Low Cr Concentrations Research Articles

Hexavalent Chromium Reduction and Accumulation by Acinetobacter AB1 Isolated from Fez Tanneries in Morocco

Hexavalent chromium reduction and accumulation by Acinetobacter AB1 isolated from Fez tanneries effluents were tested. The effects of some environmental factors such as pH, temperature, and exposure time on Cr(VI) reduction and resistance were investigated. We found that this strain was able to resist to concentrations as high as 400mg/l of Cr(VI). Moreover, pH 10 and the temperature 30°C constitute favourable conditions to the growth and reduction of Acinetobacter AB1. Complete reduction of Cr(VI) was observed at low initial Cr(VI) concentrations of 50mg/l after 72h of incubation. Furthermore, Transmission electron microscope (TEM) analysis showed morphological changes in AB1 strain due 48H exposure to 100mg/l chromate concentration and revealed circular electron dense (dark black point) inclusion within the cell cytoplasm suggesting chromium deposition within the cells.

Room temperature ferromagnetism in sputtered Zn 1 − x Cr xO thin films

Cr doped ZnO (Zn 1 − x Cr xO) thin films with different Cr concentrations (0.4, 1.5, and 8.9 at.%) were deposited on Si substrates using RF magnetron sputtering. Film crystal structure was characterized using X-ray diffraction, and vibrating sample magnetometer measurements were used to investigate their magnetic properties. Unstable ZnO structure is present at low Cr concentrations, while secondary phases appear at higher Cr concentrations. 8.9 at.% Zn 1 − x Cr xO film exhibits room temperature ferromagnetism and high 325 K Curie temperature, even after 300 °C annealing for 1 h. This result is promising and demonstrates Cr doped ZnO film's potential use in practical applications.

Magnetic cluster expansion model for high-temperature magnetic properties of iron and iron–chromium alloys

Magnetic cluster expansion model is developed for bcc Fe–Cr alloys, and applied to the investigation of magnetic properties of these alloys over a broad interval of concentrations ranging from pure Fe to pure Cr, and over a broad interval of temperatures extending well over 1000 K. Finite-temperature configurations simulated using the magnetic cluster expansion Hamiltonian describe various magnetically ordered ferromagnetic and antiferromagnetic phases, partially magnetically ordered phases, and transitions between them and paramagnetic phases. We investigate the dependence of the Curie and Néel transition temperatures on the composition of the alloy. Analysis of the magnetic specific heat treated as a function of Cr concentration shows that in the low Cr concentration limit the Curie temperature increases as a function of Cr content. We find that for alloys containing high level of Cr the Curie temperature depends sensitively on the degree of Cr precipitation, varying by as much as 150 K between random alloy configurations and configurations containing Cr precipitates.

Influence of Cr-doping on the magnetic and electrical transport properties of Nd 0.75Na 0.25MnO 3

Polycrystalline Nd 0.75Na 0.25Mn 1- x Cr x O 3 (0= x=0.1) samples were prepared by sol-gel method and their magnetic and electrical transport properties were investigated experimentally. The parent compound with x=0 was a charge ordered manganite and the charge ordering transition occurred at 170 K. For lower Cr concentration ( x<0.03), the samples preserved the charge ordering features of the parent compound, but the charge ordering transition temperature decreased with increasing x, in particular from 170 K for x=0 to 154 K for x=0.02. For the x≥0.03 samples, paramagnetic to ferromagnetic phase transition took place and the Curie temperature increased from 112.8 K for x=0.04 to 125.5 K for x=0.1. The electrical transport properties were also influenced by Cr doping. For x<0.03, the samples displayed insulator characteristics below 300 K. For x=0.04, the sample showed insulator-metal transition around 75 K. For x≥0.05, the insulator-metal transition disappeared and the compounds showed insulator features again. The magnetic and electrical properties could be well explained by the phase separation scenario.

Evaluating the toxicity of environmental concentrations of waterborne chromium (VI) to a model teleost, oncorhynchus mykiss: a comparative study of in vivo and in vitro

Toxic effects of environmental concentrations (50, 100, and 200μg/L) of waterborne chromium (VI) were evaluated in rainbow trout by comparison of in vitro and in vivo assays. Multiple biomarkers were measured including oxidative stress indices and antioxidant response parameters in liver and brain, as well as Na+-K+-ATPase in gill. Superoxide dismutase (SOD) and glutathione reductase (GR) activities were significantly induced (1.54-fold and 1.37-fold, respectively) in fish brain in vivo, but no significant differences were observed in any other biomarker or in vivo test group. Oxidative stress was apparent in vitro as significantly higher levels of oxidative indices, with the highest induction of TBARS and CP found in brain at 200μg/L Cr(VI) (2.41-fold and 1.95-fold, respectively), and SOD and GR activities and reduced glutathione in brain were significantly inhibited (65%, 44%, and 36%, respectively). In vitro Na+-K+-ATPase activity in gill was also significantly inhibited at concentrations of 100 and 200μg/L (69% and 45%, respectively). Short-term exposure to environmental concentrations of Cr(VI) does not therefore evoke marked effects in fish in vivo. Based on the present results, a set of in vitro tests with tissue homogenate can be evoked more remarkable effects by the lower concentrations of Cr(VI) than in vivo, which could provide some useful information and might be a potential alternative approach for monitoring heavy metal pollution in aquatic environments. However, it needs more detailed studies in other area, such as hormonal response or genotoxicity, before these findings could be applied in the field investigation.

Recycling Mg(OH)2Nanoadsorbent during Treating the Low Concentration of CrVI

Investigations about how to recycle the deactivated nanomaterials are well-needed. This work was designed to explore the recycling strategy of Mg(OH)(2) nanoadsorbent during treating low concentration of Cr(VI) solution as an example. It was demonstrated that a reversible route between Cr-adsorbed nano-Mg(OH)(2) and Cr-desorbed bulk-MgCO(3) · 3H(2)O can be established by using CO(2) as a phase transformation medium. In each adsorption-desorption cycle, Cr(VI) solution with initial concentration of 10 mg · L(-1) could be enriched over 40 times. An aggregation-induced rapid phase transformation mechanism from nano-Mg(OH)(2) to bulk-MgCO(3) · 3H(2)O was discovered, which was one of the critical factors to ensure the disposing efficiency of this environmental-friendly Cr(VI) disposal system. A pilot-scale experiment was conducted with this strategy to deal with 50 L Cr(VI)-containing simulated industrial wastewater. The enrichment of Cr(VI) and the recycle of nano-Mg(OH)(2) can be successfully achieved simultaneously.

Preconcentration of Cr(III) from Natural Water by Modified Nano Polyacrylonitrile Fiber by Methanolamine

Modified nano polyacrylonitrile fiber (PANF) was prepared by adding acrylic fibers to methanolamine (MMA) with different concentration solutions. The stability of a chemically modified nano polyacrylonitrile fiber especially in concentrated hydrochloric acid which was then used as a recycling and pre‐concentration reagent for further uses of modified nano polyacrylonitrile fiber. The application of this modified nano polyacrylonitrile fiber for sorption of a series of metal ions was performed by using different controlling factors such as the pH of metal ion solution and the equilibration shaking time by the static technique. Cr(III) was found to exhibit the highest affinity towards extraction by these modified nano polyacrylonitrile fiber phases. The pronounced selectivity was also confirmed from the determined distribution coefficient (Kd) of all the metal ions, showing the highest value reported for Cr(III) to occur by modified nano polyacrylonitrile fiber. The modified nano polyacrylonitrile fiber for selective extraction of Cr(III) were successfully accomplished in aqueous solution as well as preconcentration of low concentration of Cr(III) (60 pg mL-1) from natural tap water with a preconcentration factor of 100 for Cr(III) and then off‐line Cr(III) in water samples were determined by flame atomic absorption.

Trace element variation in olivine in the Skaergaard intrusion: petrologic implications

Olivine from the Layered Series (LS), Upper Border Series (UBS), and Marginal Border Series (MBS) of the Skaergaard intrusion was analyzed to examine trace element variations. In general, olivine from all three series shows similar trends in trace elements with differentiation. Ba, Cs, Rb, and Sr, acted as excluded trace elements and the transition elements, Co, Cr, Cu, Ni, Sc, Zn, and V, are included in Skaergaard olivine. Owing to the high DNi in olivine, Ni decreases with differentiation in both olivine and the calculated Skaergaard magma. The low concentration of Cr in olivine is attributable to early depletion of Cr by pyroxene crystallization. Decreases in the abundances of V and Co are related to the onset of magnetite crystallization and the separation of immiscible Co-rich sulphide. In general, calculated partition coefficients (Di) for Skaergaard olivine show similar trends in the LS, UBS, and MBS. Calculated Di’s for Sc, Cr, and Ga in olivine, progressively increase, and Di’s for Zr, Nb, Hf, Cs, Ta, Th, and U progressively decrease, with differentiation. The systematic variation in trace element contents of Skaergaard olivine during differentiation would appear to preclude the possibility of any significant injection of new magma into the chamber during differentiation. The Ni content in Skaergaard olivine systematically decreases with differentiation as would be expected if the intrusion remained a closed system. In fact, no abrupt increases are observed in the abundances of any of the transition metal in olivine during differentiation.

Synthesis of Iron Oxide Based Gelatin Nanocomposites and their Applications in Removal of Cr (VI) Ions from Aqueous Solutions

In the present study, iron oxide based gelatin nanoparticles (FeOGel) have been used as an efficient low cost adsorbent to remove the low concentrations of toxic Cr(VI) ions from aqueous solution. The adsorption experiments were carried out by batch contact method and the effect of the significant process parameters such as initial pH of solution, contact time, adsorbent dose and the initial Cr (VI) concentration were investigated on the metal ion removal capacity. The optimum adsorption of Cr(VI) on the gelatin nanoparticles was observed at an initial pH value of 2-3. The maximum adsorption capacities of FeOGel for Cr(VI) were 120 mg/g at 25°C. The equilibrium sorption data fit satisfactorily to the Langmuir adsorption model. The characterization of the prepared FeOGel was accomplished by FTIR, SEM, TEM, XRD and ζ-potential measurements. The results obtained in this study illustrated that the prepared nanoparticles of iron oxide impregnated gelatin could be an effective and economically viable adsorbents for Cr(VI) removal at low concentration levels from aqueous systems.

Caura River basin: Weathering rates, CO2consumption, and chemistry of major and trace elements in an Orinoco River tributary coming from the Precambrian Guayana Shield, Venezuela

This study describes the geochemistry of dissolved elements in the Caura River and gives information about weathering rates and associated CO2 consumption in an Orinoco River subbasin. Physicochemical variables (pH, conductivity, HCO3−, dissolved O2, and temperature), dissolved elements (Na, K, Ca, Mg, Si, Al, Fe, Cu, Mn, Zn, and Cr), total suspended sediments (TSS), and dissolved organic carbon (DOC) concentrations were measured monthly from June 2007 to August 2008 in the Caura River. Major element concentrations (Na, Ca, Mg, and Si) showed an inverse correlation with discharge, whereas K showed high concentration values during the rising waters, probably due to biogenic sources. All these elements are provided mainly from weathering of plagioclases and K feldspars. The weathering rate (riverine flux of dissolved major cations and SiO2 derived from weathering per unit area) and the CO2 consumption rate in the Caura basin (15.4 tons km−2 yr−1 and 1.1 × 105 mol km−2 yr−1, respectively) were higher than those reported for the Orinoco basin and other black water river basins. This fact can be due to several factors such as lithology (volcanic rocks), high runoff, and the presence of organic acids, which can enhance the chemical weathering. The variability of the trace elements showed a different behavior than major elements. Fe and Al concentrations were correlated with DOC. Dissolved Mn content was correlated with pH, whereas the low concentrations of Cu and Cr are possibly associated with the low content of small size organic colloids. The high values of Zn observed during the decreasing stage suggest biogenic input of Zn to river waters.

Synthesis, characterization and properties of the DLC films with low Cr concentration doping by a hybrid linear ion beam system

A small amount of Cr-doped diamond-like carbon (Cr-DLC) films were deposited on silicon wafers by a hybrid deposition system composed of a DC magnetron sputtering with a Cr target (99.99% purity) and a linear ion source. Cr concentration in the films was controlled by varying the gas flow ratio of Ar/CH 4 in the supply gas. XPS, Raman spectroscopy, and HRTEM were employed to analyze the composition and microstructures of the films. The film residual stress was calculated via the Stoney equation, where the curvature of the film/substrate was measured by the laser reflection method. The mechanical properties and tribological behavior of the films were studied by the nano-indentor and ball-on-disc tribometer, respectively. With a small amount of Cr (< 0.3 at.%) doping, the films exhibited a typical amorphous structure feature as the pure DLC film, and neither Cr–C boding nor particulate microstructure was observed in the carbon matrix. The residual stress of the films showed a significant reduction compared with that of the pure DLC film, while the hardness of the films still retained a high value. Furthermore, the films with a low Cr content also exhibited a low friction coefficient and better wear resistance.

Variation in structural, optical and magnetic properties of Zn 1− xCr xO ( x = 0.0, 0.10, 0.15, and 0.20) nanoparticles: Role of dopant concentration on non-saturation of magnetization

Cr-doped ZnO, i.e. Zn 1− x Cr x O ( x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by sol–gel route. The structural and morphological properties of these nanoparticles were investigated by high resolution transmission electron microscope (HRTEM). The average particle size of Zn 1− x Cr x O nanoparticles decreases from 75 to 40 nm with the increase in x from 0.00 to 0.20. The rings observed in selected area diffraction pattern revealed that up to x = 0.10 these nanoparticles have single phase ZnO. However, a secondary spinel phase of ZnCr 2O 4 was observed for higher Cr doping ( x ≥ 0.15). The optical band gap calculated using UV–visible absorption was decreased from 3.27 to 2.27 eV with the increase in Cr-doping from 0.00 to 0.20 in ZnO nanoparticles. The undoped ZnO (Zn 1− x Cr x O; x = 0.00) nanoparticles did not show any hysteresis loop at room temperature, however, clear loops were obtained for x = 0.05–0.20. Additionally, magnetization ( M) vs. applied magnetic field ( H) loops for lower Cr-concentration ( x = 0.05) saturate at 5 kOe, and while those with higher Cr concentration ( x > 0.05) do not show saturation even at 10 kOe. This may be attributed to increase in the defects at higher Cr-doping into ZnO. The value of saturation magnetization was found to decrease from 4.24 emu g −1 to 1.96 emu g −1 with the increase in Cr doping from x = 0.05 to 0.20 in ZnO and may be due to the secondary ZnCr 2O 4 phase.

PENGOLAHAN LIMBAH LOGAM BERAT CHROMIUM (VI) DENGAN FOTOKATALIS TiO2

Photocatalytic Treatment of Heavy Metal Waste Cr(VI) with TiO2 Photocatalyst. The photocatalytic reduction of hexavalent chromium/Cr(VI) using TiO2 and copper-doped TiO2 as photocatalysts have been studied in stirred tank and circulating photoreactors. All photocatalysts were characterized with FTIR (Fourier Transform Infra Red), BET (Brunauer-Emmett-Teller), XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscope). TiO2 Merck and Degussa P-25 are the commercial photocatalysts used to compare the photocatalytic activity of all the prepared catalysts. Blank test experiments as well as the effect of dopants, EDTA (ethylenediaminetetraacetic acid) and activated carbon addition were studied. Cr(VI) reduction on various pH and initial Cr(VI) concentration were also conducted. The results of the experiments showed that the addition of EDTA as a hole scavenger can increases the activity of all catalysts at about 10%. Rate of Cr(VI) photoreduction is more feasible at low pH and low initial Cr(VI) concentration. The addition of activated carbon (AC) increases the photocatalytic activity at about 5% due to the synergy effect between catalyst and AC. Pure TiO2 powder prepared from TiCl4 has the highest activity in reducing Cr(VI) with the conversion of 80% due to the high crystalline (anatase) and surface area. Photoreduction of Cr(VI) over TiO2 film photocatalyst in circulating photoreactor has not shown a significant result yet. Therefore it is needed to improve furthermore the photoreactor system especially for the film type photocatalyst.

Geophagic clays: Their mineralogy, chemistry and possible human health effects

Randomly chosen representative geophagic clay samples from Cameroon and Nigeria were mineralogically and chemically analysed. The primary objectives of the study were to qualitatively and quantitatively identify the mineral constituents and to determine selected elemental compositions in the clay samples in order to infer on possible human health effects. Laboratory tests performed on the samples included X-ray powder diffractometry (XRPD), Fourier transform infra red (FTIR) spectrophotometry, and selected trace elemental analysis using inductively coupled plasma-mass spectrometer (ICP-MS). Quartz and kaolinite were conspicuously dominant in the samples. Very significantly, low concentrations of Rb, Ba, Sr, Sc, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo as well as Th and Pb were detected in the samples. Results depict purified and refined clays of sedimentary origin with medicinal and nutritional values beneficial to the geophagic individual though there are possibilities of associated human health risks. Key words : Kaolinite, quartz, medicinal and nutritional values, health risks.

Use of tree bark for comparing environmental pollution in different sites from Buenos Aires and Montevideo

Multi-elemental profiles in bark of green ash trees collected in three representative areas of Buenos Aires, Argentina and Montevideo, Uruguay, were assessed as potential air pollution indicators. Ten elements: Al, Ba, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn, were measured using inductively coupled plasma optical emissions spectrometry from 70 samples collected in different environments: central, residential and rural (reference site), in order to compare spatial patterns of metal concentration. The samples used as a control were collected from a nature reserve situated far away from any significant influences, not even a nearby road. The reference site (RF) exhibited the lowest concentrations of Al, Cr, Fe, Ni, Pb, and Zn. However, Ba and Mn showed similar concentrations in all measured sites. Magnesium is the only element that had a greater concentration in RF than at the other sites. Copper did not show any clear pattern. The Centre of Montevideo (MVD) showed higher concentrations of Al, Ba, Cr, Fe, Pb and Zn than the Centre of Buenos Aires (BA). In the A sectors, Montevideo (SAMVD) showed higher concentrations of Al, Cu, Mg, Ni, and Zn and lower concentrations of Ba, Cr, Fe, Mn, and Pb than Buenos Aires (SABA). In the B sectors, Montevideo (SBMVD) showed higher concentrations of Al, Ba, Cu, Fe, Pb, and Zn and lower concentrations of Cr and Mg than Buenos Aires (SBBA), but similar concentrations of Mn and Ni. The use of bark for biomonitoring metals allowed us to detect concentration differences related to the urban fabric and the different kinds of vehicles and their fuels. In the cities, the differences in metal concentrations detected in bark were more striking between the sectors than between centers, despite CBA being much larger than CMVD in population, extension and vehicular traffic.

Microstructural Observations on Oxidized Ni-Based Superalloy TMS-75 and PGM-Doped Derivatives

The isothermal oxidation behavior of experimental third and fourth generation Ni-based superalloys was studied at temperatures between 900 and . It was found that the lower Cr concentration in third and fourth generation alloys compared to second generation alloys negatively affects the ability of the alloy to form and maintain a protective alumina scale especially at lower temperatures . An extensive internal reaction zone comprised of oxide and nitride phases is observed underneath a nonprotective external oxide scale. At higher temperatures, a continuous alumina scale forms underneath (Ni,Co)O and spinel layers. Due to the low level of reactive element (RE) additions in these experimental alloys, scale adhesion is poor. An increase of Cr content is necessary to ensure formation of a protective alumina scale at lower temperatures. Addition of Y and/or Zr is recommended for improved oxide adhesion, resulting in better overall oxidation performance.

Effect of the supporting zeolite structure on Cr biosorption: Performance of a single-step reactor and of a sequential batch reactor—A comparison study

This work presents a study on the applicability of a zeolite-biomass system to the entrapment of metallic ions, starting from Cr(VI) solutions up to 100 mg Cr/L, in batch processes. The effect of the zeolitic support on the overall system performance was evaluated comparing two large pore zeolitic structures which differ in chemical composition and ion-exchange capacity: Faujasite (HY and NaY) and Mordenite (HMOR and NaMOR) zeolites. The systems were tested in single-step and in sequential processes. In single-step studies, HY zeolite was found to be the most efficient support when applied to low Cr concentrations (overall Cr removal of 93.4%), whereas for the higher initial Cr concentration, the higher ion-exchange capacity of NaY zeolite was determinant to achieve the highest overall Cr removal of 77.6%. The evolution of Cr(VI) entrapment was strongly dependant on the zeolitic support used in the system. In sequential batch processes, HY zeolite was found to be the most efficient support with a 98.2% overall Cr removal. The reduction of Cr(VI) promoted by the biomass is more suited to the dynamics of the sequential process. NaY zeolite behaved similarly to HMOR and NaMOR zeolites, as these systems removed between 87.3 and 93.4% of the initial Cr.

Geochronology, geochemistry and petrogenesis of rhyodacite lavas in eastern Jamaica: A new adakite subgroup analogous to early Archaean continental crust?

Rhyodacite lavas (Newcastle Volcanic Formation) from the Wagwater Basin in eastern Jamaica dated at 52.74 ± 0.34 Ma (2σ) have adakitic-like major element compositions, low Y and heavy rare Earth element (REE) concentrations and negative Nb and Ta anomalies on a normal mid-ocean ridge basalt normalised multi-element diagram. They also have lower Sr (< 400 ppm), MgO (≤ 2.0 wt.%), Ni (mostly ≤ 30 ppm) and Cr (mostly ≤ 40 ppm) concentrations compared to other modern adakites and middle-late Archaean (3.5–2.5 Ga) trondhjemite, tonalite and granodiorite/dacites (TTG/Ds). ε Nd(i) and ε Hf(i) values indicate that the Newcastle adakite-like lavas cannot be formed by assimilation and fractional crystallisation processes involving any other igneous rock in the area and so the composition of the lavas is largely the result of the residual mineralogy in the source region. Low Sr and Al 2O 3 contents indicate a fluid/vapour-absent source with residual plagioclase and REE systematics point to residual amphibole and garnet in the source region. Similarly, high silica values and constant Zr and P 2O 5 concentrations suggest residual quartz and accessory zircon and apatite. The plagioclase and garnet residue implies that the Newcastle magmas were derived from partially melting a metabasic protolith at 1.0–1.6 GPa, which would intersect the amphibole dehydration partial melt solidus at ~ 850–900 °C. Radiogenic isotopes along with the low MgO, Ni and Cr concentrations in the Newcastle lavas demonstrate that the garnet amphibolite source region cannot be part of (1) the lower Jamaican arc crust, (2) delaminated lower crust or (3) subducted Proto-Caribbean “normal” oceanic crust that may, or may not, have detached. This data, in addition to partial melting models involving a theoretical garnet-amphibolite source region for the Newcastle lavas, shows that the adakite-like rocks are derived from metamorphosed Caribbean oceanic plateau crust that underthrust Jamaica in the early Tertiary. The underplated oceanic plateau crust partially melted by either (1) influx of basaltic magma during lithospheric extension in the early Tertiary or (2) direct partial melting of the underthrusting (subducting) plateau crust. The Newcastle magmas ascended and erupted without coming into contact with a mantle wedge thus forming the low MgO, Ni and Cr contents. Most Cenozoic adakites have compositions similar to the middle-late Archaean TTG/D suite of igneous rocks. In contrast, early (> 3.5 Ga) Archaean TTG/D crustal rocks have lower Sr, MgO, Ni and Cr concentrations and prior to this study had no modern adakite analogue. However, the Newcastle adakites have similar compositions to the, early Archaean TTG/D. The discovery of these rocks has important implications for our understanding of the formation of the Earth's earliest continental crust and so it is proposed that the Newcastle lavas be classified as a unique subgroup of adakites: Jamaican-type adakite.

Various physico-chemical stress factors cause prophage induction in Nitrosospira multiformis 25196- an ammonia oxidizing bacteria

Bacteriophages are virsues that infect bacteria and contribute significant changes in the overall bacterial community. Prophages are formed when temperate bacteriophages integrate their DNA into the bacterial chromosome during the lysogenic cycle of the phage infection to bacteria. The prophage (phage DNA integrated into bacterial genome) on the bacterial genome remains dormant, but can cause cell lysis under certain environmental conditions. This research examined the effect of various environmental stress factors on the ammonia oxidation and prophage induction in a model ammonia oxidizing bacteria Nitrosospira multiformis ATCC 25196. The factors included in the study were pH, temperature, organic carbon (COD), the presence of heavy metal in the form of chromium (VI) and the toxicity as potassium cyanide (KCN). The selected environmental factors are commonly encountered in wastewater treatment processes, where ammonia oxidizing bacteria play a pivotal role of converting ammonia into nitrite. All the factors could induce prophage from N. multiformis demonstrating that cell lysis due to prophage induction could be an important mechanism contributing to the frequent upset in ammonia oxidation efficiency in full scale treatment plants. Among the stress factors considered, pH in the acidic range was the most detrimental to the nitrification efficiency by N. multiformis. The number of virus like particles (VLPs) increased by 2.3E+10 at pH 5 in 5 h under acidic pH conditions. The corresponding increases in VLPs at pH values of 7 and 8 were 9.67E+9 and 1.57E+10 in 5 h respectively. Cell lysis due to stress resulting in phage induction seemed the primary reason for deteriorated ammonia oxidation by N. multiformis at lower concentrations of Cr (VI) and potassium cyanide. However, direct killing of N. multiformis due to the binding of Cr (VI) and potassium cyanide with cell protein as demonstrated in the literature at higher concentrations of these toxic compounds was the primary mechanism of cell lysis of N. multiformis. Organics represented by the chemical oxygen demand (COD) did not have any effect on the phage induction in N. multiformis. This AOB remained dormant at low temperature (4 °C) without any phage induction. Significant decrease in the number of live N. multiformis cells with a corresponding increase in the number of VLPs was recorded when the temperature was increased to 35 °C. Death of N. multiformis at 45 °C was attributed to the destruction of cell wall rather than to the phage induction.

Effect of humic acid on the Cr(VI) adsorption onto Kaolin

The adsorption of chromate on kaolin/humic acid was studied at various conditions of initial solution pH, ionic strength, water hardness and temperatures. The increased adsorption of chromate in the presence of HA was attributed to the reducing action and complexation of HA. The addition of inorganic salts (Na +, Ca 2+ and Mg 2+) reduced the adsorption of chromate because of the high coagulation power of these ions. The Langmuir isotherm model fitted the equilibrium data well at low Cr(VI) concentrations. The saturation amounts for Cr(VI) adsorbed by kaolin were 0.14, 0.16 and 0.20 mmol Cr/g at 283 K, 293 K and 303 K, respectively. The adsorption process was endothermic.