| As a kind of high value-added alkaloid, Nicotine widely exists in tobacco plants. It can be used to produce highly effective pesticide, foodstuff, dietary supplements, flavours — fragrances, animal feed additive and something else. Meanwhile, its derivative niacin can effectively prevent senile dementia. However, the manufacture of tobacco produces large amounts of tobacco processing wastewater(TPW) which contains significant amounts of nicotine. Unfortunately, the nicotine is failed to get reasonable utilization. Hence, sufficiently recovering and utilizing the nicotine in the TPW will have wide prospects. This paper has focused on researching the processes of pretreatment of Ca/Mg/Al coagulant on TPW, nicotine adsorption on chark and nicotine recovery.Coagulation stage: Ca/Mg/Al coagulant was employed to pretreat TPW and the experimental conditions regarding 3 main factors(initial p H, coagulant time, coagulant dosage) were optimized by response surface methodology(RSM) using chemical oxygen demand(COD) removal. The optimum conditions achieved by Design-expert software through Box-Behnken design were p H 8.2, coagulant time 11.3 min and coagulant dosage of 47.8 g L-1. Under this condition, the maximum COD removal reached 62 % and the color decreased to 10 times. The Ca/Mg/Al coagulant had no significant effect on nicotine removal from the wastewater with more than 92% remaining. IR spectroscopy of the flocculated slurry showed that the Ca/Mg/Al coagulant mainly removed organics including protein, carbohydrate, cellulose, hemicelluloses, pigment and nitrogen compounds from TPW.Adsorption stage: chark was applied to adsorb nicotine and the adsorption behavior of nicotine was investigated detailedly. The results indicate that Langmuir model is found to best simulate the experimental data compared to Freundlich model, the maximum adsorption capacity reaches to 32.79 mg g-1 at 50 ℃. Under this temperature, the surface area of chark occupied by nicotine is only 0.275 which shows large fraction of chark surface is unoccupied by nicotine. With the research of thermodynamics, it indicates the adsorption of nicotine on chark is a spontaneous process along with entropy increase and endothermic. For better comprehension of nicotine adsorption on chark, first order kinetic model, second order kinetic model, Bennahum kinetic model and intraparticle diffusion kinetic model were applied to describe the adsorption kinetics, respectively. The results show Bennahum kinetic model is the best one that can perfectly explain the adsorption behavior of nicotine on chark.Nicotine recovery stage: Chark was applied to treat the TPW which had already pretreated by Ca/Mg/Al coagulant. This part discussed the influence of dosage of chark, solvent types, liquid-solid ratio and temperature to nicotine adsorption and desorption. The results reveal there is nothing obvious effect for nicotine adsorption when the dosage of chark is greater than 30 g L-1. And trichloromethane has better desorption property compared to other solvents. In this system, the lower temperature, the better desorption ability. For example, the desorption efficiency of nicotine as high as 95.3% at 30 ℃. Finally, 40 L TPW was treated by Ca/Mg/Al coagulant and chark at the optimal parameters, the COD eventually decreased to 98 mg L-1 from initial 2000 mg L-1 and the color decreased to 2 times. Using trichloromethane as the desorption solvent to desorb nicotine at room temperature, Finally, 60% purity nicotine was obtained after distillation. |
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