Investigating the adsorption performance of calcium-rich biochar on CDOM from actual rifapentine pharmaceutical wastewater using spectroscopic techniques†

The use of calcium-rich biochar as a sustainable and low-cost adsorbent prepared from crab shells is an effective resource utilization method. Crab shell biochar (CSB) was used to adsorb chromophoric dissolved organic matter (CDOM) from actual rifapentine pharmaceutical wastewater (RPWW). Synchronous fluorescence spectroscopy (SFS) and Fourier transform infrared spectroscopy (FTIR) in combination with two-dimensional correlation spectroscopy (2D-COS) were used to investigate the adsorption performance and mechanism of CDOM components. Results showed that CSB had the best adsorption effect on the chemical oxygen demand (COD) of RPWW (pH 7.0, COD = 100 mg L⁻¹) when the biochar dosage was 1.2 g L⁻¹, and the removal rate of COD reached 75.33%. The removal rate of fluorescent components, including protein-like (284 nm), fulvic-like (367 and 375 nm), and humic-like (390, 402, 422, 430, 465, and 490 nm) substances, ranged from 59.77% to 81.88% when the COD was <200 mg L⁻¹. Substances correlated to peaks at 334 nm (fulvic-like), 367 nm (fulvic-like) and 422 nm (humic-like) play an important role in the adsorption of biochar to rifampicin in wastewater, showing strong correlation coefficients. 2D-COS analysis indicated that humic-like substances at 422 nm could be preferentially removed by biochar adsorption, while the removal of fulvic-like substances at 334 nm showed a lag. Meanwhile, substances corresponding to the band at 1450 cm⁻¹ (e.g. carboxyl δ_O–H and alkane δ_CH3) could preferentially participate in adsorption, suggesting that the π–π EDA effect and the formation of hydrogen bonds are a potential adsorption mechanism. The present study provides valuable insights into the development of efficient technologies for the treatment of antibiotic pharmaceutical wastewater.