Water quality analysis of mixtures obtained from tannery waste effluents

Quantification of Tl (I) and Tl (III) based on microcolumn separation through ICP-MS in river sediment pore water

Thallium (Tl) is a typical toxic element, whose biological effects and geochemical behavior are closely related with its chemical speciation in the environment. In this context, the objective of the present study was to develope an effective method for separation of Tl (I) and Tl (III) based on solid-phase extraction (SPE) using anion exchange resin AG1-X8 as a sorbent and ICP-MS measurement. In this proposed method, Tl (I) and Tl (III) could be separated by selective adsorption of Tl (III)-DTPA in the resin, while Tl (III) was eluted by the solution mixed with HCl and SO₂. The validity of this method was confirmed by assays of standard solutions of Tl (I) and Tl (III), as well as with spike of contaminated samples. The present study results revealed that higher concentration of Tl (I) (245.48 μg/l) and Tl (III) (20.92 μg/l) had been found near the acid mine drainage (AMD) sample of sediment pore water. The results revealed that Tl (I) of 61.47 μg/l and Tl (III) of 9.73 μg/l were present in the river water contaminated by acid mine drainage. This thallium speciation analysis implied that the dominant Tl (I) species in the river water studied might be due to the weathering of sulfide mineral-bearing rocks, mining, and smelting activities in the studied area.

Chromium speciation in tannery effluent after alkaline precipitation: Isolation and characterization

It is difficult to completely remove Cr(III) from tannery effluent by alkaline precipitation due to the abundance of strong organic ligands. Thereby, the speciation of the residual Cr after alkaline precipitation is of crucial significance to guide the selection and design of further treatment process. For the first time, we revealed the speciation of the residual Cr with the aid of comprehensive analytical techniques. Results showed that the residual Cr(III) mostly located in two size ranges, i.e. the 13-100nm fraction and the <4nm fraction. Combined spectral analyses demonstrated Cr(III) was coordinated by carboxyl groups or hydroxyl groups in both fractions, while the complexation by nitrogen-containing groups was excluded by the total nitrogen and UPLC-MS analysis in the two fractions, respectively. Based on the comprehensive analyses, the structures of Cr(III) complexes in both fractions were proposed. Cr(III) cross-linked the carboxyl groups from polyacrylic acid chains to form the network gel structure in the 13-100nm fraction, while the complex structure of Cr(III) in the <4nm fraction was formed through hydroxyl-carboxyl chelation by masking agents such as tartrate and citrate. Although polyoxyethylene ether was abundantly present, it was responsible for the complexation of Cr(III) in neither fraction.

Chromium Distribution and Spatial Variations in the Finer Sediment Grain Size Fraction and Unfractioned Surficial Sediments on Nyanza Gulf, of Lake Victoria (East Africa)

Surficial sediments collected from the Nyanza Gulf of Lake Victoria (East Africa) were used to determine spatial concentrations of Cr and determine differences in contents of the unfractioned (whole sediment) and the finer grain size sediments, establishing any changes in Cr enrichment and potential ecological risks using sediment quality guidelines. A single pollution index was also used to evaluate level of Cr contamination. The spatial mean Cr contents in the <63 µm (silt-clay) fraction were found to be significantly lower than those in the unfractioned sediments, but with a strong linear positive correlation. The study results show decreasing spatial amounts of Cr in surficial sediments of the Nyanza Gulf, when compared to a study done 20 years earlier. However, the 95% confidence limits of the overall mean Cr in unfractioned sediments exceed the threshold effect concentration (TEC), indicating the potential for Cr remobilization from sediments. In general the sediment enrichment is evidence of possible dominance of lithogenous sources of Cr in the surface lake sediments, with potential anthropogenic sources from the drainage system and nearshore urban areas. The sediments are unpolluted with respect to geoaccumulation index, and sediment enrichment factors suggest a minor to moderate enrichment of Cr in surficial sediments of three sites around the Nyanza Gulf zones and around the river mouth in the main lake.

Cytotoxicity assays to evaluate tannery effluents treated by photoelectrooxidation

The advanced oxidation process (AOP) is used to increase the treatment efficiency of effluents however, it is necessary to compare the toxicity of treated and untreated effluents to evaluate if the decontamination process does not cause any biological harm. Cultured cells have been previously used to assess the genotoxic and cytotoxic potential of various compounds. Hence, the aim of this work was to assess the applicability of cytotoxicity assays to evaluate the toxicity related to the AOP treatment. Samples of an industrial effluent were collected after their treatment by a conventional method. Cytotoxicity of standard and AOP treated effluents was assessed in CRIB and HEp-2 cell line using the MTT and neutral red assays. We observed decrease at cell viability in the both assays (50% MTT and 13% NRU) when cells were exposed to the AOP treatment in the highest concentration. Thus, cytotoxic assays in cultured cells can be explored as an useful method to evaluate toxicity as well as to optimize effluents treatment process.

Water for human and livestock consumption in rural settings of Ethiopia: assessments of quality and health aspects

The study aimed to assess the quality and health aspects of water intended for human and livestock consumption in two rural districts of the Rift Valley of Ethiopia. The study involved two parts: the first consisted of a questionnaire survey and farmers' group discussions, complemented by secondary health data, and the second part determined the chemical (total dissolved solids, pH, manganese, hexa-valent chromium, fluoride) and microbiological quality of different water sources during dry and wet seasons. The result showed a lack of sustainable access to safe water in the communities. Industrial pollution and mismanagement of water sources by human and livestock was found to be a source of potential health risk. Potentially linked human health problems like malaria, diarrhoea and gastrointestinal parasites were common in the districts. Overall, 76% of the assessed water sources (n = 25) failed to comply with World Health Organization guidelines for human drinking water, for at least one assessed parameter, mostly irrespective of the season. The non-compliance was mainly attributed to Escherichia coli contamination and/or high fluoride concentration. At least 20% of the water samples were also found to be unfit for livestock consumption based on assessed chemical parameters in both dry and wet seasons. To minimize the health risk associated with mismanagement and poor quality of water sources in the area, targeted action in the protection of surface water sources should be given priority.

Delineating shallow saline groundwater zones from Southern India using geophysical indicators

A geophysical survey was conducted over an industrial belt encompassing 80 functional leather factories in Southern India. These factories discharge untreated effluents which pollute shallow groundwater where electrical conductivity (EC) value had a wide range between 545 and 26,600 μS/cm (mean, 3, 901 μS/cm). The ranges of Na(+) and Cl(-) ions were from 46 to 4,850 mg/L (mean, 348 mg/L) and 25 to 10,390 mg/L (mean, 1,079 mg/L), respectively. Geoelectrical layer parameters of 37 vertical electrical soundings were analyzed to demarcate fresh and saline water zones. However, the analysis not did lead to a unique resolution of saline and fresh waters. It was difficult to assign a definitive value to the aquifer resistivity of any area. Thus, geophysical indicators, namely longitudinal unit conductance (S), transverse unit resistance (T), and average longitudinal resistivity (Rs), were calculated for identifying fresh and saline waters. Spatial distributions of S, T, and R s reflected widely varying ranges for the saline and fresh water zones. Further, the empirical relation of formation factor (F) was established from pore-water resistivity and aquifer resistivity for fresh and saline aquifers, which may be used to estimate local EC values from the aquifer resistivity, where well water is not available.

Performance of pilot-scale constructed wetlands for secondary treatment of chromium-bearing tannery wastewaters

Tannery operations consist of converting raw animal skins into leather through a series of complex water- and chemically-intensive batch processes. Even when conventional primary treatment is supplemented with chemicals, the wastewater requires some form of biological treatment to enable the safe disposal to the natural environment. Thus, there is a need for the adoption of low cost, reliable, and easy-to-operate alternative secondary treatment processes. This paper reports the findings of two pilot-scale wetlands for the secondary treatment of primary effluents from a full tannery operation in terms of resilience (i.e., ability to produce consistent effluent quality in spite of variable influent loads) and reliability (i.e., ability to cope with sporadic shock loads) when treating this hazardous effluent. Areal mass removal rates of 77.1 g COD/m2/d, 11 g TSS/m2/d, and 53 mg Cr/m2/d were achieved with a simple gravity-flow horizontal subsurface flow unit operating at hydraulic loading rates of as much as 10 cm/d. Based on the findings, a full-scale wetland was sized to treat all the effluent from the tannery requiring 68% more land than would have been assumed based on literature values. Constructed wetlands can offer treatment plant resilience for minimum operational input and reliable effluent quality when biologically treating primary effluents from tannery operations.

Chromium speciation in river sediment pore water contaminated by tannery effluent

Cr(VI) is far more soluble and toxic than Cr(III). Sediment pore water was investigated in a river adjacent to the property of a large former tannery, into which Cr-contaminated effluent was discharged over a 55-year period, and where extremely high Cr concentrations have been found in the sediments. Dialysis cells, or peepers, were used to generate depth profiles of Cr concentration in sediment pore water. Samples were analyzed for total Cr using inductively coupled plasma-mass spectrometry (ICP-MS) and for Cr species using high performance liquid chromatography (HPLC)-ICP-MS. The results show an absence of Cr(VI) in all samples. Furthermore, incomplete recovery of Cr(VI) added to the samples collected at the locations with highest sediment Cr concentrations indicate strong reducing conditions at those locations, which are not conducive to the presence of Cr(VI).

Study of Chromium Removal by the Electrodialysis of Tannery and Metal-Finishing Effluents

The metal-finishing and tannery industries have been under strong pressure to replace their current wastewater treatment based on a physicochemical process. The electrodialysis process is becoming an interesting alternative for wastewater treatment. Electrodialysis is a membrane separation technique, in which ions are transported from one solution to another through ion-exchange membranes, using an electric field as the driving force. Blends of polystyrene and polyaniline were obtained in order to produce membranes for electrodialysis. The produced membranes were applied in the recovery of baths from the metal-finishing and tannery industries. The parameter for electrodialysis evaluation was the percentage of chromium extraction. The results obtained using these membranes were compared to those obtained with the commercial membrane Nafion 450.

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination--a review

Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.

Analysis of the environmental impact on a stream: is only tannery to blame?

The contribution of wastewater from a tannery industry to the pollution of a stream was investigated. The main parameters studied were biochemical oxygen demand, chemical oxygen demand, chromium, dissolved oxygen, fecal and total coliforms, nitrogen, oils and greases, pH, phosphorous, sulfides, suspended solids, turbidity, and volatile solids. Three sampling points were located: (1) at the discharge point of tannery wastewater, (2) 50 m upstream, and (3) 80 m downstream of discharge point. Also was investigated the pollution at the stream source.

Evaluation of chromium contamination in water, sediment and vegetation caused by the tannery of Jijel (Algeria): a case study

In order to evaluate the chromium (Cr) contamination due to the discharge of waste waters from the tannery of Jijel in the Mouttas river (Algeria), samples of water, sediment and vegetation (Agropyrum repens) were collected during a 6 month period in four stations located upstream (control) and downstream of the tannery. The total chromium was measured by atomic absorption spectrophotometry. Metal inputs were clearly related to effluent discharges from the tannery into the river. Although only traces of chromium were found in water samples upstream of the tannery, very high concentrations (up to 860 times higher) were detected downstream. The contamination was not limited to water of Mouttas River because a same difference in chromium concentrations was also found in sediments and plants Agropyrum repens that were sampled upstream and downstream of the tannery. This work showed that the treatment process used in the wastewater treatment plant of the tannery of Jijel is not able to remove the chromium detected in their influents. The occurrence and chromium levels detected in the aquatic environment represent a major problem concerning drinking water resources and environmental protection of water bodies.

Electrochemical treatment of tannery wastewater using DSA electrodes

In this work we studied the electrochemical treatment of a tannery wastewater using dimensionally stable anodes (DSA) containing tin, iridium, ruthenium, and titanium. The electrodes were prepared by thermal decomposition of the polymeric precursors. The electrolyses were performed under galvanostatic conditions, at room temperature. Effects of the oxide composition, current density, and effluent conductivity were investigated, and the current efficiency was calculated as a function of the time for the performed electrolyses. Results showed that all the studied electrodes led to a decrease in the content of both total phenolic compounds and total organic carbon (TOC), as well as lower absorbance in the UV-vis region. Toxicity tests using Daphnia similis demonstrated that the electrochemical treatment reduced the wastewater toxicity. The use of DSA type electrodes in the electrochemical treatment of tannery wastewater proved to be useful since it can promote a decrease in total phenolic compounds, TOC, absorbance, and toxicity.

EDTA excess Zn(II) back-titration in the presence of 4-(2-pyridylazo)-resorcinol indicator and naphthol green beta as inert dye for determining Cr(III) as Cr(III)/EDTA complex: application of the method to a leather industry wastewater

The colour changes of 4-(2-pyridylazo)-resorcinol and naphthol green beta as new screening metallochromic indicator in back-titration of EDTA excess with Zn(II) to determine Cr(III)/EDTA complex was investigated with the help of tristimulus colorimetry. Specific colour discrimination (SCD) and L*, a*, b* 1976 parameters were successfully applied to evaluate the quality of colour transition at the end-point in non-alkaline media and in the presence of Zn(II) and Ca(II) which resulted in non-interfering species at 1x10(-3) M and 2x10(-3) M, respectively. The above concentrations are comparable with those used for Cr(III). Validation of the fast and accurate reported method was performed by atomic absorption spectroscopy. Moreover, the method was applied for determining Cr as Cr(III) in a wastewater effluent deriving from a leather industry.

Phytoremediation of chromium by model constructed wetland

Chromium is a pollutant present in tannery wastewater, its removal is necessary for protection of the environment. Penisetum purpureum, Brachiaria decumbens and Phragmites australis were grown hydroponically in experimental gravel beds to determine their potential for the phytoremediation of solutions containing 10 and 20 mg Cr dm(-3). These concentrations, similar to tannery wastewater after initial physico-chemical treatment were used with the aim of developing an economic secondary treatment to protect the environment. All the systems achieved removal efficiencies of 97-99.6% within 24 h. P. purpureum and B. decumbens removed 78.1% and 68.5% respectively within the first hour. Both P. purpureum and B. decumbens were tolerant of the concentrations of chromium applied, but P. purpureum showed the greatest potential because its faster growth and larger biomass achieved a much greater chromium removal over the whole length of time of the experiment.