Solid leather wastes as adsorbents for cationic and anionic dye removal

The removal of anionic and cationic dyes from aqueous solutions was investigated by different leather shavings, which are solid wastes generated in the leather industry. Wet-blue leather shavings (WB), vegetable-tanned leather shavings (VT), pickled hide (not tanned) shavings (PIC) and wet-white leather (pre-tanned) shavings (WW) were used. The cationic dye was Basic Red 2 and the anionic dye was Acid Brown 414. Point of zero charge, functional groups, shrinkage temperature and adsorbent surface area were characterized. The point of zero charge was 4.0, 6.0, 3.9 and 4.1 for WB, VT, PIC and WW, respectively. The specific surface area showed low values which was expected for this type of material. Tanning agent influence was verified through shrinkage temperature analysis of leather shavings. Main functional groups of the acid dye and the collagen structure of the solid wastes were determined. The tests with Basic Red 2 solutions showed only VT had a considerable removal for this cationic dye (96.7%). The tests with Acid Brown 414 were carried out with different contact times and adsorbent mass. Results showed high efficiency of WW and PIC, whose percentages of dye removal were above 96% at contact time of 30 min and above 90% using 20 mg of adsorbent. In this way, the final dye removal was 98.1% and 98.3% for contact time tests and 97.7% and 98% for adsorbent mass tests for WW and PIC, respectively. These results highlight the promising use of leather shavings as alternative adsorbents for the treatment of wastewater containing dyes.

Nanomaterials to help eco-friendly leather processing

The leather industry converts the hide, a byproduct of slaughterhouses, into leather, a value-added product. This old industry generates wastes, causing environmental pollution. However, nanomaterials can help to decrease this problem. These tiny particles (1-100 nm) can replace chemicals in various steps of leather processing. This paper aims at giving an overview of the fundamentals of classical leather process and how nanomaterials can be applied in each step to obtain a more sustainable manufacturing. After a comprehensive literature review of journal articles, six steps were identified for potential for application of nanomaterials: unhairing, tanning, retanning, dyeing, fatliquoring, and finishing. With nano-oxides, polymers, and metals, it is feasible to reduce the amount of chemical products and also improve the properties of leather. Thus, it is possible to reach a more eco-friendly and effective process with the use of nanomaterials to turn hide/skins into finished leather.

Current technologies for post-tanning wastewater treatment: A review

Leather post-tanning is responsible for producing effluents that are difficult to treat due to several recalcitrant pollutants. Dyes, tannins, and fatliquoring agents are mainly related to this characteristic. This study, as the state-of-the-art, attempts to systematically review treatment technologies applied in recent years to the post-tanning effluents. The Scopus database was used to identify articles related to post-tanning pollutants removal. Through the review, Advanced Oxidation Processes (AOPs) and adsorption proved to be good alternatives to increase the effluent biodegradability when applied before biological treatment. AOPs and adsorption were also efficient for the final polishing of the effluents, to reach the regulation standards for disposal, as well as enzymatic treatment. Furthermore, Membrane Separation Processes demonstrated good applicability when the reuse of the treated effluent is aimed.

Phosphate removal from industrial wastewaters using layered double hydroxides

In the present study, Mg-Al and Zn-Al layered double hydroxides (LDH) were synthesized by the co-precipitation method and employed to remove phosphate from synthetic aqueous solutions and industrial wastewaters. LDH were characterized by X-ray diffraction (XRD), N₂ adsorption/desorption isotherms (BET method), thermal analyses (TG-DTA) and Fourier transform infrared spectroscopy (FTIR). XRD and TG-DTA analysis showed that Mg-Al and Zn-Al formed the LDH structure. Experimental adsorption data indicated that pseudo-second order model best described phosphate adsorption kinetics. Data of equilibrium experiments fitted well to Sips and Freundlich models for Mg-Al and Zn-Al, respectively. The effect of co-existing anions on the phosphate adsorption capacity was analyzed by utilizing industrial wastewater. The results showed that the phosphate removal decreases in the presence of other anions. Mg-Al adsorbent exhibited 74% removal of phosphate with a dosage of 5 g/L in industrial wastewater.

Occurrence of Cryptosporidium and Giardia in surface water supply from 2016 to 2020 in South Brazil

The objectives of this research are to evaluate Giardia and Cryptosporidium contamination in surface water supply in Rio Grande do Sul (RS) State in South Brazil in the years 2016 to 2020, assess seasonality, and to infer the population that may have been exposed to these protozoa through drinking water based on drinking water treatment efficiency. Data were obtained through the drinking water surveillance national information system. From 204 DWT plants in the state, 66 have been analyzed for protozoa. A total of 2304 analyses of protozoa in raw water were evaluated, of which 223 had both Giardia spp. cysts and/or Cryptosporidium spp. oocysts in concentrations that varied from 0.1 to 21.5/L. A total of 2,712,125 people from 48 cities were at risk of having the presence of pathogenic protozoa in their drinking water. The probability of finding these protozoa was higher in winter. Giardia cysts were more likely to be found in a period without rain, suggesting that sewage was the main source of contamination. It is concluded that the springs of Rio Grande do Sul are impacted and the circulation of pathogenic protozoa through the territory is endemic with a probable source of contamination to sewage and livestock activity.

Chemical contaminants in Brazilian drinking water: a systematic review

The goals of this research are to evaluate which chemical contaminations were detected in Brazil's drinking water reported in papers published from 2012 to 2019, to propose guideline values for emerging contaminants and assess which are the priority parameters from a health risk perspective. The methodology used was a systematic review. The chemical contaminants quantified were evaluated according to Brazilian drinking-water standards, and Guideline Values were proposed for emerging pollutants using conservative endpoints from NOAEL and LOAEL available in literature. From 1351 articles evaluated, 15 reached the research goal. Seventy-seven parameters were quantified in Brazilian drinking water from underground, surface and rainwater sources. Soil composition, mining, sewage and agricultural activities were the main sources for the seven classes framed: pesticides, metals, organic, endocrine disruptors, drugs, personal care products and illicit drugs. Twenty-two parameters are listed in the current Brazilian drinking water quality standard and 54 are not. Water was not considered appropriate to drink due to cadmium, aluminum, iron, nickel, mercury, atrazine, propionaldehyde, beryllium, acetone and 17 α-ethinyl estradiol (carcinogenic). Measures to reduce chemical contamination in drinking water need to be taken such as the expansion of sewage treatment and upgrading to tertiary treatment, and controlling and reducing the application of pesticides.

Degradation of a leather-dye by the combination of depolymerised wood-chip biochar adsorption and solid-state fermentation with Trametes villosa SCS-10

Adsorption into biochar-derived materials and mycoremediation are promising technologies for removing dyes from solid and liquid matrices. This study presents a combined treatment with adsorption into wood-chip biochar and mycodegradation under solid-state fermentation by Trametes villosa for removing the leather-dye Acid Blue 161. In the first stage, untreated wood-chip biochar, NaOH–depolymerised biochar and KMnO4–depolymerised biochar were assessed for their dye removal efficiency by adsorption. KMnO4–depolymerised biochar exhibited the highest adsorption (85.1 ± 1.9%) after 24 h of contact. KMnO4–depolymerisation modified some physical and chemical properties on the untreated wood-chip biochar, increasing the surface area (50.4 m2 g–1), pore size (1.9 nm), and presence of surface functional groups. Response surface methodology coupled with a Box–Behnken design was used to optimise the AB161 adsorption into the KMnO4–depolymerised biochar. The optimised conditions, pH 3.0, dye concentration 100 mg L–1 and sorbent dosage 2 g L–1, led to a higher dye removal efficiency by adsorption (91.9 ± 1.0%). In a second stage, the wood-chip biochar supplemented with nutrients (1% malt extract and 0.5% peptone) was employed as a solid matrix for growing T. villosa and regenerating the dye-saturated material. After 15 days, T. villosa was able to grow (86.8 ± 0.8%), exhibit laccase activity (621.9 ± 62.3 U L–1), and biodegrade (91.4 ± 1.3%) the dye adsorbed into the KMnO4–depolymerised biochar. Finally, the mycoregenerated biochar was reutilised in a new cycle of adsorption reaching 79.5 ± 2.0% of dye removal efficiency by adsorption. This study revealed the potential of the combined treatment and is an initial assessment for developing commercial alternatives for treating leather industry wastewaters.

Impact of post-tanning chemicals on the pollution load of tannery wastewater

The leather industry uses a large amount of chemicals to transform a raw hide into finished leather. Chemicals are not fully taken up by leather and thus end up in tannery wastewater. Physicochemical and toxicological characterization of tannery effluents has been widely assessed. However, the characterization of processing chemicals and their relation to the pollution load of effluents remains unknown. Thus, this study aimed to assess a physicochemical and cytotoxic characterization of chemicals used in the leather post-tanning process and to evaluate the contribution of each chemical to the pollution load of raw wastewater. This study was performed using a leather post-tanning formulation applied by a large tannery located in Brazil. Deacidulation agents caused high conductivity and dissolved solids in wastewater. Retanning agents (natural and synthetic tannins) were responsible for the largest inorganic pollution load, and synthetic tannins were more toxic than natural ones. Fatliquoring agents released the highest chemical oxygen demand load in wastewater and they were the chemical group that presented the highest toxicity. Fixing agent and black dye provided inorganic pollution load to wastewater, and nitrogen pollution of wastewater was mainly related to the neutralizing retanner and the black dye.

Photodegradation of Emerging Contaminant 2-(tiocyanomethylthio) Benzothiazole (TCMTB) in Aqueous Solution: Kinetics and Transformation Products

Direct photolysis of the emerging contaminant 2-(thiocyanomethylthio) benzothiazole (TMCTB) was performed in aqueous solution at different concentrations with high-pressure mercury lamp (5.0, 8.0, 13.0, 16.0, 20.0, 23.0, 27.0, 35.0, 40.0, 45.0, and 50.0 mg L^- 1) and with natural sunlight radiation (6.0, 30.0, and 60.0 mg L^- 1). TCMTB underwent rapid degradation by direct photolysis with a high-pressure mercury lamp in aqueous solutions, with 99% removal after 30 min at all concentrations studied. For sunlight photolysis, TCMTB degradation was observed with 96%, 81%, and 64% removal for initial concentrations of 6.0, 30.0, and 60.0 mg L^- 1, respectively, after 7 h of exposure to sunlight. The degradation of TCMTB in lab-scale wastewater had kinetic constant and t_1/2 in the same order when compared to the photodegradation of TCMTB in aqueous solutions. In addition, the results showed that photolysis with a high-pressure mercury lamp and sunlight were governed by the same kinetic order, however the kinetic parameters showed that degradation with sunlight was 40 times slower than photolysis with the mercury lamp. Twelve transformation products (TP) were identified, and eight of the TP have not been described in the literature. Furthermore, prediction of toxicity with ECOSAR software was carried out for fish, daphnids, and green algae species. It showed that photolytic treatment is efficient for reducing the toxicity of the compound, since the degradation formed compounds with lower toxicity than the primary compound. In conclusion, this study suggests that photolysis is an efficient way to remove the studied contaminant, and it highlights the potential of this technique for the degradation of emerging contaminants in industrial wastewater treatment plants.

Nutrient balance for anaerobic co-digestion of tannery wastes: Energy efficiency, waste treatment and cost-saving

The macronutrients ratio present in tannery wastes is normally not ideal for anaerobic digestion (AD). In most cases, it is necessary to add nutrients to obtain a more balanced AD process and to ensure favorable conditions for the growth and metabolism of microorganisms. The aim of this study was to verify the influence of the components of nutrient solution added to AD of tannery wastes with regard to the energy and waste treatment efficiency and to the cost-saving analysis. The findings provides better understanding of the nutritional requirement of co-AD of tannery wastes, with the highest value of biogas production of 30.14 mL/g of added VSS, besides representing a step in the search for a more balanced, efficient and viable process. The results obtained proving the competitiveness of co-AD of tannery wastes instead of disposing it in landfills (saving off about 71% in terms of electric consumption).

Preparation and characterization of activated carbon produced from tannery solid waste applied for tannery wastewater treatment

The removal of toxic compounds (azo dyes) from dyeing wastewater was investigated by an environmentally friendly activated carbon produced from solid waste generated in the tannery process, the cattle hair (CHW), activated with H₃PO₄ (AC-CHW), suggesting a life cycle extension for this material from leather processing. Preliminary tests with aqueous solutions containing Acid Brown 414 (AB-414) and Acid Orange 142 (AO-142) removed 71.06% and 73.05%, respectively. The activated carbon was characterized by zeta potential (ZP), functional groups (FTIR), elemental composition, sorbent specific surface area, and pore size distribution (BET/BJH). The specific surface area showed low values when compared to commercial activated carbon, but average pore diameter was higher, which facilitates the adsorption of larger and complex molecules, such as those present in real wastewaters. Through SEM and FTIR, the presence of the toxic compounds studied in the AC-CHW after sorption process was observed, where the results indicated that the functional groups of -CH=CH- participated in the removal process for these compounds. The removal efficiency obtained with AC-CHW was 51.94% and 49.73% for the dyeing wastewater containing AB-414 and AO-142, respectively. The obtained results open a promising via to use AC-CHW as efficient eco-friendly sorbent for the treatment of leather wastewater.

Water reuse: An alternative to minimize the environmental impact on the leather industry

Tanneries are industries that may cause high environmental impact. Consequently, they are responsible for generating a large amount of wastewater with high concentrations of contaminants that require significant investment and operating costs in their treatment in order to accomplish the emission standards required by environmental legislation. This work has as main objective to minimize the environmental impact of the water used by tanneries through the study of reuse possibilities of wastewater tanning floats. The major concern is related to the pollutant chromium in the environment, since it is the tanning product that gives the best characteristics to leather and consequently the most used product. The reuse tests were performed on pilot and industrial scales. During the experiments, the following process control parameters were evaluated: pH, density, acid-base indicators for hide and shrinkage temperature. To validate the water reuse in tanneries, samples of wet-blue leather and residual floats were collected from pilot and industrial processes to perform chemical analyses to prove the validity of the process with reuse. Research has shown that reuse techniques, when properly evaluated, can be used in industries. In addition to reducing water demand, the reuse of wastewater in tanning processes minimizes the disposal of the wastewater with chromium and uses the residual chromium float.

Fungal biomass as biosorbent for the removal of Acid Blue 161 dye in aqueous solution

Physical and thermal treatment was used to inactivate Trametes sp. SC-10 fungus. The resulting biomass was named BTV, characterized by analytical techniques such as SEM, EDX, FTIR, BET, and Barrett-Joyner-Halenda (BJH) model. pH, kinetic, and equilibrium adsorption studies with the Acid Blue 161 (AB-161) dye were investigated at 303.15 K. The kinetics of the biosorption process were examined at 600.00 and 1300 mg L^-1, using pseudo-first-order, pseudo-second-order, and Avrami fractional-order models. The maximum biosorption capacity of BTV for AB-161 dye was 221.6 mg g^-1. Considering the biosorption data and the functional groups of BTV, it can be inferred that the sorption mechanism of AB-161 is regulated by electrostatic interactions between ionized dye molecules and negative charges on BTV in an aqueous solution. Finally, the BTV was tested with a simulated effluent with 89.47% efficiency, presenting the BTV as a biosorbent for real effluents polluted with dyes.

Production of basic chromium sulfate by using recovered chromium from ashes of thermally treated leather

Leather wastes tanned with chromium are generated during the production process of leather, hence the wastes from hand crafted goods and footwear industries are a serious environmental problem. The thermal treatment of leather wastes can be one of the treatment options because the wastes are rich in chromium and can be used as a raw material for sodium chromate production and further to obtain several chromium compounds. The objective of this study was to utilize the chromium from leather wastes via basic chromium sulfate production to be subsequently applied in a hide tanning. The obtained results have shown that this is the first successful attempt to achieve desired base properties of the product. The result was achieved when the following conditions were applied: a molar ratio between sodium sulfite and sodium dichromate equal to 6; reaction time equal to 5 min before addition of sulfuric acid; pH of sodium dichromate solution equal to 2. Summarizing, there is an opportunity to utilize the dangerous wastes and reused them in the production scheme by minimizing or annulling the environmental impact and to attend a sustainable process development concept.