Showing papers in "Journal of water process engineering in 2017"

Nanofiltration membranes and processes: A review of research trends over the past decade

Abstract: Nanofiltration technology has come a long way since first inception in the late 1980s. Research activity in this area covers a great many topics and the aim of this review is to quantify the level interest in each of these areas. The number of annual publications directly related to nanofiltration technology has been harvested from ScienceDirect since 2007. This quantification of research has shown that interest in nanofiltration technology has grown over the past decade, particularly over the past five years. The primary journals reporting articles on nanofiltration are the Journal of Membrane Science, Desalination and Separation and Purification Technology, although articles have been spread across a further 139 journals. Unsurprisingly, the major topics of interest have been water processing, membrane fabrication and membrane surface modification. There has been clear growth in the areas of organic solvent nanofiltration, pharmaceutical and biological applications, design and economics of nanofiltration processes and review articles. Nanofiltration modelling has received less support over the period reviewed and has experienced a steady decline. Clearly the overall growing trend in nanofiltration research indicates that the technology remains popular and this interest should materialise into further applications for a robust and sustainable future.

A review of the potentials, challenges and current status of microalgae biomass applications in industrial wastewater treatment

Abstract: Wastewaters from agro-industrial and industrial sources have significant organic matter contents, and some also contain oil and grease, heavy metals and toxic chemicals. Limits have been set for pollutants, especially wastewaters, entering water bodies. Conventional methods of treatment generally require large inputs of energy, large areas of land, and high operation and maintenance costs. Microalgae biomass offers an alternative treatment approach that removes nutrients and other pollutants, such as heavy metals, nitrogen compounds and harmful chemicals. Microalgae harvested after wastewater treatment can be used as value-added products because the microalgae is rich in carbohydrates, proteins and lipids. This paper presents the types of treatment processes, current application of microalgae and high-value products derived from microalgae used in wastewater treatment processes.

Recent strategies for the removal of iron from water: A review

Abstract: Iron is the 4th most abundant element on Earth and is found naturally in the water in diverse forms. It is a vital mineral nutrient, which acts as a co-factor for many enzymes and plays role in the maintenance of energy metabolism. According to WHO standards, the permissible limit of iron in drinking water is 0.3 mg/L. However, the dumping of domestic and industrial wastes in the water bodies is responsible for elevated levels of iron in the water. The continuous consumption of such water with high iron content may lead to various health problems. Bad odor, unpleasant taste, red color of water and stains on laundry and plumbing fixtures are also some of the issues related with high iron content in water. A variety of techniques have been adapted for the remediation of iron from different water sources. This review summarizes the different approaches used worldwide till date for the removal of high iron content from water. These methods have been classified into 4 different categories: conventional strategies, biological strategies, membrane technology-based strategies and nanotechnology-based strategies. The conventional strategies involve 11 different remediation techniques for removing iron from water, which have different iron removal efficiencies. The review also classifies the diverse types of iron available in water based on its mineral form, solubility and chemical nature.

Removal of Pb (II) and Cu (II) ions from wastewater using composite electrospun cellulose acetate/titanium oxide (TiO2) adsorbent

Abstract: Electrospun cellulose acetate (CA)/titanium oxide (TiO2) adsorbents were prepared using the electrospinning technique. The adsorbents were analyzed using Brunauer–Emmett–Teller (BET) surface area analyses, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and Energy dispersive X-ray spectroscopy (EDS) characterization methods. The impacts of various adsorption parameters, namely, pH, the amount of TiO2 nanoparticles, contact time, temperature, and kinetics of metal uptake were investigated using batch adsorption experiments. The highest removal capacities of Pb (II) and Cu (II) after 300 min using CA/TiO2 adsorbent at 35 °C were estimated as 25 mg/g and 23 mg/g at pH of 5.2 and 5.8, respectively. The model isotherms, such as Dubinin–Radushkevich (D-R), Freundlich, and Langmuir were used to analyze the adsorption equilibrium data. Comparing the regression values (R2), the Langmuir model isotherm was well fitted than D-R and Freundlich isotherms with the adsorption equilibrium data for both metals. In general, pseudo-first-order and pseudo- second order are preferred for kinetic models. Pseudo-second order kinetic equation was well fitted to the adsorption experimental data for both lead and copper ions. The removal efficiencies didn’t change significantly when four adsorption–desorption experimental cycles were conducted.

Treatment of textile wastewaters by electrocoagulation employing Fe-Al composite electrode

Abstract: In the present study, electrocoagulation process employing Fe-Al composite electrode was applied for treatment of different types of textile wastewaters. Effect of major operating parameters such as pH, reaction time, current density, voltage and inter-electrode distance were investigated for chemical oxygen demand (COD) and colour removal efficiency. The process was found promising and produced more than 90% COD and colour removal efficiency at optimised operating conditions of pH 8, reaction time 80 min, current density 20 A/m2 with an inter-electrode distance of 3 cm. Robustness of the process was investigated on real and anaerobically pre-treated textile wastewater. For real textile effluents, the process produced approximately 99% colour removal efficiency, creating virtually colourless solution even at a lesser reaction time of 60 min. Electrocoagulation effectively detoxified the anaerobically pre-treated textile wastewater by eliminating 78% of aromatic amines within a reaction time of 180 min.

Electrospun lignin carbon nanofiber membranes with large pores for highly efficient adsorptive water treatment applications

Abstract: The adsorption performance of activated carbon largely depends on its physical and chemical properties. Carbon formed into nanofiber mats/membranes has the potential to improve the performance of traditional activated carbon. For this study, electrospun carbon nanofiber membranes were prepared from lignin or polyacrylonitrile (PAN). These carbon nanofibers, along with PAN microfibers (MF), and a commercial granulated activated carbon (GAC), were evaluated by determining methylene blue adsorption capacity, iodine number, kinetics of adsorption, efficacy in removing organic acids from a contaminated water and flow permeability. Results suggest that the electrospun lignin nanofiber membranes offer approximately 10-times higher adsorption capacity, provide two-times faster adsorption kinetics, and six-times higher permeability than traditional activated carbon sources. A high specific surface area (583 m2/g), larger average pore diameter (3.5 nm), and high pore volume (0.29 cm3/g) for the lignin nanofibers relative to other carbon adsorbents provided the opportunity to capture more contaminants in shorter residence times, making them highly efficient for adsorptive water treatments. A preliminary energy and economic evaluation for implementation of the lignin carbon nanofiber membranes into a water treatment process showed that lignin nanofibers could reduce energy consumption by 87%.

Adsorption and antimicrobial studies of chemically bonded magnetic graphene oxide-Fe3O4 nanocomposite for water purification

Abstract: The present work describes the synthesis of covalent composite of graphene with Fe 3 O 4 , through the formation of amide bond between chloride functionalized graphene oxide (GO) and amine containing Fe 3 O 4 . The synthesized chemically bonded graphene oxide- Fe 3 O 4 (GO-Fe 3 O 4 ) nanocomposite was used as an adsorbent for the removal of malachite green oxalate (MGO) and Eriochrome black T (EBT) in wastewater. The structure, morphology and magnetic properties of prepared nano composite was characterized by X Ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),Transmission Electron Microscope (TEM) and Vibrating Sample Magnetometer (VSM). The effect of the experimental conditions on the adsorption behavior has been investigated by varying the initial concentration, contact time,pH and temperature. The nanocomposite showed a good performance for the adsorption of MGO and EBT from aqueous solution with an adsorption capacity of 179.15 and 160.08 mg g −1 respectively. The Langmuir and Freundlich equations were used to examine the experimental isotherm data. Further it properly fitted with pseudo-second-order kinetic model.The results of this study demonstrate that GO-Fe 3 O 4 can be used as a potential alternative adsorbent for the proficient removal of dyes from aqueous solution. The GO-Fe 3 O 4 nanocomposite has been tested against Gram-positive and Gram-negative bacterial strains including Staphylococcus aureus , Bacillus subtilis, Pseudomonas aerugino and Salmonella typhimurium upon which it showed promising antimicrobial activities, thus emphasizing the fact that it can be used for dual purpose in waste water management.

Wastewater reclamation and reuse trends in Turkey: Opportunities and challenges

Abstract: Climate change, rapid urbanization, industrialization, tourism with a huge amount of wastewater discharge means that wastewater reuse has a great potential in Turkey and reclamation and reuse is the promising candidate to conserve the valuable fresh water sources. The water reuse applications are becoming increasingly a matter of interest in Turkey however it is strongly dependent on following factors: rapid adaptation of urban wastewater reuse programs, the establishment of integrated water resources management framework and guidelines for wastewater reuse programs but on the contrary slow pace of projects, unclear or absence of water quality requirements, the limited commercial development of reclaimed water and lack of public awareness, lack of knowledge about the consequences of untreated or partially treated wastewater discharge into water bodies, difficulties in accepted planning procedures and emerging new technologies in real time scale are the main hurdles in the way of water reclamation and reuse. This paper aims to give an overview of water reuse activities in Turkey and the opportunities and challenges in expanding reclaimed water reuse. This review precisely presents the research trends performed in different institutes to meet the wastewater reuse goal along with the wastewater treatment plants currently working in Turkey.

Current status and technology trends of zero liquid discharge at coal chemical industry in China

Abstract: Coal chemical industry, referring to the large scale production of fuels and chemicals from coal, has been growing rapidly in China in the past decade and the trend is expected to continue in the following years. Since most large scale coal chemical plants have been built in coal rich areas lack of environmental capacity to receive wastewater discharge, Zero Liquid Discharge (ZLD) has been becoming more and more commonly used as the wastewater management strategy in the newly proposed coal chemical plants, which drives quick implementation and fast evolution of ZLD technologies in China. This paper examines the current status of ZLD practice for wastewater management and the representative ZLD processes used in the coal chemical industry in China. Additional analysis shows that major technical challenges exist in current ZLD solutions and the technology evolution trends are to further incorporate enhanced organics removal technologies, hybrid membrane and room temperature crystallization technologies, high salinity membrane concentration technologies and pure salts oriented crystallization technologies so as to achieve better system stability, lower treatment cost and beneficial recycling of pure salts.

Biologically active filtration for fracturing flowback and produced water treatment

Abstract: Reclamation of fracturing flowback and produced water associated with unconventional oil and gas resource development is becoming a more widely applied management practice because it protects freshwater resources through elimination of surface discharge and by reducing demand for high quality water sources Reduction of organic matter has been a notable wastewater treatment challenge and has limited practical opportunities for reuse of these waste streams This research focuses on harnessing the ability of microorganisms to biodegrade organic carbon present at high concentrations in flowback and produced water Bench-scale and lab-scale biofiltration systems were investigated to determine adaptability of biofilms and measure biodegradation of organic carbon under different operating conditions Microorganisms associated with biologically active carbon filters were initially acclimated to a produced water stream from the Piceance Basin Following successful acclimation, the bench-scale system consistently achieved more than 90% dissolved organic carbon removal (Co ∼ 240 mg/L) Similar performance was observed for the lab-scale system, demonstrating system scalability After treating distinct wastewater feeds (produced water [Co ∼ 350 mg/L] and flowback water [Co ∼ 2150 mg/L] from the Denver-Julesburg Basin), the system further demonstrated robustness and flexibility Results from the performance evaluation validated the ability of the system to maintain treatment efficiency under variable operating conditions, including different pretreatment, aeration rates, temperatures, and empty-bed contact times

Improving sludge settleability by introducing an innovative, two-stage settling sequencing batch reactor

Abstract: Sludge settleability is considered one of the main drawbacks of sequencing batch reactors. The aim of this study therefore is to improve sludge settleability by introducing a novel, two-stage settling sequencing batch reactor (TSSBR) separated by an anoxic stage. The performance of the TSSBR was compared with that of a normal operating sequencing batch reactor (NOSBR), operating with the same cycle time. The results show a significant improvement in sludge settleability and nitrogen compound removal rates for the TSSBR over the NOSBR. The average removal efficiencies of NH3-N, NO3-N and NO2-N have been improved from 76.6%, 86.4% and 87.3% respectively for the NOSBR to 89.2%, 95.2% and 96% respectively for the TSSBR. In addition, the average SVI30 for the NOSBR has been reduced from 42.04 ml/g to 31.17 ml/g for the TSSBR. After three months of operation, there was an overgrowth of filamentous bacteria inside the NOSBR reactor, while the morphological characteristics of the sludge inside the TSSBR reactor indicated a better and homogenous growth of filamentous bacteria.

Simultaneous polycyclic aromatic hydrocarbon degradation and lipid accumulation by Rhodococcus opacus for potential biodiesel production

Abstract: Biomass gasification effluent primarily contains polycyclic aromatic hydrocarbons (PAHs) generated during wet scrubbing of synthetic gas. These PAHs are toxic, mutagenic, carcinogenic and teratogenic, which, therefore, need to be removed prior to their release into the environment. This study was performed to determine the valorization of PAHs from biomass gasification effluent as a substrate for Rhodococcus opacus and its potential for biodiesel production. Using synthetic media containing 2-, 3- or 4- ring PAH compounds, at an initial concentration in the range 50–500 mg L −1 , along with 5% (v/v) inoculum, the bacterium degraded 75.9% naphthalene, 79.1% phenanthrene and 72.1% fluoranthene, with a corresponding lipid accumulation of 68.1%, 72.4% and 63% (w/w) of cell dry weight (CDW) respectively, within 7 days. The maximum specific growth rate (μ max ) of the organism was found to be 1.267 × 10 −4 min −1 , 2.47 × 10 −4 min −1 and 2.317 × 10 −4 min −1 using naphthalene, phenanthrene and fluoranthene, respectively. Further, an increase in the inoculum size to 10% (v/v) had a positive effect on both PAHs biodegradation and lipid accumulation by the bacterium. 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy affirmed that the fatty acids accumulated by the bacterium primarily contained saturated fatty acids. Gas chromatography (GC) analysis of the transesterified lipids to biodiesel further revealed the presence of methyl palmitate and methyl stearate as the major fatty acid methyl esters (FAMEs). The estimated properties of the transesterified product indicated its best potential for biodiesel application.

Wastewater treatment by microalgae can generate high quality biodiesel feedstock

Abstract: Botryococcus braunii strains are high-lipid producers. Despite this, their use as biodiesel feedstock is limited by their slow growth, which increases production costs. B. braunii wastewater bioremediation power, however, may be able to overcome this problem. This research evaluated the performance of two strains (UTEX-USA and IBL-Brazil) grown in pre-treated (influent) and treated (effluent) wastewater. The goal was to optimize algal-productivity and wastewater treatment in order to provide biomass rich in high-quality oil for biodiesel. The standard CHU-medium was used as control. Phosphorus was 100% removed in all treatments for both strains. Nitrogen removal was higher in wastewater (61–65%) than in CHU medium (48 and 61%), respectively for UTEX and IBL strains. Cultivation in the effluent generated higher biomass and lipid productivity for the UTEX strain, while the influent was the best for the IBL strain. The composition of the fatty-acids produced by Botryococcus was used to estimate the biodiesel quality. Hence, the biodiesels may have good fuel quality (high ignition and combustion efficiency) but limited application at low temperatures. The composition of fatty-acids, however, can be optimized by growing or mixing strategies. Therefore, Botryococcus braunii is a potential source for high quality biodiesel production.

Wastewater phytoremediation by Salvinia molesta

Abstract: In natural biological treatment systems, floating macrophytes have been used in maturation pond in recent years to upgrade effluents from stabilization ponds and are to achieve secondary treatment effluent quality from primary sewage effluent. In this study, the performance of phytoremediation by Salvinia molesta macrophytes on treated Palm Oil Mill Effluent (POME) is investigated. The objectives of the study are to determine the nutrient uptake by S. molesta from treated POME and its effect towards the biomass and biochemical content. The water quality after phytoremediation were monitored. The wastewater phytoremediation by S. molesta was conducted outdoor for 16 days in a raceway pond rig. The results showed that S. molesta achieved 95% phosphate removal efficiency from the wastewater, lowering concentration to 0.17 mg/l. Nitrate concentration was determined to be at 0.50 mg/l at the end of the experiment. Ammonia concentration showed a dynamic fluctuation trend with average value of 2.62 mg/l. For water quality assessment, turbidity decreased from 7.56 NTU to 0.94 NTU in just 2 days’ time. MLVSS analysis was significantly low by day 2 of experiment. COD removal efficiency was determined at 39%. All six water quality assay met their respective statutory discharge limit. The S. molesta cultivated in the raceway pond rig also showed increment toward the biomass gain, carbohydrate and protein at the end of the experiment. This study indicates that S. molesta plants have the potential to be used in the phytoremediation of treated POME and showed a superior biochemical composition.

Application of photosynthetic bacteria for removal of heavy metals, macro-pollutants and dye from wastewater: A review

Abstract: Photosynthetic bacteria not only can be applied for wastewater treatment, but also are used to generate quality added products such as biodiesel and hydrogen. Although many articles have been published on the utilization of photosynthetic bacteria to treat wastewater, there is no comprehensive literature review on this field. Therefore, the aims of this study are (1) to review the ability of photosynthetic bacteria for removal of different pollutants such as heavy metals, nutrients and dye from wastewater and (2) to review effective parameters such as light intensity and temperature on the growth rate of photosynthetic bacteria. Photosynthetic bacteria have a high ability to remove heavy metals, dyes and macro-pollutants from wastewater. Production of photosynthetic bacterial biomass depends on temperature, light intensity and amount of nutrients in the environment. The yellow light is able to enhance the removal of chemical oxygen demand by photosynthetic bacteria. Also, photosynthetic bacterial biofilms can be deteriorated if insufficient amount of nutrients are accessible. Using photosynthetic bacteria is a promising technology to treat different types of wastewater effectively and economically.

Effective coagulation-flocculation treatment of highly polluted palm oil mill biogas plant wastewater using dual coagulants: Decolourisation, kinetics and phytotoxicity studies

Abstract: The performance of several chemical coagulants including ferric chloride, calcium lactate, magnesium hydroxide, aluminium chlorohydrate, and polydiallyldimethylammonium chloride (polyDADMAC) were investigated in removing colour of palm oil mill biogas plant wastewater (POMBPW). The results show that ferric chloride as a sole coagulant can achieve high colour removal of more than 80% without needed for pH adjustment, which indicates the effectiveness of the coagulant to treat palm oil mill biogas plant wastewater (POMBPW).However, dual coagulants i.e. ferric chloride-anionic polyacrylamide (APAM) shows better performance than ferric chloride-polyDADMAC in terms of colour removal, pH, with shorter sedimentation time. The addition of polymer to system not only reduces the ferric chloride dosage, but also increases the colour removal of more than 20%. Comparison between APAM and polyDADMAC as flocculant aids shows that APAM can achieve stable removal at wider pH range and lowest sedimentation time at 20 min while polyDADMAC was at one hour. Both dual coagulants were followed second order kinetic and APAM shows the highest rate over polyDADMAC i.e. 3 × 10−5/PtCo.min and 2 × 10−5/PtCo.min respectively. Addition of polymers reduced phytotoxicity of generated sludge and the sludge has potential to be reused for land application.

Preparation of novel polysulfone-Fe3O4/GO mixed-matrix membrane for humic acid rejection

Abstract: In this study, novel polysulfone-Fe 3 O 4 /GO mixed-matrix membrane was prepared by embedding the iron-decorated graphene oxide (Fe 3 O 4 /GO) into polysulfone (PSf) polymer. First, graphene oxide (GO) nanoplates were synthesized using natural graphite powder according to the Hummers method. Fe 3 O 4 /GO was then prepared by mixing both GO and Fe 3 O 4 in the presence of ammonia hydroxide (NH 4 OH) according to co-precipitation method. A series of test, such as X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) were performed to characterize the produced Fe 3 O 4 /GO nano-hybrid. Mixed-matrix membrane was fabricated by casting the pre-mix PSf-Fe 3 O 4 /GO polymer solution mixture using phase inversion method. The performance of both neat PSf membrane and novel polysulfone-Fe 3 O 4 /GO mixed-matrix membrane were evaluated by measuring the membrane permeate flux and humic acid rejection. Experiment demonstrated that the novel polysulfone-Fe 3 O 4 /GO mixed-matrix membrane was having 3 times higher permeate flux than the neat PSf membrane despite the drop in humic acid rejection from 89 ± 2% to 84 ± 2%. However, polysulfone-Fe 3 O 4 /GO mixed-matrix membrane permeability was increased with the compensation of decreasing retention capacity due to pore size enlargement, higher porosity as well as higher hydrophilicity.

Photocatalytic degradation of 2,4-dichlorophenol by Co-doped TiO2 (Co/TiO2) nanoparticles and Co/TiO2 containing mixed matrix membranes

Abstract: Chlorophenols are special groups of organic pollutants which are widespread in water and soil sources. Advanced oxidation processes (AOPs) appear to be well-established techniques for degradation of chlorophenols. In this research, TiO2 nanoparticles containing different amounts of cobalt, Co/TiO2, (as AOP photocatalysts) were synthesized by sol-gel method and characterized by FTIR, XRD, SEM and DRS analysis. According to the XRD patterns, pure TiO2 and Co/TiO2 samples are in anatase phase. According to DRS results, the presence of cobalt in TiO2 lattice shifted the absorption edge to higher wavelengths (red shift) and Co/TiO2 exhibited the higher photocatalytic activity under visible light. The best degradation performance was achieved when TiO2 nanoparticles containing 1.34 mol% −Co (Co/TiO2 (1.34)) was used as photocatalyst for 2,4-dichlorophenol (2,4-DCP) degradation under visible light irradiation. Photocatalytic mixed matrix membranes (MMMs) containing Co/TiO2 (1.34) were fabricated by phase inversion technique and the effect of these nanoparticles on separation, thermal and morphological properties of polymeric (here polyethersulfone (PES)) membranes was investigated by using FESEM, DSC and photocatalytic permeation experiments respectively. Permeation test results showed that addition of Co/TiO2 (1.34) to PES matrix can improve both flux and rejection percent of the resulting membrane. It was found that addition of 1 wt.% Co/TiO2 (1.34) to PES matrix can increase membrane flux and 2,4-DCP rejection percent (under visible light) by 53% and 25.3% respectively in which a nearly 2,4-DCP free solution is achievable in permeate site. Therefore fabricated photocatalytic mixed matrix membranes containing Co/TiO2 nanoparticles are suitable for photocatalytic separation of 2,4-DCP.

Removal of phenolic compounds from oil refinery wastewater by electrocoagulation and Fenton/photo-Fenton processes

Abstract: A coupling between electrocoagulation (EC) and the Fenton and photo-Fenton processes was used to treat oil refining industry wastewaters that contained phenolic compounds. The effect of several experimental parameters of the EC treatment, such as current density (j), treatment time (t), and orientation and configuration of the electrodes was studied. In addition, treatment time and concentration of Fe2+ and H2O2 in the Fenton and photo-Fenton processes were varied to detect possible changes on the coupling capabilities. The EC treatment removed 51% of total phenols content and 42% of total organic carbon (TOC) content by applying 40 mA cm−2 during 20 min with electrodes horizontally positioned. The Fenton process application to the previously electrocoagulated water provided total phenols removal beyond the detection limit (0.01 mg L−1) and 57.6% of TOC removal by using a 1:66 Fe2+/H2O2 molar ratio. The application of the photo-Fenton process to the electrocoagulated water provided a TOC removal of 88%; the remaining TOC is associated to the presence of biodegradable short chain carboxylic acids.

Photocatalytic degradation of a model textile dye using Carbon-doped titanium dioxide and visible light

Abstract: Rhodamine B (RhB), a dye widely used in the textile manufacturing, contributes with other dyes to harm the environment. Here, with the final goal to provide new tools for the removal of dyes from water, visible light activated carbon-doped titanium dioxide was used to investigate on the decolourization and the photocatalytic degradation of RhB dye from water solutions. The photodegradation activity was tested varying the initial concentration of RhB and the amount of carbon-doped titanium dioxide, taking into account the ratio between the amount of catalyst and the amount of RhB (TiO2/RhB), thus obtaining a parameter that allows the method to be scaled up without losing its effectiveness. Values of k2 and t0.5 were obtained by fitting kinetics data to a second-order kinetic adsorption model. The important role played by doped TiO2 particles is demonstrated by the highly efficient color removal obtained during the visible light-induced photocatalysis. The presence of different degradation intermediates was demonstrated by means of UV–vis Absorption and Fluorescence spectroscopy. Such results underline that the whole photodegradation process does not end with the decolourization occurrence.

Removal of Ni2+ ion from waste water by Geopolymeric Adsorbent derived from LD Slag

Abstract: In the present study LD slag geopolymer (LDSGP) was synthesised from calcium oxide rich raw LD slag, a waste of steel making industries for the use as a potential low cost adsorbent for high removal of Ni 2+ ions from aqueous solution. The geopolymerisation of LD slag was performed in a plastic mould where the colloid mixture of raw LD slag and alkaine activator (sodium hydroxide and sodium sillicate (1:1 w/w)) were cured for 3 days at room temperature. The LDSGP was characterized by using XRF technique, BET surface area, SEM & TEM images, XRD patterns, FTIR spctra and TGA. Batch experiments for the adsorption study of Ni 2+ ions were conducted at different temperatures (298 K, 308 K, 318 K). The equlibrium data was successfully fitted the Langmuir isotherm and the maximum adsorption uptake of Ni 2+ , onto LDSGP, was found to be 85.29 mg/g and at 318 K. The adsorption rate data was fitted well to pseudo-second-order model indicating the process to be dominated by chemisorption. Thermodynamic analysis proved that the adsorption process was spontaneous in nature.

Cathodic groundwater denitrification with a bioelectrochemical system

Abstract: Nitrate-contaminated groundwater has become a common issue during the last decades, due to the increased levels of detected contamination, the related potential health hazards caused by this contaminant presence in drinking water, and the applicable regulations on water supply quality. In this work, the design, start-up and operation of a bioelectrochemically-based system (BES) for groundwater autotrophic denitrification is described, with the aim to investigate its removal capacity in terms of nitrogen forms. The dual-chamber BES reactor was operated for 27 days, reaching stabile nitrate reduction in its cathodic chamber. Initially, an acetate oxidizing biofilm was grown in the anode chamber in step-feeding operation mode, at a fixed potential of +0.397 V vs. Standard Hydrogen Electrode (SHE). After a 3-day-long inoculation time, and 7 days operation as a microbial fuel cell (MFC), the anode and cathode electrodes were functionally inverted, originating a newly configurated BES process. The biologically active electrode was then fed with nitrate-enriched solution (NO3− concentration = 100 mg L−1), functioning as a biocathode with fixed negative potential of −0.303 V vs. SHE. Results show that the successfully-induced switch in bacterial metabolism lead to consistent nitrate removal by the BES system with efficiency exceeding 90%. Determination of energy consumption by the process show that these are significantly lower than electrodialysis and other similar reported systems.

Bio-derived MgO nanopowders for BOD and COD reduction from tannery wastewater

Abstract: MgO nanopowders were synthesised via a simple and “ greener ” route using Carica papaya leaf extract at 500 °C. The bio-derived MgO nanopowders (MgONPs) were characterised by Brunauer–Emmett–Teller (BET), differential thermal and thermogravimetric (DTA-TGA) analysis, powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) equipped with an energy-dispersive spectroscopy (EDS). The COD and BOD reduction efficiency of the MgO—NPs was evaluated in the presence of raw and simulated tannery wastewater. Under optimum conditions, the COD of raw tannery wastewater reduced from 2725.9 mg/L to 126.5 mg/L and BOD from 1899.5 mg/L to 104.5 mg/L in a batch system. Also, the turbidity was reduced from the initial concentration of 588 NTU to a level of 98 NTU within 120 min. Impressively, 93.5% COD reduction and 96.9% BOD reduction were obtained by the fixed-bed system. The spent MgO was regenerated and reused several times without significant loss of capacity. Hence, the bio-derived MgO nanopowders offered potential benefits for BOD and COD removal from tannery wastewater.

A novel visible light active N-doped ZnO for photocatalytic degradation of dyes

Abstract: A new, simple synthesis route based on combustion reaction was introduced for preparing N-doped ZnO (N-ZnO). The structure and properties of N-ZnO were characterized using various techniques, including XPS, XANES, XRD, FTIR, TGA, SEM, TEM, DRS, BET, and zeta potentiometry. Its photocatalytic activity for the degradation of amaranth (AM) and methylene blue (MB) was evaluated under visible and UV light. It was found that N doping significantly extended the spectral response to the visible region and even up to the near-infrared region. N dopants were photostable and highly soluble within the doped matrix. Using 1 g/L of N-ZnO at pH 7, 89.3% of MB with initial concentration of 10 mg/L could be degraded within 1.5 h under visible light of 16.5 W/m2. Under identical experimental conditions, it took 4 h for N-ZnO to degrade 88.5% of AM. Moreover, the photocatalytically treated dyes are nontoxic against Bacillus cereus, an important soil microorganism.

Comparing young landfill leachate treatment efficiency and process stability using aerobic granular sludge and suspended growth activated sludge

Abstract: The treatment of young landfill leachate was investigated using two 3 L sequencing batch reactors (SBR) with different biomass: aerobic granular sludge (GSBR) and the suspended growth activated sludge (ASBR). According to the nature of aerobic granular sludge, high settling velocities were expected in the GSBR and it was confirmed with 60 ml/g VSS of 5-min sludge volume index (SVI5). However, the activated sludge required 30 min for the ASBR to achieve a SVI of 42 ml/g VSS. Compared to the ASBR, the GSBR was also more efficient in nitrogen and carbon removal. During the steady period of the experiment, 99% of total ammonium nitrogen (TAN) was removed through nitritation and nitrification in the GSBR with an average influent TAN concentration of 498 mg/L. With high influent TAN concentration, the GSBR could achieve a full nitrification efficiency of 56 ± 12% without accumulating nitrite. On the contrary, complete nitrification was not achieved in the ASBR as it was exposed to high concentrations of free ammonia (FA) and free nitrous acid (FNA), 16 and 0.2 mg/L respectively. Partial nitrification (nitritation) with the efficiency of 77 ± 10% was observed in the ASBR. The GSBR also presented higher efficiency in denitrification compared to the ASBR. 23% denitrification was observed in the GSBR during the anaerobic phase. Moreover, higher chemical oxygen demand (COD) removal efficiency was observed in GSBR than ASBR. Phosphorus removal efficiency was almost identical in both reactors. Overall, compared with the activated sludge, the aerobic granular sludge showed the best nutrients removal performance and higher tolerance to toxic compounds in young landfill leachate.

Evaluation of kinetic and statistical models for predicting breakthrough curves of phosphate removal using dolochar-packed columns

Abstract: The sustainability in utilizing dolochar packed columns under dynamic conditions for phosphate removal from aqueous solutions, has been carried out in this study. The assessment of efficacy of the bed under varying experimental conditions of bed depth, flow rate and influent phosphate concentration revealed that, an increase in bed depth and initial phosphate concentration or a decrease in flow rate resulted in increased breakthrough and exhaustion time. Thomas, modified dose response (MDR) and Clark models were applied to simulate the experimental breakthrough curves following nonlinear regression analysis. Also bed depth service time (BDST) model was engaged to scale up the adsorption process by means of linear regression approach. All the models with a very high coefficient of correlation (R2 > 0.93) predicted the breakthrough curves equally well. Good consistency was observed among experimental bed adsorption capacity (8.56 mg g−1) and those predicted by Thomas (9.21 mg g−1) and MDR models (8.81 mg g−1). Statistical modeling proposed quadratic models for breakthrough and exhaustion time, with R2 values of 0.99 in both the cases. Soil column analytical test confirms slow release of phosphate from spent dolochar. The results confirm the sustainable application of dolochar packed columns for phosphate abatement in large scale accompanied by the utilization of spent dolochar as a source of phosphate.

Evaluation of chitosan-carbon based biocomposite for efficient removal of phenols from aqueous solutions

Abstract: Nanocomposite particles of chitosan and activated carbon were prepared for removal of phenols from aqueous solutions. The nanoparticles were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) spectroscopy, and particle size and charge analysis. Removal of phenol from aqueous solution was optimized by varying experimental conditions like initial concentration of phenol, pH, adsorbent doses, temperature and contact time. Equilibrium adsorption studies and kinetics of adsorption process showed that adsorption process followed Freundlich isotherm and pseudo-second order kinetic model, respectively. The maximum adsorption capacity of phenol was found to be 409 mg/g.

Electrochemical decolorization and biodegradation of tannery effluent for reduction of chemical oxygen demand and hexavalent chromium

Abstract: Tannery effluent contains enormous quantities of toxic chemicals and high level of chemical oxygen demands, which gets directly discharged into natural aqueous system, thus contaminating the water quality. Hence, it is important to develop an eco-friendly and cost effective technology to treat the tannery effluent wastewater. Our present investigation on integrated approach of electrochemical oxidation (EO) of tannery effluent (TE) using RuO2-IrO2-TiO2 anode and titanium mesh electrode as cathode and followed by the biodegradation process (BP) of the treated EO effluent. Various parameters viz., sodium chloride concentration (NaCl) (1–5 g/L) and current density (10–30 mA/cm2) are optimized. The agro waste peanut hull (PH) and rice hull (RH) are utilized as carbon source for biodegradation of tannery effluent. A maximum of 87% decolorization is observed at 5 g/L of NaCl concentration and 30 mA/cm2 of current density after 135 min of EO treatment. The EO treated TE is further treated by BP with Pseudomonas stutzeri MN1, Acinetobacter baumannii MN3 and mixed consortia of MN1 and MN3. The 97% of chemical oxygen demand (COD) and 96% of Cr(VI) reduction was observed after 72 h of BP with mixed consortia and rice hull as carbon source. Thus, the integrated approach of EO with BP can be implied for complete a decolorization and degradation of tannery effluent.

Removal of phosphorus from phosphonate-loaded industrial wastewaters via precipitation/flocculation

Abstract: Phosphonates are to be removed from industrial wastewater before they reach municipal wastewater treatment plants or surface waters. Industrial wastewaters contaminated with the phosphonates 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), 1-hydroxyethylidene-(1,1-diphosphonic acid) (HEDP), nitrilotrimethylphosphonic acid (NTMP), ethylenediamine tetra(methylene phosphonic acid) (EDTMP) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) can be subdivided into: (1) mostly clear concentrates with a high water hardness, and (2) organically polluted wastewaters, for instance from the paper and textile industries. Our own flocculation experiments with FeIII and AlIII salts showed that, at a pH of 7.5, the adsorption affinity of polyphosphonates onto iron hydroxides and aluminum hydroxides significantly decreases with an increasing number of C-P bonds (HEDP > NTMP > EDTMP > DTPMP). In comparison to pure water spiked with phosphonates, the total P removal from concentrates occurred at similar and even lower flocculant dosage concentrations (s = 4–8) (s is the molar ratio of dosed metal concentration to total P concentration in the raw sample). In organically polluted industrial wastewaters, the formation of flocks, and therefore the total P decrease, only occurred after exceeding a certain flocculant concentration, which varied strongly depending on the wastewater type (s = 0.6–86). Below that concentration, the flocculant underwent complexation, and no elimination could be observed. For most of the wastewaters, the required s values for at least 80% total P decrease were very similar for both FeIII and AlIII. Furthermore, Ca(OH)2 as flocculant turned out to be an effective tool for total P removal and simultaneous softening of calcareous concentrates.

Synthesis of cryptocrystalline magnesite–bentonite clay composite and its application for neutralization and attenuation of inorganic contaminants in acidic and metalliferous mine drainage

Abstract: The primary aim of this study was to synthesize cryptocrystalline magnesite–bentonite clay composite by mechanochemical activation and evaluate its usability as low cost adsorbent for neutralization and attenuation of inorganic contaminants in acidic and metalliferous mine drainage. The composite was synthesized at 1:1 weight to weight ratio. The capacity of the composite to neutralize acidity and remove toxic chemical species from synthetic and field AMD was evaluated at optimized conditions. Interaction of the composite with AMD led to an increase in pH (pH > 11) and lowering of metal concentrations. The removal of chemical species was optimum at 20 min of equilibration and 1 g of dosage. The composite removed ≈99% (Al 3+ , Fe 3+ , and Mn 2+ ) and ≈90% (SO 4 2− ) from raw mine effluent. Adsorption kinetics fitted better to pseudo-second-order kinetic than pseudo-first-order kinetic hence confirming chemisorption. Adsorption data fitted better to Freundlich adsorption isotherm than Langmuir hence confirming multisite adsorption. Gibbs free energy model predicted that the reaction is spontaneous in nature for Al, Fe and sulphate except for Mn. Geochemical model indicated that Fe was removed as Fe(OH) 3 , goethite, and jarosite, Al as basaluminite, boehmite and jurbanite, Al(OH) 3 and as gibbsite and diaspore. Al and Fe precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite and manganite. Ca was removed as gypsum. Sulphate was removed as gypsum, and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite and dolomite. It was concluded that the composite has the potential to neutralize acidity and attenuate potentially toxic chemical species from acidic and metalliferous mine drainage.