Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse

Authors: NDOUN, MARLENE - Pennsylvania State University; ELLIOT, HERSCHEL - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University; Williams, Clinton; Knopf, Allan; WATSON, JOHN - Pennsylvania State University

Submitted to: Biochar
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2020
Publication Date: 11/16/2020
Citation: Ndoun, M., Elliot, H., Preisendanz, H., Williams, C.F., Knopf, A.L., Watson, J.E. 2020. Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse. Biochar. 3:89-104. https://doi.org/10.1007/s42773-020-00070-2.
DOI: https://doi.org/10.1007/s42773-020-00070-2

Interpretive Summary: Current treatment processes in waste water treatment plants are not designed to remove pharmaceuticals that are present leading to concern when using treated wastewater for irrigation. Biochar produced from organic waste material can be a cost effective sorbant to remove pharmaceuticals from water. Biochar produced from cotton gin waste and guayule bagasse was evaluated for efficacy at removing pharmaceuticals. The removal of sulfapyridine, docusate and erythromycin from water by biochar was measured. It was found that the cotton gin biochar was more effective at removal and that removal was also greater for biochars produced at higher temperatures. In addition, removal increased as pH increased from 7 to 10. Biochar produced from cotton gin waste can be effective at removing pharmaceuticals from water.

Technical Abstract: Biochars produced from cotton gin waste (CG) and guayule bagasse (GB) were characterized and explored as potential adsorbents for the removal of pharmaceuticals [sulfapyridine (SPY), docusate (DCT) and erythromycin (ETM)] from aqueous solution. An increase in biochar pyrolysis temperature led to an increase in pH, specific surface area, and surface hydrophobicity. The electronegative surface of all tested biochars indicated that non-Coulombic mechanisms were involved in adsorption of the anionic or uncharged pharmaceuticals under experimental conditions. The extent of SPY, DCT and ETM adsorption was influenced by the contact time and solution pH, as well as biochar surface area and functionality. Adsorptive removal of these pharmaceuticals reflected a complex interplay of hydrophobic partitioning, hydrogen bonding and p- p electron donor-acceptor (EDA) interactions. Adsorption was minimal for the relatively polar SPY (log KOW = 0.35) onto the GB biochars characterized by low surface hydrophobicity. Adsorption of SPY unexpectedly increased from 40% to 70% with increase in pH from 7 to 10 despite increased electrostatic repulsion between anionic SPY- and the electronegative CG biochar surface, weaker '-' EDA interactions, and a reduced hydrophobicity of SPY- compared to SPY'. Formation of strong negative charge-assisted H-bonding between the sulfonamide moiety of SPY and surface carboxylic group apparently dominated adsorption under alkaline pH conditions. Adsorption followed pseudo-second-order kinetics and the data fit a Langmuir-type isotherm. Results suggest CG and GB biochars could act as effective adsorbents for the removal of pharmaceuticals from reclaimed water prior to irrigation of food crops. High surface area biochars with physico-chemical properties conducive to strong interactions with polar-nonpolar functionality of the targeted pharmaceuticals should be used.