Chromium Discharge Research Articles

A Numerical Model for the Transport of Chromium and Fine Sediments

A mathematical model which represents the transport processes of heavy metals and fine sediments in a fluvial stream was developed. The model consists of a three-equation system: the first one for total chromium concentration in the water column, CTw, the second one for total suspended sediment concentration, Sw, and the third one for chromium concentration in bed sediments, r. The third equation represents the chromium exchange between the water column and bed sediments by two processes: diffusion of soluble chromium and erosion/deposition of chromium sorbed to sediments. The basic assumption of the model is the instantaneous equilibrium. The main parame- ters are the partition coefficients in the water column and bed sediments, the depth of the active bed sediment layer, and the mass transfer coefficient between the water column and sediment pore water. The numerical model approx- imates the equations of advection-dispersion for chromium in water and suspended sediments by using a Eulerian third-order scheme. Numerical vs. analytical solutions were considered satisfactory for different initial, boundary, and sedimentological conditions. In order to estimate the impact of a chromium side discharge, the model was implemented for the Salado River in a reach of 65.6-km long (Santa Fe, Argentina). The results showed the effect of chromium discharge on almost the whole reach, then the vulnerability of the water quality in the Salado River when the flow was low was evidenced. When comparing the computed and measured results, the former showed a reasonable repre- sentation of the presence of chromium in water and bed sediments.

Removal of Cr 3+ by electrocoagulation with multiple electrodes: Bipolar and monopolar configurations

Removal of Cr 3+ from aqueous solutions by electrocoagulation (EC) with multiple electrodes was studied with both bipolar and monopolar configurations. The influence of chloride ions, pH, initial Cr 3+ concentration and cell current on removal performance was investigated in a batch stirred cell. It was noted that, the enhancement of solubility of Cr(OH) 3 and co-precipitated [Cr, Fe](OH) 3 in presence of chloride ions results in reduction of removal efficiency. Removal of Cr 3+ improved at higher pH due to combined effect of precipitation, co-precipitation as solid solution like species, adsorption, cathodic reduction and sweep coagulation. The maximum Cr 3+ removal per unit charge loading was found to be increasing with increase in initial Cr 3+ concentration. The cell current efficiency was less than that predicted from Faraday's law of electrolysis for both configurations. The operating cost was estimated from the power cost and cost of electrode material. The former was 40% and the later was 43% higher for bipolar configuration compared to monopolar configuration for achieving final chromium discharge limit of 2.0 mg/l.

The dewatering of a mining sludge containing hexavalent chromium using a tubular filter press - a South African development

A chromium smelting process can result, under oxidising conditions, in the production of a dust which when slurried and pumped to a waste dump heap is likely to pollute the environment. South Africa is a large producer of chromium metal and the problem of the release of hexavalent chromium (Cr6+) to the environment is a serious concern. The department of Water Affairs and Forestry in South Africa monitors all environmental discharges and regulate the levels of toxic chemicals and pollutants. The ‘Tubular Filter Press’ a South African developed sludge dewatering system was proposed for the recovery of dust in this effluent. The filter press was operated for the dewatering of waterworks sludges and promises to be successful for this application. A single tube pilot study shows that chromium discharge to the environment can be eliminated. Feed solids concentrations of between 40 and 50 g/l were fed to the tubular filter resulting in cake solids concentrations in excess of 50%. The operating pressure of the system was between 200 and 300 kPa and the flux reduced to 200 L/m2.h during the filtration cycle. The filtration was modelled using a variable pressure, internal cylindrical compressible cake filtration model and operating parameters for a full scale plant were proposed.

The Electrodeposition of Cobalt–Chromium Alloys from Sulfate–Oxalate Solutions

The kinetics of separate and concurrent discharge of cobalt and chromium ions from sulfate–oxalate solutions is studied. Cobalt–chromium alloys with the cobalt content of 4 to 94% and carbon content of 1 to 4% are obtained. At a concurrent discharge of chromium and cobalt ions, the deposition potential of chromium is shifted by 150 to 200 mV in the positive direction. The shift depends on the current density and cannot be accounted for by the energy of mixing of the components. The alloying of chromium with cobalt decreases the overpotential of the hydrogen discharge. The codeposition with chromium did not decelerate the reduction of cobalt ions in contrast to the electrodeposition of nickel. The main reasons for the difference between the effect the alloying with chromium produces on the electrochemical reduction of nickel and cobalt, which are similar in their properties, are considered.

Effects of cadmium on salamander survival and limb regeneration

Chromium discharged in industrial effluents frequently occurs as an environmental pollutant, but the lethal and sub-lethal effects the heavy metal might cause in animals exposed to it have been insufficiently investigated. Selecting the amphibian Duttaphrynus melanostictus, we carried out laboratory tests to investigate the effects of short and long term exposure to hexavalent chromium (Cr(VI)) in both tadpoles and adult toads. The concentrations used were 0.002, 0.02, 0.2, 1.0 and 2.0 mg/L, the first three corresponding to field levels. In vitro exposures were also carried out using toad erythrocytes and Cr(VI) concentrations of 0.0015, 0.003, 0.015, 0.03, 0.15 mg/ L. Mortality, growth retardation, developmental delays and structural aberrations were noted in the metal-treated tadpoles, with increasing incidence corresponding to increase in Cr(VI) level and duration of exposure. Many of the sub-lethal effects were evident with long term exposure to environmentally relevant levels of the toxicant. Changes in selected blood parameters and erythrocyte morphometry were also detected in Cr(VI) exposed toads, indicating anaemic and leucopenic conditions. In the genotoxicity study, DNA damage indicated by comet assay and increased micronuclei frequency, occurred at the low Cr(VI) concentrations tested. The multiple deleterious effects of exposure to chromium signal the need for monitoring and controlling the discharge of chromium to the environment. The dose-dependency and genotoxic effects observed in this widely distributed Asian toad indicates its suitability for monitoring heavy metal pollution in aquatic systems.