Electroflotation as disinfection method for secondary municipal wastewater effluent
A literature review
S. van der Poel (TU Delft - Civil Engineering & Geosciences)
B. Bicudo Perez – Mentor (TU Delft - Sanitary Engineering)
D van Halem – Mentor (TU Delft - Sanitary Engineering)
Gertjan Medema – Graduation committee member (TU Delft - Sanitary Engineering)
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Abstract
Due to increasing water consumption and stress on natural water resources, enhanced treatment of wastewater and reuse of water are becoming more important. Treated municipal wastewater has potential to be used for irrigation purposes, but pathogens are a major concern to protect environmental and human health. Therefore, an advanced treatment step is required to reduce the levels of microorganisms, nutrients and suspended solids. This literature review focusses on electroflotation (EF) as disinfection method of secondary municipal wastewater treatment. EF is a combination of electrocoagulation (EC) and dissolved air flotation (DAF). In EC treatment, a sacrificial metallic anode releases metal ions (usually iron or aluminium) into the solution while hydroxyl ions and hydrogen gas are produced at the cathode. Coagulants are created in situ by the hydrolysis of these metal ions to hydroxides that can destabilize pollutants. DAF is an adsorptive bubble separation process where generated gas bubbles (of 10-100 µm) separate the impurities by flotation. This paper outlines the processes involved in EF technology and its applications in (waste)water treatment. Therefore, the processes of EC and DAF are discussed first. Influencing parameters such as electrode material, pH, retention time, charge dosage, charge dosage rate, bubble formation and size are discussed, as well as pollutant removal mechanisms. The main mechanisms responsible are charge neutralization, adsorption, sweep coagulation, microbial destruction by the electric field and deactivation by free radicals. The conclusion is drawn that the hybrid EF technique, which has been implemented in different water treatment processes, promises to increase removal efficiencies compared to single EC and DAF treatment, but the full potential of EF as a tertiary treatment step for secondary municipal wastewater effluent is yet to be fully realized. The process needs to be empirically optimized, a challenging task due to the involvement of complex chemical and physical processes.