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. (C) 2011 Elsevier B.V. All rights reserved.