# Reduction of Water Color in a Spinning Disc Reactor
## 3 Results
### Colored Water Treatment with Selected Adsorptive Materials in SD Experimental Setup
#### 3.1.1 Influence of Colored Water Flow Rate on Discoloration for All Tested Adsorbents  
_Testing ZnAllDH as an adsorbent in the SD setup_. The influence of the colored water flow rate treated with ZnAllDH (2 g/L) at four different constant spinning disc rotational speeds, namely 100, 250, 500 and 800 rpm, respectively, is indicated in Figure 1a-d, where the abscissa indicates the processing residence time. For all the investigated flow rate values of 5.76, 6.00, 7.44 and 8.16 L/h, the color removal increased, attaining the highest measured value of 49.03% after a 55 min working time period at 250 rpm. Other operating parameter values rendering data higher than 40%, which is useful for water discoloration in an SD setup, as presented in Figure 1, are synthesized in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Investigated Samples** & **t = 0 min** & **t = 30 min** & **t = 60 min** & **t = 90 min** & **t = 120 min** \\ \hline Sample 1 (pH = 7) & 0.344 & 0.182 & 0.233 & 1.292 & 2.003 \\ \hline Sample 2 (pH = 2.5) & 0.330 & 1.429 & 1.758 & 2.051 & 2.071 \\ \hline Sample 3 (pH = 4.5) & 0.374 & 0.305 & 0.659 & 1.052 & 1.340 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured absorbances (A\({}_{456}\)) of three different colored water samples containing 0.1 g of ZnAllDH/50 mL (2 g/L) at different mixing times. Figure 1: Colored water flow rate influence on RR-dye-based color removal in an SD system with ZnAILDH: (**a**) 100 rpm, (**b**) 250 rpm, (**c**) 500 rpm, (**d**) 800 rpm. Table 3 includes the maximum discoloration values at different disc rotational speeds and water flow rates attained within the SD experimental setup. One can observe that these values ranged between \(\sim\)30% and almost 50% color removal in the SD setup, within a less than one hour working time period. The maximum obtained color removal and the corresponding working conditions are highlighted in bold font. _Testing TiO\({}_{2}\) as an adsorbent in the SD setup_. The colored water treated with solid TiO\({}_{2}\) (2 g/L) at the same colored water flow rate values of 5.76, 6.00, 7.44 and 8.16 L/h, respectively, at constant disc rotational speeds of 100, 250, 500 and 800 rpm, rendered increasing trends of color removal over time, with the maximum attained values ranging from \(\sim\)40% to the highest of 67.55% (obtained at 6.00 L/h and 800 rpm, after 70 min), as presented in Figure 2a-d. Based on the obtained results, TiO\({}_{2}\) was confirmed as having good adsorbent properties when used in correlation with the SD technology. A somewhat similar system formed of TiO\({}_{2}\) stored as a thin layer on a spinning disc was used to investigate the photo-oxidation of Methylene Blue dye dissolved in a water stream, with the largest reaction rate reported at 100 and 200 rpm [7]. The maximum color removal values obtained using TiO\({}_{2}\), in an SD experimental setup together with the corresponding working conditions, namely water flow rate and disc rotational speed values, are included in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rotation Speed** & **Flow Rate** & **Color** & **Time Period** \\
**[rpm]** & **[L/h]** & **Removal [\%]** & **[min]** \\ \hline \multirow{4}{*}{100} & 5.76 & 52.74 & 95 \\ \cline{2-4}  & 6.00 & 52.84 & 90 \\ \cline{2-4}  & 7.44 & 45.98 & 59 \\ \cline{2-4}  & **8.16** & **56.52** & 55 \\ \cline{2-4}  & **5.76** & **61.00** & 90 \\ \cline{2-4}  & 6.00 & 52.85 & 84 \\ \cline{2-4}  & 7.44 & 46.62 & 60 \\ \hline \multirow{4}{*}{500} & 5.76 & **56.90** & 85 \\ \cline{2-4}  & 6.00 & 46.93 & 75 \\ \cline{2-4}  & 7.44 & 56.08 & 95 \\ \hline \multirow{4}{*}{800} & 5.76 & 39.23 & 90 \\ \cline{2-4}  & **6.00** & **67.55** & 70 \\ \cline{2-4}  & 7.44 & 59.68 & 93 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Maximum discoloration values for tested water flow rates and disc rotational speeds using TiO\({}_{2}\) within an SD experimental setup.