Introduction to Issues and Technology in Water Contaminants

About 70% of the earth’s surface is covered with water. Although the quantity of water on earth is vast, most of this does not fit for direct human consumption, particularly the saline water. The most accessible source of fresh water for human consumption is the surface water, including rivers and lakes, which consist of about 0.3% of the total fresh water volume on earth (Gleick, 1996). Unfortunately, the access to clean fresh water is inadequate in many parts of the world. This is largely due to the deterioration of raw water quality and the threat of water contaminants

Biodegradation of nonylphenol ethoxylates (NPEOs) in a membrane aerated biofilm reactor (MABR)

The degradation intermediates of NPEOs surfactants (NP and short chain NPEOs) are of growing concern in environmental studies. These intermediates, recognised as endocrine disrupting chemicals (EDCs), are more toxic and refractory than their parent compounds. Their formation is assisted by anaerobic process, while their further breakdown to less harmful compounds is more easily achieved in aerobic environments. In this study, an hybrid MABR was exploited to completely degrade NPEOs, based on the concept of a multi-layered biofilm in the MABR that permits a simultaneous anaerobic-aerobic process to occur in a single reactor. This is the first study conducted on NPEOs biodegradation in an MABR. Batch microcosm experiments were conducted primarily to simulate NPEOs biodegradation behaviour in the MABR. The results showed that NPEOs removal was improved in a simultaneous anaerobic-aerobic system, as compared to a fully anaerobic system. A microporous polypropylene membrane with a non-woven polypropylene scrim heat-sealed to the surface was then used as an aeration device and biofilm support in a flat sheet MABR. Under steady state conditions (NPEOave9 surface loading of 0.49 g/m2.d; at 48 hr HRT), the reactor achieved an excellent removal of NPEOs (up to >99%) and organics in terms of COD (up to 93%). The disruption of MABR performance was less pronounced under hydraulic shock loads (reduced HRT) compared to organic shock loads (increased NPEOave9 concentration), and this was postulated to be due to improved NPEOave9 mass transfer into the biofilm. Despite the slow MABR recovery from shock loads, a stable NPEOs removal of more than 95% was achievable after the recovery periods. Based on HPLC-UV and GC-MS analyses, the EO units of NPEOave9 were sequentially shortened (commonly via a nonoxidative pathway) over 500 days of operation to the major intermediate of NPEO1. Nevertheless, complete removal of NPEO1 was unsatisfactory, and more work needs to be done to optimise and investigate the role of the aerobic layer in degrading the compound. Nevertheless, this study has shown that the MABR is very reliable for the removal of both COD and NPEOs under long term operation, and the presence of toxic intermediates did not appear to inhibit overall reactor performance

Preparation and characterisation of inexpensive porous kaolin hollow fibre as ceramic membrane supports for gas separation application

Low-cost, porous ceramic kaolin-based hollow fibre membrane support (HFMS) for gas separation application was developed via phase inversion technique. The ceramic suspensions with various ratios of kaolin to polyethersulfone (PESf) binder (5:1 to 9:1) were extruded and then sintered at 1200 to 1500 °C. The HFMSs were characterised by several analyses to investigate the effects of kaolin/PESf ratio and sintering temperature on the sample properties. The results showed that the kaolin/PES ratio and sintering temperature affected the considerable structure and physical properties of the kaolin membrane. It is observed that with increasing sintering temperature, the porosity and gas permeation of the HFMS decreased, while the bending strength and density of the HFMS increased. As a result, a porous HFMS with sufficient mechanical strength and high gas permeation characteristics is achievable if the appropriate kaolin/PESf ratio and sintering temperature are chosen

Evaluating the sintering temperature control towards the adsorptivity of ammonia onto the natural zeolite based hollow fibre ceramic membrane

The disproportionate quantity of ammonia presence in water has led to serious drinkable water scarcity worldwide. The abundant source of mineral and superior cations selectivity has made natural zeolite as a good adsorbent for the ammonia removal. This work aims to fabricate natural zeolite based hollow fibre ceramic membrane (HFCM) via extrusion-based phase inversion and sintering techniques for the ammonia removal in wastewater. The physical properties of the fabricated HFCM were investigated through surface morphologies and pure water permeation. The performance of the HFCM for ammonia removal was studied using synthetic wastewater with HFCM prepared at different sintering temperatures. Of all studied sintering temperatures, it was found that 1050 °C was the best fabrication conditions. The membrane also revealed acceptable morphologies (roughness) and water permeation flux of 249.57 L/m 2 .h to which both contributed to the performance of the HFCM. The ammonia removal using the fabricated HFCM gave an outstanding performance with nearly 90% rejection, which probably is due to the synergistic effect of the two processes in the HFCM system, i.e. adsorption and separation. It was found that natural zeolite based HFCM has a great potential to be developed as a single – step ammonia removal in wastewater treatment

Phosphorus and eutrophication in water

Since early 1970, the presence of phosphorus (P) in domestic wastewater has attracted attention due to the awareness of its adverse impacts on the environment, specifically in receiving water such as a river. In the wastewater treatment system, P is a crucial nutrient for bacteria required to degrade and biologically stabilise the organic wastes (Hussain et al., 2001). P is a key nutrient that stimulates the growth of algae and other biological organisms (Mainstone and Parr, 2002). P appears exclusively as orthophosphate, condensed phosphates (polyphosphates), and organically bound phosphate. Condensed phosphates are utilised in cleaning products, and organic phosphates are elements of the body and food waste (Howard, 1985). According to Tjandraatmadja et al. (2010), household products can be a significant contributor to the P load in domestic wastewater. The release of high quantities of P from domestic wastewater treatment plants is of concern, as it is one of the key nutrients that have the potential to contribute to eutrophication in surface water, which can result in excessive growth of algae (Daniel et al., 1994)

Utilization of durian peel as potential adsorbent for bisphenol a removal in aquoeus solution

This study explored the low-cost adsorbent of durian peel for BPA removal from aqueous solutions. The effect of various operational parameters such as contact time, temperature, concentration, agitation and pH on the adsorption of BPA was investigated using the batch adsorption study. It was found that Durian peel can be used as a low cost adsorbent for the removal of BPA in aqueous solution after treated with sulfuric acid. The effects of morphology, functional groups, and surface area of adsorbent, before and after pretreatment with sulfuric acid and reaction were investigated by using FESEM, FTIR, and BET. The present study indicates that durian peel had removed 69.63% of BPA with adsorption capacity of 4.178 mg/g for 24 hours. The result proved that this treated agricultural waste was promising material as an alternative adsorbent for the removal of BPA from aqueous solution. Kinetic study of the results gave a pseudo-second order type of mechanism while the adsorption characteristics of the adsorbent followed the Langmuir adsorption isotherm

WO3–based photocatalysts: A review on synthesis, performance enhancement and photocatalytic memory for environmental applications

A significant drawback of the traditional photocatalysts such as titanium dioxide (TiO2) is their inability to absorb visible light from the solar spectrum due to their wide band gap energy. They are only photoactive in the ultraviolet (UV) region which is just a little fraction of the solar spectrum and could be harmful with much exposure to it. Due to its abundance in the solar spectrum, visible light needs to be harnessed for environmental applications. However, we lack visible light driven photocatalysts with long-lasting energy storage capacity for “round-the-clock photocatalytic” (RTCP) applications. For this reason, there is a growing need to find new photocatalysts that can mitigate these bottlenecks. It is evident from some carefully selected published articles (1976–2021) that tungsten oxide (WO3) and its composites have attracted popularity in recent years because of its outstanding properties and particularly its smaller band gap energy of 2.8 eV. However, pristine WO3 is limited due to relatively low energy density and smaller specific surface area. These drawbacks can be addressed by developing various WO3 – based materials to improve their performance. This paper reviews and discusses their recent development in surface advancement, morphology control, modification of nanostructured WO3 and its composites, and their RTCP energy storage for photocatalytic activities in visible light and the dark for environmental applications. Specific aspects focused on its nature, structure, properties, synthesis, coatings, deposition, approaches at modifying and enhancing its visible light photoactivity for enhanced performance and energy storage potential

Fabrication and characterisation of superhydrophobic bio-ceramic hollow fibre membranes prepared from cow bone waste

Superhydrophobic membranes have great potential towards various application, especially for thermal-based membrane system such as membrane distillation. In this study, bioceramic hollow fibre membranes derived from cow bone waste were prepared by phase inversion/sintering method, followed by surface modification via immersion grafting with fluoroalkylsilane (FAS) agent. Interestingly, the grafting process led to the formation of hydroxyapatite nanorods, mimicking the unique structure of electrospun nanofiber membranes. The hydrophobicity of the modified membranes was assessed by measuring the water contact angle and showed excellent improvement from hydrophilic property to superhydrophobic with the highest value of 174° After the modification, the water entry pressure also improved from 0 to 1 bar. In addition, the presence of FAS agent on the membrane surface was observed using X-ray photoelectron spectroscopy (XPS). A correlation between pore size, porosity, and mechanical strength of the modified membrane was discussed; the increment of membrane pore size after grafting process is synonym to the dental erosion mechanism. The result indicates that the superhydrophobic bioceramic hollow fibre membranes derived from cow bone waste have significant potential to be developed for membrane distillation application in treating water and wastewater

High flux polysulfone braided hollow fiber membrane for wastewater treatment role of zinc oxide as hydrophilic enhancer

Incorporation of zinc oxide (ZnO) nanoparticles has played an important role on the improvement of unique membrane characterization and performance, most notably the hydrophilic modification of the membrane for higher pure water permeability. Additionally, the permeability of the membrane can be improved via introduction of braid support by reducing the thickness of the membrane separation layer. Moreover, the braided hollow fiber membrane (BHFM) is able to perform under higher pressure conditions compared to hollow fiber membranes. In this paper, hybrid polysulfone (PSf)/ZnO BHFMs were fabricated via phase inversion method. Hydrophilic 10 ± 1.8 nm polycrystalline ZnO nanoparticles synthesized via sol-gel method were incorporated on BHFM to improve the hydrophilicity and increase flux with constant rejection under high pressure and the effect of the ZnO loading on the membrane properties and performance were thoroughly studied. The fabricated BHFMs with 0.0, 0.5, 1.0 and 1.5 wt% of ZnO nanoparticles concentration were defined as BHFM1, BHFM2, BHFM3 and BHFM4 respectively. Scanning electron microscopy (SEM), contact angle, mechanical strength, flux performance, rejection with bovine serum albumin (BSA) and fouling of best performed membrane were conducted to achieve the target of this paper. The performance of these hybrid ZnO/PSf BHFMs were compared with neat PSf hollow fiber membrane (HFM) and previous studies. The findings from this research work shows that BHFM4 has the most desired properties for wastewater treatment application. The ZnO nanoparticles in BHFM4 have improved hydrophilicity from 108.79° to 71.02°, and thus BHFM4 has increased flux performance from 36.20 to 919.12 L/m2 h at 1.0 bar pressure and 193.48 to 1909.11 L/m2h at 4.0 bar pressure when compared with BHFM1. Constant BSA rejection rates (> 90%) were observed in all BHFMs. The improved hydrophilicity and pure flux performance with constant rejection rate in high pressure conditions illustrates the suitability of fabricated ZnO/PSf BHFMs in wastewater treatment applications

Novel ceramic hollow fibre membranes contactor derived from kaolin and zirconia for ammonia removal and recovery from synthetic ammonia

The adverse effects of ammonia found in wastewater streams lead to the development of advanced water treatment technology, i.e. membrane contactor (MC). In this study, single layer hollow fibre membrane (SLZK) and dual layer hollow fibre membrane (DLZK) were prepared from zirconia and kaolin and modified into hydrophobic membrane through simple grafting process via fluoroalkylsilane (FAS) agent. The properties of membranes such as morphology, surface roughness, mechanical strength, wettability and liquid entry pressure were analysed through scanning electron microscopy (SEM), atomic force microscopy (AFM), 3-point bending strength, contact angle and LEPw setup. Finally, the performance of the membranes was also investigated towards ammonia removal via membrane contactor system. Our findings showed that hydrophobicity properties significantly improved for both SLZK and DLZK membranes after grafting modification process as indicated by the increase of contact angle value from 5° and 1° to 132.7° and ~180.0° respectively. Based on the morphological analysis, the surface of DLZK showed more porous structure as compared to the SLZK. In addition, DLZK also displayed the highest mechanical strength and contact angle reading of 125 MPa and ~180° respectively. This suggests that the DLZK showed an excellent membrane contactor performance with highest value of mass transfer coefficient (3.77 x 10-5 ms-1) and almost complete removal of ammonia removal (91%). Overall, these results implied that dual layer ceramic membrane developed from kaolin and zirconia could provide the basis for the development of alternative ceramic membrane with excellent properties for membrane contactor system