# Electrospark Method in Galvanic Wastewater Treatment for Heavy Metal Removal
## 3 Results  
The peculiarity of the experiment was that the electro erosion powder, which is formed during the electrospray process, is a coagulant. At volumetric fluid flow rates of 50 dm\({}^{3}\)/h, the system is in a suspended state. Auto sedimentation is observed (Figure 6) immediately after sampling (order of time: min). The color of the liquid was changed from light yellow to transparent. To visualize the effect of self-sedimentation, i.e., the formation of a large amount of electro erosion powder, the treatment was performed for a long time: about 3 h with looping of the fluid flow. A sampling of wastewater from the reactor was carried out immediately after the end of each treatment. The wastewater was filtered using F-type filter paper. The volume of the sample filtrate for chemical analysis was 1.5 dm\({}^{3}\). The content of heavy metal ions in wastewater generated by the enterprise is not constant. Therefore, for all through treatments, one source material was used: sewage selected at treatment plants (Table 1). The study also used another concentrated content of harmful substances source material (Table 1, second line) of the same galvanic origin, which was selected at treatment plants at other times. So, the source material for treatment is natural sewage of galvanic production from different streams of a machine-building enterprise. The choice of the range of variation of parameters and processing schemes is based on the following assumptions. The specific energy is varied taking into account the data given in paper [17], which relates \begin{table}
\begin{tabular}{c c c c c} \hline
**pH** & **Color** & **Zn\({}^{2+}\), mg/dm\({}^{3}\)** & **Cr\({}^{3+}\) + Cr\({}^{6+}\), mg/dm\({}^{3}\)** & **Cu\({}^{2+}\), mg/dm\({}^{3}\)** \\ \hline
7.45 & light yellow & 0.26 & 1.27 & 0.06 \\
6.00 & light yellow & 0.06 & 4.69 & 5.28 \\ \hline \end{tabular}
\end{table} 
Table 1: The content of heavy metal ions in the source wastewater (basic galvanic discharge). Figure 6: Deposition of electro erosion powder after sampling. to the purification from highly concentrated solutions of heavy metal ions (from 8500 mg/dm\({}^{3}\)--total content of heavy metals and up to 600 mg/dm\({}^{3}\) Cr\({}^{6+}\), respectively) with high-voltage electric discharges in reactors with granular metal loading in a column electrocoagulator. We used data on the electrospray method for producing highly dispersed powders of metals and alloys to select the value of the pulse energy (W\({}_{\text{p}}\)) [50]. This process can be implemented with pulse frequencies (\(f\)) up to several kHz using capacitor banks with capacities from 10 to 120 uF. For research, we chose a capacitance corresponding to the middle of the range: 65 uF. The charging voltage was determined experimentally. To do this, we first set the charging voltage (U\({}_{0}\)), which corresponds to the extremum of the relative energy release in the interelectrode gap of the dispersion reactor to the stored energy of the capacitor bank. \[\eta_{W}=\frac{W_{p}}{W_{0}}=\frac{\int\limits_{0}^{\tau 1}i(t)u(t)dt}{W_{0}} \tag{1}\]  
where W\({}_{\text{p}}\) is the energy that is released in the interelectrode gap of the reactor during one discharge pulse, J; W\({}_{0}\) = CU\({}_{0}\)\({}^{2}\)/2 is the energy stored by the capacitor bank to the beginning of the discharge, J; and \(\tau\)1, i(t), and u(t) are the discharge time, discharge current (time dependence), and the voltage on the electrode gap (time dependence), respectively, which are calculated from the results of oscillography (Figure 7). Further increase of the charging voltage translates the discharge into the oscillating phase, which is very rarely used in the implementation of the electro spark method, both for fundamental reasons and for technical reasons, as there is a need to use a high-frequency diode connected to the switch. The maximum value of \(\eta_{W}\) can be equal to 0.9-0.95 (Figure 7a).