Evaluating tannery wastewater treatment performance based on physicochemical and microbiological characteristics: An Ethiopian case study

Molecular characterization of chromium tolerant and gelatin hydrolyzing bacterial isolates from tannery wastes: Perspective on chrome-tanned leather waste biodegradation in Bangladesh

Improper management of chrome-tanned leather waste (CTLW) might potentially cause adverse environmental consequences. To mitigate that harmful impact, this study aims to find and conduct molecular characterization of bacteria from tannery wastes that can tolerate chromium (Cr) and hydrolyze gelatin. Bacteria from tannery wastes are naturally adapted to Cr; eight Cr(III) tolerant bacteria, namely bacterial isolate (BI) 1 to 8, were isolated from the collected waste samples. The isolated bacteria showed the maximum tolerance concentration (MTC) range of 700 to 1500 ppm for Cr(III) and 200 to 600 ppm for Cr(VI). Physiological and biochemical analysis, including the gelatin hydrolysis activity, identified those isolates up to the genus level. Among the isolates, BI 4, 5, and 7 were able to hydrolyze gelatin. Therefore, 16S rRNA molecular characterization was conducted for those isolates, which confirmed BI 4, 5, and 7 as Bacillus wiedmannii (Accession No: OR564007), Enterococcus faecium (Accession No: OR564008), and Bacillus cereus (Accession No: OR564009), respectively. Bacteria with gelatin hydrolyzing activity can be the potential for degrading hydrothermally treated CTLW. Thereby, those three isolates were applied to explore their biodegradation ability in real world scenario. The biodegradation experiments showed that Enterococcus faecium, Bacillus cereus, and Bacillus wiedmannii were able to biodegrade hydrothermally treated CTLW at 98.67 %, 98.33 % and 98.00 %, respectively. The present study demonstrates Enterococcus faecium, Bacillus cereus, and Bacillus wiedmannii having biodegradation of CTLW applications might mitigate environmental pollution caused by this waste in the perspective of Bangladesh.

Valorization of treated wastewater from the soaking of baby alpaca skin fur

Baby alpaca fur industry generates considerable wastewater during the soaking process, which contains high levels of total suspended solids (TSSs), proteins, and salts, among other components. The valorization of wastewater after precipitation, coagulation-flocculation, and aeration treatments was evaluated for use in irrigation water, fertigation, groundwater recharge, concrete construction, and disposal. The precipitation treatment sludge and the coagulation-flocculation treatment were evaluated as a protein source, soil quality improvement, and disposal. The treatment system included evaluations of nine pH levels, seven coagulant doses, and seven aeration times. The contents of TSSs, chemical oxygen demand (COD), total Kjeldalh nitrogen (TKN), ammonia nitrogen (N-NH3), and oils and fats (O&G), among other parameters, were determined in the treated and untreated wastewater. Before entering the treatment system, the physicochemical characterization of the wastewater showed a high concentration of parameters related to organic matter and dust, such as O&G, five-day biological oxygen demand (BOD5), COD, TSSs, TKN, and N-NH3. The optimal removal parameters were pH 12 for the chemical precipitation of proteins, a dose of 480 mg/L FeCl3 as a coagulant for TSSs removal, and 150 min of aeration; removal efficiencies of 99.02 %, 77.49 %, 79.93 %, and 64.62 % for TSSs, Cod, TKN, and N-NH3, respectively, were obtained. The wastewater after treatment can be used for groundwater recharge and concrete construction, and the wastewater with 2 % dilution can be used for irrigation water and fertigation. The sludge after precipitation is rich in protein and can be used as a protein source or soil quality improver.

Comparative Removal of Cr(VI) and F− Ions from Water by Freezing Technology

Trace element ions, such as Cr(VI) and F−, are of particular interest due to their environmental impact. Both ions exhibit an anionic nature in water that can show similar removal tendencies except for their significant differences in ionic radius, speciation forms, and kosmotropic-chaotropic behaviors. Accordingly, partial freezing was performed to examine the comparative freeze separation efficiencies of Cr(VI) and F– from aqueous solutions. Freeze desalination influencing parameters such as initial ion concentration, salt addition, and freeze duration were explored. Under optimal operating conditions, freeze separation efficiencies of 90 ± 0.12 to 95 ± 0.54% and 58 ± 0.23% to 60 ± 0.34% from 5 mg/L of Cr(VI) and F–, respectively, were demonstrated. The salt addition into the F–-containing solutions revealed more F– ion intercalation into the ice, initiating the decrement of freeze separation efficiency. The influences of structuring-destructuring (kosmotropicity-chaotropicity) and the size-exclusion nature of ice crystals were used to explain the plausible mechanism for the difference in freeze separation efficiency between Cr(VI) and F– ions.