Fouling and performance of outer selective hollow fiber membrane in osmotic membrane bioreactor: Cross flow and air scouring effects

© 2019 Elsevier Ltd This study assessed impacts of cross-flow velocity (CFV) and air scouring on the performance and membrane fouling mitigation of a side-stream module containing outer-selective hollow fiber thin film composite forward osmosis membrane in osmosis membrane bioreactor (OMBR) system for urban wastewater treatment. CFV of draw solution was optimized, followed by the impact assessment of three CFVs on feed solution (FS) stream and periodic injection of air scouring into the side-stream module. Overall, the OMBR system exhibited high and stable performance with initial water flux of approximately 15 LMH, high removal efficiencies of bulk organic matter and nutrients. While FS's CFVs insignificantly affected the performance and membrane fouling, regular air scouring showed substantial impact with better performance and high efficiency in mitigating membrane fouling. These results indicated that periodic air scouring can be applied into the side-stream membrane module for efficient fouling mitigation without interruption the operation of the OMBR system

Fertilizer drawn forward osmosis process for sustainable water reuse to grow hydroponic lettuce using commercial nutrient solution

© 2017 Elsevier B.V. This study investigated the sustainable reuse of wastewater using fertilizer drawn forward osmosis (FDFO) process through osmotic dilution of commercial nutrient solution for hydroponics, a widely used technique for growing plants without soil. Results from the bench-scale experiments showed that the commercial hydroponic nutrient solution (i.e. solution containing water and essential nutrients) exhibited similar performance (i.e., water flux and reverse salt flux) to other inorganic draw solutions when treating synthetic wastewater. The use of hydroponic solution is highly advantageous since it provides all the required macro- (i.e., N, P and K) and micronutrients (i.e., Ca, Mg, S, Mn, B, Zn and Mo) in a single balanced solution and can therefore be used directly after dilution without the need to add any elements. After long-term operation (i.e. up to 75% water recovery), different physical cleaning methods were tested and results showed that hydraulic flushing can effectively restore up to 75% of the initial water flux while osmotic backwashing was able to restore the initial water flux by more than 95%; illustrating the low-fouling potential of the FDFO process. Pilot-scale studies demonstrated that the FDFO process is able to produce the required nutrient concentration and final water quality (i.e., pH and conductivity) suitable for hydroponic applications. Coupling FDFO with pressure assisted osmosis (PAO) in the later stages could help in saving operational costs (i.e., energy and membrane replacement costs). Finally, the test application of nutrient solution produced by the pilot FDFO process to hydroponic lettuce showed similar growth pattern as the control without any signs of nutrient deficiency

Pressure assisted fertiliser drawn osmosis process to enhance final dilution of the fertiliser draw solution beyond osmotic equilibrium

© 2015 Elsevier B.V. Adequate dilution of fertiliser draw solution (DS) during fertiliser drawn forward osmosis (FDFO) desalination is important to meet nutrient concentration level for direct fertigation. The maximum DS dilution, however, occurs until the point of osmotic equilibrium between DS and feed solution (FS) thereby limiting the extent of DS dilution. Post-treatment such as nanofiltration (NF) process is required to reduce the fertiliser concentration. In this study however, pressure assisted fertiliser drawn osmosis (PAFDO) process was investigated to enhance DS dilution beyond the point of osmotic equilibrium and potentially eliminate NF post-treatment. The hydraulic pressure applied enhanced water flux significantly depending on the pressure. The applied pressure was found more effective at lower DS concentrations than at higher DS concentrations. For example, when a pressure of 10bar was applied to 10g/L NaCl FS with 0.1M (NH4)2SO4 DS, the water flux increased by 1928% against 38% with 3.0M (NH4)2SO4 DS. This additional water flux could dilute the fertiliser DS beyond the osmotic equilibrium concentrations thereby meeting the fertigation standard. PAFDO could potentially eliminate NF post-treatment significantly helping reduce the footprint and capital cost. However, the effective gain in water flux due to applied pressure at osmotic equilibrium decreased with the increase in the FS concentrations

Controlling the inner surface pore and spherulite structures of PVDF hollow fiber membranes in thermally induced phase separation using triple-orifice spinneret for membrane distillation

In this study, we controlled the inner surface structures of polyvinylidene fluoride (PVDF) hollow fiber membranes via a thermally induced phase separation process using a triple-orifice spinneret for direct-contact membrane distillation (DCMD). The coextrusion of propylene carbonate (PC) through the outermost channel of the spinneret led to porous outer surfaces with similar pore sizes and spherulitic structures for all the PVDF hollow fiber membranes. In the innermost channel, the extrusion of solvents having different compatibilities with PVDF and the diluent (PC) as the bore liquids controlled the inner surface pore sizes and spherulite structures, and the effects of these inner surface structures on the DCMD performance were investigated in detail. Increasing the compatibility of the bore liquids toward the diluent led to an increase in the inner surface pore size because of the formation of loose, isolated spherulites, which remarkably enhanced the water vapor permeability from 4 to 8.3 L m−2 h−1, while reducing the membrane hydrophobicity, liquid entry pressure, and salt rejection. When increasing the bore liquid compatibility with the polymer, the surface pore size decreased because of the tight spherulite contact, enhancing membrane salt rejection and wetting resistance. Given the significance of bore liquid compatibility with the diluent and the polymer in controlling the inner surface structures, a useful guideline is presented for selecting the appropriate bore liquids to prepare hollow fiber membranes with the desired inner surface structures for high MD performance

Synthesis and characterisation of porous titania-silica composite aerogel for NO<inf>x</inf> and acetaldehyde removal

Copyright © 2016 American Scientific Publishers All rights reserved. In this study, the synthesis of porous titania-silica (TiO2-SiO2) composite aerogel at ambient pressure by using non-hazardous chemicals as a source of silica was investigated. TiO2-SiO2 composite aerogels were characterised and their photocatalytic performances were investigated for the removal efficiency of acetaldehyde and NOx under UV light. Results showed that porous composite aerogel with aggregated morphology, high surface area and an increased mesoporosity were formed. TiO2-SiO2(1.8) composite, with high Ti/Si ratio, showed the best results in terms of photocatalytic removal of acetaldehyde and nitrogen oxide

Dimensionally controlled graphene-based surfaces for photothermal membrane crystallization.

Membrane-based photothermal crystallization - a pioneering technology for mining valuable minerals from seawater and brines - exploits self-heating nanostructured interfaces to boost water evaporation, so achieving a controlled supersaturation environment that promotes the nucleation and growth of salts. This work explores, for the first time, the use of two-dimensional graphene thin films (2D-G) and three dimensional vertically orientated graphene sheet arrays (3D-G) as potential photothermal membranes applied to the dehydration of sodium chloride, potassium chloride and magnesium sulfate hypersaline solutions, followed by salt crystallization. A systematic study sheds light on the role of vertical alignment of graphene sheets on the interfacial, light absorption and photothermal characteristics of the membrane, impacting on the water evaporation rate and on the crystal size distribution of the investigated salts. Overall, 3D-G facilitates the crystallization of the salts because of superior light-to-heat conversion leading to a 3-fold improvement of the evaporation rate with respect to 2D-G. The exploitation of sunlight graphene-based interfaces is demonstrated as a potential sustainable solution to aqueous wastes valorization via recovery in solid phase of dissolved salts using renewable solar energy