Fabrication of thin film composite poly(amide)-carbon-nanotube supported membranes for enhanced performance in osmotically driven desalination systems

The search for lower energy consumption desalination systems has been driving research in the past decade towards the investigation of osmotically driven membrane processes, such as forward osmosis (FO) or osmotic distillation (OD). Despite similarities with reverse osmosis (RO) membranes, thin film composite (TFC) for FO membranes require careful design to reduce salt concentration polarization formation within the large pores composing the supporting layer. An investigation of a novel, highly stable, robust support made solely of carbon nanotubes (CNTs), which could find applications in both RO and FO was undertaken. TFC membranes were fabricated by interfacially polymerizing for the first time a dense poly(amide) (PA) layer on self-supporting bucky-papers (BPs) made of hydroxyl-functionalized entangled CNTs. These hydrophilic supports exhibited low contact angle with water (90%), making it a promising material when compared with poly(sulfone) (PSf), the traditional polymer used to fabricate TFC membrane supports in RO. In addition, the impact of the support hydrophilicity on the stability of the interfacially polymerized film and on water adsorption was investigated by oxygen-plasma treating various potential support materials, exhibiting similar geometrical properties. The morphology and salt diffusion of both CNT BP and PSf supports were investigated, and the novel BP–PA composite membranes were found to be superior to commercially available TFC membranes

Fouling of dairy components on hydrophobic polytetrafluoroethylene (PTFE) membranes for membrane distillation

This study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds — skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hat 54 C feed inlet temperature and 5 C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency.Skim milk flux was found to be lower but stable overtime compared to whey.The study using single components as well as combinations the reofrevealed that fouling was primarily driven by proteins and calcium, but only in combination.Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration,but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchorpoint to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins;however salts were needed to form a thick and dense cake layer.Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer.Wheyproteins, on the other hand, deposited to alesse rextent. In general membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk

Cultivation and enrichment of anammox culture in a submerged membrane bioreactor

Results of a research project comparing membrane fouling rates of PVDF to PTFE membrane

Scalability of advanced oxidation processes (AOPs) in industrial applications: a review

Disinfection and decontamination of water by application of oxidisers is an essential treatment step across numerous industrial sectors including potable supply and industry waste management, however, could be greatly enhanced if operated as advanced oxidation processes (AOPs). AOPs destroy contaminants including pathogens by uniquely harnessing radical chemistry. Despite AOPs offer great practical opportunities, no reviews to date have highlighted the critical AOP virtues that facilitate AOPs’ scale up under growing industrial demand. Hence, this review analyses the critical AOP parameters such as oxidant conversion efficiency, batch mode vs continuous-flow systems, location of radical production, radical delivery by advanced micro-/mesoporous structures and AOP process costs to assist the translation of progressing developments of AOPs into their large-scale applications. Additionally, the state of the art is analysed for various AOP inducing radical/oxidiser measurement techniques and their half-lives with a view to identify radicals/oxidisers that are suitable for in-situ production. It is concluded that radicals with short half-lives such as hydroxyl (10−4 μsec) and sulfate (30–40 μsec) need to be produced in-situ via continuous-flow reactors for their effective transport and dosing. Meanwhile, radicals/oxidisers with longer half-lives such as ozone (7–10 min), hydrogen peroxide (stable for several hours), and hypochlorous acid (10 min −17 h) need to be applied through batch reactor systems due to their relatively longer stability during transportation and dosing. Complex and costly synthesis as well as cytotoxicity of many micro-/mesoporous structures limit their use in scaling up AOPs, particularly to immobilising and delivering the short-lived hydroxyl and sulfate radicals to their point of applications. Overall, radical delivery using safe and advanced biocompatible micro-/mesoporous structures, radical conversion efficiency using advanced reactor design and portability of AOPs are priority areas of development for scaling up to industry

Application of membrane-based technology for purification of bromelain

About 60% of world’s commercial enzyme products are proteases, giving promising opportunity to derive such enzymes sustainably from waste sources. Bromelain is a crude protease occurring naturally in pineapple, and it possesses properties of benefit for pharmaceutical, medical and food products. The production of bromelain involves a purification stage, normally performed by small-scale conventional operations which lead to high operating cost and low product recovery, while being difficult to scale up and produce polluting by-products. Membrane-based technology offers an alternative to produce high quality purified bromelain in a more efficient and sustainable process. This review identified the current state and future needs for utilising membrane processes for sustainable bromelain production at larger scales. It was found that declining membrane flux due to fouling have been reported, but may be effectively overcome with more appropriate (and advanced) membrane types and/or processing conditions. For example, interactions between macromolecules present in the pineapple derived bromelain mixture (particularly polysaccharides) and the membrane may cause performance limiting fouling, but can be overcome by enzymatic pre-treatment. Membrane fouling can be further reduced by the employment of ceramic membrane filters operating at optimised trans-membrane pressure, cross-flow velocity, feed pH and temperature. Two-stage ultrafiltration together with diafiltration or gas sparging was suggested as a means to reduce fouling and improve enzyme purity. Despite these promising technical findings, the review identified the need for a valid economic assessment to properly guide further work towards purifying bromelain from pineapple waste for sustainable production of commercial proteases

Hybrid processes combining photocatalysis and ceramic membrane filtration for degradation of humic acids in saline water

This study explored the combined effects of photocatalysis with ceramic membrane filtration for the removal of humic acid in the presence of salt; to simulate saline wastewater conditions. The effects of operating parameters, such as salinity and TiO2 concentration on permeate fluxes, total organic carbon (TOC), and UV absorbance removal, were investigated. The interaction between the humic acids and TiO2 photocatalyst played an important role in the observed flux change during ceramic membrane filtration. The results for this hybrid system showed that the TOC removal was more than 70% for both without NaCl and with the 500 ppm NaCl concentration, and 62% and 66% for 1000 and 2000 ppm NaCl concentrations. The reduction in UV absorbance was more complete in the absence of NaCl compared to the presence of NaCl. The operation of the integrated photoreactor-ceramic membrane filter over five repeat cycles is described. It can be concluded that the overall removal performance of the hybrid system was influenced by the presence of salts, as salt leads to agglomeration of TiO2 particles by suppressing the stabilising effects of electrostatic repulsion and thereby reduces the effective surface contact between the pollutant and the photocatalyst

Membrane scaling and prevention techniques during seawater desalination by air gap membrane distillation

Membrane scaling and mitigation techniques during air gap membrane distillation (AGMD) of seawater were investigated. The results showed a strong influence of AGMD operating temperature on not only the process water flux but also membrane scaling and subsequent cleaning efficiency. Elevating feed/coolant temperature from 35/25 to 60/50 °C increased water flux, but also exacerbated membrane scaling of the AGMD process. Membrane scaling was more severe, and occurred at a lower water recovery (68%) when operating at 60/50 °C compared to 35/25 °C (78%) due to increased concentration polarisation effect. Operating temperature also affected the efficiency of the subsequent membrane cleaning. Membrane scaling that occurred at low temperature (i.e. 35/25 °C) was more efficiently cleaned than at high temperature (i.e. 60/50 °C). In addition, membrane cleaning using vinegar was much more efficient than fresh water. Nevertheless, vinegar cleaning could not completely restore the membrane surface to the original condition. Traces of residual scalants on the membrane surface accelerated scaling in the next operation cycle. On the other hand, anti-scalant addition could effectively control scaling. Membrane scaling during AGMD of seawater at 70% water recovery and 60/50 °C was effectively controlled by anti-scalant addition

Membrane distillation and membrane electrolysis of coal seam gas reverse osmosis brine for clean water extraction and NaOH production

Membrane distillation (MD) and membrane electrolysis (ME) were evaluated for simultaneous fresh water extraction and NaOH production from a mixture of NaCl and NaHCO3 to simulate the composition of coal seam gas (CSG) reverse osmosis (RO) brine. Experimental results demonstrate the potential of MD for producing fresh water and simultaneously concentrating CSG RO brine prior to the ME process. MD water flux was slightly reduced by the increased feed salinity and the decomposition of bicarbonate to CO2 during the concentration of CSG RO brine. MD operation of CSG RO brine at a concentration factor of 10 (90% water recovery) was achieved with distillate conductivity as low as 18 μS/cm, and without any observable membrane scaling. Exceeding the concentration factor of 10 could lead to deterioration in both water flux and distillate quality due to the precipitation of NaCl, NaHCO3, and Na2CO3 on the membrane. With respect to ME, current density and water circulation rates exerted strong influences on the ME process performance. Combining ME with MD reduced the thermal energy requirement of ME by 3 MJ per kg of NaOH produced and the thermal energy consumption of MD by 22 MJ per m3 of clean water extracted

Membrane distillation of meat industry effluent with hydrophilic polyurethane coated polytetrafluoroethylene membranes

Meat rendering operations produce stick water waste which is rich in proteins, fats, and minerals. Membrane distillation (MD) may further recover water and valuable solids, but hydrophobic membranes are contaminated by the fats. Here, commercial hydrophobic polytetrafluorethylene (PTFE) membranes with a hydrophilic polyurethane surface layer (PU-PTFE) are used for the first time for direct contact MD (DCMD) on real poultry, fish, and bovine stick waters. Metal membrane microfiltration (MMF) was also used to capture fats prior to MD. Although the standard hydrophobic PTFE membranes failed rapidly, PU-PTFE membranes effectively processed all stick water samples to colourless permeate with sodium rejections >99%. Initial clean solution fluxes 5–6 L/m2/h declined to less than half during short 40% water recovery tests for all stick water samples. Fish stick water uniquely showed reduced fouling and up to 78% water recovery. Lost flux was easily restored by rinsing the membrane with clean water. MMF prior to MD removed 92% of fats, facilitating superior MD performance. Differences in fouling between stick waters were attributed to temperature polarisation from higher melt temperature fats and relative proportions to proteins. Hydrophilic coated MD membranes are applicable to stick water processing but further studies should consider membrane cleaning and longer-term stability