Simultaneous adsorption of amoxicillin and ciprofloxacin on agricultural soils and by-products used as bio-adsorbents: Unraveling the interactions in complex systems

Effect of Soil-pH, temperature and moisture content on sorption dynamics of metformin and erythromycin

The rising soil-groundwater quality issues due to pharmaceuticals and personal care products (PPCPs) contamination have spurred significant concern. To understand the sorption characteristics of metformin (MTN) and erythromycin (ETM) in sandy and sandy loam soils with varying organic matter and particle composition, sorption kinetics (single and competitive), isotherms, and thermodynamics were studied. The effects of pH and soil moisture content (SMC) were also investigated at environmentally relevant concentrations. The equilibrium time of MTN and ETM sorption by the three soils in a competitive solute system was about 4 h, and the sorption process was in line with a pseudo-second-order model. The rate-determining step in the process involved both intraparticle diffusion and liquid film diffusion mechanisms for the two PPCPs. The highest pollutant uptake occurred in soils with higher organic matter, driven by enhanced H-bonding, electrostatic interactions, and π-π and n-π interactions facilitated by the organic matter. The equilibrium data in the three soils was well described by the Freundlich model and confirmed favourable adsorption (1/nf = 1.01-1.90). The sorption coefficient (Kd) on the three soils ranged from 2.1 to 332 L/kg for MTN and from 6.25 to 845 L/kg for ETM. The adsorption process was feasible at 293 K and 303 K (ΔG° = - 0.16 to -10.24 kJ/mol), physical and exothermic in nature (ΔH° = -75.21 to -10.30 kJ/mol) for both the contaminants. Observed alterations in Qe with pH confirmed the participation of electrostatic interactions. A low SMC favoured both MTN and ETM sorption onto the sandy soil. Overall, ETM exhibits higher expected sorption, whereas MTN has a greater tendency for migration in the soils and is thus liable to contaminate the groundwater. The study accentuates novel insights into the transport and fate of MTN and ETM in soil-groundwater systems at environmentally relevant concentrations.

Evaluation of acetanilide and antipyrine adsorption on lignin-derived activated carbons

In this study, the removal of two emerging pollutants (EPs), antipyrine and acetanilide, through adsorption on activated carbons (ACs) prepared by chemical activation of Organosolv lignin with H3PO4 were evaluated. ACs with different pore size distribution were obtained at different impregnation ratios (H3PO4/lignin, 0.5-3.0 w/w) and activating temperatures (500-900 °C). The porosity and surface chemistry of the ACs were determined, and a bimodal size distribution of micropores and narrow mesopores was observed for the different ACs. These ACs were tested for antipyrine and acetanilide adsorption in aqueous solutions in a batch system at 20 °C and low concentration levels (0.5-10 ppm). In general, the ACs exhibited higher adsorption affinity to acetanilide than to antipyrine due to its smaller molecular size. Langmuir adsorption isotherm was able to describe the adsorption equilibrium data. A new Linear Driving Force (2-LDF) kinetic model, based on the bimodal size distribution of micropores and narrow mesopores observed for the ACs has been developed. The new model provided a more accurate description of the batch adsorption rates than that obtained from conventional kinetic models, and also enabled to relate the pore size distribution of the adsorbent with the adsorption kinetics. The validity of this model was checked in small-scale column fixed bed adsorption for the AC showing the highest affinity for both EP. The kinetic model and equilibrium adsorption isotherm obtained from the batch experiments were successfully used to provide an accurate description of the bed service time and the full breakthrough profile of acetanilide and antipyrine.

Efficient Sequential Detection of Two Antibiotics Using a Fiber-Optic Surface Plasmon Resonance Sensor

Antibiotic residues have become a worldwide public safety issue. It is vital to detect multiple antibiotics simultaneously using sensors. A new and efficient method is proposed for the combined detection of two antibiotics (enrofloxacin (Enro) and ciprofloxacin (Cip)) in milk using surface plasmon resonance (SPR) sensors. Based on the principle of immunosuppression, two antibiotic antigens (for Enro and Cip) were immobilized on an optical fiber surface with conjugates of bovine serum albumin using dopamine (DA) polymerization. Each single antigen was bound to its corresponding antibody to derive standard curves for Enro and Cip. The fiber-optic sensor's sensitivity was 2900 nm/RIU. Detection limits were calculated to be 1.20 ng/mL for Enro and 0.81 ng/mL for Cip. The actual system's recovery rate was obtained by testing Enro and Cip in milk samples; enrofloxacin's and ciprofloxacin's mean recoveries from the milk samples were 96.46-120.46% and 96.74-126.9%, respectively. In addition, several different regeneration solutions were tested to analyze the two target analytes' regeneration ability; NaOH and Gly-HCl solutions were found to have the best regeneration ability.