Integration of Forward Osmosis in Municipal Wastewater Treatment Applications

In recent years, the research community has made constant efforts to develop new technologies for the recovery and valorization of water, nutrient and energy content of municipal wastewater. However, the recovery process is significantly limited due to the low-strength of sewage. Over the last 10 years, the Forward Osmosis (FO) process, has gained interest as a low-cost process with low membrane fouling propensity, which can convert municipal wastewater into a concentrated low-volume effluent, characterized by high organic and nutrient concentration. This chapter presents the main configurations that have been implemented for the concentration of municipal wastewater using FO, including their performance in terms of contaminant removal and water/reverse salt flux (Jw/Js). Furthermore, the draw solutions and respective concentrations that have been used in FO for the treatment of sewage are reported, while at the same time the positive and negative characteristics of each application are evaluated. Finally, in the last section of this chapter, the spontaneous FO followed by anaerobic process is integrated in a municipal wastewater treatment plant (WWTP) and compared with a conventional one. The comparison is done, in terms of the mass balance of the chemical oxygen demand (COD) and in terms of the energy efficiency.

Development of Polydopamine Forward Osmosis Membranes with Low Reverse Salt Flux

Application of forward osmosis (FO) is limited due to membrane fouling and, most importantly, high reverse salt fluxes that deteriorate the concentrated product. Polydopamine (PDA) is a widely used, easily applicable, hydrophilic, adhesive antifouling coating. Among the coating parameters, surprisingly, the effect of PDA coating temperature on the membrane properties has not been well studied. Polyethersulfone (PES) 30 kDa ultrafiltration membranes were PDA-coated with varying dopamine concentrations (0.5–3 g/L) and coating temperatures (4–55 °C). The quality of the applied coating has been determined by surface properties, water permeability and reverse salt flux using a 1.2 M MgSO4 draw solution. The coating thickness increased both with the dopamine concentration and coating temperature, the latter having a remarkably stronger effect resulting in a higher PDA deposition speed and smaller PDA aggregates. In dead-end stirred cell, the membranes coated at 55 °C with 2.0 g/L dopamine showed NaCl and MgSO4 retentions of 41% and 93%, respectively. In crossflow FO, a low reverse MgSO4 flux (0.34 g/m2·h) was found making a very low specific reverse salt flux (Js/Jw) of 0.08 g/L, which outperformed the commercial CTA FO membranes, showing the strong benefit of high temperature PDA-coated PES membranes to assure high quality products.

Effect of biosurfactant as a novel draw solution on photocatalytic treatment and desalination of produced water by different forward osmosis membranes

Water stress and environmental concerns have driven research into the treatment of produced water. In this study, a combination of forward osmosis and photocatalyst system was used for simultaneous salt removal and treatment of produced water. Furthermore, biosurfactant as a novel draw solution and the three types of forward osmosis membranes (cellulose triacetate with and without titanium dioxide (TiO2) and graphene oxide (GO) nanoparticles) were investigated. The morphology and distribution of the TiO2 and TiO2/GO on the membrane surface were assessed by various analyses including field emission scanning electron microscopy, energy dispersive X-ray and contact angle analysis. The results demonstrated that the reverse salt flux was only 0.2 g/m2 h. Moreover, benzene, toluene, ethylbenzene, and xylene (BTEX) removal efficiency in the cellulose triacetate with TiO2 and TiO2/GO membrane under UVC radiation was 62% and 78%, respectively, while the data obtained in visible light reached 80%. The use of TiO2 and TiO2/GO membranes significantly improved the permeability, water flux, photocatalytic degradation of pollutants and desalination of produced water.

Fabrication of a novel cyanoethyl cellulose substrate for thin-film composite forward osmosis membrane

In this study, cyanoethyl cellulose (CEC) was used as a membrane material, and polyvinylpyrrolidone (PVP) was used as pore-forming agent to prepare the substrates for the thin-film composite (TFC) forward osmosis (FO) membrane for the first time. The experimental results demonstrate that the properties of the substrates were significantly improved after PVP was added. The scanning electron microscope (SEM) images show that a two-sublayer structure, a fringe-like top sublayer and macrovoids with sponge-like wall bottom sublayer, were formed after the addition of PVP. These improvements contributed to improved membrane performance during FO tests. Meanwhile, after adding PVP, the TFC membranes exhibited good water flux, and excellent specific reverse salt flux. For instance, the TFC-M2 exhibited 9.10/20.67 LMH water flux, 1.35/2.24 gMH reverse salt flux, and 0.15/0.11 g/L specific reverse salt flux in FO/pressure-retarded osmosis mode while using 1 M NaCl as the draw solution and deionized (DI) water as the feed solution.

Comparative Study for Organic and Inorganic Draw Solutions in Forward Osmosis

The present work aims to study forward osmosis process using different kinds of draw solutions and membranes. Three types of draw solutions (sodium chloride, sodium formate, and sodium acetate) were used in forward osmosis process to evaluate their effectiveness with respect to water flux and reverse salt flux. Experiments conducted in a laboratory-scale forward osmosis (FO) unit in cross flow flat sheet membrane cell. Three types of membranes (Thin film composite (TFC), Cellulose acetate (CA), and Cellulose triacetate (CTA)) were used to determine the water flux under osmotic pressure as a driving force. The effect of temperature, draw solution concentration, feed and draw solution flow rate, and membrane types, were studied with respect to water flux. The results showed an increase in water flux with increasing feed temperature and draw solution concentrations In addition, the flux increased with increasing feed flow rate while the flux was inversely proportional with the draw solution flow rate. The results showed that reverse osmosis membranes (TFC and CA) are not suitable for using in FO process due to the relatively obtained low water flux when compared with the flux obtained by forward osmosis membrane (CTA). NaCl draw solution gave higher water flux than other draw solutions and at the same time, revealed higher reverse salt flux.