Fabrication of sand-based novel adsorbents embedded with biochar or binding agents via calcite precipitation for sulfathiazole scavenging

Fabrication of efficient and low-cost adsorbents through enzyme induced carbonate precipitation (EICP) of sand embedded with binding agents for sulfathiazole (STZ) removal is reported for the first time. Sand enriched with biochar (300 degrees C, 500 degrees C, and 700 degrees C), xanthan gum, guar gum, bentonite, or sodium alginate (1% w/w ratios) was cemented via EICP technique. Enrichment with binding agents decreased the unconfined compressive strength, improved the porosity, and induced functional groups. Biochar enrichment reduced the pH, and increased the calcite contents and electrical conductivity. Fixed-bed column adsorption trials revealed that biochars enrichment resulted in the highest STZ removal (64.7-87.9%) from water at initial STZ concentration of 50 mg L-1, than the adsorbents enriched with other binding agents. Yoon-Nelson and Thomas kinetic models were fitted well to the adsorption data (R-2 = 0.91-0.98). The adsorbents embedded with 700 degrees C biochar (BC7) exhibited the highest Yoon-Nelson rate constants (0.087 L min(-1)) 50% breakthrough time (58.056 min), and Thomas model- predicted maximum adsorption capacity (4.925 mg g(-1)). Overall, BC7 removed 168% higher STZ from water than pristine cemented sand. Post-adsorption XRD and FTIR analyses suggested the binding of STZ onto the adsorbents. pi-pi electron-donor-acceptor interactions, aided-by electrostatic interactions and H-bonding were the main STZ adsorption mechanisms.

Automated summary

Efficient and low-cost adsorbents for sulfathiazole removal were fabricated through enzyme induced carbonate precipitation (EICP) of sand embedded with binding agents. Enrichment with binding agents improved the performance of the adsorbents, with biochar enrichment showing the highest removal efficiency for sulfathiazole. The adsorption mechanisms were mainly attributed to pi-pi electron-donor-acceptor interactions, assisted by electrostatic interactions and H-bonding.