Harnessing selenium nanoparticles (SeNPs) for enhancing growth and germination, and mitigating oxidative stress in Pisum sativum L.

Selenium, an essential micronutrient for plants and animals, can cause selenium toxicity as an oxyanion or at elevated doses. However, the toxic selenite (SeO32-) oxyanion, can be converted into less harmful elemental nano-selenium (Se0), with various practical applications. This research aimed to investigate two methods for reducing SeO32-: abiotic reduction using cell-free extract from Enterococcus spp. (abiotic-SeNPs) and chemical reduction involving L-ascorbic acid (chemical-SeNPs). Analysis with XPS confirmed the presence of Se0, while FTIR analysis identified surface functional groups on all SeNPs. The study evaluated the effects of SeO32-, abiotic-SeNPs, and chemical-SeNPs at different concentrations on the growth and germination of Pisum sativum L. seeds. SeO32- demonstrated detrimental effects on germination at concentrations of 1 ppm (germination index (GI) = 0.3). Conversely, both abiotic- and chemical-SeNPs had positive impacts on germination, with GI > 120 at 10 ppm. Through the DPPH assay, it was discovered that SeNPs exhibited superior antioxidant capabilities at 80 ppm, achieving over 70% inhibition, compared to SeO32- (less than 20% inhibition), therefore evidencing significant antioxidant properties. This demonstrates that SeNPs have the potential to be utilized as an agricultural fertilizer additive, benefiting seedling germination and development, while also protecting against oxidative stress.

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants.

Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x%Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials' photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy.

Influence of wastewater matrix on the visible light degradation of phenol using AgCl/Bi24O31Cl10 photocatalyst.

A significant amount of research has been conducted on the development and application of photocatalytic materials for the visible light degradation of organic pollutants in wastewater. However, most pollutant degradation studies are conducted using simulated wastewater often prepared using DI water. This is far removed from the realities of environmentally relevant water systems. It is therefore important to investigate the activity of these semiconductor materials with real water samples. In this study, the photocatalytic activity of the photocatalyst was investigated in the secondary effluent of a wastewater treatment plant (WWTP) in Pretoria, South Africa, for the degradation of phenol under visible light irradiation. The experimental design was done using the Taguchi method L16 orthogonal tray with three factors (pH, initial phenol concentration, and photocatalyst dosage) and four levels. The results show that pH is the highest-ranked significant factor influencing the degradation rate, closely followed by the initial concentration of the pollutant. The photocatalyst dosage had the least significant impact on degradation. The effects of individual anion components such as Cl-, NO3-, NO2-, SO42- and cations such as Ca2+, Mg2+, Zn2+, and K+ were investigated. While Cl- did not negatively influence the degradation rate, the results show that NO3- and SO42- inhibit the degradation of phenol. More specifically, the presence of nitrites resulted in total impeding of the degradation process illustrating that nitrite concentrations ≥ 20 ppm should be removed from wastewater prior to photocatalytic degradation. The cations investigated promoted the degradation of phenol. Generally, there was enhanced degradation in the water matrix when compared to DI water, and the results revealed improved degradation efficiency due to the cumulative impact of various components of the wastewater.

The Role of pH, Electrodes, Surfactants, and Electrolytes in Electrokinetic Remediation of Contaminated Soil.

Electrokinetic remediation has, in recent years, shown great potential in remediating polluted environments. The technology can efficiently remove heavy metals, chlorophenols, polychlorinated biphenyls, phenols, trichloroethane, benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and entire petroleum hydrocarbons. Electrokinetic remediation makes use of electrolysis, electroosmosis, electrophoresis, diffusion, and electromigration as the five fundamental processes in achieving decontamination of polluted environments. These five processes depend on pH swings, voltage, electrodes, and electrolytes used in the electrochemical system. To apply this technology at the field scale, it is necessary to pursue the design of effective processes with low environmental impact to meet global sustainability standards. It is, therefore, imperative to understand the roles of the fundamental processes and their interactions in achieving effective and sustainable electrokinetic remediation in order to identify cleaner alternative solutions. This paper presents an overview of different processes involved in electrokinetic remediation with a focus on the effect of pH, electrodes, surfactants, and electrolytes that are applied in the remediation of contaminated soil and how these can be combined with cleaner technologies or alternative additives to achieve sustainable electrokinetic remediation. The electrokinetic phenomenon is described, followed by an evaluation of the impact of pH, surfactants, voltage, electrodes, and electrolytes in achieving effective and sustainable remediation.

Microbial Precipitation of Pb(II) with Wild Strains of Paraclostridium bifermentans and Klebsiella pneumoniae Isolated from an Industrially Obtained Microbial Consortium.

The study focused on determining the microbial precipitation abilities of bacterial strains that were isolated from an industrially obtained Pb(II)-resistant microbial consortium. Previous research has demonstrated the effectiveness of the consortium on the bioprecipitation and adsorption of Pb(II) from solution. The bioremediation of Pb(II) using microbial precipitation provides an alternative option for Pb(II) removal from wastewater. Both strains, Klebsiella pneumoniae and Paraclostridium bifermentans, were successfully isolated from the consortium obtained from a battery recycling plant in South Africa. The experiments were conducted over both 30 h and 5 d, providing insight into the short- and long-term precipitation abilities of the bacteria. Various initial concentrations of Pb(II) were investigated, and it was found that P. bifermentans was able to remove 83.8% of Pb(II) from solution with an initial Pb(II) concentration of 80 mg L-1, while K. pneumoniae was able to remove 100% of Pb(II) with the same initial Pb(II) concentration after approximately 5 d. With the same initial Pb(II) concentration, P. bifermentans was able to remove 86.1% of Pb(II) from solution, and K. pneumoniae was able to remove 91.1% of Pb(II) from solution after 30 h. The identities of the precipitates obtained for each strain vary, with PbS and Pb0 being the main species precipitated by P. bifermentans and PbO with either PbCl or Pb3(PO4)2 precipitated by K. pneumoniae. Various factors were investigated in each experiment, such as metabolic activity, nitrate concentration, residual Pb(II) concentration, extracellular and intracellular Pb(II) concentration and the precipitate identity. These factors provide a greater understanding of the mechanisms utilised by the bacteria in the bioprecipitation and adsorption of Pb(II). These results can be used as a step towards applying the process on an industrial scale.

Non-Destructive Impedance Monitoring of Bacterial Metabolic Activity towards Continuous Lead Biorecovery.

The adverse health effects of the presence of lead in wastewater streams are well documented, with conventional methods of lead recovery and removal suffering from disadvantages such as high energy costs, the production of toxic sludge, and low lead selectivity. Klebsiella pneumoniae and Paraclostridium bifermentans have been identified as potential lead-precipitating species for use in a lead recovery bioreactor. Electrical impedance spectroscopy (EIS) on a low-cost device is used to determine the potential for the probe-free and label-free monitoring of cell growth in a bioreactor containing these bacteria. A complex polynomial is fit for several reactive equivalent circuit components. A direct correlation is found between the extracted supercapacitance and the plated colony-forming unit count during the exponential growth phase, and a qualitative correlation is found between all elements of the measured reactance outside the exponential growth phase. Strong evidence is found that Pb(II) ions act as an anaerobic respiration co-substrate for both cells observed, with changes in plated count qualitatively mirrored in the Pb(II) concentration. Guidance is given on the implementation of EIS devices for continuous impedance monitoring.

Enterococcus spp. Cell-Free Extract: An Abiotic Route for Synthesis of Selenium Nanoparticles (SeNPs), Their Characterisation and Inhibition of Escherichia coli.

Selenite (SeO32-), the most toxic and most reactive selenium (Se) oxyanion, can be reduced to elemental selenium (Se0) nanoparticles by a variety of bacteria, including Enterococcus spp. Previously, the orthodox view held that the reduction of SeO32- to Se0 by a wide range of bacteria was solely accomplished by biological processes; however, recent studies have shown that various bacterial strains secrete metal-reducing metabolites, thereby indirectly catalysing the reduction of these metal species. In the current study, selenium nanoparticles were synthesised from the abiotic reduction of selenite with the use of Enterococcus spp. cell-free extract. Once separated from the cell-free extract, the particles were analysed using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and a Zetasizer. The results revealed that the SeNPs were spherical in shape, containing both amorphous and crystalline properties, and the sizes with the highest frequency ranged close to 200 nm. Additionally, the obtained nanoparticles exhibited antimicrobial properties by directly inhibiting the viability of an E. coli bacterial strain. The results demonstrate not only the potential of abiotic production of SeNPs, but also the potential for these particles as microbial inhibitors in medical or similar fields.

Comparative analysis of biological versus chemical synthesis of palladium nanoparticles for catalysis of chromium (VI) reduction.

The discharge of hexavalent chromium [Cr(VI)] from several anthropogenic activities leads to environmental pollution. In this study, we explore a simple yet cost effective method for the synthesis of palladium (Pd) nanoparticles for the treatment of Cr(VI). The presence of elemental Pd [Pd(0)] was confirmed by scanning electron microscope (SEM), electron dispersive spectroscopy and X-ray diffraction (XRD). We show here that the biologically synthesized nanoparticles (Bio-PdNPs) exhibit improved catalytic reduction of Cr(VI) due to their size being smaller and also being highly dispersed as compared to chemically synthesized nanoparticles (Chem-PdNPs). The Langmuir-Hinshelwood mechanism was successfully used to model the kinetics. Using this model, the Bio-PdNPs were shown to perform better than Chem-PdNPs due to the rate constant (kbio = 6.37 mmol s-1 m-2) and Cr(VI) adsorption constant (KCr(VI),bio = 3.11 × 10-2 L mmol-1) of Bio-PdNPs being higher than the rate constant (kchem = 3.83 mmol s-1 m-2) and Cr(VI) adsorption constant (KCr(VI),chem = 1.14 × 10-2 L mmol-1) of Chem-PdNPs. In addition, product inhibition by trivalent chromium [Cr(III)] was high in Chem-PdNPs as indicated by the high adsorption constant of Cr(III) in Chem-PdNPs of KCr(III),chem = 52.9 L mmol-1 as compared to the one for Bio-PdNPs of KCr(III),bio = 2.76 L mmol-1.

Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms.

The objective of the study was to gather insight into the metabolism of lead-removing microorganisms, coupled with Pb(II) removal, biomass viability and nitrate concentrations for Pb(II) bioremoval using an industrially obtained microbial consortium. The consortium used for study has proven to be highly effective at removing aqueous Pb(II) from solution. Anaerobic batch experiments were conducted with Luria-Bertani broth as rich growth medium over a period of 33 h, comparing a lower concentration of Pb(II) with a higher concentration at two different nutrient concentrations. Metabolite profiling and quantification were conducted with the aid of both liquid chromatography coupled with tandem mass spectroscopy (UPLC-HDMS) in a "non-targeted" fashion and high-performance liquid chromatography (HPLC) in a "targeted" fashion. Four main compounds were identified, and a metabolic study was conducted on each to establish their possible significance for Pb(II) bioremoval. The study investigates the first metabolic profile to date for Pb(II) bioremoval, which in turn can result in a clarified understanding for development on an industrial and microbial level.

Improved performance and cost efficiency by surface area optimization of granular activated carbon in air-cathode microbial fuel cell.

Microbial fuel cell (MFC) architectural modification is increasingly becoming an important area of research due to the need to improve energy recovery. This study presents a low-cost modification method of the anode that does not require pre-treatment-step involving hazardous chemicals to improve performance. The modification step involves deposition of granular activated carbon (GAC) which is highly conductive and provides a high specific surface area inside a carbon cloth that acts as an anode and as a supporting material. The GAC particle size of 0.6-1.1 mm resulted in an increase in air-cathode MFC performance due to an increase in available surface area of 879.5 m2 g-1 for attachment of cells based on Brunauer, Emmett, and Teller (BET) results, and an increase in the appropriate surface for attachment of cells which was rough based on the scanning electron microscope (SEM) results. On the other hand, although GAC with size of particles of 0.45-0.6 mm had the highest available surface area for attachment of cells, it lacked the appropriate surface for attachment of cells and reduced MFC performance. This means that particle size optimization of GAC is essential since there is a limit to which the particle diameter can be reduced. The utilization of the GAC with the optimized particle size produced an output voltage of 507.5 mV and maximum power output of 1287.7 mW m-3 at current output of 2537.5 mA m-3. This study also showed that there is an economic benefit in modifying carbon cloth using GAC with optimized particle size.

Fabrication of monodispersed copper oxide nanoparticles with potential application as antimicrobial agents.

Cuprous oxide nanoparticles (Cu2O NPs) were fabricated in reverse micellar templates by using lipopeptidal biosurfactant as a stabilizing agent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrum (EDX) and UV-Vis analysis were carried out to investigate the morphology, size, composition and stability of the nanoparticles synthesized. The antibacterial activity of the as-synthesized Cu2O NPs was evaluated against Gram-positive B. subtilis CN2 and Gram-negative P. aeruginosa CB1 strains, based on cell viability, zone of inhibition and minimal inhibitory concentration (MIC) indices. The lipopeptide stabilized Cu2O NPs with an ultra-small size of 30 ± 2 nm diameter exhibited potent antimicrobial activity against both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 62.5 µg/mL at pH5. MTT cell viability assay displayed a median inhibition concentration (IC50) of 21.21 µg/L and 18.65 µg/mL for P. aeruginosa and B. subtilis strains respectively. Flow cytometric quantification of intracellular reactive oxygen species (ROS) using 2,7-dichlorodihydrofluorescein diacetate staining revealed a significant ROS generation up to 2.6 to 3.2-fold increase in the cells treated with 62.5 µg/mL Cu2O NPs compared to the untreated controls, demonstrating robust antibacterial activity. The results suggest that lipopeptide biosurfactant stabilized Cu2O NPs could have promising potential for biocompatible bactericidal and therapeutic applications.

Synthesis of biosurfactant stabilized silver nanoparticles, characterization and their potential application for bactericidal purposes.

Uniformly dispersed silver nanoparticles (AgNPs) with remarkable colloidal stability were synthesised using chemical reduction method in lipopeptide biosurfactant reverse micelles. Transmission Electron microscopy (TEM), Scanning electron microscopy (SEM) and UV-vis spectroscopy analysis exhibited monodisperse nanoparticles with spherical morphology of diameter of 21 ±â€¯2. The lipopeptide stabilized AgNPs displayed remarkable antibacterial activity with minimum inhibitory concentration (MIC) value of 15.625 µg/mL against Gram-negative Pseudomonas aeruginosa CB1 and Gram-positive Bacillus subtilis CN2 strains with a significant dose-dependent reduction of cell viability and loss of membrane integrity. Investigation of AgNPs internalization and dissolution assays demonstrated 42-fold higher leaching of the lipopeptide-stabilized AgNPs compared to the bare AgNPs, and concentration dependent increase in cellular uptake with subsequent damage to intracellular organelles. Further ultrastructural observation using TEM revealed internalization and strong binding of considerable amount of AgNPs on the lipopolysaccharide layer of the Gram-negative and peptidoglycans layer of Gram-positive bacteria indiscriminately, demonstrating robust antibacterial activity and potential application to treat multidrug resistant bacteria.

Live and lyophilized fungi-algae pellets as novel biosorbents for gold recovery: Critical parameters, isotherm, kinetics and regeneration studies.

This study aimed to evaluate the potential of live and lyophilized fungi-algae pellets as biosorbents for gold recovery and their regeneration ability. The optimum conditions determined by Taguchi method were 1 g/L co-pellets, 9-10 mm size at 250 rpm of agitation speed and pH 3.5 and 2.0 for live and lyophilized co-pellets, respectively. The porous characteristics of fungi-algae pellets played an important role on gold adsorption. Lyophilized co-pellets achieved adsorption capacity of 112.36 mg/g which were comparable with some synthesized granular adsorbents and performed better than the live co-pellets due to more cell-wall polysaccharides involved in gold interaction. 97.77% of gold was selectively absorbed by the lyophilized co-pellets from multi-metal wastewater in column reactor. This study may provide new insights into the application of fungi-algae pelletized reactor in bioremediation of contaminated wastewater by precious metals and their recovery and the in-situ regeneration of biosorbents.

In situ bioremediation of hexavalent chromium in presence of iron by dried sludge bacteria exposed to high chromium concentration.

Stability of chromium in the ferrochrome slag dumps and leachate are affected by pH, redox potential and the presence of other metallic species in the slag. It is desirable to keep chromium in slag dumps in the trivalent [Cr(III)] state because trivalent chromium is 1000 times less toxic to living organisms than the hexavalent form [Cr(VI)]. Due to the low toxicity and low mobility of Cr(III), it is recommended to convert Cr(VI) to Cr(III) wherever possible to protect the health of living organisms. In this study, the role of Cr(VI) reducing organisms for stabilising chromium in slag dumps was evaluated in the presence of iron [oxidation states Fe(II) and Fe(III)]. The study showed that stabilisation of chromium species in the trivalent state was most favourable under aerated conditions. Up to 100 mg/L Cr(VI) was reduced in less than 24 h by cultures grown under aerobic conditions in the presence of Fe(III). A much shorter time (6 h) was required to reduce the same amount of Cr(VI) in the presence of Fe(II). When oxygen was completely excluded, it was only possible to reduce 20 mg/L in about 48 h which was much slower than the removal of 100 mg/L in less than 24 h under aerated conditions. Fe(II) contributed directly to catalytic reduction of Cr(VI) reduction whereas Fe(III) was beneficial to Cr(VI) reduction up to an initial Cr(VI) concentration of 75 mg/L. Evaluation of Cr(VI) reduction kinetics showed that Cr(VI) reduction under aerobic conditions followed the non-competitively inhibited mixed-order reaction. Cr(VI) reduction in sealed reactor vessels, under anaerobic conditions, followed a modified non-competitive inhibition reaction model. The results indicate that chromium stabilisation in ferrochrome slag dumps would require maintenance of a fully aerated dump supplemented by a culture of Cr(VI) reducing organisms.

Characterization of the biochemical-pathway of uranium (VI) reduction in facultative anaerobic bacteria.

Cultures of U(VI) reducing bacteria sourced from abandoned uranium mine tailing dam were evaluated for their ability to reduce U(VI) to U(IV). The species in the cultures reduced U(VI) in solutions with initial U(VI) concentration up to 400mgL(-)(1) under a near neutral pH of 6.5. The electron flow pathway and fate of reduced species was also analysed in the individual species in order to evaluate the potential for control and optimisation of the reduction potential at the biochemical level. The results showed that U(VI) reduction in live cells was completely blocked by the NADH-dehydrogenase inhibitor, rotenone (C23H22O6), and thioredoxin inhibitor, cadmium chloride (CdCl2), showing that U(VI) reduction involves the electron flow through NADH-dehydrogenase, a primary electron donor to the electron transport respiratory (ETR) system. Mass balance analysis of uranium species aided by visual and electron microscopy suggest that most U(VI) reduction occurred on the cell surface of the isolated species. This finding indicates the possibility of easy uranium recovery for beneficial use through biological remediation. Should the U(VI) be reduced inside the cell, recovery would require complete disruption of the cells and therefore would be difficult. The study contributes new knowledge on the underlying mechanisms in the U(VI) reduction in facultative anaerobes.

Protein from preprocessed waste activated sludge as a nutritional supplement in chicken feed.

Five groups of broiler chickens were raised on feed containing varying substitutions of single cell protein from preprocessed waste activated sludge (pWAS) in varying compositions of 0:100, 25:75, 50:50, 75:25, and 100:0 pWAS: fishmeal by mass. Forty chickens per batch were evaluated for growth rate, mortality rate, and feed conversion efficiency (ηє). The initial mass gain rate, mortality rate, initial and operational cost analyses showed that protein from pWAS could successfully replace the commercial feed supplements with a significant cost saving without adversely affecting the health of the birds. The chickens raised on preprocessed WAS weighed 19% more than those raised on fishmeal protein supplement over a 45 day test period. Growing chickens on pWAS translated into a 46% cost saving due to the fast growth rate and minimal death losses before maturity.

Modelling biological Cr(VI) reduction in aquifer microcosm column systems.

Several chrome processing facilities in South Africa release hexavalent chromium (Cr(VI)) into groundwater resources. Pump-and-treat remediation processes have been implemented at some of the sites but have not been successful in reducing contamination levels. The current study is aimed at developing an environmentally friendly, cost-effective and self-sustained biological method to curb the spread of chromium at the contaminated sites. An indigenous Cr(VI)-reducing mixed culture of bacteria was demonstrated to reduce high levels of Cr(VI) in laboratory samples. The effect of Cr(VI) on the removal rate was evaluated at concentrations up to 400 mg/L. Following the detailed evaluation of fundamental processes for biological Cr(VI) reduction, a predictive model for Cr(VI) breakthrough through aquifer microcosm reactors was developed. The reaction rate in batch followed non-competitive rate kinetics with a Cr(VI) inhibition threshold concentration of approximately 99 mg/L. This study evaluates the application of the kinetic parameters determined in the batch reactors to the continuous flow process. The model developed from advection-reaction rate kinetics in a porous media fitted best the effluent Cr(VI) concentration. The model was also used to elucidate the logistic nature of biomass growth in the reactor systems.

Biosurfactants as demulsifying agents for oil recovery from oily sludge--performance evaluation.

The oil producing and petroleum refining industries dispose of a significant amount of oily sludge annually. The sludge typically contains a mixture of oil, water and solid particles in the form of complex slurry. The oil in the waste sludge is inextractible due to the complex composition and complex interactions in the sludge matrix. The sludge is disposed of on land or into surface water bodies thereby creating toxic conditions or depleting oxygen required by aquatic animals. In this study, a fumed silica mixture with hydrocarbons was used to facilitate stable emulsion ('Pickering' emulsion) of the oily sludge. The second step of controlled demulsification and separation of oil and sludge into layers was achieved using either a commercial surfactant (sodium dodecyl sulphate (SDS)) or a cost-effective biosurfactant from living organisms. The demulsification and separation of the oil layer using the commercial surfactant SDS was achieved within 4 hours after stopping mixing, which was much faster than the 10 days required to destabilise the emulsion using crude biosurfactants produced by a consortium of petrochemical tolerant bacteria. The recovery rate with bacteria could be improved by using a more purified biosurfactant without the cells.

Biological Cr(VI) immobilisation in saturated aquifer zone using culture inoculated soil columns.

Remediation of Cr(VI) requires the reduction of the mobile state [Cr(VI)], which exists in the natural environment as the oxyanionic species (CrxOy(z)(-)), to the less mobile trivalent state [Cr(III)], which readily forms the hydroxide precipitate [Cr(OH)3(s)] under natural pH conditions. In this study, Cr(VI) reduction is investigated using inoculated microcosm aquifer systems operated as fully submerged plug flow systems. The system was design to simulate the operation of a microbial contaminant barrier in the saturated zone of an open aquifer system. No organic carbon sources and no air was introduced to simulate Cr(VI) reduction under oxygen free conditions. The inoculated microcosm column operated at influent feed concentrations of 10, 20, and 40 mg/L, and a hydraulic retention time of 12 hours achieved complete removal of Cr(VI) over a 90 cm distance. Steady-state conditions were obtained in less than 48 hours under feed concentrations of 10 and 20 mg/L. Very little Cr(VI) reduction was observed in non-inoculated microcosm controls operated under identical conditions.

Computational simulation of flocculent sedimentation based on experimental results.

Computerised interpolation algorithms as well as the empirical model for analysing the flocculent settling data were developed. A mechanistic semi-empirical model developed from fundamental physical principles of a falling particle in a viscous fluid was tested against actual flocculation column data. The accuracy of the mechanistic model was evaluated using the sum of the squared errors between the interpolated values (real values) and the model predictions. Its fitting capabilities were compared with Özer's model using nine flocculent data sets of which four were obtained from literature and the rest were actual data from the performed experiments. The developed model consistently simulated the flocculation behaviour of particles in settling columns better than Özer's model in eight of the nine data sets considered. It is recommended that the model's performance be further compared with other models like the Rule based and San's model. The errors due to the use of interpolated values when determining the performance of the empirical models need to be investigated. Furthermore, a three-way rather than two-way interpolation should now be achievable using the interpolation algorithm developed in this study thereby reducing the effects of interpolation bias. The above work opens the way to full automation of design of flocculation sedimentation basins and other gravitational particle separation systems which at present are designed manually and are susceptible to a wide range of human and random errors.