JERDFO ENHANCEMENT OF INDUSTRIAL WASTEWATER TREATMENT PROCESS USING NEW GENERATION FILTERS

Filters are used for integrated wastewater treatment by removing suspended particles after me-chanical, chemical, physical and chemical, as well as biological wastewater treatment. Wastewater from industrial facilities contain contaminants specific for the industries, even after biological treatment. Therefore, the output of filters at one industry cannot mechanically transferred to the performance of filters at other industries. Floating medium filters (FMF) are used over recent years for removing organic and mineral contaminants from wastewater [1-3]. Principle of operation of FMF can be described as retention of contaminants in monodisperse or polydisperse layer of float-able filter medium during direct flow or cross flow filtration. Floating filter media have two main advantages over non-floating (heavy) media:

DOI : http://doi.org/10.26480/jmerd.02.2018. 18.21 Natural water and wastewater is treated at public utilities and industrial facilities using filters of various designs that are filled with filtering materials containing electric-chemical sources of cur-rent. Main limitations of common filters are: iron case internal corrosion; high electrode resistivity; low current collection from 1m2 of electrode surface area; poor water treatment efficiency. En-hancement of industrial wastewater treatment process is aimed to create a new filter design that would allow to eliminate the above-listed limitations of filter designs currently applied. The pro-posed design of new generation filters includes: iron case filled with filter material, electropositive and electronegative electrodes placed vertically inside the filter case. Electropositive electrodes are made of carbon-containing electrode composition consisting of calcined coke fines, pyrrhotite tailings from mining and refining facilities and tall oil pit. The applied composition of electrode shell allows to decrease their resistivity and to increase their current collection, as well as to slow down the corrosion of iron filter case. Using new generation filters allows to improve the quality of treated water: for example, in case of using common filters iron residual concentration after treatment of wastewater makes 0,35 mg/l; using new generation filters reduces the iron residual concentration to 0,18 mg/l. The purpose of this study is to develop the electrochemical wastewater treatment methods in order to save the energy costs, to reduce the consumption of metal for electrodes, as well as to improve the wastewater treatment efficiency. Following tasks have been performed within the frame of the above-mentioned pur-pose:

KEYWORDS
1. Performance analysis of existing filter designs 2. Elaboration of a composition for electropositive electrode 3. Elaboration of design for new generation filters.
Concentrated effluents are purified using electrochemical methods based on electrolytic wastewater treatment, i.e. they receive flow of direct current through immersed electrodes. At the cathode, hydrogen gas is produced, water-dissolved metallic ions are discharged with relevant metal cathode deposits being formed, certain ions and organic compounds present in water are reduced , followed by formation of new substances and ions [7]. At the anode, oxygen and halo-gens are produced of materials that are not subject to electrochemical dissolution, depending on composition of salt in wastewater and on electrolysis conditions, certain ions and organic com-pounds present in water are oxidized with formation of new substances and ions. Using iron, aluminum anodes or some other metal anodes results in their electrodis solution and in transition of the relevant metal ions into the wastewater. The latter form thereafter oxide hydrates or basic salts of relevant metals that are able to coagulate.
Furthermore, wastewater electrolysis may be followed by transport of ions through on a semi-permeable membrane, water demineralization, production of mineral and organic acids, as well as of caustic alkali. Electrophoresis, colloidal particle discharge and coagulation, as well as flotation of solid and emulsified compounds by gas bubbles produced on electrodes may be observed during the electrolysis of wastewater containing various dispersed or emulsified foreign matters.
As can be seen from the above, wastewater electrolysis may be followed by a number of physico-chemical processes that provide removal of dissolved and dispersed contaminants from wastewater. These treatment methods have sometimes certain advantages over chemical wastewater treatment: • numerous valuable products can be extracted during treatment process, • process flow diagrams and production plant operation can be considerably streamlined and sim-plified, • automation of their performance is relatively simple, • processing area required for treatment facilities can be reduced.
The main issue of electrochemical wastewater treatment seems to be high power and metal consumption in numerous cases. Sometimes electrochemical processes that follow wastewater treatment show low current yield (anodic oxidation and cathodic reduction of organic foreign mat-ters at low concentration thereof, electrodialysis treatment of concentrated wastewater. The treat-ment process may be enhanced by combining operating principles of floating medium filters and electrochemical source of current [8][9][10][11]. Water passes through the filter grain material from the bottom upwards. Filter material is placed between two perforated disks: aluminum anode and mineral carbon cathode. Anode has electronegative potential, cathode has positive, so that water is filtered opposite to the electric lines of force. Simultaneously, aluminum dissolves, hydrolyzes and produces coagulant AI(OH)3 that forms flocs on the surface of filter grain material. Coagulant and electrical field polarizing mineral filter grains, facilitate binding of removed particles to the grains of filter material. The deposit that appears is removed by washing. However, the internal surface of the filter steel case is subject to corrosion during the filter operation. This reduces the efficiency of treatment [12][13][14][15][16].
Using rapid filters also seems to be possible. Rapid filter includes steel case, flushing water inlet and outlet, lower drainage system, flushwater collecting launder, filter medium, underdrain-age bed. Filter medium of this type of filter contains bar electrodes made of electronegative (anode) and electropositive (cathode) materials arranged in alternating series, the electrodes being placed chequerwise. Siliconized calc-spar with a 2-5 mm grading fraction is used as filter medium. An-ode-tocathode separation is within the range of 187-241 mm [17][18][19][20][21]. Aluminum is used as elec-tronegative material; mineral carbon is used as electropositive material. Main issues of this type of filter are: -internal corrosion of its steel case, -no transfer of electric power produced by the source of current; -low efficiency of contaminant removal from wastewater.

RESEARCH TECHNIQUES
A complex of lab and production techniques was used in order to solve the tasks set, including X-ray phase and differential thermal analysis, electron microscopy, traditional chemical and physi-cochemical techniques for examination of filtration processes in developed filter design and for observation of wastewater treatment processes.

FINDINGS
We propose to use the new filter design that allows to solve the tasks of enhancement of indus-trial wastewater treatment process, improvement of corrosion protection efficiency inside the steel case of the filter, as well as enhancement of current collection. This filter includes steel case filled with filter material, water supply, distribution and collection systems. Inside the filter, vertical alternating series are placed parallel to the filter case walls arranged as closed circuits of electro-positive and electronegative electrodes connected with a conductor that form electrochemical sources of current loaded on load resistance. Electronegative electrodes 4 and 6 are made of alu-minum, electropositive electrodes 3 and 5 are made of carbon containing electrode compound consisting of 60%wt calcined coke breeze, 8-10%wt pyrrhotite tailings from the tailing storage facility of a mining and refining plant and of tall oil pit for the rest (ТU 13-410177-184-84). The filter has a distribution 10 and a collection 11 system for water supply and distribution. The pro-posed composition is selected on a trial basis and corresponds to the highest possible particle pack-ing that allows to increase mechanical strength and to prevent release of carcinogenic substances. Figure 1 shows a water filter seen from above, Figure 2side-view.
In order to decrease the electrical resistivity of the electrode composition pyrrhotite tailings from the tailing storage facility of a mining and refining plant were added containing high concentra-tions of metals (Table 1).

Figure 2:
A water filter side-view 10 -distribution system; 11collection system; The proposed composition for electrodes is prepared as follows. Oil calcined coke breeze of a certain gravimetric consist is mixed in normal conditions with tall oil pit and pyrrhotite tailings at a preset ratio, the obtained compound is heated up to 60-80°С with a simultaneous agitation. The obtained composition is placed into a special container with a pre-mounted metal core in the center. After 3h the ready-made electrode is drawn out of the container. Example 1. Composition of carbon containing electrode compound improved. Composition of 60% wt coke breeze and 40%wt tall oil pit was used as a basis that allowed to obtain electrodes with a high mechanical strength of 400-425 kgf/cm, a pore content of 7-8% and an electrical resistivity of 450 ohm·mm 2 /m.
Introducing pyrrhotite tailings into the composition of the compound allowed to reduce the resistivity of electrodes. Resistivity of electrodes was calculated at a concentration of 60% for coke breeze, 0% to 10% for pyrrhotite tailings and tall oil pit for the rest ( Table 2).
The best result was obtained with a pyrrhotite tailings concentration of 10%wt, the electric resistivity decreased by 26,7%. Further increase of pyrrhotite tailings concentration degrades electrode mechanical strength.

RESULTS AND DISCUSSION
The proposed new generation filter will allow obtaining higher quality of removal of various dispersed foreign matters from industrial wastewater and natural water by means of anodic oxida-tion and cathodic reduction. During electrochemical oxidation, contaminants dispersed in the wastewater degrade completely producing CO2, NH3 (ammonia), water and easily removable ele-mentary substances. Along with anodic oxidation, cathodic reduction may also run concurrently in a filter of the proposed design that causes metal deposition at the cathode. Given certain condi-tions anodic oxidation and cathodic reduction may be combined at the filters. Based on the laws of physical chemistry and of process chemistry, the proposed filters may provide a faster removal of contaminants from wastewater [7]. The proposed filter design ensures unattenuated current dis-tribution over the electrode surface, as well as low resistance loss at all electrical circuit sections. In practical work, common voltage is determined from findings on relationship among voltage and current density on electrodes produced for a specific type of wastewater and selected electrode material at a specified interelectrode distance.
Electrodes are critical elements of the filter design defining efficiency of oxidation or reduction process. Design of electrode is determined in many ways by the mode it is connected to the elec-trical power network [22]. Electrodes made with a new composite material are proposed to beused in the elaborated new generation filter design. Composite anode slurry for electropositive electrode is produced from pyrrhotite tailingsmining and refining plant waste (1-10%), tall oil pit (35-40%) and calcined coke-breeze (45-50%). This material allows to reduce the electrical resistivity from 600 Ohm*mm 2 /m down to 330 Ohm * mm 2 /m. It is able to reach the iron residual concentration level of 0,2 mg/l during treatment of natural water with an iron residual concentra-tion of 4,6 mg/l at a filter rate of 6,2 m/h. The produced pilot batch of new generation filters of our new design are applied presently at existing treatment facilities of the Republic of Bashkorto-stan, Russian Federation.
Example 3. Tests were carried out on removal of iron from natural water. Inlet iron concentration was 4,6 mg/l. Tests were carried out at a filter rate of 6 m/h ( Table 4). The proposed utility model allowed to obtain a higher quality of treated water.  (Table 3). Based on the test results it follows that filter design elaborated by us allows to increase current collection from elec-trodes and to reduce the corrosion rate.

CONCLUSION
Electroplating industry is one of large consumers of nonferrous metals and considerably expensive chemicals. This industry consumes minimum 30% of stannum, 15% of nickel and 50% of cad-mium produced in Russia. In cases of chemical conversion and preliminary operations, loss of chemicals with flushing water exceeds sometimes by decades the amounts consumed for surface treatment. Environmental pollution comes not only from flushing water, but also from spent stock solutions in the electroplating industry. When treating the electroplating effluents, particular at-tention is paid to electrochemical treatment methods. The developed new generation filter design renders possible treatment of electroplating and other industry effluents, as well as its efficient usage for natural water treatment.