## 2 Materials and Methods
### Design of Full-Scale Cartridge  
A series of eight structures for passive treatment were installed in Eckert's Ditch, which are referred to as gates. These gates house four cartridges, each containing a mesh bag filled with Al-WTR. The design included selecting appropriate dimensions, manufacturing process, and material and size of both the gates and the mesh bags. The design of each individual cartridge dimension was primarily driven by the unit weight of the WTRs. Additional factors included the cartridge material type, the typical cross-sectional geometry necessary for support, and measured flow conditions in Eckert's Ditch. Each gate had a length restriction which limited the full size to no more than half the cross-sectional length of Eckert's Ditch to facilitate a serpentine flow in a channelized \begin{table}
\begin{tabular}{c c c c} \hline
**Screen Size** & **Mass Loss** & **Mass Lost, Individual 11.35 kg (25 lb) Bag** & **Mass Lost, Total (kg)** \\ \hline
53/120 & 0.56 & 0.064 & 2.03 \\
70/160 & 0.56 & 0.064 & 2.05 \\
70/120 & 0.59 & 0.068 & 2.14 \\
53 & 0.91 & 0.104 & 3.31 \\ \hline \end{tabular}
\end{table} 
Table 1: Mass loss calculation over a one month period for the full-scale system. A bag weight of 11.35 kg was assumed. Mass Loss, Total considers all 32 bags in the system. stream. On average, the length of each gate was 3.66 m; a 1.22 m wide gate design, divided into four 0.3-m sections (to allow for to 0.3-m cartridges in parallel). The two middle 0.3-m sections house the cartridges, and the two outside 0.3-m sections provide a solid face made of 2.54-cm thick PVC, angled slightly to direct water flow towards the cartridges. The average water depth in Eckert Ditch is 0.61 m). Parallel cartridges were stacked two high to making the height 0.62 m. The final dimension was the width which was designed specifically to the specifications of the cartridge design. Figure 1 shows a representation of the final gate design. The cartridge dimensions were 0.31 m-L, by 0.31 m-H, by 7.62 cm-W. The actual cartridge design was U shaped, with cross bars for support. The goal was to have as much open space as possible, to allow for greater flow through the area. However, additional support was necessary to keep the mesh bag containing WTR stationary. Therefore, a star design was ultimately incorporated, with 1.27-cm members running laterally, longitudinally, and diagonally in both directions. Each cartridge has a small cut in the bottom and extra material in the same spot on top to \"lock\" the cartridges in place and prevent cartridge movement within the gate. Additionally, each cartridge has a semi-track on the outside edge to accommodate nylon rope leads, which assist with installation and removal in field. A semi-track along the sides and bottom was selected instead of continuous track to save on print volume, reduce weight, and reduce material costs. The full-sized custom cartridges required custom 3D printing, chosen primarily due to the flexibility in 3D printing capabilities. Fusion Deposition Modeling (FDM) was chosen because of the wide range of printing materials available. Since the cartridges will be submerged for long periods of time in source waters for a drinking water treatment plant, it was determined that the material selected must be in-line with other materials used to make potable water. Other considerations included potential for leaching, potential degradation due to UV-exposure, and potential degradation due to being submerged for long periods of time. Two common 3D printing materials, acrylonitrile butadiene styrene (ABS) and poly-lactic acid (PLA), were ruled out. ABS due to leaching concerns of the styrene component, and PLA because it was not suitable for use in submerged applications. Two other materials met the conditions necessary for the gate installation: biocompatible polycarbonate (PC-ISO) and UltemTM 1010. Polycarbonate is a biocompatible grade, high-strength, high-impact resistant thermoplastic.