Sivan Bleich (Mekorot), Chaim Vanunu (Mekorot), Eti Mansharov Aluf (Mekorot), Ziki Livni (CQM)
Background
The most common water disinfection method is chlorination by dosing water with a sodium hypochlorite solution.
Mekorot is considering alternative methods of purifying drinking water, including electrolytic chlorination.
Electrolytic chlorination enables production of chlorine on-site by transferring an electric current through water (that contains chloride ions). This eliminates the need to transport hazardous material, store it at Mekorot sites, and dispose of expired solutions.
• There are currently 24 electrolytic chlorination systems used at Mekorot sites, the majority of which are manufactured by CQM
• The electrolysis technology used until recently required reversal of electrical polarity between electrodes in order to reduce salt sedimentation upon the cathodes. At the same time, polarity reversal between electrodes significantly shortens the lifespan of the electrodes from approximately 5 years to 1.5 years, and increases system maintenance costs.
• In addition, salt sedimentation upon the cathodes requires periodical chemical cleaning (using salt acids), which has operational and safety implications on the system.
• After understanding the need for a system that operates without frequent acidic cleanings, via WaTech®, CQM and Mekorot decided to evaluate the possibility of operating a system using ongoing mechanical cleaning of the cathodes, thus eliminating the need for salt acids.
• CQM accepted the challenge and developed a mechanical cleaning mechanism for cathodes in order to resolve the problem.
Assess the following performances of the CQM innovative electrolytic chlorination system that is equipped with a continuous mechanical cleaning system:
• Stability of chlorine production
• Electricity consumption, to evaluate disinfection costs
• Performance of the mechanical cleaning system over time without malfunctions or need for chemical cleanings
• General function of the power supply systems, control systems and mechanical systems
• Impact on water quality
Technology
The photos below display the mechanical cleaning system which operates by spinning cathodes against blades in order to clean them.
Beta Site
• The site selected for comparison of the new system equipped with the mechanical cleaning mechanism with the standard system is the Ein Karem 16 drilling site in Jerusalem.
• General features of the site: Flow rate – 140 m2/h; chlorides – 48 mg/L; hardness – 280 mg/L
• The site previously used the CQM standard chlorination system. During operation, the electrodes were clogged with scale after two months of use.
Results
• The system produces and maintains the required chlorine residue in the water, 0.40-0.45 mg/L, despite the low chloride concentration rates in groundwater drawn while drilling (only 48 mg/L).
• During initial operation, problematic water turbidity was observed due to fluidization of the scale sediment at the bottom of the reactor. This problem was successfully resolved by optimizing the filling method of the reactor and the frequency of scale drainage from its bottom.
• During the entire operation period (9 months), no chemical cleanings were required for the system
• Energy consumption – during the first four months of operation, an increase in the system’s electricity consumption was observed. After that period, the electricity supply rates stabilized as shown in the Image below.
Achievements
• The system operated successfully without any significant malfunctions throughout the 9 trial months and chemical cleanings were not required
• An advantage of installing this system in well sites located in residential areas is that it eliminates the need to transport hazardous materials through densely populated areas. This advantage applies to remote sites and areas with special security vulnerabilities as well.
• Mekorot has already marketed this technology in Malta. It has been installed in water well with a flow rate of 200 m2/h in order to replace gas-operated chlorination facilities on the island.
• Today, following the successful pilot run in Malta, Mekorot is negotiating a contract to supply approximately 40 additional systems to the island in order to completely eliminate hazardous use of chlorine gas.
