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Fate of trimethoprim, sulfamethoxazole and caffeine after hydrothermal regeneration of activated carbon
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Chemistry)
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0001-7589-9653
2023 (English)In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 421, article id 139477Article in journal (Refereed) Published
Abstract [en]

Emerging contaminants are found in all parts of our environment. Adsorption of these contaminants by activated carbon in water treatment plants is well-known; however, a problem resides in the handling of the spent adsorbents. As current regenerative technologies are expensive, the adsorbents are often destructed or landfilled. Here, we examine a novel regeneration method for the used adsorbents with subcritical water – i.e., hydrothermal treatment. The degradation of three well-known emerging contaminants – caffeine, trimethoprim and sulfamethoxazole – was studied with regard to processing temperature (160–280 °C), concentration (2 and 20 mg/L), and the impact of adsorbents. In addition to trimethoprim in the mix at 20 mg/L, the other contaminants were entirely degraded at 280 °C. To obtain insight into transformation products formed during hydrothermal regeneration, we performed non-target and targeted analyses with LC-MS-QTOF using two types of columns, C18 and ZIC-HILIC. This approach ensured a wide range of hydrophilicities. Results showed more transformation products for trimethoprim (20) compared to sulfamethoxazole and caffeine (4). To assess the regeneration efficiencies of the activated carbons, we conducted three cycles of regeneration at 280 °C and between 61 and 120 % degradation was achieved. Moreover, only two transformation products were detected and readsorbed on the adsorbent after regeneration. Hydrothermal regeneration efficiently degraded the target emerging contaminants, suggesting a potential approach for enabling alternative, sequential uses for regenerated activated carbon.

Place, publisher, year, edition, pages
Elsevier, 2023. Vol. 421, article id 139477
Keywords [en]
Non-target analysis, Adsorption, Emerging contaminants, Hydrochar, Transformation products, HTC
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-215195DOI: 10.1016/j.jclepro.2023.139477Scopus ID: 2-s2.0-85175552036OAI: oai:DiVA.org:umu-215195DiVA, id: diva2:1803978
Funder
Bio4EnergyUmeå University
Note

Originally included in thesis in manuscript form. 

Available from: 2023-10-11 Created: 2023-10-11 Last updated: 2023-11-27Bibliographically approved
In thesis
1. Exploring the fate of emerging contaminants during hydrothermal regeneration of carbonaceous adsorbents
Open this publication in new window or tab >>Exploring the fate of emerging contaminants during hydrothermal regeneration of carbonaceous adsorbents
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Studier av ödet för nya föroreningar under hydrotermisk regenerering av koladsorbenter
Abstract [en]

Wastewater from households and industries commonly contain emerging contaminants that are not easily removed by most wastewater treatment plants. These contaminants can be removed through adsorption onto adsorbents, such as activated carbon or biochars. Previously, attention has been given to waste residues from the agriculture and forestry industry as potential raw materials for activated biochars, which could replace coal and coconut, common feedstocks for activated carbon production. This thesis investigates the factors governing the adsorption efficiencies of these activated biochars and explores the potential of hydrothermal regeneration as a post-treatment. 

The adsorption experiments showed that iron-doped (i.e., magnetic) activated biochar had two times more adsorption capacity than non-doped activated biochar (i.e., non-magnetic). However, the adsorption capacity of magnetic activated biochar was still inferior to activated carbon for removing sulfamethoxazole (8 mg/g vs. 42 mg/g) and caffeine (40 vs. 56 mg/g). Of the three conditions tested (i.e., salts, humic acids, and pH), only pH had a significant influence on the adsorption of the three selected contaminants onto activated biochars, and the biochars preferentially adsorbed neutral species. This observation is most likely explained by the π-π bonds. 

Hydrothermal regeneration effectively degraded trimethoprim, sulfamethoxazole, and caffeine at temperatures above 240 °C in the absence of adsorbent. Only trimethoprim generated transformation products that could be identified and quantified from non-targeted analysis. In presence of adsorbent, caffeine was not completely degraded at 280 or even 320 °C, suggesting that the activated biochars adsorb and to some extent shelter the contaminants from degradation.

After hydrothermal regeneration, the activated biochars had an enhanced adsorption capacity for sulfamethoxazole, whereas lower adsorption capacity was observed for trimethoprim and caffeine. These changes in performance are believed to be related to the alteration of surface characteristics of activated biochar induced by the adsorbed contaminants during the hydrothermal reaction. Overall, the regeneration efficiency for the activated biochars was found to exceed 50 %. After three regeneration cycles, the regeneration efficiency was as high as 320 %. The results of this thesis suggest that activated biochars could remove emerging contaminants in water and hydrothermal regeneration could degrade most of the emerging contaminants, allowing the spent adsorbent to be reused.

Abstract [sv]

Avloppsvatten från hushåll och industrier innehåller ofta nya föroreningar (så kallade ’emerging contaminants’) som avloppsreningsverk inte är utformade för att avskilja. En effektiv metod för att avlägsna dessa nya föroreningar är genom adsorption på exempelvis aktivt kol eller biokol. Råvaran för produktion av aktivt kol är, utöver specialiserade råvaror som kokosnötskal, ofta stenkol eller brunkol, vilket medför klimat- och resurshushållningsmässiga utmaningar. För att övervinna dessa utmaningar har restprodukter från jordbruks- och skogsindustrin de senaste åren fått ökad uppmärksamhet som potentiella råvaror för aktiverade biokol. Den här avhandlingen syftar till att öka förståelsen kring de faktorer som styr adsorptions-effektiviteten för aktiverade biokol och att utforska potentialen för hydrotermisk regenerering som en möjlig efterbehandling. Hydrotermisk regenerering innebär att man hettar upp kolmaterialen till 180–320 °C i en sluten behållare, liknande den industriella processen hydrotermisk förkolning (HTC) som används för att göra kolmaterial av ursprungsmaterial med hög fukthalt.

Initialt utvärderades kolmaterialens förmåga att adsorbera en mindre grupp nya föroreningar (sulfametoxazol, trimetoprim och koffein). Adsorptionsexperimenten visade att magnetiskt (järndopat) aktiverat biokol hade dubbelt så hög kapacitet jämfört med icke-magnetiskt aktiverat biokol. Adsorptionskapaciteten hos magnetiskt aktiverat biokol var dock fortfarande lägre än för aktivt kol, till exempel 8 mg/g jämfört med 42 mg/g för sulfametoxazol och 40 resp. 56 mg/g för koffein. Den enda studerade parametern som hade en signifikant inverkan på adsorptionen av de utvalda föroreningarna var pH, och de aktiverade biokolen adsorberade företrädesvis neutrala substanser. Denna observation förklaras troligen av interaktioner med ämnenas π-π-bindningar.

Den hydrotermiska regenereringen studerades i två steg, först med bara de enskilda substanserna sulfametoxazol, trimetoprim och koffein i vatten, och sen i närvaro av adsorbent. Hydrotermisk regenerering bröt effektivt ned de undersökta föroreningarna i vatten vid temperaturer över 240 °C, men endast trimetoprim genererade omvandlingsprodukter som kunde identifieras och kvantifieras genom non-targetanalys. Koffein i närvaro av adsorbent bröts inte ned helt vid 280 °C eller ens vid 320 °C, vilket tyder på att de aktiverade biokolen adsorberar och i viss mån skyddar föroreningarna från nedbrytning.

Efter hydrotermisk regenerering ökade de aktiverade biokolens adsorptionskapacitet för sulfametoxazol, medan den försämrades för trimetoprim och koffein. Detta tros höra ihop med att ytegenskaperna hos det aktiverade biokolet förändrats på grund av de adsorberade föroreningarnas reaktioner under den hydrotermiska regenereringen. Över lag översteg regenereringseffektiviteten för de aktiverade biokolen 50 %, och efter tre regenereringscykler steg den så högt som 320 %.

Den forskning som ligger till grund för denna avhandling tyder därför på att (1) aktiverade biokol har potential att ta bort den här typen av nya föroreningar från vatten, och (2) hydrotermisk regenerering skulle kunna bryta ned de flesta av föroreningarna och möjliggöra återanvändning av den använda adsorbenten.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2023. p. 80
Keywords
Activated biochars, HTC, regeneration, analytical chemistry, adsorption, degradation, nontarget analysis, wastewater, circular economy, emerging contaminants, surface chemistry
National Category
Analytical Chemistry Environmental Sciences
Research subject
Analytical Chemistry; environmental science; Pharmaceutics; analytical material physics; Analytical Pharmaceutical Chemistry
Identifiers
urn:nbn:se:umu:diva-215198 (URN)9789180701846 (ISBN)9789180701853 (ISBN)
Public defence
2023-11-10, Stora hörsalen, KBE303, KBC-huset, Umeå, 09:00 (English)
Opponent
Supervisors
Funder
Bio4Energy
Available from: 2023-10-20 Created: 2023-10-11 Last updated: 2023-10-16Bibliographically approved

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Oesterle, PierreGallampois, ChristineJansson, Stina

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