# Engineering Hydroponic Systems for Sustainable Wastewater Treatment and Plant Growth
## 3 Results
### The Plants  
All plants created dense roots, particular the AP and GP systems, with GP roots vacating the effluent pipe (Figure S6). The dense mat of roots serves as an anchor for plants and facilitates biofilm growth. However, it posed challenges for accurate plant measurements when removing them due to tangled roots, requiring cutting for removal (Figure S7). The difference between the mass plants before and at the end of each experiment is shown in Figure 2. Overall, ivy showed the highest plant mass, ranging from 34.60 to 86.20 g, followed by wheat (3.20-43.00 g) and rice (6.60-23.90 g). It can be seen from Figure 2 that there was a significant mass increase for all plants (\(p\leq 0.001\)).  
The length of the plants at the start and end of the experiment is shown in Figure 3. EF (10-25 cm) and FF (10-5 cm) systems showed the lowest growth, while MT (28-60 cm) and AP (25-50 cm) presented the highest growth.  
The hydroponic system that provided the highest average plant growth (Figure 4) was MT (90.15%), followed by AP 86.95%), NFT (59.83%), GP (50.81%), EF (39.33%) and FF (15.59%). In terms of average plant mass, again MT (136. 30%) showed the highest performance, followed by NFT (101.09%), AP (91.33%), EF (74.07%), GP (69.98%) and FF (27.78%).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Variable** & **Frequency** & **Methods** & **Reference** \\ \hline Length & Start and End & Simple scale measuring method & [21] \\ Biomass & Start and End & Dry-weight measuring method & [21] \\ Retention Time & 168 h & Set by the time of the experiment & \\ Volume & 200 L & Spectrophotometric method & [22] \\ Temperature & 1 min intervals & Partial immersion method & [23] \\ Electrical Conductivity & 24 h intervals & Spectrophotometric screening method & [23] \\ pH & 24 h intervals & Electro method & [23] \\ Carbon Dioxide & 1 min intervals & ISO 12039:2001 \\ DO & 24 h intervals & Azide modification Winkler’s method & [23] \\ Free Ammonia & 24 h intervals & Molecular absorption spectrophotometry & [23] \\ Nitrite & 24 h intervals & Molecular absorption spectrophotometry & [23] \\ Nitrate & 24 h intervals & Molecular absorption spectrophotometry & [23] \\ Total Phosphorous & 24 h intervals & Molecular absorption spectrophotometry & [23] \\ COD & 24 h intervals & Closed reflux titrimetric method & ISO 6060 \\ BOD & 24 h intervals & 5-Day dilution BOD test method & ISO 5815 \\ TOC & 24 h intervals & ISO 8245:1999 \\ Humidity & 1 min intervals & ISO 4677:1985 \\ TDS & 24 h intervals & Thermal evaporation method & [23] \\ TSS & 24 h intervals & Filtration and thermal evaporation method & [23] \\ TS & 24 h intervals & TDS = TS \(-\) TSS & [23] \\ \hline \end{tabular} Note: chemical oxygen demand (COD); total organic carbon (TOC); total dissolved solids (TDS); total suspended solids (TSS); total solids (TS); total solids (TS).  
\end{table}
Table 1: The variables within the study.  
Overall, the MT and AP systems showed the greatest root growth (Table S1 and Figure 4). This was to be expected, due to the saturated environment that these systems create.  
Figure 4: Average growth as a measurement of length (**a**) and mass (**b**) as a percentage for each system across all experiments. Geyser pump (GP), nutrient film technique (NFT), misting (MT), ebb and flow (EF), full flow (FF), aeroponics (AP).  
Figure 3: Total growth of the plants including root and body parts of the plants. Geyser pump (GP), nutrient film technique (NFT), misting (MT), ebb and flow (EF), full flow (FF), aeroponics (AP).  
Figure 2: Change in mass (g) for all experiments for the rice, ivy and wheat grass. The tomato experiment is not shown as the plant growth failed. Geyser pump (GP), nutrient film technique (NFT), misting (MT), ebb and flow (EF), full flow (FF), aeroponics (AP).