Fluvial responses towards the tannery effluent: Tracing the anthropogenic foot-prints

Tannery-effluent is one of the top-ranked hazardous waste which is generally discharged into the river. To study the fluvial response toward the tannery-effluents and to trace anthropogenic foot-prints in the fluvial-system, a suite of systematically collected sediment and water samples were analyzed for radioactive (226Ra, 232Th, and 40K) and non-radioactive elements (Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb). Neutron activation analysis and atomic absorption spectroscopy were used for elemental analysis, whereas HPGe-gamma-detector was used for measuring the primordial-radionuclides. Ranges of Cr-abundances in sediment and water were 63-4373 μg.g-1 and 15.6-52.2 μg.L-1, respectively which were ∼4-14 times higher than the geological background. Radioactivity concentrations of 226Ra, 232Th, and 40K ranged from 17.7-48.5, 36.1-81.6, and 687-1041 Bq.kg-1, respectively which were significantly depleted in effluent discharge point. Hence, primordial-radionuclides were used as natural tracers for tracing anthropogenic foot-prints which were explained in terms of dilution effect, redox environment and differential geo-environmental events/characteristics. From statistical-approaches and geochemical reasoning, elemental sources and responses in fluvial system were explored. Surprisingly, ecological & radiological risks were reduced while sediment quality guideline-based ecotoxicity & water-mediated health risks were increased by the incorporation of tannery effluents. This study describes the sedimentary response toward the received tannery effluents which is particularly explored by the primordial radionuclides.

Electrochemical conversion of chromium from tannery effluents for potential reuse in industrial applications

Electrochemical oxidation of trivalent chromium from leather tanning mud waste leachates (containing ca 6 g^.L^-1 Cr(III)) to its hexavalent form was carried out using a PbO_x/Pb anode electrode in a prototype small (0.4 L) cylindrical batch electrochemical reactor. The PbO_x/Pb anode was prepared by electrochemical anodization at constant current (75 mA cm^-2 for 30 min) in a sulfuric acid solution and characterized by the cyclic voltammetry technique to investigate the effect of pH on the process. It was found that at pH = 3, Cr(III) oxidation prevails over the competing water oxidation-oxygen evolution reaction (OER), hence increasing the efficiency of the process. A detailed study of pH (0-3), current density (12-24 mA cm^-2), and cell type (divided-undivided) effects on bulk electrolysis of Cr(III) leachates in the batch prototype reactor resulted in process optimization. At pH = 3, 12 mA cm^-2 and a cathode inserted in a porous diaphragm envelope, nearly 70% conversion was achieved at a nearly 60% current efficiency, among the highest in the previously reported literature. The method (further optimized with an ion-selective membrane separator) could offer an attractive route for tannery Cr(III) conversion to Cr(VI) for reuse as an etchant or electroplating agent.

Isolation and characterization of chromium (VI) tolerant bacteria from tannery effluents

BACKGROUND

The tannery industry is a potent environment polluting agent worldwide. Chromium (VI) is a major heavy metal in tannery effluents and their accumulation in soil and water is a serious environmental problem. This study investigates the capacity of indigenous bacteria isolated from tannery effluents for tolerance to chromium (VI).

METHODS

The chromium tolerance of isolates assessed through both agar dilution and broth microdilution methods. Isolates were identified by morphological and biochemical analysis. The tolerance of isolates to cadmium, nickel, lead, and vanadium and also their multidrug-resistant (MDR) profile were determined. Then the top isolate was characterized via 16S rRNA sequencing and its growth temperature and pH were optimized. Finally, the kinetic of chromium biosorption and chromium removal efficiency was determined using a Nutrient broth medium and wastewater containing 20 mg/L chromium, respectively.

RESULTS

Of 32 screened chromium tolerant isolates, 14 isolates with higher chromium tolerance were selected for further study. 78.57% of isolates represented simultaneous MDR and Multi Heavy Metal tolerance (MHMT) phenotypes and MDR indices of 0.2-1 indicating their source from niches with high antibiotic contamination. However, there was no significant correlation between MDR and MHMT phenotypes among isolates. The top isolate was identified as Lactococcus lactis and showed optimal growth at pH 6 and 25 °C. The maximum chromium biosorption occurred at the end of the exponential phase upon optimized conditions and the approximate chromium removal efficiency of 52.5% was obtained.

CONCLUSION

The isolated bacteria specifically L. lactis after more evaluations, may show the potential for bioremediation of chromium from tannery effluents.

Treatment of tannery effluent by chemical coagulation combined with batch-recirculated electro-oxidation at different anode materials

The aim of this work was to evaluate the pollutant load from tannery effluents treated by chemical coagulation (CC) followed by electro-oxidation (EO), performed in two different experimental batch-recirculated setups, one with a BDD anode and the other with Ti/Pt/PbO₂ and Ti/Pt/SnO₂-Sb₂O₄ anodes (PS). Results were compared with those obtained from EO of the raw sample. CC was performed with a Fe³⁺ concentration of 0.25 g L^-1, and the applied current densities for EO in each setup were 60 mA cm^-2 for BDD and, in the PS setup, 20 and 40 mA cm^-2 for Ti/Pt/SnO₂-Sb₂O₄ and Ti/Pt/PbO₂, respectively. During CC, removals of 27% in chemical oxygen demand (COD), 14% in total nitrogen, 100% in sulfide, and 73% in Cr(VI) were observed. COD removal in the EO of the raw sample was higher than that obtained for the combined CC + EO, for both setups, showing that the organic compounds removed by CC are mainly those that would be more easily removed by EO. For most of the other parameters related with carbon and nitrogen, the removals for CC + EO were higher than for EO alone. During EO, sulfide is converted to sulfate, especially with BDD. Concerning Cr(VI) concentration, it increases during EO, in particular for PS setup. Combined treatment, with both setups, proved to be an effective choice to treat tannery effluents.

The use of Callitriche cophocarpa Sendtn. for the reclamation of Cr-contaminated freshwater habitat: benefits and limitations

This work is the first attempt to evaluate suitability of Callitriche cophocarpa Sendtn. (water-starwort) to remove Cr under real-world conditions. Our earlier laboratory-scale studies demonstrated outstanding hyperaccumulation properties of this aquatic higher plant (macrophyte) toward chromium in solution. We introduced C. cophocarpa plants into the watershed with sediments heavily polluted (on average 1400 mg/kg d.w. of Cr) by a tannery. The plants grew vigorously and exhibited no physiological or anatomical disorders. Based on chemical fractionations of bottom sediments, we found low Cr bioavailability. The element was strongly associated with the sediments and could be classified into the following fractions (%): oxidizable III (68.2) > residual IV (28.8) > reducible II (1.6) > exchangeable I (1.4). Despite this, Cr content in plant organs at the contaminated sites was 33 up to 83 times greater than in the control leaf/stem and roots, respectively. Altering redox potential during, i.e., sediment deposition on land may change chemical forms of bound metals in a solid phase, and thus further increase Cr phytoextraction by plants. With this in mind, we concluded that the species, being an outstanding Cr accumulator under laboratory conditions, can be useful in the reclamation of Cr-polluted sediments under controlled, oxidizing conditions.

Chromium (VI) bioremediation potential of filamentous fungi isolated from Peruvian tannery industry effluents

The tannery is an important trade in various Peruvian regions; however, tannery effluents are a serious local environmental threat due to its highly toxics components and lack of efficient treatment. The untreated effluents produced by tannery factories in Arequipa Rio Seco Industrial Park (PIRS) have formed a lake in the region nearby. In this work, we study the capability of filamentous fungi species found in this effluents lake with potential for chromium (VI) bioremediation. Fourteen species of filamentous fungi were isolated; only two species were identified Penicillium citrinum and Trichoderma viride, and third strain identified as Penicillium sp. The filamentous fungi showed that are fully tolerant to chromium (VI) concentrations up to 100 mg/L. These fungal strains showed significant growth in chromium (VI) concentrations up to 250 mg/L. Tolerant index (TI) analysis revealed that P. citrinum and T. viride began adaptation to chromium (IV) concentrations of 250 and 500 mg/L, after 6 and 12 days, respectively. When exposed to higher Cr (VI) concentrations (1000 mg/L), only T. viride was able to show growth (enhance phase). Interestingly, one of the significant responses from these fungal strains to increasing chromium (VI) concentrations was an increment in secreted laccase enzymes. Our results show tolerance and adaptation to elevated concentrations of chromium (VI) of these fungal strains suggesting their potential as effective agents for bioremediation of tannery effluents.

Modelling heavy metals in the Buriganga River System, Dhaka, Bangladesh: Impacts of tannery pollution control

Heavy metal pollution from tanneries is a global problem in many rapidly developing economies. Effluent discharges into rivers cause serious problems for water quality, damaging ecology and threatening the livelihoods of people, especially in developing urban centres which often have a high concentration of factories. The industry intensive capital area of Bangladesh is impacted with high levels of metals pollution in rivers in the Greater Dhaka Watershed. Sampling and modelling studies have been undertaken to assess pollution in the Buriganga River System in Dhaka. The process based, dynamic model INCA (Integrated Catchments) model has been used to simulate metals along the Buriganga River System in Central Dhaka. Observed and simulated metals concentrations are high, and the model shows that the proposed transfer of the tannery industry upstream helps to reduce the pollution significantly downstream. However, moving the industry upstream may be counterproductive as it is discharged into the upper reaches of the river. This will create pollution upstream unless the newly constructed effluent treatment system can operate at a high level.

Isolating, screening and applying chromium reducing bacteria to promote growth and yield of okra (Hibiscus esculentus L.) in chromium contaminated soils

Hexavalent chromium [Cr (VI)], extensively used in different industries, is one of the most toxic heavy metals. The Cr (VI) reducing bacteria could be helpful in decreasing its toxic effects. The present study was conducted to evaluate the potential of Cr (VI) reducing bacteria to improve growth and yield of okra (Hibiscus esculentus L.) in Cr-contaminated soils. Most of the selected bacterial isolates significantly increased the growth and yield of okra. Maximum response was observed in the plants inoculated with the isolate K12 where plant height, root length, fruit weight and number of fruits per plant increased up to 77.5 percent, 72.6 percent, 1.4 fold and 2.9 fold, respectively. Moreover, inoculation with bacteria caused significant decrease in Cr (VI) concentration in soil and plant parts across all treatments. The maximum decrease of 69.6, 56.1 and 40.0 percent in Cr (VI) concentrations in soil, plant vegetative parts and plant reproductive parts, respectively, was observed in the treatment inoculated with the strain K12. Based on amplification, sequencing and analysis of 16S rDNA sequence, the strain K12 was found belonging to genus Brucella and was designated as Brucella sp. K12. These findings suggest that the strain K12 may serve as a potential bioresource to improve crop production in Cr-contaminated soils.

Isolation and Characterization of Chromium(VI)-Reducing Bacteria from Tannery Effluents

Two chromium-resistant bacteria (IFR-2 and IFR-3) capable of reducing/transforming Cr(VI) to Cr(III) were isolated from tannery effluents. Isolates IFR-2 and IFR-3 were identified as Staphylococcus aureus and Pediococcus pentosaceus respectively by 16S rRNA gene sequence analyses. Both isolates can grow well on 2,000 mg/l Cr(VI) (as K(2)Cr(2)O(7)) in Luria-Bertani (LB) medium. Reduction of Cr(VI) was found to be growth-associated in both isolates and IFR-2 and IFR-3 reduced 20 mg/l Cr(VI) completely in 6 and 24 h respectively. The Cr(VI) reduction due to chromate reductase activity was detected in the culture supernatant and cell lysate but not at all in the cell extract supernatant of both isolates. Whole cells of IFR-2 and IFR-3 converted 24 and 30% of the initial Cr(VI) concentration (1 mg/l) in 45 min respectively at 37°C. NiCl(2) stimulated the growth of IFR-2 whereas HgCl(2) and CdCl(2) significantly inhibited the growth of both isolates. Optimum temperature and pH for growth of and Cr(VI) reduction by both isolates were found to be between 35 and 40°C and pH 7.0 to 8.0. The two bacterial isolates can be good candidates for detoxification of Cr(VI) in industrial effluents.