# Electrospark Method in Galvanic Wastewater Treatment for Heavy Metal Removal
## 1 Introduction  
Wastewaters that contain heavy metals present an environmental risk. Anthropogenic sources of biosphere pollution by heavy metals include ferrous and nonferrous metallurgy enterprises (aerosol emissions, industrial discharges), mechanical engineering (galvanic baths, copper plating, nickel plating, chrome plating, cadmium plating), battery recycling plants, road transport, and so on [1; 2; 3; 4; 5; 6]. Heavy metals enter into reservoirs with discharges from mining and metallurgical enterprises, as well as chemical and light industry enterprises, where their compounds are used in various technological processes. So, many chromium and nickel salts are used to galvanically coat the surfaces of metal products. Compounds of copper, zinc, cobalt, and titanium are used in the production of dyes, etc. Issues of water quality and status are among the priorities in the environmental policy of European countries [7; 8; 9; 10; 11]. Therefore, the question of finding effective wastewater treatment methods containing heavy metals is an urgent issue. There are different physical, chemical, biological,electrochemical, and galvanocoagulation methods that are used for the treatment of wastewater [12; 13]. The most common method of wastewater treatment is a reagent. Its advantages are the relatively high productivity and low energy consumption, and its disadvantages are low efficiency (up to 10% of heavy metal salts remain in solution). The traditionally used biological treatment processes need a large operational area and much time. Chemical coagulation processes are very slow, with a large amount of sludge. The disadvantage of ion exchange techniques is the high cost of purification. Electrocoagulation and electroflotation are promising electrochemical methods. The advantages of the electrocoagulation method are its environmental friendliness, versatility, low operating costs, low energy requirements, minimal chemical additives, and sludge minimization. In particular, it is used for wastewater treatment in the printing, textile, meat processing, oil refining, dairy, and leather industries, in agriculture, and in the service sector: car washes, restaurants, cafes, laundries, etc. Among many methods, coagulation methods for wastewater treatment from heavy metal ions are the most effective and used [14; 15]. Reagent coagulation is based on the hydrolysis of polyvalent metal salts (aluminum and iron), which lead to the formation of highly dispersed oxides and hydroxides of these elements, which can actively adsorb impurities of heavy metal ions from wastewater. Significant disadvantages by the reagent purification method are the additional pollution of effluents due to the introduction of cations and anions of reagents, obtaining dehydrated and not recyclable sludge. Coagulants based on iron and aluminum are capable of forming multiply charged multinuclear complexes; therefore, such coagulants have good adsorption characteristics [15; 16]. In electrocoagulation methods of galvanic wastewater treatment, adsorption-active hydroxides of iron or aluminum are formed by electro erosion by the electrolytic dissolution of steel or aluminum anodes, respectively. In this case, phenomena such as water electrolysis, particles' polarization, electrophoresis, redox processes, and the interaction of electrolysis products with each other can occur in the electrolyzer [17; 18; 19; 20]. Galvanic coagulation consists of passing wastewater through a galvanic coagulator that contains an active anode and cathode mixture, for example, iron and aluminum chips, coke [13], etc. Various investigators have been successfully applied the electrocoagulation process (EC) to remove soluble ions of heavy metals from solutions [21; 22]. During the electrocoagulation process, the coagulant continuously enters the contaminated water.