•Limitations of Fenton oxidation and approaches to address them are discussed.•Heterogeneous Fenton and fluidized bed Fenton can reduce sludge generation.•Chelating agents extend the application of ...homogeneous Fenton to circumneutral pH.•Electro-Fenton & bioelectro-Fenton can reduce cost associated with Fenton’s reagent.•Perspectives on future research are offered.
Fenton oxidation is an effective technology for the degradation of recalcitrant organic pollutants. However, conventional Fenton oxidation possesses some drawbacks such as the requirement of acidic pH condition, production of iron sludge and requirement of high chemical inputs. Strategies such as heterogeneous Fenton, fluidized bed Fenton, use of chelating agents and in-situ production of Fenton’s reagent have been studied as possible solutions to these limitations. Although there have been reviews on the fundamentals and applications of Fenton oxidation, a review with focus on the limitations of Fenton oxidation and their possible solutions is lacking. Here, we review the limitations of Fenton oxidation and the recent strategies toward addressing them. For each approach, fundamentals and applications in the removal of recalcitrant pollutants are reviewed. Heterogeneous Fenton process is the most widely investigated due to the progress in catalysis. Fluidized bed Fenton process could lower sludge generation and enhance process performance. Chelating agents are used to conduct homogeneous Fenton at circumneutral pH, though the potential detrimental effect of some chelating agents remains a source of concern. In situ production of Fenton’s reagent through bioelectrochemical technology (bioelectro-Fenton) is emerging as a possible strategy to reduce the cost associated with Fenton’s reagent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fenton Process, a type of Advanced Oxidation Processes is an efficient method for treating textile wastewaters. However, excessive use of hydrogen peroxide and catalyst has made this process ...economically non-feasible. Besides, industrial grade hydrogen peroxide costs $390–500 per ton. One of the means to overcome this problem is the in-situ production of hydrogen peroxide. In this paper, a detailed review was conducted on the generation methods, degradation potential and optimum operating parameters for in-situ production of hydrogen peroxide/hydroxyl radicals. Additionally the scavenging aspect for hydroxyl radicals was also investigated. From this review, it can be concluded that hydroxyl radical is highly oxidative and non selective in nature and its in-situ production can be performed through application of catalyst, ozonation, photocatalysis, electro and microbial fuel cells. Furthermore, optimization of operating parameters can result in an increase in the yield of hydroxyl radicals/hydrogen peroxide. Sonolysis as an auxiliary tool has potential to induce synergetic effects in combination with Advanced Oxidation Processes to increase in-situ hydrogen peroxide production. However, the problem of the scavenging effect is an aspect that needs to be dealt with, as hydroxyl radicals are prone to deactivation by scavengers. Therefore based on the review, it is concluded that in-situ production of hydrogen peroxide/hydroxyl radical for treating textile wastewater is economically viable and practically feasible if careful selection of process is conducted through selective research.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Renewable energy sources e.g. biofuels, are the focus of this century. Economically and environmental friendly production of such energies are the challenges that limit their usages. Microalgae is ...one of the most promising renewable feedstocks. However, economical production of microalgae lipid in large scales is conditioned by increasing the lipid content of potential strains without losing their growth rate or by enhancing both simultaneously. Major effort and advances in this area can be made through the environmental stresses. However, such stresses not only affect the lipid content and species growth (biomass productivity) but also lipid composition. This study provides a comprehensive review on lipid enhancement strategies through environmental stresses and the synergistic or antagonistic effects of those parameters on biomass productivity and the lipid composition. This study contains two main parts. In the first part, the cellular structure, taxonomic groups, lipid accumulation and lipid compositions of the most potential species for lipid production are investigated. In the second part, the effects of nitrogen deprivation, phosphorus deprivation, salinity stress, carbon source, metal ions, pH, temperature as the most important and applicable environmental parameters on lipid content, biomass productivity/growth rate and lipid composition are investigated.
•Cellular structure and taxonomy of potential microalgae for biofuel production were considered.•The quality of lipid accumulation and lipid compositions of those strains were investigated.•The effect of environmental stressors on lipid enhancement in those strains was investigated.•The effect of stressors on biomass productivity and lipid composition was investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In recent decades, the concern over depletion of the world׳s petroleum reserves and environmental pollution has increased the demand to develop a renewable and environmental friendly fuel. Biodiesel, ...which mainly consists of Fatty Acid Methyl Esters (FAME) is one of the best substitutes for diesel fuel. Currently, vegetable oils, edible or non-edible, are the main resources of biodiesel. This review aims at providing comprehensive information and analyzes on biodiesel produced from edible and non-edible vegetable oils, their composition and specifications. Accordingly, the Fatty Acid (FA) profiles of 28 edible vegetable oils and 40 non-edible vegetable oils were collected. Their main specifications including sulfur content, density, viscosity, flash point, cloud point, pour point, cold filter plugging point, cetane number, iodine number, heating value, acid value and carbon residual before and after transesterification (vegetable oil and biodiesel, respectively) were analyzed in detail.
Many researchers have developed prediction models to quantify biodiesel specifications to optimize its manufacturing and obtain biodiesel with the best specifications. Three factors that are especially influential are the fatty acids profiles, the degree of unsaturation within the FA structures and molecular weight. Accordingly, many models have been constructed on these features. There are also models that quantify the relationship between the biodiesel specifications and its thermodynamic properties or other specifications. Accordingly, the second part of this work was conducted on the existing prediction models. All the models were discussed along with their deviation in prediction.
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Heterogeneous Fenton reaction is an advanced oxidation process which has gained wide spread acceptance for higher removal efficiency of recalcitrant organic contaminants under wide range of pH ...compared to homogeneous reactions. Conventionally, iron oxides are used as heterogeneous catalysts for Fenton oxidation system because of their abundance, easy separation and lower cost. This paper reviews the substitution of iron in an iron oxide with other transition metals as a mean to improve the properties of the iron oxide towards higher performance for contaminant degradation. Several studies have reported enhanced performance resulted from this substitution based on two possible mechanisms. First is the conjugation of redox pairs of iron species and imported active ion in hydroxyl radical production cycle. Second: the generation of oxygen vacancies as active sites on the surface of catalyst via adjustments for unequal charge substitutions. This class of catalysts is anticipated to work effectively for treatment of various recalcitrant wastewaters using Fenton oxidation system. Subsequently, the stability of the produced catalyst needs to be examined under various experimental conditions to prevent the adverse effects of transition metals on the receiving environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Recently, biomass has been understood and investigated to develop adsorbents for carbon dioxide (CO2)adsorption due to their non-hazardous nature, availability, low disposal cost, and thermal ...stability. In thisperspective, the sustainable approach of converting biomass into activated carbon (BAC) for the adsorptionof CO2 is promising for solid waste management while reducing anthropogenic greenhouse gas emissions.
Among other biomass adsorbents, metal oxide impregnated activated carbon (MBAC) hasdemonstrated excellent adsorption affinity for CO2 adsorption. Therefore, in this review, an evaluationand detailed study of various MBACs for CO2 adsorption is presented for the first time. BAC synthesizemethod, including various carbonization techniques, surface activation and functionality approacheshave been discussed. This study also provides detailed overview of MBAC in the context of various preparationmethods, critical factors and operating parameters for a high CO2 adsorption capacity. Besides, thesolid–gas reactor configuration, cyclic regeneration techniques, CO2 adsorption process mechanism, andCO2 adsorption kinetics also have been discussed. Finally, concluding remarks and future perspectives forbiomass-derived MBAC for CO2 adsorption capture were addressed. This review will also assist in thesearch for alternatives to CO2 adsorption technology, which is both cost-effective and environmentallyfriendly. KCI Citation Count: 1
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Sonochemical reactors operate based on the release of high amount of energy from ultrasonic irradiations. More application in chemical processes are being developed using these reactors. But the ...potential of their applications are still limited largely due to the lack of understanding about their design, operational and performance characteristics. A detail review is therefore conducted on available literature in this paper. From the review, the design features of sonochemical reactors are defined by different types, number and position of ultrasonic transducers, whereas their operational parameters are determined by ultrasonic frequency and intensity. As in the case of stirred vessel, sonochemical reactors can be also characterized for their performance based on mass transfer, mixing time and flow pattern. The review claims that sonochemical reactors have potential to be more energy efficient compared to stirred vessel if designed and operated appropriately.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
One of the current challenges of wastewater treatment is the presence of recalcitrant pollutants which are difficult to remove using conventional treatment technologies. This poses a threat to ...environmental sustainability and hinders the efforts of many industries to adopt cleaner production through zero-discharge and subsequent wastewater reuse. Effective wastewater treatment technologies are therefore needed to address this challenge. Accordingly, the last few years have seen intensified effort to develop more effective wastewater treatment technologies. The use of fluidized bed reactor in wastewater treatment, particularly Advanced Oxidation Processes and biological treatment, represents a unique opportunity for cost-effective treatment of wastewater containing recalcitrant pollutants. Although the application of fluidized bed reactor in biological wastewater treatment is well established with many large-scale plants in existence, its application in advanced oxidation processes is mostly at laboratory-scale. For proper design, upscaling and process improvement, information on the major parameters affecting the processes is important. This paper offers an overview on the applications of fluidized bed reactor in wastewater treatment, with emphasis on the important design and operational parameters affecting its performance. The discussion covers liquid-solid and gas-liquid-solid fluidized bed reactors and their applications in advanced oxidation processes, biological as well as adsorption processes which are effective wastewater treatment technologies. Fluidized bed reactors are excellent contacting devices and have the potential to enhance the effectiveness and energy efficiency of these treatment processes if properly design and utilized. An energy efficient and cost-effective wastewater treatment technology is crucial to industries adopting cleaner production. Important parameters such as reactor geometry, aspect ratio, support materials, reactor internal, superficial fluid velocity and other operational parameters are reviewed. The review concluded with some perspectives on future research interests.
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•An overview of FBR applications in wastewater treatment is offered.•Common applications in AOPs, Biological and Adsorption processes.•Major design parameters of FBR in wastewater applications are reviewed.•Operational parameters affecting specific applications of FBR are discussed.•Perspectives on future research interest of FBR in wastewater treatment are offered.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Advanced oxidation process involves production of hydroxyl radical for industrial wastewater treatment. This method is based on the irradiation of UV light to photocatalysts such as TiO2 and ZnO for ...photodegradation of pollutant. UV light is used for irradiation in photocatalytic process because TiO2 has a high band gap energy which is around 3.2 eV. There can be shift adsorption to visible light by reducing the band gap energy to below 3.2 eV. Doped catalyst is one of the means to reduce band gap energy. Different methods are used for doped catalyst which uses transition metals and titanium dioxide. The band gap energy of three types of transition metals Fe, Cd and Co after being doped with TiO2, are around 2.88 ev, 2.97ev and 2.96 ev, respectively which are all below TiO2 energy. Some of the transition metals change the energy level to below 3.2 eV and the adsorption shifts to visible light for degradation of industrial pollutant after being doped with titanium dioxide. This paper aims at providing a deep insight into advanced oxidation processes, photocatalysts and their applications in wastewater treatment, doping processes and the effects of operational factors on photocatalytic degradation.
•Different types of doped catalyst including transition metals and titanium dioxide were investigated.•Effects of doped catalyst on the catalyst surface area, band-gap energy, and crystallinity were studied.•The influence of doped catalyst on degradation of Methyl orange and Methylene blue was explored.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This work aimed at providing additional information and knowledge on the possibility to overcome the limitation of conventional advanced oxidation processes (AOPs) through hybridization. In the ...present work, a number of photochemical and non-photochemical AOPs such as direct photolysis (UV), photolysis of hydrogen peroxide using UV light (UV/H2O2), UV assisted coagulation (UV Fe2+ coagulation), Fenton process, Fe2+ coagulation and photo-Fenton process were compared to determine their feasibility to treat real textile wastewater. The Batik industry, which is a textile cottage industry in Malaysia has reported problems related to safe environmental disposal of its pollutants, mainly dyestuff. The comparison was made in terms of Chemical oxygen demand (COD), Total organic carbon (TOC) and colour removal together with electricity consumption. Among the processes evaluated, the highest COD removal was achieved for photo -Fenton oxidation (91.2%), followed by Fenton oxidation (81.4%), UV/H2O2 (68.0%), UV- Fe2+ coagulation (55.0%), Fe2+ coagulation (43.0%) and UV photolysis (10.0%). At the optimal operating conditions (room temperature, undiluted contaminants), the photo-Fenton hybrid process achieved complete decolourization and higher removal of COD (91.2%) and TOC (78.5%) with minimum electrical energy per order of 0.02 kWhr/m3 compared to other AOPs. About 13% reduction in the total chemical cost and 10% increase in the degradation were observed by combining the Fenton process with UV radiation compared to the conventional Fenton process. The GC/MS analysis revealed that the photo-Fenton process successfully removed 87% of organic compounds. The sludge characterization studies by Particle Size Distribution proved that the Fenton-generated sludge achieved quality suitable for disposal. Photo-Fenton is the cheapest option with highest removal (91%) as its required only $0.0016 to degrade 1 g of COD compared to Fenton which cost $0.0021. Therefore, this study concluded that the photo-Fenton process was an economically viable and appropriate treatment method for enhancing biodegradability of recalcitrant contaminants.
•Textile wastewater treatment by different AOPs is compared.•The highest pollutant removal was achieved for photo -Fenton oxidation.•Photo-Fenton can work at initial pH between 5 and 6.•UV lamps gave the best result in pollutant degradation.•The hybrid method introduces the idea of zero-water emission.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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