Advanced coagulation using in-situ generated liquid ferrate, Fe (VI), for enhanced pretreatment in seawater RO desalination during algal blooms

Abstract

Harmful algal blooms (HABs) are considered a major threat for seawater reverse osmosis (SWRO) plants. The presence of HABs in the raw feed water can cause increase of chemical consumption within the desalination plant, increase membrane fouling rate and might lead to plant shutdown. The removal of Algal Organic Matters (AOMs) during the pretreatment will help in increasing the membrane lifetime, reduce operation cost and increase the plant reliability. In this study, the efficiency of liquid ferrate and ferric chloride during coagulation on the removal of AOMs was investigated. The liquid ferrate was generated in-situ by wet oxidation of ferric iron using hypochlorite in a caustic medium. Two seawater models were employed, the first one contains 10 mg c/L of sodium alginate and the second one contains also 10 mg c/L of Chaetoceros Affinis algae (CA). During the advanced coagulation, liquid ferrate proved to be more effective in removing AOM than ferric chloride, with an overall DOC removal of 90%, enabling 100% algal removal and the inactivation of 99.99% of the

Fouling investigation of a full-scale seawater reverse osmosis desalination (SWRO) plant on the Red Sea: Membrane autopsy and pretreatment efficiency

“…Although many approaches to mitigate fouling can be found in the literature, the most effective control of membrane fouling is to improve the feedwater quality entering the membrane process [12,13]. Hence, a well-designed pretreatment is crucial to enhance process performances [14,15]. The pretreatment processes and design should be selected based on the feedwater analysis and type of intake [16,17].…”

Clinical Autopsy of a Reverse Osmosis Membrane Module

“…This is because ferric chloride (FeCl 3 ) is one of the most commonly used coagulants in the pretreatment of seawater to remove organic colloids (Al-Sheikh, 1997;Edzwald and Haarhoff, 2011). A recent laboratory study showed that using liquid ferrate, ten times less iron might be required to achieve similar pretreatment efficiencies (Alshahri et al, 2019). However, convincing practitioners to replace FeCl 3 with liquid ferrate may need a demonstration of its benefits at pilot scale.…”

On the Origins of Some Spectroscopic Properties of “Purple Iron” (the Tetraoxoferrate(VI) Ion) and Its Pourbaix Safe-Space

“…An example of recycling-and-reuse of wastes was announced by Munyengabe et al [ 4 ] who illustrated the potential of ferrate(VI)-treated sludge, from acid drainages from coal and gold mines, as a starting material for the synthesis of magnetic nanoparticles. A useful application of ferrate(VI) recently brought to light by Alshahri et al [ 5 ] is the mitigation of shutdowns of water desalination plants, often caused by the fouling of reverse osmosis membranes by algae blooms; the pre-emptive method was the treatment of sea water by ferrate(VI) before filtration. This work is followed by that of Addison et al [ 6 ] who optimized the process of the attack of ferrate(VI) on algae, an informative piece of operational research which focused not only on significant parameters in physical chemistry but also on the influence of fluid dynamics on the number of particle collisions between oxidant and reductant per unit time.…”