Performance of biochar-based filtration bed for the removal of Cr(VI) from pre-treated synthetic tannery wastewater.

In the present study, the performance of biochar-based filtration bed was assessed to enhance the removal efficiency of Cr(VI), from the pre-treated synthetic tannery wastewater. The pre-treatment of wastewater was carried out with aluminium formate (AF) as a coagulant and 80% Cr(VI) removal was observed which might be due to the formation of carboxylic complexation reaction. The purity of coagulant and the sludge components were validated with XRD analysis and the results revealed the formation of pure aluminium formate compound as well as a clear change in the crystalline structure in the treated sludge. FT-IR spectra demonstrated the carboxylic compound participated in the removal of Cr(VI) during the coagulation process. The pre-treated wastewater having 20 mg/L (residual) Cr(VI) was passed through a three-layered filtration bed containing biochar, which showed complete removal of Cr(VI) ∼ 99.99% by precipitating into bind form under the influence of CaCO3 and formate ions. The possible mechanistic approach might be due to the presence of formate ions in the pre-treated wastewater, the precipitation of Cr(VI) occurred in the form of Cr(OH)2 by the release of bicarbonate (HCO3-), carbonate ion (CO3 2-) and hydroxide (OH-) ions in the filtration bed. The properties of the biochar were investigated by XRD and FTIR analysis and the results revealed the existence of hydroxyl, carboxyl and carbonyl groups, which participated during the removal of Cr(VI). The results suggest that biochar-based filtration bed could be a promising method for the treatment of pre-treated tannery wastewater.

An experimental approach for the utilization of tannery sludge-derived Bacillus strain for biosorptive removal of Cr(VI)-contaminated wastewater.

Biosorption efficacy of Bacillus strain DPAML065, isolated from the tannery sludge, was appraised for the removal of toxic hexavalent chromium (VI) ions from synthetic wastewater. Effects of the process variable on biosorbent surface by variation in pH, metal Cr(VI) concentration and retention time were examined using batch experiments. The isolated Bacillus strain biosorbent was studied for its morphology and surface chemistry through FE-SEM, EDX and FTIR. It discloses that, the reduction mechanism of Cr(VI) during the process is mainly attributed to precipitation in addition to the functional groups (such as -COOH, -OH, C-O, P=O) present on the cellular matrix of Bacillus. Biochemical tests and 16s rRNA sequencing were also performed to identify the biosorbent at the genus level. A 95% Cr(VI) removal efficiency was procured by Bacillus strain DPAML065 biosorbent at pH 6, incubation period 24 h, 80 mg/L initial feed concentration and operational temperature 35 °C. Equilibrium behaviour of chromium binding follows the Langmuir isotherm model (R2 = 0.968) with an adsorption capacity of 106.38 mg/g. Kinetic modelling disseminates that biosorption of Cr(VI) ions by Bacillus strain DPAML065 obeyed pseudo-second-order model (R2 = 0.984) rather than the pseudo-first-order model. Concisely, the results indicate that the Bacillus strain DPAML065 is a potential, economically feasible and eco-friendly biosorbent which can be effectively used for removal of chromium (VI) from wastewater.

Comprehensive review on wastewater discharged from the coal-related industries - characteristics and treatment strategies.

Wastewaters discharged from various coal-related activities deteriorate fresh water quality and inflict possibilities of groundwater contamination. Their characteristics mostly depend on the parent coal properties, though some of the pollutants are cyanide, thiocyanate, ammonia, phenol, heavy metals and suspended solids. This paper has reviewed the treatment techniques along with the characteristics of all such kinds of wastewater and also identified the challenges and future perspectives. Primarily, demineralization of coal can attenuate and control release of pollutants in wastewaters if implemented successfully. Mine water from non-lignite mines can be purified using simple techniques, for its reutilization. Acidic mine water and leachates can be treated using passive bioreactors with microbial activity, different organic substrates and limestone drains. Additionally bio-electrochemical systems, membranes, macrocapsules, zeolite filters, ores, physical barriers, and aquatic plants can also be used at various stages. Coal washery wastewater can be treated using natural coagulants obtained from plant extracts along with conventional coagulants. Nitrification and denitrification bacteria fixed in reactors along with activated carbon and zero-valent iron can treat coke oven wastewater. Some other sophisticated techniques are vacuum distillation, super critical oxidation, nanofiltration and reverse osmosis. Practical use of these methods, wisely in an integrated way, can reduce freshwater consumption.