Effect of dissolved organic matter and bacteria on contaminant transport in riverbank filtration

A mathematical model for the transport of hydrophobic organic contaminants in an aquifer under simplistic riverbank filtration conditions is developed. The model considers a situation where contaminants are present together with dissolved organic matter (DOM) and bacteria. The aquifer is conceptualized as a four-phase system: two mobile colloidal phases, an aqueous phase, and a stationary solid phase. An equilibrium approach is used to describe the interactions of contaminants with DOM, bacteria, and solid matrix. The model is composed of bacterial transport equation and contaminant transport equation. Numerical simulations are performed to examine the contaminant transport behavior in the presence of DOM and bacteria. The simulation results illustrate that contaminant transport is enhanced markedly in the presence of DOM and bacteria, and the impact of DOM on contaminant mobility is greater than that of bacteria under examined conditions. Sensitivity analysis demonstrates that the model is sensitive to changes of three lumped parameters: K+1 (total affinity of stationary solid phase to contaminants), K+2 (total affinity of DOM to contaminants), and K+3 (total affinity of bacteria to contaminants). In a situation where contaminants exist simultaneously with DOM and bacteria, contaminant transport is mainly affected by a ratio of K+1/K+2/K+3, which can vary with changes of equilibrium distribution coefficient of contaminants and/or colloidal concentrations. In riverbank filtration, the influence of DOM and bacteria on the transport behavior of contaminants should be accounted to accurately predict the contaminant mobility.     

A simple approach to modeling microbial biomass in the rhizosphere

Microorganisms make an important contribution to the degradation of contaminants in bioremediation as well as in phytoremediation. An accurate estimation of microbial concentrations in the soil would be valuable in predicting contaminant dissipation during various bioremediation processes. A simple modeling approach to quantify the microbial biomass in the rhizosphere was developed in this study. Experiments were conducted using field column lysimeters planted with Eastern gamagrass. The microbial biomass concentrations from the rhizosphere soil, bulk soil, and unplanted soil were monitored for six months using an incubation–fumigation method. The proposed model was applied to the field microbial biomass data and good correlation between simulated and experimental data was achieved. The results indicate that plants increase microbial concentrations in the soil by providing root exudates as growth substrates for microorganisms. Since plant roots are initially small and do not produce large quantities of exudates when first seeded, the addition of exogenous substrates may be needed to increase initial microbial concentrations at the start of phytoremediation projects.     

A micromodel analysis of factors influencing NAPL removal by surfactant foam flooding

A methodology to study the trichloroethylene (TCE) and dodecane removal in porous media by surfactant foams (SF) was presented by using etched-glass micromodels. The purpose of this work was to systematically evaluate the impact of various physicochemical factors such as gas fraction (GF), surfactant concentration, pore structure and nonaqueous phase liquid (NAPL) types on NAPL removal during SF flooding. The TCE displacement by SF was dependent on the gas fraction of SF. Low GFs (50% and 66%) were more efficient for TCE removal and sweep efficiencies than a high GF (85%). An increase in TCE removal was observed with increasing surfactant concentration at a fixed GF. TCE removal by SF flooding appeared to be dependent more to the value of Capillary number rather than to the concentration of surfactant solution. The effect of the pore heterogeneity was evaluated by employing two different types of micromodels. The Capillary number is an important parameter in the determination of sweep efficiency or gas saturation of SF in a nonhomogeneous porous medium. However, the TCE removal from a nonhomogeneous porous medium may not be associated with sweep efficiency. The initial configuration of residual TCE blobs in a nonhomogeneous porous medium would also be influential in displacing TCE. Sweep efficiencies and pressure responses of two NAPL systems (TCE and dodecane) were monitored to evaluate foam stability when the foam contacts the NAPLs. Stable foam contacting with TCE is implied, while it appears that dodecane cause the SF to collapse. All results indicate that the Capillary number (a ratio of viscous forces to capillary forces) is the most important parameter for TCE removal by SF flooding. Micromodel visualizations of water, surfactant and SF floods were showed and also discussed.     

Determination of some organochlorine pesticide residues in honeys from Konya, Turkey

In this study, 24 organochlorine pesticide residues in 109 different honey samples collected from stores and open markets in Konya, Turkey were analyzed by gas chromatography-electron capture detection. Aldrin, cis-chlordane, trans-chlordane, oxy-chlordane, 2,4^′ -DDE, and 4,4^′ -DDE were found in all honey samples. The mean value was 0.0540 μg g^???1 for oxy-chlordane. In the 55 samples of 109, levels of organochlorine pesticide residues of oxy-chlordane were determined as higher than those of Turkish Alimentarius Codex maximum residual limits (MRLs). Other organochlorine pesticide residues also exceeded MRLs except for cis-heptachlor epoxide and α-hexachlorocyclohexane. Since all of the honey samples are found contaminated and most of these samples exceeded MRLs, a control of organochlorine pesticide residues in honey is necessary for consumer health.     

Phytoremediation of landfill leachate using Pennisetum clandestinum

Landfills are still the most widely used solid waste disposal method used across the world. Leachate generated from landfill areas exerts environmental risks mostly on surface and groundwater, with its high pollutant content, most notably metals, which cause an unbearable lower water quality. During dumping or after the capacity of the landfill has been reached, a decontamination and remediation program should be taken for the area. This study was conducted to assess the capacity and efficiency of Pennisetum clandestinum, a prostrate perennial plant, to accumulate chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), zinc (Zn) and lead (Pb). Leachate, taken from the Sofulu Landfill Site, was given to Pennisetum clandestinum for 180 days, in 3 dilution sets as 1/1, 1/2 and 1/4, in batch configuration. An additional control set was also installed for comparison. Results showed that, even though the metal content of soil had risen, plants accumulated 2 to 8.5 times higher concentrations than the control set. It is important to see, the plant showed almost no stress symptoms even if the set was fed by pure leachate. Pennisetum clandestinum was observed to accumulate metals mostly in the upper bodies, excluding Fe and Cu. 76% of accumulated Cr, 85% of Ni, 66% of Zn and 100% of Pb was observed to accumulate in above-ground parts, where only 20% of Cu and 4% of Fe was accumulated. Due to the high pollution tolerance of Pennisetum clandestinum, makes this plant suitable for decontamination and remediation of landfill sites.     

Gel barrier formation in unsaturated porous media

The gel barrier formation by a gelling liquid (Colloidal Silica) injection in an unsaturated porous medium is investigated by developing a mathematical model and conducting numerical simulations. Gelation process is initiated by adding electrolytes such as NaCl, and the gel phase consisting of cross-linked colloidal silica particles grows as the gelation process proceeds. The mathematical model describing the transport and gelation of Colloidal Silica (CS) is based on coupled mass balance equations for the gel mixture (the sol phase plus the gel phase), gel phase (cross-linked colloidal silica particles plus water captured between cross-linked particles), and colloidal silica particles (discrete and cross-linked) and NaCl in the sol (suspension of discrete colloidal silica particles in water) and gel phases. The solutions in terms of volumetric fraction of the gel phase yield the gel mixture viscosity via the dependency on the volumetric fraction of gel phase. This dependency is determined from a kinetic gelation model with time-normalized viscosity curves. The proposed model is verified by comparing experimentally and numerically determined hydraulic conductivities of gel-treated soil columns at different CS injection volumes. The numerical experiments indicate that an impermeable gel layer is formed within the time period twice the gel-point in a one-dimensional flow system. At the same normalized time corresponding to twice the gel-point, the CS solutions with lower NaCl concentrations result in further migration and poor performance in plugging the pore space. The viscosity computation proposed in this study is compared with another method available in the literature. It is observed that the other method estimates the viscosity at the mixing zone higher than the one proposed by the authors. The proposed model can simulate realistic injection scenarios with various combinations of operating parameters such as NaCl concentration and NaCl mixing time, and thus providing guidelines in performing this technology on site.     

The impact of recycled coarse aggregates obtained from waste concretes on lightweight pervious concrete properties

Environmental Science and Pollution Research - Significant environmental damage can result from the use of natural resources such as cement, aggregate, and water in concrete production. Thus, more...     

Geological and technical characterisation of Iscehisar (Afyon-Turkey) marble deposits and the impact of marble waste on environmental pollution

Turkey, due to its location in the Alpine-Himalayan belt, has numerous marble deposits. More than 250 marble types with different colours and patterns have been produced from these deposits and one hundred of these are well known around the world. One such well-known marble type is Afyon-Iscehisar. Afyon-Iscehisar is Palaeozoic in age and has been quarried since the era of the Roman empire. The Afyon region is known as one of the most important marble production and processing centres in Turkey. The Afyon province, which possesses 3.5% of exploitable marble reserves (3,872,000,000 tonne) in Turkey, yields 9% of the total marble block production. The 409 marble processing plants in Afyon produce 19% of the total slab in Turkey. As a result of marble production activities, approximately 340,000 tonne of marble waste has accumulated in the area. While some of these unshaped marble blocks are re-used and returned to the economy, the majority are discarded. There are two waste marble storage fields located in the Afyon-Iscehisar region. All of the solid and fine-grained marble waste is stored in waste marble storage fields in Susuz Bo?az? and in the nearby Iscehisar marble quarries. The ecological effects of the marble waste, which were once discharged everywhere and exhibited visual pollution, has now been reduced to a minimal level.     

Treatment of Basic Red 29 dye solution using iron-aluminum electrode pairs by electrocoagulation and electro-Fenton methods

The aim of this study is the treatment of Basic Red 29 (BR29) dye solution using hybrid iron-aluminum electrodes by electrocoagulation and electro-Fenton methods. The effect of current density, initial pH, supporting electrolyte, H₂O₂, and initial dye concentration on dye removal efficiency was investigated, and the best experimental conditions were obtained. Time-coarse variation of UV-Vis spectra and toxicity and chemical oxygen demand (COD) removal were also examined at the best experimental conditions. Both systems were found very successful for the removal of BR29 dye. The removal efficiency of >95 % for BR29 dye solution was reached easily in a short time. At the best experimental conditions, for the initial BR29 concentration of 100 mg/L, >95 % BR29 dye and 71.43 % COD removal were obtained after 20 and 40 min of electrolysis, respectively. Additionally, toxicity results for electro-Fenton treatment of 100 mg/L BR29 were also very promising. According to the results obtained, although electro-Fenton is more effective, both systems can be used successfully to treat textile wastewater including dyes.