Response surface modeling of ceftriaxone removal from hospital wastewater.

In recent decades, an emerging concern of widespread antimicrobial resistance has been raised due to the existence of pharmaceutical samples such as antibiotics in an aqueous medium. Herein, antibiotic ceftriaxone (CTX) removal from hospital wastewater employing a hybrid process of electrocoagulation (EC) and adsorption (AD) was investigated. The response surface methodology (RSM) was employed to study the influences of main operating variables, including initial CTX concentration, pH, current density, reaction time, and chitosan dosage, on the removal efficiency of the treatment process. Under the optimum condition of the employed EC/AD hybrid treatment process, where initial CTX concentration, pH solution, the current density, adsorbent dosage, and reaction time were set at 20.0 mg L-1, 7.5, 6.0 mA cm-2, 0.75 g L-1, and 12.5 min, respectively, the removal efficiency of 100% was achieved. Analysis of variance (ANOVA) confirmed that the developed quadratic treatment model is highly significant. The applied EC/AD hybrid treatment process revealed the electrical energy consumption of 0.84 kWh m-3 and 0.2168 kWh (g Al)-1 per cubic meter of hospital wastewater and gram of consumed aluminum electrode, respectively. The second-order kinetic model with R2 of 0.9514 and the Langmuir isotherm model with R2 of 0.973 best fit the developed EC/AD hybrid treatment process, and qm was found to be 111.1 mg g-1. The obtained experimental results confirmed that the CTX concentration of the hospital wastewater was reduced to zero after applying the EC/AD hybrid process.

On urea and temperature dependences of m-values.

The denaturing or stabilizing influence of a cosolvent on a protein structure is governed by a fine balance of the energetics of the excluded volume effect and the energetics of direct protein-cosolvent interactions. We have previously characterized the energetic contributions of excluded volume and direct interactions with urea for proteins and protein groups. In this work, we examine the molecular origins underlying the relatively weak temperature and urea dependences of the m-values of globular proteins. Our combined experimental and computational results collectively paint a picture in which the relative independence of protein m-values of urea concentration originates from fortuitous compensatory effects of a progressive increase in the solvent-accessible surface area of the unfolded state and a slightly higher urea binding constant of the unfolded state relative to the folded state. Other denaturing cosolvents which lack such a compensation make poor candidates for linear extrapolation model-based protein stability determination studies. The observed diminution in m-values with increasing temperature reflects, in addition to the aforementioned compensatory effects, a decrease in protein-urea binding constants with temperature in accordance with the negative sign of the binding enthalpy.