Sequential removal of heavy metals ions and organic pollutants using an algal-bacterial consortium

The residual algal-bacterial biomass from photosynthetically supported, organic pollutant biodegradation processes, in enclosed photobioreactors, was tested for its ability to accumulate Cu(II), Ni(II), Cd(II), and Zn(II). Salicylate was chosen as a model contaminant. The algal-bacterial biomass combined the high adsorption capacity of microalgae with the low cost of the residual biomass, which makes it an attractive biosorbent for environmental applications. Cu(II) was preferentially taken-up from the medium when the metals were present both separately and in combination. There was no observed competition for adsorption sites, which suggested that Cu(II), Ni(II), Cd(II), and Zn(II) bind to different sites and that active Ni(II), Cd(II) and Zn(II) binding groups were present at very low concentrations. Therefore, special focus was given to Cu(II) biosorption. Cu(II) biosorption by the algal-bacterial biomass was characterized by an initial fast cell surface adsorption followed by a slower metabolically driven uptake. pH, Cu(II), and algal-bacterial concentration significantly affected the biosorption capacity for Cu(II). Maximum Cu(II) adsorption capacities of 8.5+/-0.4 mg g-1 were achieved at an initial Cu(II) concentration of 20 mg l-1 and at pH 5 for the tested algal-bacterial biomass. These are consistent with values reported for other microbial sorbents under similar conditions. The desorption of Cu(II) from saturated biomass was feasible by elution with a 0.0125 M HCl solution. Simultaneous Cu(II) and salicylate removal in a continuous stirred tank photobioreactor was not feasible due to the high toxicity of Cu(II) towards the microbial culture. The introduction of an adsorption column, packed with the algal-bacterial biomass, prior to the photobioreactor reduced Cu(II) concentration, thereby allowing the subsequent salicylate biodegradation in the photobioreactor.     

Drift of 10 herbicides after tractor spray application. 1. Secondary drift (evaporation)

In the present study the evaporation of 10 herbicides was investigated during five field experiments, and the amount deposited per surface area was quantified inside the field using simple passive dosimeters consisting of microscope slides placed on plastic lids. On an average basis 90% of the applied amount reached the field. The accumulated evaporation from the microscope slides was largest during the first hours after application, and the losses in 24 h (from 0% for tribenuron-methyl, fluroxypyr-1-methylheptylester and phenmedipham to 80% for prosulfocarb) was similar to other studies of losses from plant surfaces. An indication of a diurnal difference in the evaporation was observed, probably caused by the differences in temperature or by global radiation. The evaporation did not generally correlate to the vapour pressure. The amounts collected at t=0 on the passive dosimeters were for all field experiments in the same range as the reported amounts applied to the field, and the passive-dosimeters method was found to be a good and reliable method for collection of sprayed pesticides. The advantage of this method was also that it was simple and cheap and easy to set up for screening of evaporation of pesticides from the field after spraying.     

In situ and laboratory bioassays using Poecilia reticulata Peters, 1859 in the biomonitoring of an acidic lake at Camaçari, BA, Brazil

The suitability and viability of acute in situ bioassays were investigated in the biomonitoring program of an acidic lake contaminated with sulphur residues. Responses of organisms observed in laboratory and in situ bioassays were also assessed to determine whether or not they were similar and comparable, regarding accuracy and precision. Newborn Poecilia reticulata were employed as test organisms and exposed to the same water samples under in situ and laboratory conditions. Mortality/immobility was the endpoint assessed and dead/immobile organisms were counted at various time intervals during exposure. The mean calculated LT50 values and 95% confidence intervals were 1.61 (1.36-1.87) h in the laboratory bioassays and 0.72 (0.55-0.89) h in the in situ bioassays. Statistical comparison of these values revealed a significant difference (p<0.05). In situ bioassays were more accurate than those carried out in the laboratory, demonstrating higher sensitivity and better reproduction of what occurs in nature, while laboratory bioassays were more precise.     

Changes in amino acid profile and metal content in seeds of Cicer arietinum L. (chickpea) grown under various fly-ash amendments

Seeds of Cicer arietinum L. plants are edible and a valuable source of protein. Accumulation of toxic metals in the edible part of the plant, grown in fields close to fly-ash (FA) landfills, may pose a threat to human health. In the present study, the effects of FA and its amendments with different ameliorants viz., garden soil (GS), press mud (PM) and saw dust (SD), on total soluble protein contents, amino acid composition and metal accumulation in seeds were investigated in var. CSG-8962 and var. C-235 of C. arietinum. Plants accumulated adequate amounts of essential metals viz. Fe, Cu, Zn in seeds, while the toxic metals such as Cd and Cr were taken up in smaller quantities. The accumulation of Cr and Cd was less in var. C-235 than var. CSG-8962. Amendment of FA with PM enhanced the amount of soluble protein and amino acids in both varieties and was found to be superior among all tested ameliorants. Both quantitative and qualitative analysis of amino acids showed better response in var. C-235 as compared to var. CSG-8962. Thus var. C-235 seems to be suitable for cultivation in FA contaminated areas due to more accumulation of essential metals and less accumulation of toxic metals in seeds. Application of PM may further improve the growth of plants and nutritional quality of seeds.     

Effects of initial saturation on properties modification and displacement of tetrachloroethene with aqueous isobutanol

Packed column experiments were conducted to study effects of initial saturation of tetrachloroethene (PCE) in the range of 1.0-14% pore volume (PV) on mobilization and downward migration of the non-aqueous phase liquid (NAPL) product upon contact with aqueous isobutanol ( approximately 10 vol.%). This study focused on the consequences of swelling beyond residual saturation. Columns were packed with mixtures of neat PCE, water and glass beads and waterflooded to establish a desired homogeneous residual saturation, and then flooded with aqueous isobutanol under controlled hydraulic conditions. Results showed a critical saturation of approximately 8% PV for these packed column experimental conditions. At low initial PCE saturations (<8% PV), experimental results showed reduced risk of NAPL-product migration upon contact with aqueous isobutanol. At higher initial PCE saturations (>8% PV), results showed NAPL-product mobilization and downward migration which was attributed to interfacial tension (IFT) reduction, swelling of the NAPL-product, and reduced density modification. Packed column results were compared with good agreement to theoretical predictions of NAPL-product mobilization using the total trapping number, N(T). In addition to the packed column study, preliminary batch experiments were conducted to study the effects of PCE volumetric fraction in the range of 0.5-20% on density, viscosity, and IFT modification as a function of time following contact with aqueous isobutanol ( approximately 10 vol.%). Modified NAPL-product fluid properties approached equilibrium within approximately 2 h of contact for density and viscosity. IFT reduction occurred immediately as expected. Measured fluid properties were compared with good agreement to theoretical equilibrium predictions based on UNIQUAC. Overall, this study demonstrates the importance of initial DNAPL saturation, and the associated risk of downward NAPL-product migration, in applying alcohol flooding for remediation of DNAPL contaminated ground water sites.     

A review and numerical assessment of the random walk particle tracking method

We review the basic mathematical concepts of random walk particle tracking (RWPT) and its advantages and limitations. Three different numerical approaches to overcome the local mass conservation problem of the random walk methodology are examined: (i) the interpolation method, (ii) the reflection principle, and (iii) the generalized stochastic differential equations (GSDE). Analytical solutions of the spatial moments for a two-layer system are compared to model predictions using the different techniques and results demonstrate that the interpolation method reproduces correctly average velocity, but fails to reproduce macrodispersion at higher hydraulic conductivity contrasts between the two layers. On the contrary, the reflection principle and the GSDE approach underestimate average velocity, but reproduce macrodispersion better for high contrasts. The different behavior is based on an artificial shift of mass for increasing heterogeneities for the GSDE approach and the reflection principle, whereas the interpolation method suffers from the smoothing of the dispersion tensor. The behavior of these approaches was furthermore analyzed in two-dimensional heterogeneous hydraulic conductivity fields, which are characterized by different random function models. Solute transport was simulated correctly by all three approaches for the reference fields having Gaussian structures or non-Gaussian structures with an isotropic spatial correlation, even for a variance of the natural log of hydraulic conductivity of sigma(lnK)(2)=4. However, for the non-Gaussian model with a strong anisotropic spatial correlation and a variance of sigma(lnK)(2)=2 and higher, the interpolation method was the only technique modelling solute transport correctly. Furthermore, we discuss the general applicability of random walk particle tracking in comparison to the standard transport models and conclude that in advection-dominated problems using a high spatial discretization or requiring the performance of many model runs, RWPT represents a good alternative for modelling contaminant transport.     

Dip-angle influence on areal DNAPL recovery by co-solvent flooding with and without pre-flooding

A two-dimensional (2D) laboratory model was used to study effects of gravity on areal recovery of a representative dense non-aqueous phase liquid (DNAPL) contaminant by an alcohol pre-flood and co-solvent flood in dipping aquifers. Recent studies have demonstrated that injection of alcohol and co-solvent solutions can be used to reduce in-situ the density of DNAPL globules and displace the contaminant from the source zone. However, contact with aqueous alcohol reduces interfacial tension and causes DNAPL swelling, thus facilitating risk of uncontrolled downward DNAPL migration. The 2D laboratory model was operated with constant background gradient flow and a DNAPL spill was simulated using tetrachloroethene (PCE). The spill was dispersed to a trapped, immobile PCE saturation by a water flood. Areal PCE recovery was studied using a double-triangle well pattern to simulate a remediation scheme consisting of an alcohol pre-flood using aqueous isobutanol ( approximately 10% vol.) followed by a co-solvent flood using a solution of ethylene glycol (65%) and 1-propanol (35%). Experiments were conducted with the 2D model oriented in the horizontal plane and compared to experiments at the 15 degrees and 30 degrees dip-angle orientations. Injection was applied either in the downward or upward direction of flow. Experimental results were compared to theoretical predictions for flood front stability and used to evaluate effects of gravity on areal PCE recovery. Sensitivity experiments were performed to evaluate effects of the alcohol pre-flood on PCE areal recovery. For experiments conducted with the alcohol pre-flood and the 2D model oriented in the horizontal plane, results indicate that 89-93% of source zone PCE was recovered. With injection oriented downward, results indicate that areal PCE recovery was 70-77% for a 15 degrees dip angle and 57-59% for a 30 degrees dip angle. With injection oriented upward, results indicate that areal PCE recovery was 57-60% at the 30 degrees dip angle, which was similar to PCE recovery for injection in the downward flow direction. Lower areal PCE recovery at greater dip angles in either direction of flow was attributed to DNAPL swelling and migration, flood front instabilities and bypassing of the displaced fluid past the extraction wells during the alcohol pre-flood. Additional results demonstrate that the use of an alcohol pre-flood can be beneficial in improving DNAPL recovery in the horizontal orientation, but pre-flooding may reduce areal recovery efficiency in dip-angle orientations. This study also demonstrates the use of theoretical perturbation (fingering) analysis in predicting NAPL recovery efficiency for flooding processes in remediating aquifers with dip angles.     

Tradescantia micronucleus test indicates genotoxic potential of traffic emissions in European cities

Urban atmospheres contain complex mixtures of air pollutants including mutagenic and carcinogenic substances such as benzene, diesel soot, heavy metals and polycyclic aromatic hydrocarbons. In the frame of a European network for the assessment of air quality by the use of bioindicator plants, the Tradescantia micronucleus (Trad-MCN) test was applied to examine the genotoxicity of urban air pollution. Cuttings of Tradescantia clone #4430 were exposed to ambient air at 65 monitoring sites in 10 conurbations employing a standardised methodology. The tests revealed an elevated genotoxic potential mainly at those urban sites which were exposed to severe car traffic emissions. This bioassay proved to be a suitable tool to detect local 'hot spots' of mutagenic air pollution in urban areas. For its use in routine monitoring programmes, however, further standardisation of cultivation and exposure techniques is recommended in order to reduce the variability of results due to varying environmental conditions.     

Soil amendments reduce trace element solubility in a contaminated soil and allow regrowth of natural vegetation

We tested the effects of three amendments (a biosolid compost, a sugar beet lime, and a combination of leonardite plus sugar beet lime) on trace element stabilisation and spontaneous revegetation of a trace element contaminated soil. Soil properties were analysed before and after amendment application. Spontaneous vegetation growing on the experimental plot was studied by three surveys in terms of number of taxa colonising, percentage vegetation cover and plant biomass. Macronutrients and trace element concentrations of the five most frequent species were analysed. The results showed a positive effect of the amendments both on soil chemical properties and vegetation. All amendments increased soil pH and TOC content and reduced CaCl(2)-soluble-trace element concentrations. Colonisation by wild plants was enhanced in all amended treatments. The nutritional status of the five species studied was improved in some cases, while a general reduction in trace element concentrations of the aboveground parts was observed in all treated plots. The results obtained show that natural assisted remediation has potential for success on a field scale reducing trace element entry in the food chain.     

Modelling the extra and intracellular uptake and discharge of heavy metals in Fontinalis antipyretica transplanted along a heavy metal and pH contamination gradient

Samples of the aquatic bryophyte Fontinalis antipyretica Hedw. were transplanted to different sites with the aim of characterizing the kinetics of the uptake and discharge of heavy metals in the extra and intracellular compartments. The accumulation of metals in extracellular compartments, characterized by an initial rapid accumulation, then a gradual slowing down over time, fitted perfectly to a Michaelis-Menten model. The discharge of metals from the same compartment followed an inverse linear model or an inverse Michaelis-Menten model, depending on the metal. In intracellular sites both uptake and discharge occurred more slowly and progressively, following a linear model. We also observed that the acidity of the environment greatly affected metal accumulation in extracellular sites, even when the metals were present at relatively high concentrations, whereas the uptake of metals within cells was much less affected by pH.