Precipitate adsorbent was produced from aluminum tanning wastewater by alkali precipitation and characterized by XPF, XRD, and FTIR. The results showed that the main components of the precipitate were Al, Ti, and Zr. The adsorption equilibrium for Cr³⁺ on the precipitate was reached within 60 min. The precipitate had better removal for Cr³⁺ from wastewater at pH 7.0. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation, and the adsorption isotherm fitted to the Langmuir model very well. Co-existed cations (Na⁺, Ca²⁺) in aqueous solution restrained Cr³⁺ adsorption on the precipitate. The adsorption of Cr³⁺ on the precipitate was mainly through the complexation and ion-exchange mechanisms, and oxide may play a major role in Cr³⁺ adsorption process.

Three different combinations of treatment techniques, i.e. electrocoagulation combined with microfiltration (EMR), membrane bioreactor (MBR) and electrocoagulation integrated with membrane bioreactor (hybrid MBR, (HMBR)), were analysed and compared for the treatment of tannery wastewater operated for 7 days under the constant trans-membrane pressure of 5 kPa. HMBR was found to be most suitable in performance as well as fouling reduction, with 94 % of chemical oxygen demand (COD) removal, 100 % chromium removal and 8 % improvement in percentage reduction in permeate flux compared to MBR with only 90 % COD removal and 67 % chromium removal. The effect of mixed liquor suspended solids on fouling was also investigated and was found to be insignificant. EMR was capable of elevating the flux but was not as efficient as HMBR and MBR in COD removal. Fouling reduction by HMBR was further confirmed by SEM-EDX and particle size analysis.

Chromate-resistant bacterial strain isolated from the soil of tannery was studied for Cr(VI) bioaccumulation in free and immobilised cells to evaluate its applicability in chromium removal from aqueous solution. Based on the comparative analysis of the 16S rRNA gene, and phenotypic and biochemical characterization, this strain was identified as Paenibacillus xylanilyticus MR12. Mechanism of Cr adsorption was also ascertained by chemical modifications of the bacterial biomass followed by Fourier transform infrared spectroscopy analysis of the cell wall constituents. The equilibrium biosorption analysed using isotherms (Langmuir, Freundlich and Dubinin–Redushkevich) and kinetics models (pseudo-first-order, second-order and Weber–Morris) revealed that the Langmuir model best correlated to experimental data, and Weber–Morris equation well described Cr(VI) biosorption kinetics. Polyvinyl alcohol alginate immobilised cells had the highest Cr(VI) removal efficiency than that of free cells and could also be reused four times for Cr(VI) removal. Complete reduction of chromate in simulated effluent containing Cu²⁺, Mg²⁺, Mn²⁺ and Zn²⁺ by immobilised cells, demonstrated potential applications of a novel immobilised bacterial strain MR12, as a vital bioresource in Cr(VI) bioremediation technology.

This study presents simultaneous hexavalent chromium (Cr(VI)) reduction and phenol degradation using Stenotrophomonas sp., isolated from tannery effluent contaminated soil. Phenol was used as the sole carbon and energy source for Cr(VI) reduction. The optimization of different operating parameters was done using Placket-Burman design (PBD) and Box-Behnken design (BBD). The significant operating variables identified by PBD were initial Cr(VI) and phenol concentration, pH, temperature, and reaction time. These variables were optimized by a three-level BBD and the optimum initial Cr(VI) concentration, initial phenol concentration, pH, temperature, and reaction time obtained were 16.59 mg/l, 200.05 mg/l, 7.38, 31.96 °C and 4.07 days, respectively. Under the optimum conditions, 81.27 % Cr(VI) reduction and 100 % phenol degradation were observed experimentally. The results concluded that the Stenotrophomonas sp. could be used to decontaminate the effluents containing Cr(VI) and phenol effectively.

Preservation or curing of hides and skins is performed as the primary step of leather processing. Common salt is employed as the conventional agent for curing purpose. Use of salt enhances the pollution load of tannery effluent which becomes highly contaminated with increased total dissolved solids and chlorides. To overcome this hurdle, researchers are in constant search of alternative preservation techniques which are either totally void of salt or use only a meager amount of salt. In the present study, we had explored the possibility of using Semecarpus anacardium nut extract as an alternative to salt for the curing process by assessing different parameters like hair slip, putrefaction odor, volatile nitrogen content, moisture content, bacterial count, and shrinkage temperature in comparison to the salt curing method. The antibacterial property of the plant extract was also investigated. The results obtained substantiated that the nut extract of S. anacardium effectively could preserve the skins for more than a month, by its antibacterial activity along with the dehydrating property of acetone.

Click chemistry approaches are tailored to generate molecular building blocks quickly and reliably by joining small units together selectively and covalently, stably and irreversibly. The vegetable tannins such as hydrolyzable and condensed tannins are capable to produce rather stable radicals or inhibit the progress of radicals and are prone to oxidations such as photo and auto-oxidation, and their anti-oxidant nature is well known. A lot remains to be done to understand the extent of the variation of leather stability, color variation (lightening and darkening reaction of leather), and poor resistance to water uptake for prolonged periods. In the present study, we have reported click chemistry approaches to accelerated vegetable tanning processes based on periodates catalyzed formation of oxidized hydrolysable and condensed tannins for high exhaustion with improved properties. The distribution of oxidized vegetable tannin, the thermal stability such as shrinkage temperature (T ₛ) and denaturation temperature (T d), resistance to collagenolytic activities, and organoleptic properties of tanned leather as well as the evaluations of eco-friendly characteristics were investigated. Scanning electron microscopic analysis indicates the cross section of tightness of the leather. Differential scanning calorimetric analysis shows that the T d of leather is more than that of vegetable tanned or equal to aldehyde tanned one. The leathers exhibited fullness, softness, good color, and general appearance when compared to non-oxidized vegetable tannin. The developed process benefits from significant reduction in total solids and better biodegradability in the effluent, compared to non-oxidized vegetable tannins.

The rice-husk-based mesoporous activated carbon (MAC) used in this study was precarbonized and activated using phosphoric acid. N₂adsorption/desorption isotherm, X-ray powder diffraction, electron spin resonance, X-ray photoelectron spectroscopy and scanning electron microscopy, transmission electron microscopy,²⁹Si-NMR spectroscopy, and diffuse reflectance spectroscopy were used to characterize the MAC. The tannery wastewater carrying high total dissolved solids (TDS) discharged from leather industry lacks biodegradability despite the presence of dissolved protein. This paper demonstrates the application of free electron-rich MAC as heterogeneous catalyst along with Fenton reagent for the oxidation of persistence organic compounds in high TDS wastewater. The heterogeneous Fenton oxidation of the pretreated wastewater at optimum pH (3.5), H₂O₂(4 mmol/L), FeSO₄[Symbol: see text]7H₂O (0.2 mmol/L), and time (4 h) removed chemical oxygen demand, biochemical oxygen demand, total organic carbon and dissolved protein by 86, 91, 83, and 90 %, respectively.

Background, aim, and scope In the Water Framework Directive 2000/60/EC, environmental objectives for the proper quality of inland, surface, transitional, coastal, and ground waters have been set. Member states are required to identify chemical pollutants of significance in the water bodies, to establish emission control measures, and to achieve quality standards. A specific category of pollutants are the compounds that may possess endocrine-related functions known as endocrine disrupting compounds (EDCs). This means that member states have the obligation to take action in order to prevent human exposure to these compounds via aquatic environment. The objective of this research was to study the occurrence and distribution of phenolic and steroid EDCs in inland waters and wastewaters discharged in the area of Thermaikos Gulf, Thessaloniki, Northern Greece. Materials and methods Samples were collected from three rivers, four streams, and four municipal and industrial wastewaters from the area of Thessaloniki, Northern Greece, during the period 2005-2006. The samples were analyzed for 14 EDCs (nonylphenol, octylphenol, their mono- and di-ethoxylate oligomers, bisphenol A, estrone, 17α-estradiol, 17β-estradiol, estriol, mestranol, and 17α-ethynylestradiol). The compounds were recovered by solid phase extraction and ultrasonic extraction from the dissolved phase and particulate phase, respectively, and determined by employing gas chromatography-mass spectrometry. Results Results revealed the presence of phenolic EDCs (NP, NP1EO, NP2EO, tOP, OP1EO, OP2EO, and BPA) in all water and wastewater samples. Steroid EDCs were not found at detectable concentrations. The relationships between field partition coefficients of EDCs and concentration of total suspended solids, dissolved, and particulate organic carbon were investigated. Discussion Rivers exhibited concentrations of EDCs similar to minimally impacted surface waters worldwide. The concentrations of NP and OP occasionally exceeded the environmental quality criteria proposed for inland waters. The concentrations of EDCs in streams exhibited wide variations due to low flow rate in these systems and the impact of wastewaters from various pollution sources. Wastewater from tannery activities showed extremely high concentrations of NP, whereas relatively high concentrations of EDCs were determined in effluents from the industrial wastewater treatment plant. Field partition coefficients of EDCs are negatively correlated with concentrations of total suspended solids and dissolved organic carbon and positively correlated with particulate organic carbon. Conclusions The examined rivers (Aliakmon, Axios, and Loudias) exhibited concentrations of EDCs similar to minimally impacted surface waters worldwide. However, special attention should be paid to these systems since the concentrations for NP and OP occasionally were above the proposed quality standards, revealing the impact of urban, industrial, and agricultural activities. High concentrations of EDCs were determined in streams, urban, and industrial wastewater posing significant risk to the aquatic environment they discharged. Recommendations and perspectives The occurrence of EDCs in inland waters and wastewaters discharged to Thermaikos Gulf results in an increased risk to the marine environment. Thus, these systems should be regularly monitored, especially for NP, OP, and BPA that are considered as priority hazardous compounds in the Water Framework Directive.