Forward Osmosis as a Pre-Treatment Step for Seawater Dilution and Wastewater Reclamation

This chapter presents the exploration of the combined process of wastewater reclamation and seawater dilution using forward osmosis (FO). Wastewater and seawater are the two most abundant water sources that are free of the hydrological cycle and could serve as an alternative potable water source. Forward osmosis was chosen as the an ideal pre-treatment step to dilute seawater prior to desalination at relatively lower energy demand and low fouling propensity. Membrane fouling behavior was studied and investigated using different feed compositions bearing fractions of effluent organic matter (EfOM). The negative surface charge of all organic foulants was reduced by the adsorption of calcium ions. Filtration of feed streams containing single, simple organic foulants revealed that alginate (polysaccharides) and bovine serum albumin (BSA) resulted in significant loss in process performance as a result of permeate flux reduction. The complex mixture of alginate, BSA and humic acid caused severe loss in membrane performance due to dominant favorable synergistic interactions between foulants and between foulants and membrane surface. The forward osmosis process presents a viable alternative for a simple and effective seawater dilution step using wastewater as the feed solution. Process performance can be improved by selecting a foulant resistant membrane with matching flux

Photocatalytic Membranes for Efficient Water Treatment

Membrane processes which combine the physical separation through filtration and pollutant degradation or antibacterial properties achieved by photocatalysis in a single unit are gaining popularity as wastewater treatment alternatives. There has been considerable progress in the development of photocatalytic membranes through incorporation of metal-oxide photocatalysts to enhance the performance of the membranes. An optimum amount of the photocatalyst should be incorporated into the membrane in order to realise reasonable photocatalytic activity with minimal consequences on water flux. Besides TiO2 loading, membrane performance is also affected by light intensity and irradiation time. This chapter highlights some of the recent progresses in photocatalytic membrane fabrication, reactor configuration and membrane application in disinfection and pollutant removal from wastewater

Forward osmosis membrane performance during simulated wastewater reclamation : fouling mechanisms and fouling layer properties

A thin-film composite (TFC) FO membrane was used to study the fouling characteristics of effluent organic matter (EfOM) fractions in treated wastewater effluent represented by alginate, bovine serum albumin, humic acid and octanoic acid. These model foulants were chosen to represent carbohydrates, proteins, humic substances and fatty acids. Inter foulant interactions and their influence on membrane flux loss was established by running series of fouling tests with feed solutions containing mixtures of model foulants. The obtained results demonstrated that under our experimental conditions humic acid (HA) and octanoic acid (OA) had no significant role on permeate flux loss during wastewater treatment over short periods. However, alginate and bovine serum albumin (BSA) and their mixtures caused significant total flux loss, through alginate-calcium complexation that led to the formation of a resistant gel layer on the membrane surface. Protein fouling was mainly attributed to multiple layer adsorption onto the polyamide membrane surface. Mixing alginate with BSA saw a further decline in permeate flux, worse than that caused individually by either of the foulants, and gives an indication of the synergistic effect between the two foulants. There were favourable inter-foulant interactions between the carbohydrates and the proteins that promoted the formation of hybrid aggregates that were deposited on the membrane surface and enhanced flux loss. The additional presence of humic acid to the mixture of BSA and alginate further aggravated membrane fouling. Polysaccharides and proteins were found to be the most dominant foulants during wastewater reclamation. The extent of interactions between the organic foulants had an effect on the fouling layer structure and its role in permeate flux loss

Recent Developments in Environmental Photocatalytic Degradation of Organic Pollutants: The Case of Titanium Dioxide Nanoparticles—A Review

The presence of both organic and inorganic pollutants in water due to industrial, agricultural, and domestic activities has led to the global need for the development of new, improved, and advanced but effective technologies to effectively address the challenges of water quality. It is therefore necessary to develop a technology which would completely remove contaminants from contaminated waters. TiO2 (titania) nanocatalysts have a proven potential to treat “difficult-to-remove” contaminants and thus are expected to play an important role in the remediation of environmental and pollution challenges. Titania nanoparticles are intended to be both supplementary and complementary to the present water-treatment technologies through the destruction or transformation of hazardous chemical wastes to innocuous end-products, that is, CO2 and H2O. This paper therefore explores and summarizes recent efforts in the area of titania nanoparticle synthesis, modifications, and application of titania nanoparticles for water treatment purposes

Platinum Group Metal Based Nanocatalysts for Environmental Decontamination

Research and development in chemical engineering is currently focused on design of highly active and selective catalytic systems for process intensification. In recent years, there has been growing interest in the use of catalysts based on nanosized metal particles to improve catalytic processes. Among the many metal catalysts, platinum group metals (PGMs) have received greater attention because of their physical and catalytic properties. They have found applications in a wide range of chemical conversion and environmental decontamination reactions due to their chemical stability and enhanced catalytic reactivity in the nano range. This chapter reviews some of the major innovative applications of PGM nanocatalysts for catalytic environmental decontamination

Electrochemical studies and sensing of iodate, periodate and sulphite ions at carbon nanotubes/ Prussian blue films modified platinum electrode

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Fouling of nanofiltration membranes by organics, colloids and their combinations in cross-flow filtration: Effects of the presence of various ions on membrane-foulant non-electrostatic interactions

The presence of macromolecules such as organic and colloidal foulants in the feed has been reported to result in membrane fouling. Fouling is aggravated when the organics and colloids co-exist in the feed due to synergistic effects. In addition, the presence of ions has been observed to promote organic fouling as the ions (especially Ca2+) act as a bridge binding foulants to the membrane (membrane-Ca2+-foulant complexation). Different cations have been reported to have different effects on membrane fouling. However, there are no clear explanations for the fluctuations in the fouling trends. Mostly, the deviations have been linked to the affinity of the cations to bind foulants to the membrane (membrane-foulant interactions) and also complex organic foulants. Membrane fouling in the presence of Na+, Ca2+ and La3+ as model cations is systematically investigated in more detail in this study. Sodium alginate, latex and silica are used as model organic and colloidal foulants. Specifically, more attention is paid on the effects of the presence of various cations on membrane-foulant as well as foulant-foulant non-electrostatic interactions, which determine initial and later membrane fouling, respectively. These interactions were computed from contact angles of membranes and foulants based on the Lifshitz-van der Waal and acid-base interaction energies. Fouling (especially organic fouling) was exacerbated in the presence of cations due to organic complexation and and the reduction in foulant–membrane repulsive interactions. Initial and later membrane fouling related well with membrane-foulant as well as foulant-foulant interactions. Membrane-foulant interactions were more attractive for fouling in the presence of La3+, intermediate for Ca2+ and least for Na+ for all fouling types. This correlated well with alginate and latex fouling trends where fouling was severe in the presence of La3+ and least in the presence of Na+. However, there was insignificant effect for the addition of cations on silica fouling showing that not only membrane-foulant non-electrostatic interactions control flux decline. For combined fouling, different observations were made. However, fouling was highest for fouling in the presence of Ca2+. Fouling was not only influenced by membrane-foulant interactions but also competition for cations between organic and colloidal foulants. It was concluded from these experiments that the extent of membrane fouling is controlled by the affinity of foulants for the membrane surface. These affinity interactions are dependent on the presence of various cations in the feed water