基于生命周期的污泥基活性炭制备工艺环境影响研究

ENVIRONMENTAL IMPACT ASSESSMENT OF SLUDGE-BASED ACTIVATED CARBON PREPARATION PROCESS BASED ON LIFE CYCLE

利用污泥制备活性炭是具有广泛应用前景的污泥资源化利用途径。但是目前对污泥基活性炭(SDAC)制备工艺进行评价的研究较少。以污水厂污泥制备活性炭为对象,建立了制备工艺流程图,运用生命周期评价(LCA),定量揭示制备工艺的环境影响及关键影响因素。结果表明,整个制备工艺中焙烧步骤对环境的影响占主导地位,其次是研磨或浸渍步骤,最后是洗涤和干燥步骤。水蒸气物理活化、CO_(2)物理活化、KOH浸渍法、ZnCl_(2)浸渍法、H_(3)PO_(4)浸渍法、ZnCl_(2)熔融盐法、物理化学法的能量消耗量分别为68.976,79.776,47.376,53.964,48.564,45.828,46.764 MJ/kg活性炭,而全球变暖潜力值分别为14.93,17.06,15.54,13.42,14.51,12.65,13.91 kg CO_(2)eq/kg活性炭。LCA结果表明,利用CO_(2)物理活化方法制备活性炭对环境影响最大,而ZnCl_(2)熔融盐法对环境影响最小。对ZnCl_(2)熔融盐法敏感性分析结果表明,用电量和活化剂是进一步优化活性炭制备方法的两个关键因素。基于生命周期视角,ZnCl_(2)熔融盐法制备SDAC效果更优,同时应强化设备节能改造,可显著降低SDAC制备过程环境影响。

The preparation of activated carbon from sludge is a resourceful way to utilize sludge and with a wide range of applications.However,few studies have been conducted to evaluate the process of sludge-based activated carbon(SDAC)preparation.In this study,the activated carbon prepared from sewage plant sludge was used as an object,and a flow chart of the preparation process was established to quantitatively reveal the environmental impacts and key influencing factors of the preparation process by applying life cycle assessment(LCA).The results showed that the environmental impact of the roasting step dominated the whole preparation process,followed by the grinding or impregnation step,and then the washing and drying steps.The energy consumption of water vapor physical activation,CO_(2) physical activation,KOH impregnation,ZnCl_(2) impregnation,H_(3)PO_(4) impregnation,ZnCl_(2) molten salt method,and physicochemical method were 68.976,79.776,47.376,53.964,48.564,45.828,and 46.764 MJ/kg of activated carbon,respectively,whereas the values of global warming potential were 14.93,17.06,15.54,13.42,14.51,12.65 and 13.91 kg CO_(2) eq/kg of activated carbon,respectively.The LCA results showed that the preparation of activated carbon using the CO_(2) physical activation method had the highest environmental impact,while the ZnCl_(2) molten salt method had the lowest environmental impact.The results of sensitivity analysis on the ZnCl_(2) molten salt method showed that electricity consumption and activator are the two key factors for further optimization of the activated carbon preparation method.Based on the life cycle perspective,the ZnCl_(2) molten salt method is more effective in preparing SDAC,and the energy-saving modification of the equipment should be strengthened,which can significantly reduce the environmental impact of the SDAC preparation process.