Revamp of existing lab-scale electrolytic cell design for electrolyzed water study in cleaning application

Sulaiman, N.S., Khalid, N.I., Fauzi, E.M.H., Ab Aziz, N., Yusof, N.A., Sobri, S. and Hasnan, N.Z.N. Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. Halal Products Research Institute, University Putra Malaysia, 43300 UPM Serdang, Selangor, Malaysia. Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia.


Introduction
The lab-scale electrolytic cell was designed with two chambers separated with a membrane to allow the reactions of ions exchange (Hsu et al., 2015;Khalid et al., 2018). The unit was used to produce acidic and alkaline electrolyzed water at anode and cathode electrodes, respectively. By passing an electric current Hricova et al. (2008) discovered that acidic electrolyzed water (AcEW) is generated when negatively charged ions move to anode and become oxygen gas (O 2 ), chlorine gas (Cl 2 ), hypochlorite ion (-OCL), hypochlorous acid (HOCL), and hydrochloric acid (HCL). Meanwhile, alkaline electrolyzed water (AlEW) is generated when positively charged ions move to the cathode and become hydrogen gas (H 2 ) and sodium hydroxide (NaOH). AcEW has reported having an antimicrobial effect on various microbes and high chlorine concentration was the main contributor (Koseki and Itoh, 2001;Park et al., 2009). While AlEW is compatible to be an alkaline wash use for cleaning application (Khalid et al., 2018). EW with a pH of 2.5-6.0 resulted in an approximately 5-log reduction of Listeria monocytogenes (Rahman et al., 2010). Stevenson et al. (2016) reported that ORP value higher than 850 mV caused an efficient inactivation of E. coli O157:H7. According to Park et al. (2004), complete inactivation of Listeria monocytogenes and E. coli O157:H7 was performed with chlorine levels above 1.0 mg/l. Therefore, appropriate quality of electrolyzed water is needed for cleaning application in food industries. However, the chlorine concentration in AcEW obtained by using the lab-scale electrolytic cell was too low to efficiently act as a disinfecting agent.
The objective of the study is to improve the design of the electrolytic cell which focused on current generation and good chemical properties (pH, oxidationreduction potential and chlorine concentration) of acidic and alkaline electrolyzed water.

Revamp design methodology
The revamp study has been conducted for the following aspect:

Analytical measurement of electrolyzed water
Free chlorine was measured by Photometer PF-3 (Macherey-Nagel, Germany) after the electrolysis process. pH was measured by AP85 Portable Waterproof pH/conductivity meter (Fisher Scientific, USA). Oxidation-reduction potential (ORP) was measured by PT-380 Hand-held pH/ORP/Temperature Meter with redox electrode (Boeco, Germany).

Results and discussion
Findings of this work have eliminated corrosion problems due to the previous electrode arrangement, where Titanium electrode was placed at the anode. To reduce the galvanic corrosion rates, the more active metal is placed at the anode and more noble metal at the cathode (Shi et al., 2012). In galvanic series, smaller electrode potential difference will cause less corrosion thus stainless steel is chosen since it is relatively close to Titanium. Thus, Titanium which is more noble metal is placed at the cathode and Stainless Steel is placed at anode after revamp. Electrode gap also plays an important role where the smaller the gap between electrodes, the amount of current flow increased and generated more chlorine concentration (Hsu et al., 2017). The gap between both electrodes has decreased to 1.2cm and faced towards each other which significantly improved the ions exchange between electrodes.
From Figure 1, the DC power supply to the electrolytic cell before revamping used alligator clip and connected to copper hooks that held the electrodes. These causes high resistance value, thus lowering the current flow. Therefore, the electrode plate was connected directly to the DC power supply in this revamp work to increase the current flow. Furthermore, the presence of metal bolts to attach the membrane in the previous electrolytic cell has caused corrosion where electrolyzed water appeared in brownish solution. Thus, bolts were removed, and an acrylic slot was replaced to hold the membrane.
The chemical properties (pH, oxidation-reduction potential and chlorine concentration) of acidic and alkaline electrolyzed water before and after the revamp of the electrolytic cell are presented in Table 1 and Table  2 respectively. The comparison was constructed by selecting the nearest operating condition to produce acidic and alkaline electrolyzed water. It can be clearly seen from the data that after the revamp, the current has  Table 2. Chemical properties of acidic and alkaline EW after revamp, at 0.5% NaCl concentration and 10 mins of electrolysis time. increased from 0.013A to 2.50A. This leads to an increase in pH, oxidation-reduction potential, and free chlorine concentration for both electrolyzed water. This was proved by Rahman et al. (2012), where the values of chlorine concentration, pH and oxidation-reduction potential increased as the current is increased. Before revamp, the chemical properties of electrolyzed water were low even though the value of voltage is higher compared to the value after revamped. This may be due to the previous set up that caused the low current flow to the electrodes.

Conclusion
This work has shown convincing results. The current increased by 192 times higher than previous value by considering various aspect on the lab-scale electrolytic cell. The new design is indeed possible to increase the amperage and improved the chemical properties (pH, oxidation-reduction potential and chlorine concentration) for both electrolyzed water. Additionally, the selection of stainless steel 316 as anode could suppress corrosion from occurred due to its excellent corrosion resistance. Thus, this work has proved that the electrolytic cell is competent for producing EW that suits cleaning application in food industries. Electrolyzed water obtained from this study will be used for future study in cleaning application on food contact surfaces.