| Wastewater containing heavy metals is considered as a major pollutant in ecological environment pollution has caused directly or indirectly great hazards to the human health and environment. China has become the largest antibiotics manufacture country in the world. A large amount of antibiotic fermentation dregs which belongs to hazard solid waste was discharged from pharmaceutical enterprises and it is very difficult to treat. Therefore, it is urgent to find reasonable and safe treatment methods to deal with antibiotic fermentation dregs for pharmaceutical enterprises. Biosorption can be a promising alternative method to treat industrial effluents, mainly because of its low cost, high metal binding capacity, high efficiency in dilute effluents and environmental friendly.In this paper, some biosorbents were prepared using antibiotic fermentation dregs from pharmaceutical enterprises by chemical modification and adsorption properties of Cr(VI), Pb(Ⅱ) and Cd(Ⅱ) on these biosorbents in aqueous solution were studied. The structure and morphology of antibiotic fermentation dregs and modified antibiotic fermentation dregs were characterized by some instruments, such as BET-N2 adsorption, infrared spectroscopy and scanning electron microscopy technique. Also the physical and chemical characteristics such as surface area, surface charge, were examined. The mechanisms of antibiotic fermentation dregs were discussed, and the reaction conditions of modification were optimized. By using batch adsorption techniques, the influence of p H, adsorbent dosage, concentration, time and temperature on adsorption effect were investigated. In addition, the adsorption thermodynam- ics and the adsorption kinetics were studied systematically. Furthermore, the technologies of desorption and reuse for the modified antibiotic fermentation dregs and technological applica- tions for the wastewater were also tested.Raw antibiotic fermentation dregs has a certain adsorption capacity of heavy metal ions, but its adsorption capacity is low. Hence, modification of antibiotic fermentation dregs was systematically investigated. The salt and acid immersion method was tried to modify antibiotic fermentation dregs. The results indicate that acid modified antibiotic fermentation dregs(AMAFD) and salt immersed antibiotic fermentation dregs(CCMAFD) have certain adsorption capability for Cr(Ⅵ). The result showed that the removal rate was bigger with the increasing of adsorbent dose. It was founded that the suitable adsorbent dose was at 20 mg·L-1. The initial p H value of solution is an important controlling parameter in the Cr(Ⅵ) adsorption process, due to its effect on the Cr(VI) ionic state and the charge of the functional group on the adsorbent surface. The maximum binding of Cr(VI) was observed at p H 1. At different initial concentrations, the adsorption curves of Cr(VI) could be reached equilibrium in 3 h for AMAFD and 2 h for CCMAFD. The maximum adsorption capacity of Cr(VI) would decrease with the temperature up, which indicated the adsorption was of exothermic reaction. Temperature did not affect the adsorption efficiency greatly, which indicated that the modified antibiotic fermentation dregs could be used in different seasons and had better adsorption efficiency. The theoretical maximum adsorption capacity of Cr(VI) were 9.53 mg·g-1 for AMAFD and 8.02 mg·g-1 for CCMAFD. The adsorption mechanisms mainly included as follows: a little physical adsorption; As well as oxidation-reduction reaction between some group in adsorption and Cr(VI).Another modification method is alkaline immersion. The results showed that alkaline antibiotic fermentation dregs(SHMAFD) has better adsorption capability for Pb(Ⅱ) and Cd(Ⅱ). The optimum p H value were 3.5 for Pb(Ⅱ) and 5 for Cd(Ⅱ). The adsorption percentage increased with the increase of adsorbent dose. It was found that the adsorption effects of SHMAFD to Pb(Ⅱ) and Cd(Ⅱ) is better when adsorbent dose was 16 g·L-1 and 20 g·L-1 respectively. The removal rate of heavy metals on SHMAFD was rapid in the first and the equilibrium was reached after 2 h. In all other adsorption processes, adsorption capacity decreases with the adsorption temperature increasing and enthalpy Gibbs free energy and entropy change were negative. In the adsorption process, the enthalpy change(△H) was negative, which demonstrated that the adsorption process was of exothermic process. The free energy change(△G) was negative, which indicated the adsorption process was spontaneous. The adsorption mechanisms mainly included as follows: a little physical adsorption; ion exchange between Na+ and Pb(Ⅱ) and Cd(Ⅱ); as well as complexing between —OH and —COOH functional groups and Pb(Ⅱ) and Cd(Ⅱ).Pyrolysis may be an effective approach for AFDs management, because organic matter is decomposed and inorganic components are concentrated and stabilized through pyrolysis. In this study, biochars(BAFD) were produced at 500 and 1℃ h. It was found that BAFD has better adsorption capability for Pb(Ⅱ) and Cd(Ⅱ). Batch static adsorption results showed that the removal efficiency of Pb(Ⅱ) and Cd(Ⅱ) increased significantly with the dosage of BAFD. When the adsorption concentration was 20 g·L-1, BAFD has the best removal on Pb(Ⅱ) and Cd(Ⅱ), which was higher than 85%. The adsorption process of Pb(Ⅱ) and Cd(Ⅱ) onto BAFD is not very fast. The initial p H value of solution is an important controlling parameter in the Pb(Ⅱ) and Cd(Ⅱ) adsorption process. The maximum biosorption capacities is reached at p H is 4 for Pb(Ⅱ) and 5 for Cd(Ⅱ). In the adsorption process, the enthalpy change(△H) and the free energy change(△G) were all negative.The study of the adsorption thermodynamics.It was found that the experimental adsorption data for modified antibiotic fermentation dregs were fitted to the Langmuir adsorption model. From Langmuir isotherm, the adsorption capacity for Cr(VI) on AMAFD and CCMAFD increased compared with the AFD. The activation energy(Ea) of adsorption process was in the range of 8.63~12.56 k J·mol-1, showing that heavy metal ions adsorption onto the above adsorbents were activated chemical adsorption; The biosorption kinetics were mainly followed the pseudo—second order model and intra-particle diffusion model. In addition, the intra-particle diffusion was the main rate-controlling step.It found that the maximum adsorption capacity and adsorption efficiency were decreasing gradully after using some time. This caused by the changing of hole on the surface of adsorbent and some impuritical substances adsorbed. Thus, the modified adsorbents need to be desorbed some impuritical substances. The loaded biosorbent was regenerated using 0.1 mol·L-1 HCl solution for Pb(Ⅱ), 0.1 mol·L-1 EDTA solution for Cd(Ⅱ) and 0.2 mol·L-1 Na OH solution for Cr(VI). They could be used repeatedly at least for four times with little loss of adsorption capacity.These results showed that AFD could be considered as a potential and effective adsorbent for the removal of heavy metals from aqueous solution. Furthmore, a new idea will be provide to dispose and resourceutilization of antibiotic fermentation dregs discarded from pharmaceutical enterprises. |
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