## Materials and Methods
### Neutralization Method
#### 2.2.3 General Description of the Semi Industrial Plant for Two-Step Neutralization Treatment  
Specification of the semi industrial plant (Figure 2), which consists of five Units, a Compressor, and a Control Panel, and that continuously performs the pH control and flocculation-precipitation of the AMD in two steps, is given in Table 2.  
Storage tank for wastewater (volume 1000 L) is used for storage for the sampled AMD from the proposed location. Ambient conditions are 5-40 \({}^{\circ}\)C; Power Supply: 220 VAC \(\times\) 3-phase \(\times\) 50 Hz, 13 kVA. Equipment is made from acid resistance material due to the fact that the acidity of AMD is mostly between 2.5 and 4, that is some as for pH of AMD from the Robule Lake (Table 1).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Description** \\ \hline \multirow{6}{*}{Unit A: Wastewater supply} & Receiving pump, flow rate: 20 L min\({}^{-1}\), used for transport the feed wastewater in the wastewater tank. \\  & Wastewater tank, for storage of feed wastewater. \\  & Wastewater pump, flow rate: 2-7 L min\({}^{-1}\), used for feed wastewater transport in unit B. \\ \hline \multirow{6}{*}{Unit B: pH control and flocculation-precipitation, configured from: Unit B-1, Unit B-2 and Unit B-3} & Unit B-1: Thickener A, volume 410 L, used for solid–liquid separation of the feed water that has been done primary pH control (according to the first set pH value) and flocculation. Unit B-2: pH Control tank A/B (50 L each tank), flocculation tank A/B, (50 L each tank). This unit is used for the primary pH control (according to the first set pH value), secondary pH control (according to the second set pH value) and flocculation of the feed wastewater. A pH control agitator A/B is used for solution mixing in the pH Control tank A/B. \\  & Flocculation agitator A/B is used for solution mixing in the \\  & Unit B-3: Thickener B, volume 410 L, used for the solid-liquid separation of the feed water that has been done the secondary pH control (according to the second set pH value) and flocculation. \\ \hline \multirow{6}{*}{Unit E: Filtration} & Thickener A and Thickener B of Unit B should be visually checked regularly for slurry buildup, and as it has grown to a substantial level, manually operated valves under the respective thickeners should be opened for discharge of slurry by a slurry pump, flow rate 20 L min\({}^{-1}\), to Filter press, capacity 3 L. The filtrate will be discharged by a portable filtrate pump or returned to the wastewater tank depending on the level of its water quality. Filter press will be of a fully automatic type with a pneumatic press function built in. \\ \hline \multirow{6}{*}{Unit C: Slaked lime feed} & Slaked lime and water are to be charged into a Lime slurry tank, volume 250 L, in advance for controlling its concentration to 2.5 mass \%. The conditioned lime sludge will be sent automatically, by lime sludge pump A/B, (0.5 L min\({}^{-1}\)) to pH Control tank A/B according to their respective pH values. \\ \hline \multirow{6}{*}{Unit D: flocculant feed} & Polymer flocculant and water are charged into the flocculant tank, (volume 100 L), in advance for controlling its concentration up to 0.5 g L\({}^{-1}\). The conditioned flocculant will be sent to the Flocculation tank A/B at a constant feed rate irrespectively of the feed water flow rate by a flocculant pump A/B, flow rate 0.05 L min\({}^{-1}\). \\ \hline \multirow{2}{*}{Compressor} & Compressor (370 L min\({}^{-1}\)) will be used in order to supply the compressed air to filter press and solenoid valves. \\ \hline \multirow{2}{*}{Control panel} & Control panel will be used for control, operation and power supply of equipment \\ \hline \hline \end{tabular}
\end{table}
Table 2: General description of the semi industrial plant for two-step neutralization treatment.