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The presence and destination of pharmaceutical compounds in water constitutes one of the main emerging events in current environmental chemistry. The most significant effects that have been reported are a variation in the chemical composition of discharges, their identification as possible organic pollutants and the effect on some biological treatment processes due to their presence in high concentrations [1]. The pharmaceutical pollutants that generate the greatest concern are antibiotics, since their consumption reaches approximately 100 tons per year, surpassing any other types of medications [2]. Hair is found within the waste from livestock and tannery activities, which in the process is discarded mixed with other waste and compounds such as hydroxides and chromium, making its later use complex, due to the lack of specialized technology to decrease its dangerousness. During the pyrolysis process of hair, the proteins that are part of the keratin when they reach ~250 ºC are melted, then at 300 ºC the formation of aromatic compounds occurs, at 350 ºC the formation of cyclic amines and finally between 350 and 600 ºC it produces the degradation of cyclic and aromatic framework. However, the use of adsorbents from waste hair valorization is interesting because of its composition, such as the presence of keratin. The treatment temperature for the tannery hair waste was 450 °C, and the material was allowed to remain there for 20 minutes in both batch and continuous feed. According to Rodríguez et al. [3] and Herrera et al. [4], this temperature range is ideal for producing carbonaceous materials with superior surface, textural, and chemical properties for adsorption. The biochar was washed to remove any impurities that might interfere with the analysis results. A 1:3 water-biochar ratio was used, centrifuged for 5 minutes, and allowed to settle for 5 minutes before removing the supernatant and repeating the process until a clear water-biochar mixture was obtained. Tannery hair biochar obtained through the pyrolysis process at 450 °C was mixed in a 1:1 weight ratio with KOH (EMSURE, London, England) and mixed for 1 hour until a homogeneous mixture was obtained before being left in contact for 72 hours. For the tests on AMOX, DFC, AZM, and ERY, a 100 mg·L^-1 aqueous solution was used. A sample of the aqueous solution containing 100 mL was used for an adsorbable ingredient concentration of 100 mg·L^-1. However, there were reading mistakes when assessing the pharmacological mixture using concentrations of 100 mg·L^-1 of each one in the same solution due to interference produced by the wavelength associated with each one.

For the removal of drugs, two different tests were carried out: one for 28 days and the other for 4 hours, in order to evaluate the efficiency and the percentage of removal. It was found that the biochar obtained at 450 ºC is the one that presents the best efficiencies and that after being activated, the efficiency increases considerably. With the biochar at 450 ºC, removals of 90% of AMOX and more than 80% of DFC were achieved.

By examining it, biochar made from waste tannery hair has these qualities and is an excellent adsorbent. As removal percentages of more than 60% were achieved in this example for each medication, it is possible to claim that good removal percentages are provided when examining medicines separately or in mixes. The findings of this investigation allow us to draw the conclusion that pyrolysis of tannery hair at 450 °C results in a carbon with physicochemical properties acceptable for use as an absorbent. This carbon enables the removal of newly developing contaminants like antibiotics. Because biochar may partially eliminate the developing pollutants found in traditional treatment systems, its application would ensure improvements in the process. This could be accomplished by adding filtration columns or fixed bed filters after the standard filtration procedure or after the coagulation, flocculation, and sedimentation procedures. On the other hand, by forgoing a typical treatment for a waste that is deemed dangerous, pyrolysis creates a new product and a new stage within the leather industry's value chain by adding value to it. Similar to how tannery hair waste can be fully utilized by undergoing an alternative value-added treatment, the manufacturing of leather can be improved by making it more environmentally friendly.

References

1. Alvarez, S., Sheepdog Escudero, G., Garcia, Panorama., J. (2017). Elimination of Emerging Contaminants from Wastewater. Research Science. 2017, 485, 10–16.
2. Tejada, C.; Quiñonez, E.; Peña, M. (2014). Contaminantes Emergentes en Aguas: Metabolitos de Fármacos. Una Revisión. Fac.Rev. Cienc. Básicas, 10 (1), 80–101. https://doi.org/10.18359/rfcb.341.
3. Rodríguez, F., Montoya-Ruiz, C., Estiati, I. & Saldarriaga, J. F. Removal of Drugs in Polluted Waters with Char Obtained by Pyrolysis of Hair Waste from the Tannery Process. ACS Omega 5, 24389–24402 (2020).
4. Herrera, K., Morales, L. F., Tarazona, N. A., Aguado, R. & Saldarriaga, J. F. Use of Biochar from Rice Husk Pyrolysis: Part A: Recovery as an Adsorbent in the Removal of Emerging Compounds. ACS Omega 7, 7625–7637 (2022).