tag{2}\]