## 3 Results
### Textile WW Treatment Performance Using SD Technology Laboratory Setup
#### 3.1.2 Disc Rotational Speed Influence on the Treatment Efficiency Using SD Laboratory Setup
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Rotation Speed** & **Flow Rate** & **Color Removal 1** & **SS Removal 2** & **Time Period 1,2** \\
**[rpm]** & **[L/h]** & **[\%]** & **[\%]** & **[min]** \\ \hline \multirow{4}{*}{100} & 10 & **45.21** & 12.82 & 50; 45 \\  & 15 & 41.67 & **57.32** & 60; 60 \\  & 20 & 27.61 & 45.98 & 50; 60 \\  & 25 & 25.17 & 11.11 & 40; 30 \\  & 30 & 17.32 & 11.18 & 30; 30 \\ \hline \multirow{4}{*}{250} & 10 & 18.95 & **54.29** & 60; 60 \\  & 15 & 22.95 & 42.05 & 60; 60 \\  & 20 & **33.16** & 45.98 & 60; 60 \\  & 25 & 27.33 & 6.78 & 21; 30 \\  & 30 & 18.79 & 11.18 & 30; 25 \\ \hline \multirow{4}{*}{400} & 10 & 22.41 & **50.00** & 60; 60 \\  & 15 & 31.22 & 5.19 & 60; 50 \\  & 20 & **46.98** & 49.78 & 50; 50 \\  & 25 & 27.35 & 30.61 & 30; 35 \\  & 30 & 18.18 & 4.28 & 30;14 \\ \hline \multirow{4}{*}{550} & 10 & 22.41 & 10.62 & 60; 50 \\  & 15 & **53.50** & **61.13** & 50; 50 \\  & 20 & 10.63 & 16.01 & 50; 40 \\  & 25 & 17.72 & 30.60 & 35; 35 \\  & 30 & 17.51 & 9.71 & 30; 25 \\ \hline \multirow{4}{*}{850} & 10 & 43.07 & 9.33 & 60; 52 \\  & 15 & **48.03** & 45.53 & 60; 55 \\  & 20 & 36.08 & 51.88 & 50; 50 \\  & 25 & 31.58 & **54.51** & 40; 40 \\  & 30 & 30.18 & - & 30; - \\ \hline \multirow{4}{*}{1200} & 10 & 37.45 & 26.35 & 60; 60 \\  & 15 & **39.56** & **52.14** & 60; 60 \\  & 20 & 39.09 & 38.95 & 58; 53 \\  & 25 & 14.76 & 4.2 & 40; 35 \\  & 30 & - & 14.08 & -; 25 \\ \hline \multirow{4}{*}{1500} & 10 & - & - & - \\  & 15 & **49.64** & **54.98** & 30; 25 \\ \cline{1-1}  & 20 & - & - & - \\ \cline{1-1}  & 25 & - & - & - \\ \cline{1-1}  & 30 & 1.69 & 6.68 & 20; 15 \\ \hline \hline \end{tabular} Note: 1 Color removal, 2 SS removal.  
\end{table} 
Table 2: Maximum values of the color and suspended solids removals. induces increased color adsorption and SS removal. The density of such irregular waves at increasing rotational speeds of 400, 550, and 850 rpm appears to remain approximately the same, thus similar micromixing intensities were acting within the liquid film and, consequently, the highest removal values were registered in the above-mentioned rotation speed interval. However, the largest flowrates of 20, 25, and 30 L/h, in the same rotational speed interval rendered a decrease in the maximum discoloration and SS removal, possibly due to the shorter residence time periods despite the increased degree of micromixing. At larger rotational speeds, of 1200 and 1500 rpm, the liquid residence time decreases further and the intense micromixing is not efficient. Bentonite used in this study is known as a natural clay material with good adsorption capabilities for different types of pollutants, organic or inorganic compounds, including heavy metals. A WW treatment with bentonite in a spinning disc setup was expected to have increased adsorption capabilities given the intensive micromixing and the much smaller micromixing times compared to the larger disc residence times [36]. Thus, a significant decrease in color was expected and finally observed in the laboratory SD setup. Additionally, bentonite is known to promote agglomeration (as coagulation adjuvant), which typically contains two stages, the first one characterized by rapid mixing for a better dispersion of the destabilization agent (coagulation adjuvant) and the second characterized by a gentler mixing to allow for flocs formation and separation by settling. However, it is known that by varying such factors as mixing speed (an increase during the second stage of coagulation), mixing intensity, and mixing time, improvements in the suspended solids and turbidity removal can be obtained [38; 39]. That is why it is possible that certain values of the WW flowrate and disc rotational speed within the SD setup have rendered improved values for suspended solids and turbidity within relatively short time periods. The wastewater treatment efficiency by SD technology in the presented laboratory setup is reasonably good, considering that no other chemical, mechanical-physical or biological treatment processes or operations were applied.