Effect of Photocatalysis on the Membrane Hybrid System for wastewater treatment

An integrated photocatalysismembrane hybrid system was investigated for wastewater treatment with the main focus on improving the cross flow microfiltration (MF) permeate flux. Photocatalysis with TiO2 (P25 Degussa) suspension as photocatalyst was applied both as pre-treatment and as inline treatment with MF. The TiO2 slurry was found to have significant effect in permeate flux for wastewater with lower dissolved organic carbon concentration. The MF flux decline due to TiO2 slurry cake on the membrane surface was minimized by allowing the TiO2 slurry to settle and by using only the supernatant for further treatment using the hybrid system. The investigation also included the study on the effect of photocatalytic reaction time and the slurry settling times on the MF permeate flux. The irradiation of ultraviolet on the MF surface in presence of TiO2 catalyst in suspension yielded in an increase in permeate flux

A novel fertiliser drawn forward osmosis desalination for fertigation

University of Technology Sydney. Faculty of Engineering and Information Technology.Agriculture consumes maximum water of up to 70% of the total fresh water withdrawn in the world for consumptive purposes. Rapid population growth is further driving fresh water demand and putting tremendous stress on limited fresh water resources. This increasing demand can only be met by improving the current water use efficiency and by creating new water sources. Desalination could therefore play a significant role in creating a new water source by using unlimited saline water sources. However, current desalination technologies are energy intensive and energy has a significant impact on climate change. If low cost desalination technologies were made available, their impact on agriculture sector would be significant for many water stressed regions of the world. Recently, forward osmosis (FO) has been recognised as one of the most promising low energy processes for desalination. The FO process is based on the principle of natural osmotic process driven by the concentration gradient and not by hydraulic pressure like the reverse osmosis (RO) process and hence requires significantly lower energy. In the FO process, a concentrated draw solution (DS) extracts fresh water from the saline water using special membranes. The issue of membrane fouling in FO process is less challenging than the RO process where fouling constitutes a major operating issue. However, the lack of a suitable DS has limited the application of FO desalination for potable water. The separation of draw solutes from the diluted DS after desalination requires additional post-treatment processes that still consume energy, making FO uncompetitive with the already established RO desalination technology. The FO process offers novelty for those applications where the complete separation of draw solutes is not necessary and where the final diluted DS can be used directly if the presence of draw solutes adds value to the end use. Fertiliser drawn forward osmosis (FDFO) desalination for fertigation is therefore proposed based on this concept. When fertilisers are used as the draw solutes in the FDFO desalination process, the diluted fertiliser solution after desalination can be directly applied for fertigation because fertilisers are essential for plants. This concept avoids the need for an additional post-treatment process for the separation and recovery of draw solutes. The objective of this study is therefore to investigate the performance of the FDFO desalination process for fertigation, identify its limitations and investigate options to overcome these limitations. The study has been presented in eleven chapters that include a definition of the detailed concept and an assessment of the performance of eleven selected fertilisers as the DS under various conditions, through both simulation and bench-scale experiments. The energy required for FDFO for direct fertigation was estimated to be less than 0.24 kW/m3 of fertigation water, which is comparatively lower than the most efficient current desalination technologies. As such, FDFO can also be easily powered using renewable energy sources, such as solar and wind. Since fertilisers are extensively used for agriculture, FDFO desalination does not create additional environmental issues related to fertiliser usage. In fact, FDFO desalination could add more value to irrigation water, thereby providing opportunities for improving the efficiency of water and fertiliser uses. FDFO desalination can be operated at very high feed recovery rates: higher than 80% using a feed of seawater quality. However, FDFO desalination has its own process limitation. Based on the principles of natural osmosis, the net movement of water across the membrane towards the DS cannot theoretically extend beyond osmotic equilibrium, which in turn is limited by the total dissolved solids (TDS) content of the feed solution (FS). Therefore, it is not possible to achieve a concentration of the diluted DS that is lower than the equivalent concentration of the FS without external influence. Based on the models for osmotic equilibrium, the water extraction capacities of eleven selected fertiliser DS were calculated for FS, simulated for different ranges of TDS. The water extraction capacities of the fertilisers were observed to depend on the molecular weight and osmotic pressure of the draw solutes, as well as on feed concentration. Based on the water extraction capacity, the expected fertiliser nutrient concentrations in the final FDFO product water was estimated in terms of nitrogen phosphorous potassium (NPK) concentrations. The expected final nutrient concentrations for simulated brackish water (BW) feed (TDS 5,000–35,000 mg/L) failed to meet acceptable NPK concentrations for direct fertigation of crops. Hence, achieving acceptable nutrient concentrations for direct fertigation will be a major challenge for the FDFO desalination process. The rest of the study therefore focussed on investigating processes and options that would help reduce the nutrient concentrations in the final FDFO product so that the final FDFO product water could be used for direct fertigation. Before the experimental investigation on the FDFO desalination, the influence of major parameters on the performance of FO desalination process was investigated. The thermodynamic properties of the DS play a more influential role on water flux than the thermodynamic properties of the FS at higher temperature. Although water flux comparable to the RO desalination process was obtained by increasing the fertiliser DS concentrations, the internal concentration polarisation effects played a significant role in the performance of the FDFO desalination process. It was observed that any soluble fertilisers with osmotic pressure in excess of the FS can draw water in FO process; however, only eleven different chemical fertilisers commonly used for agriculture worldwide were selected and their performances studied. The performance of the fertiliser solutions as DS were assessed in terms of water flux, reverse draw solute flux, water extraction capacity and nutrient concentrations in the final product water. Blended fertilisers as the DS were able to achieved significantly lower NPK concentrations by FDFO desalination than the straight/single fertiliser as DS. However, it was observed that blending fertilisers generally resulted in a slightly reduced bulk osmotic pressure and water flux compared to the sum of the osmotic pressures and water fluxes of the two individual fertilisers when used as DS alone. An integrated FDFO-NF desalination process was investigated to reduce the nutrient concentrations in the final product water. Nanofiltration (NF) as pre-treatment or post-treatment was found to be effective in reducing the final NPK concentrations to acceptable limits for direct fertigation although it required second NF pass, especially when monovalent fertiliser was used as the DS or when a high TDS feed was used. NF as post-treatment was more advantageous in terms of both nutrient reduction and energy consumption because high quality, diluted DS was used as feed. Finally, this study has recommended a pilot test of the integrated FDFO-NF desalination process in the Murray-Darling basin. Recommendations for further investigations on reducing nutrient concentrations include pressure assisted FDFO desalination and the concept of using osmotic fillers as the DS with fertilisers. The study also recommended evaluating the potential for fertiliser drawn pressure retarded osmosis (FD-PRO) desalination for simultaneous desalination and power generation, and for self-powering the FO desalination process. The other recommendations include a study on membrane fouling and scaling issues for FDFO desalination operated at high recovery rates, boron rejection and, finally, a life cycle analysis of the FDFO desalination process

Fabricating robust thin film composite membranes reinforced on woven mesh backing fabric support for pressure assisted and forward osmosis: A dataset

© 2018 The Authors The data presented in this paper are produced as part of the original research article entitled “Thin-film composite membrane on a compacted woven backing fabric for pressure assisted osmosis” (Sahebi et al., 2017). This article describes how to fabricate a defect free membrane for forward osmosis (FO) and pressure assisted osmosis (PAO) on the woven mesh backing fabric support. Casting polymer on backing fabric support may limit the interfacial polyemirization due to wrinkled membrane surface. This paper presents data obtained from two different backing fabrics used as support for fabrication of thin film composite FO membrane. Backing fabric support were woven polyester mesh with different opening size. The data include the characterization of the intrinsic properties of the membrane samples, SEM and their performance under FO process. The structural parameters (S value) of the substrate were computed from thickness and porosity of the substrates. Thin film composite (TFC) membrane achieved a water flux of 8.1 L m2 h−1 in FO process and 37 L m2 h−1 using 0.5 M NaCl as draw solution (DS) and deionised (DI) water as the feed solution (FS) when applied hydraulic pressure was 10 bar

Investigation of pilot-scale 8040 FO membrane module under different operating conditions for brackish water desalination

© 2014, © 2014 Balaban Desalination Publications. All rights reserved. Two spiral wound forward osmosis membrane modules with different spacer designs (corrugated spacer [CS] and medium spacer [MS]) were investigated for the fertilizer-drawn forward osmosis (FO) desalination of brackish groundwater (BGW) at a pilot-scale level. This study mainly focused on examining the influence of various operating conditions such as feed flow rate, total dissolved solids (TDS) concentration of the BGW feed, and draw solution (DS) concentrations using ammonium sulfate ((NH4)2SO4, SOA) on the performance of two membrane modules. The feed flow rate played a positive role in the average water flux of the pilot-scale FO membrane module due to enhanced mass transfer coefficient across the membrane surface. Feed TDS and DS concentrations also played a significant role in both FO membrane modules because they are directly related to the osmotic driving force and membrane fouling tendency. CS module performed slightly better than MS module during all experiments due to probably enhanced mass transfer and lower fouling propensity associated with the CS. Besides, CS spacer provides larger channel space that can accommodate larger volumes of DS, and hence, could maintain higher DS concentration. However, the extent of dilution for the CS module is slightly lower

Performance comparison of thin-film composite forward osmosis membranes

Forward osmosis (FO) is an emerging low-energy technology. Much effort was given on developing a new membrane material and engineering membrane structure to improve the performance of FO membranes. The performances of two newly developed polyamide-based thin-film composite (TFC) FO membranes were tested and compared with the commercially available cellulose triacetate (CTA) FO membrane. The intrinsic properties of the two TFC FO membranes determined in RO experiments indicate superior performance of the membranes. When tested in FO experiments, TFC membranes delivered consistent results, confirming their outstanding permeability and selectivity properties. The study shows that future studies on membrane fouling will be necessary to have a better understanding of membrane performance and to further optimize membrane properties. © 2013 Copyright Balaban Desalination Publications

Defect-free outer-selective hollow fiber thin-film composite membranes for forward osmosis applications

© 2019 Elsevier B.V. This study presents the successful fabrication of a novel defect-free outer-selective hollow fiber (OSHF) thin-film composite (TFC) membrane for forward osmosis (FO) applications. Thin and porous FO membrane substrates made of polyether sulfone (PES) with a dense and smooth outer surface were initially fabricated at different air-gap distances. A modified vacuum-assisted interfacial polymerization (VAIP) technique was then successfully utilised for coating polyamide (PA) layer on the hollow fiber (HF) membrane substrate to prepare OSHF TFC membranes. Experimental results showed that the molecular weight cut-off (MWCO) of the surface of the membrane substrate should be less than 88 kDa with smooth surface roughness to obtain a defect-free PA layer via VAIP. The FO test results showed that the newly developed OSHF TFC membranes achieved water flux of 30.2 L m−2 h−1 and a specific reverse solute flux of 0.13 g L−1 using 1 M NaCl and DI water as draw and feed solution, respectively. This is a significant improvement on commercial FO membranes. Moreover, this OSHF TFC FO membrane demonstrated higher fouling resistance and better cleaning efficiency against alginate-silica fouling. This membrane also has a strong potential for scale-up for use in larger applications. It also has strong promise for various FO applications such as osmotic membrane bioreactor (OMBR) and fertilizer-drawn OMBR processes

Sulfur-containing air pollutants as draw solution for fertilizer drawn forward osmosis desalination process for irrigation use

© 2017 Elsevier B.V. This study investigated suitability and performance of the sulfur-based seed solution (SBSS) as a draw solution (DS), a byproduct taken from the photoelectrochemical (PEC) process where the SBSS is used as an electrolyte for H2 production. This SBSS DS is composed of a mixture of ammonium sulfate ((NH4)2SO4) and ammonium sulfite ((NH4)2SO3), and it can be utilized as fertilizer for fertilizer drawn forward osmosis (FDFO) desalination of saline water. The FDFO process employed with thin-film composite (TFC) membrane and showed that the process performance (i.e. water flux and reverse salt flux) is better than that with cellulose triacetate (CTA) membrane. In addition, it produced high water flux of 19 LMH using SBSS as DS at equivalent concentration at 1 M and 5 g/L NaCl of feed solution (model saline water). Experimental results showed that the reverse salt flux of SBSS increased with the increase in pH of the DS and that lowering the concentration of ammonium sulfite in the SBSS led to the higher water flux of feed solution. The result also demonstrated that this SBSS is practically suitable for the FDFO process toward development of water-energy-food nexus technology using sulfur chemicals-containing air pollutant

Draw solutes in forward osmosis processes

© 2015 by the American Society of Civil Engineers. All Rights Reserved. This chapter provides insight into the selection of suitable draw solutions (DS) and reviews different DS characteristics affecting the performance of forward osmosis (FO) processes. Although some commercial applications of FO technology exist, the development of an effective large-scale process is currently limited due to the lack of both suitable DS and membrane. The success of most FO applications also relies on how the DS can be recovered from the produced water. Therefore, in commercial FO processes, such as FO followed by reverse osmosis seawater desalination, emergency drinks and osmotic dilution are used without a DS recovery system-a simple and energy-saving solution. Research is still needed to develop more suitable DS to achieve full-scale commercialization of the FO process

Environmental and economic assessment of hybrid FO-RO/NF system with selected inorganic draw solutes for the treatment of mine impaired water

© 2017 Elsevier B.V. A hybrid forward osmosis (FO) and reverse osmosis (RO)/nanofiltration (NF) system in a closed-loop operation with selected draw solutes was evaluated to treat coal mine impaired water. This study provides an insight of selecting the most suitable draw solution (DS) by conducting environmental and economic life cycle assessment (LCA). Baseline environmental LCA showed that the dominant components to energy use and global warming are the DS recovery processes (i.e. RO or NF processes) and FO membrane materials, respectively. When considering the DS replenishment in FO, the contribution of chemical use to the overall global warming impact was significant for all hybrid systems. Furthermore, from an environmental perspective, the FO-NF hybrid system with Na2SO4 shows the lowest energy consumption and global warming with additional considerations of final product water quality and FO brine disposal. From an economic perspective, the FO-NF with Na2SO4 showed the lowest total operating cost due to its lower DS loss and relatively low solute cost. In a closed-loop system, FO-NF with NaCl and Na2SO4 had the lowest total water cost at optimum NF recovery rates of 90 and 95%, respectively. FO-NF with Na2SO4 had the lowest environmental and economic impacts. Overall, draw solute performances and cost in FO and recovery rate in RO/NF play a crucial role in determining the total water cost and environmental impact of FO hybrid systems in a closed-loop operation

A new sponge tray bioreactor in primary treated sewage effluent treatment

The new attached growth sponge tray bioreactor (STB) was evaluated at different operating conditions for removing organics and nutrients from primary treated sewage effluent. This STB was also assessed when using as a pre-treatment prior to micro-filtration (MF) for reducing membrane fouling. At a short hydraulic retention time (HRT) of 40min, the STB could remove up to 92% of DOC and 40-56% of T-N and T-P at an organic loading rate (OLR) of 2.4kg COD/m3 spongeday. This OLR is the best for the STB as compared to the OLRs of 0.6, 1.2 and 3.6kg COD/m3 spongeday. At 28mL/min of flow velocity (FV), STB achieved the highest efficiencies with 92% of DOC, 87.4% of T-P, and 54.8% of T-N removal. Finally, at the optimal OLR and FV, the STB could remove almost 90% of organic and nutrient, significantly reduce membrane fouling with HRT of only 120min. © 2010 Elsevier Ltd