Surfactants-based remediation as an effective approach for removal of environmental pollutants—A review

Deterioration of environmental quality and equilibrium by rampant industrial expansion, accelerated urbanization and unchecked population growth has become a high-priority concern. The release of an alarming number of toxic polluting agents such as volatile organic compounds, dyes, heavy metals, pharmaceuticals, pesticides, industrial wastes, and personal care products due to natural or anthropogenic activities pose direct adverse effects on human health and living entities. This issue is inescapably increased because of the lack of efficient technologies for the proper disposal, management, and recycling of waste. It is of paramount importance to track alternative solutions to address these pollution problems for an eco-sustainable environment. Conventional remediation techniques are either inefficient, cumbersome or restricted due to certain techno-economic limitations. Environmental compatibility and high pollutant-removal efficacy make surfactants valuable for removal of organic pollutants and toxic heavy metal ions from different mediums. In this review, we present recent and up-to-date information on micelles/surfactants-assisted abatement of a vast number of toxic agents of emerging concern from water/wastewater including volatile organic compounds, personal care products, pharmaceutically active residues, toxic metals, dye pollutants, pesticides, and petroleum hydrocarbons. Based on the literature survey, it can be concluded that micelles-assisted water and soil treatment technology can have a better future on large-scale decontamination of wastewater. Though bio-surfactants are environmentally friendlier matrices and have successfully been employed for environmental decontamination; their large-scale applicability is challenging owing to high costs. Additional research efforts on the development and employment of novel bio-surfactants might render wastewater treatment technology greener, smarter and economical

Development of multifunctional nanomaterials and adsorption - photocatalysis hybrid system for wastewater reclamation.

This thesis study aimed to develop multi-functional nano-catalyst and porous adsorbents from low-cost and locally available materials, and then implement this into an Adsorption-Photocatalysis hybrid system for wastewater reclamation. The project involves two major technological practices for wastewater treatment: adsorption and photocatalysis. For each technology, a specific functional nanomaterial has been developed and investigated regarding their removal capability for a pilot-scale water treatment process. The experimental studies include: 1) evaluation and characterisation of the natural clay minerals that deliver the most suitable properties for adsorption performance and immobilisation of titanium dioxide (TiO₂); 2) synthesis, modification, and characterisation of the clay mixtures as alternative adsorbents, and titania immobilised onto modified porous kaolin as the photocatalyst; 3) evaluation and optimisation of their removal capability, kinetics and mechanisms toward different surrogate indicators of both nanomaterials via the batch and continuous water treatment system; and 4) integration of the adsorption-photocatalysis hybrid system as a major technical outcome for the treatment and reclaimantion of wastewater. Three Australian natural clay minerals, bentonite, kaolins, and zeolite, were investigated to gain understanding of their physiochemical properties as well as their adsorption capabilities towards Congo red (CR) dye as a chemical surrogate indicator. Microscopic characterisations revealed the variation of the layered structures among clays, resulting in the differences in their adsorbent-adsorbate interaction profiles. The removal capacities of the clays were evaluated through the adsorption isotherms and kinetic studies, where it was found that Na-bentonite showed the best removal performance, followed by kaolin and zeolite. Thermodynamic and pH effect studies indicated that dye adsorption by the studied clays was a spontaneous and exothermic reaction, while pH conditions appeared insignificant. Further investigation has been emphasised on using different natural kaolins, in which the recyclability of these clay minerals was also taken into account. These results depicted a very high thermal stability of the kaolin structure. Repetitive recycled kaolin trials revealed good recovery of dye removal efficiency even after five experimental tests. This study demonstrated the potential employment of these natural clays as alternative adsorbents for wastewater treatment. To improve the removal efficiency of these natural clays as an economically viable adsorbent for wastewater treatment, a physical modification of the clay minerals was adopted in this present work. A feasible technical approach of combination and calcination of these natural clay materials to improve dye removal efficiency was developed to compromise the indigenous weakness of individual clays. The application of a mixture of clay minerals would be able to compromise the indigenous constraints of the individual clays. An optimisation study using calcium hydroxide or slaked lime as an additional calcium source for the clay mixture was included. Different characterisation methods, i.e. differential temperature analysis (DTA) coupled with thermogravimetric analyser (TG), scanning electron microscopy (SEM), and x-ray diffraction (XRD), were applied to comprehend the changed properties of the adsorbents during calcination treatment. The clay mixture and lime showed superior decolourisation, over 10–20 times to those of bentonite, kaolin and zeolite, at the optimum thermal condition at 300°C for 1.5 h. The great enhancement in dye removal efficiency was the contribution of the combination of an adsorption/precipitation mechanism. The instant precipitation of dissolved Ca ions with dye molecules illustrated the major contributor to dye removal, followed by the constant adsorption. The adsorbent mixture possessed the potential for recovery by heat treatment, of which their removal capacity was found comparable to the fresh materials even after the 5th cycle. The application of the adsorbent mixture was investigated in a pilot scale implementation, in which the laboratory scale fluidised-bed reactor (FBR) was developed in our research group. Optimisation of the operating parameters influencing pollutant removal performance of the FBR system, i.e. adsorbent loading, aeration rate, reaction time etc. was undertaken to facilitate the continuous operating scheme. The removal performance of oxyanion phosphate and nitrate in wastewater effluent, as well as their interference effect on dye elimination was also determined. The results revealed that the very effective elimination of CR and phosphate as complete removal can be achieved, while the reduction of nitrate became less extensive due to the difference in their removal mechanisms, i.e. adsorption and precipitation etc. The feasibility of using the FBR system in the wastewater treatment was also investigated. Several municipal primary effluent samples were treated using the FBR system in continuous operation mode. The results showed an average 10-15% and 20-40% reduction of the nitrate and chemical oxygen demand (COD), respectively, while 100% phosphate removal was obtained over the experimental period. This study demonstrated that the FBR system with the formulated clay-lime mixture can be a cost-effective alternative treatment process for large-scale application in the wastewater industry. Another advanced technology, heterogeneous photocatalysis, was used in this study to improve the quality of treated wastewater. A modified two-step sol-gel method was developed to synthesise a titanium dioxide impregnated kaolin (TiO₂-K) nanophotocatalyst, in which various parameters affecting the sol-gel formation and photocatalyst preparation were optimised. Further detailed investigation was carried out to improve the clay surface function prior to the impregnation. The natural kaolin was subjected to a series of acidic-alkali treatments to delaminate the clay structure, followed by thermal treatment. This clay pre-modification was designed to increase the specific surface area available for heterocoagulation with the microporous titania particles. Characterisation and photocatalytic activity of the TiO₂-K catalyst were performed by different microscopic techniques, i.e. XRD, SEM, TEM, UV-diffuse reflectance etc., and CR degradation, respectively. We examined thermal regeneration cycles of the catalyst lifespan, where the improvement of the photocatalytic activity was observed as a result of the change in average titania nanocrystal size and their porosity. This TiO₂-K exhibited a superior removal capability over the commercial TiO₂ in terms of initial adsorption and catalyst recovery. The self-settling capability of this catalyst can facilitate its separation after photooxidation treatment. Finally, the integration of adsorption and photocatalysis techniques was investigated as an alternative hybrid system for municipal wastewater treatment. The primary and secondary biological effluents were preliminary treated by the FBR system with the synthesised clay-lime mixture before being subjected to an annular slurry photoreactor (ASP) using the TiO₂-K catalysts. The formulated clay-FBR system demonstrated a prevailing removal efficiency towards PO₄³⁻ , NO₃⁻ and suspended solids; whereas the TiO₂-K-ASP showed superior degradation of dissolved organic content. This hybrid treatment approach demonstrated a synergetic enhancement for the chemical removal efficiency, and might be able to be employed as a feasible alternative treatment process for wastewater reclamation.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 201

Evaluation of the physical properties and photodegradation ability of titania nanocrystalline impregnated onto modified kaolin

In this study, a microporous layer photocatalyst of titania nanocrystallites heterocoagulated with structurally modified kaolin (TiO2-K) was synthesised via a modified sol-gel method. Physical properties (particle size, morphology, stability and settleability) and photodegradation capacity of the TiO2-K catalyst subject to its synthesis, regeneration and use for water treatment were studied. The modified kaolin, as a support for the titania nanocrystallites had a delaminated sandwich silica structure that minimises chemical intercalation within the nanocomposite structure. Microscopic examination revealed that the TiO2 nanocrystallites were uniformly deposited on the kaolin external surface, resulting in a high degree of photon activation. Compared to the commercial TiO2 P25, the TiO2-K demonstrated a superior photocatalytic degradation capacity to remove an anionic Congo red dye. Its removal efficiency and photo-reaction performance were improved when the TiO2-K was regenerated by a thermal treatment. The TiO2-K particles can be easily separated from the water system for further reuse. This unique nanocomposite photocatalyst shows promising technical advantages for a continuous industrial process of water treatment. © 2010 Elsevier Inc.Vipasiri Vimonses, Meng Nan Chong and Bo Ji

Insight into removal kinetic and mechanisms of anionic dye by calcined clay materials and lime

Our recent work reported that a mixed adsorbent with natural clay materials and lime demonstrated an enhanced capacity and efficiency to remove anionic Congo Red dye from wastewater. This study aims to investigate the removal kinetic and mechanisms of the mixed materials involved in the decolourisation of the dye to maximise their prospective applications for industrial wastewater treatment. The experimental results showed that dye removal was governed by combined physiochemical reactions of adsorption, ion-exchange, and precipitation. Ca-dye precipitation contributed over 70% total dye removal, followed by adsorption and ion-exchange. The dye removal kinetic followed the pseudo-second-order expression and was well described by the Freundlich isotherm model. This study indicated pH was a key parameter to govern the removal mechanisms, i.e. adsorption/coagulation at acidic pH and precipitation at basic condition. Yet, the overall removal efficiency was found to be independent to the operation conditions, resulting in more than 94% dye removal. This work revealed that the mixed clays and lime can be applied as alternative low-cost adsorbents for industrial wastewater treatment.Vipasiri Vimonses, Bo Jin and Christopher W.K. Chowhttp://www.elsevier.com/wps/find/journaldescription.cws_home/502691/description#descriptio

A novel titania impregnated kaolinite photocatalyst: from catalyst engineering to reactor development and modelling

The semiconductor photocatalysis technology has been known as a "green" approach and/or "zero" waste solution for the elimination of organic and microbial pollutants in water. Nanoscale TiO2 has received great attention in R&D as a promising photocatalyst. Application of the photocatalysis technology for an industrial water treatment process is still being impeded by a number of technical challenges. This chapter provides an overview on the development of a novel titania impregnated kaolinite (TiO2/K) photocatalyst and an annular slurry photoreactor (ASP) system. We will introduce the overall results from our recent engineering science research, including synthesis and characterisation of the TiO2/K photocatalyst, hydrodynamic analysis of the ASP system, evaluation of photo-degradation kinetics, and application of statistical and modelling method for the optimization of the ASP-TiO2/K water treatment process. © 2012 Nova Science Publishers, Inc. All rights reserved.Bo Jin, Meng Nan Chong, Chris Saint, Vipasiri Vimonse

Development of a pilot fluidised bed reactor system with a formulated clay-lime mixture for continuous removal of chemical pollutants from wastewater

This study was to determine the prospective application of a newly developed fluidised bed reactor (FBR) system using a formulated clay-lime mixture for a large-scale wastewater treatment implementation. A lab-made FBR was designed to assess the application of this formulated clay-lime mixture for the removal of several potential pollutants present in wastewater streams. The operating conditions of the FBR system was first optimised in batch mode by individual experiments prior to progressing into the continuous scheme. The results revealed that the dye elimination was enhanced significantly, by which 99% removal of 30 mg L-1 dye can be achieved with 0.8 g L-1 loading and aeration rate of 1 L min-1. This process was found effective in removal of anionic dye and phosphate while less favourable towards nitrate. This can be attributed to the different dominant removal mechanisms i.e. precipitation and adsorption. The potential reaction time of the formulated clay-lime mixture was found to be pH dependent where the removal performance was superior in strong alkaline conditions. Several municipal primary effluent samples were also treated using the developed FBR system in continuous operation mode. This system contributed an average 10-15% and 20-40% reduction of the nitrate and COD, respectively, while 100% removal of phosphate was obtained over the experimental period. This study demonstrated that the developed FBR system with the formulated clay-lime mixture can be a cost-effective alternative treatment process for a large-scale application for the treatment of industrial wastewater. © 2010 Elsevier B.V.Vipasiri Vimonses, Bo Jin, Christopher W.K. Chow and Chris Sainthttp://www.elsevier.com/wps/find/journaldescription.cws_home/601273/description#descriptio

An adsorption-photocatalysis hybrid process using multi-functional-nanoporous materials for wastewater reclamation

In this study, two of our recently developed laboratory scale wastewater treatment systems, fluidized-bed reactor (FBR) using formulated clay mixture absorbents (clay-FBR adsorption) and an annular slurry photoreactor (ASP) using TiO(2) impregnated kaolin catalysts (TiO(2)-K-ASP) were integrated as an adsorption-photocatalysis hybrid process to treat municipal wastewater as alternative secondary and tertiary treatment for wastewater reclamation. Primary effluent from sewage and secondary effluent from a membrane bioreactor treatment process were used to assess chemical removal capabilities of the FBR and ASP systems, and the hybrid process. The formulated clays-FBR system demonstrated the prevailing removal efficiency toward PO(4)(3-), NO(3)(-) and suspended solids. The TiO(2)-K-ASP showed superior degradation of dissolved organic content; while the presence of inorganic ions caused a detrimental effect on its performance. The integration of the adsorption and degradation system as a hybrid treatment process resulted in a synergetic enhancement for the chemical removal efficiency. Complete elimination of PO(4)(3-) content was obtained in the adsorption stage; while 30% and 65% NO(3)(-) removal were obtained from the hybrid treatment of the primary and secondary effluents, respectively. The corresponding COD reduction during the photodegradation was further investigated by the high-performance size exclusion chromatography technique, where it revealed the shift of apparent molecular weight of the dissolved organic contaminants toward the smaller region. This present study demonstrated that this adsorption-photocatalysis hybrid technology can be used as a feasible alternative treatment process for wastewater reclamation.Vipasiri Vimonses, Bo Jin, Christopher W.K. Chow, Christopher Sain