Assessment of hardness, microorganism and organic matter removal from seawater by electrocoagulation as a pretreatment of desalination by reverse osmosis

• Electrocoagulation was applied as a pretreatment for seawater desalination.
• Electrocoagulation is cost-effective due to the high conductivity of seawater.
• Natural organic matter and microorganisms were efficiently removed.
• Electrocoagulation can be used for disinfection, but not for softening.

Electrocoagulation (EC) process was used as an alternative pretreatment in order to assess its applicability to replace the conventional pretreatments used to mitigate membrane fouling prior to seawater desalination by reverse osmosis process, such as chemical coagulation, chlorination and scale inhibitors. Electrocoagulation was conducted in a batch cell using aluminum electrodes driven in the galvanostatic mode. Absorbance (UV254nm) and DOC were measured to follow the effectiveness of EC process for removing organic matter from seawater. Likewise, cultivable heterotrophic bacteria were enumerated to assess the disinfection ability of the process and total hardness was monitored. The influence of various operating parameters, namely mixing speed, current density, initial pH and inter-electrode distance, was investigated. The removal of organic matter from seawater by electrocoagulation was improved with higher current density and lower pH. Electrocoagulation removed 70.8% DOC, while absorbance abatement was 89.7% with a complete removal of microorganisms at high current density. Conversely, the abatement of total hardness was weak, about 10%, so that electrocoagulation could not be used as a softening process. Finally, experimental results showed the high potential of electrocoagulation as a pretreatment method to mitigate potential organic fouling and biofouling of reverse osmosis membrane owing to its ability to remove effectively dissolved organic matter and microorganisms from seawater.