# Electrospark Method in Galvanic Wastewater Treatment for Heavy Metal Removal
## 1 Introduction
This method makes it possible to remove contaminants from wastewater, in particular the metals mercury, cobalt, copper [23; 24; 25], chromium [26; 27; 28; 29], zinc, cadmium, nickel [30; 31; 32; 33], arsenic, strontium, cesium [34; 35], nitrate, phosphate, sulfide, sulfate, sulfite [36; 37; 38], fluoride, boron [39; 40], chemical oxygen demand, clay minerals, and organic substances [41; 42; 43; 44]. Electro-blasting water treatment is used to intensify coagulation processes, i.e., to accelerate a sediment formation. The essence of this method is to pass through the wastewater short-term electrical pulses with electrodes immersed in the solution. Pulsed electric discharge in a liquid is accompanied by a sharp increase in pressure (up to 100-200 MPa), exposure to strong electromagnetic and acoustic fields, cavitation, which creates a powerful flow of liquid, a sharp rise in temperature, and other effects. The discharge interval is practically a low-temperature plasma, which transmits energy to the treated medium. An electric discharge--in fact, an explosion in the aqueous phase--causes complex physicochemical processes in it, which lead to the acceleration of the coagulation of colloidal and suspended substances, as well as the precipitation of suspensions and chemical compounds. A schematic diagram of the discharge-pulse treatment of the liquid is shown in Figure 1. In practice, the electrode system can be placed directly in the pipelines through which industrial effluents are pumped. The electric discharge occurs sequentially from one electrode pair to another. The processing model is selected so that after the operation of the last pair of electrodes, work was ready for the first pair. Water treatment is continuous. The mode of processing depends on the pipe section, a flow speed and necessary sanitary indicators of treatment. All purified water has passed through the zone of high-impulse activation. The plant for the electric blasting of wastewater is not characterized by high energy consumption, does not require excess costs to ensure the safety of service, and has a relatively small size. The method can accelerate the deposition by almost 7-8 times and significantly reduce the processing time. The positive effect of the method on the deposition rate of solid suspensions is explained by the increased coagulation of mineral particles due to the squeeze of the electric double layer under the action of the high-voltage electric discharge as a result of two opposing forces: electrostatic repulsion and van der Waals gravity. Electrospark discharge in metal-containing reactors is an effective method for producing coagulative active metal oxides and hydroxides [45; 46; 47; 48]. The method is proposed as an alternative to existing methods for the cleaning of galvanic wastewater. It was shown that it is possible in principle to purify multicomponent galvanic wastewater from heavy metal ions, namely Cr\({}^{6+}\), Ni\({}^{2+}\), Cu\({}^{2+}\), and Zn\({}^{2+}\)[44]. In this case, attention is directed to expanding the capabilities of the method, which is aimed primarily at the component treatment of galvanic wastewater, by increasing the operating voltage from 300-600 V to 3-15 kV and by using monometallic metal loading (granules of one metal) [14]. This allowed the treatment of concentrated galvanic wastewater containing Cr\({}^{6+}\) to 1000 mg/dm\({}^{3}\). However, the further implementation of this method turned out to be economically inexpedient due to the high cost and limited resource of high-voltage equipment, its increased danger, and its low process productivity. The objective of the work is to study the influence of such technological parameters (specific energy, characteristics of the electric pulses and its frequency, schemes of a channel of purified water) on the efficiency of the treatment process of multicomponent galvanic wastewater in reactors with metallic combined loading using low-voltage (up to 1000 V) electrical equipment.