Application of ohmic heating technique to approach near-ZLD during the evaporation process of seawater

The aim of this study is to investigate the application of the ohmic heating during the evaporation process of the seawater for the purpose of reaching near zero liquid discharge (ZLD). Ohmic evaporator was designed and used to evaporate seawater at electrical field strengths 24, 56 and 87 V/cm using alternating electric current at frequency of 60 Hz. The apparent electrical conductivity, recovery rate and energy consumption were determined during the evaporation process. Some physico-chemical properties of the concentrated brine (sludge) were measured such as electrical conductivity, pH, density and color. Results indicate that the apparent electrical conductivity was reduced by increasing the electrical field strength. The ranges of the recovery rate and specific energy were 81–93.5% and 4550–5071 kJ/kg respectively. It was demonstrated that the ohmic evaporator performed better at electrical field strength 56 V/cm. One major output of this research is the assessment of the generation of heat in the seawater by alternating current during evaporation process for near-ZLD; although, more studies are needed for continuous pilot production system, modelling for commercial production as well as economical evaluation of the system. © 2011 Elsevier B.V. All rights reserved.

From this study it becomes clear that ohmic heating method can be applied to evaporate seawater, but more investigation is necessary to optimize the process especially in terms of energy consumption and use of renewable energy. Ohmic evaporator performed well at electrical field strength at 56 V/cm. The major output of this study is the assessment of the application of ohmic heating in the evaporation process of seawater for near zero liquid discharge process. The performance data of the ohmic evaporator will add a new perspective to system analysis, design, modelling and evaluation of the potential application of ohmic heating method to treat the discharge from desalination plants or using renewable energy for desalination system in remote areas. The economic benefits of the ohmic evaporation process cannot be immediately evaluated; further analyses and development are needed.These data will help in the scaling up the process to a pilot size for further investigation and performing cost analysis evaluation. More research work and emphases are recommended to investigate the quality of the byproduct of the process (sea salt). This study has shown preliminary indications of the effectiveness of ohmic heating during evaporation process of concentrated brine to approach near-ZLD although the energy consumption was quite high which limit its application.