ارزیابی چرخه‌ حیات روش‌های دفع نانوجاذب mgo-nh2 مورد استفاده در حذف یون‌های جیوه از محلول‌های آبی

استفاده از نانوجاذب‌ها، علی‌رغم اثرات مثبت اقتصادی و محیط‌ زیستی، به‌دلیل مصرف منابع اولیه‌ طبیعی، مصرف انرژی و تولید دی‌اکسیدکربن می‌تواند پیامدهای محیط‌ زیستی شدیدی به همراه داشته باشد. در مطالعه‌ اخیر، به بررسی پیامدهای دفع نانوجاذب سنتز شده از اکسید گرافن (mgo-nh2) استفاده شده در حذف یون‌های جیوه از محلول‌های آبی طی دو سناریوی واجذب و لندفیل به کمک روش ارزیابی چرخه‌ حیات پرداخته شد. تحلیل و ارزیابی پیامدهای محیط ‌زیستی دو سناریو، با استفاده از نرم‌افزار سیماپرو (نسخه‌ 5·9) و پایگاه داده ecoinvent (نسخه‌ 3.4) بر اساس استاندارد ایزو 14040 و ایزو 14044 انجام شد. از شاخص recipe midpoint h و شاخص recipe endpoint به‌ترتیب جهت تعیین 18 پیامد میانی و سه دسته پیامد پایانی استفاده شد. هم‌چنین، جهت بررسی پتانسیل گرمایش جهانی، ردپای بوم‌شناختی و میزان انرژی خواهی تجمعی، به‌ترتیب شاخص‌های پروتکل گازهای گلخانه‌ای، ردپای اکولوژیکی و تقاضای انرژی تجمعی محاسبه شد. نتایج نشان داد که در تمام پیامدهای مذکور، سناریوی واجذب به‌دلیل مصرف برق، بیش‌ترین سهم را بر پیامدهای مورد بررسی در مقایسه با سناریوی لندفیل دارا است. هم‌چنین، بر اساس نتایج تقاضای انرژی تجمعی، سوخت‌های فسیلی با 94/29 و 90/50 درصد مشارکت بالاترین میزان مصرف انرژی را به‌ترتیب در دو سناریوی واجذب و لندفیل داشتند و سهم سایر منابع ناچیز بود. لذا فرآیند لندفیل جهت دفع نهایی نانوجاذب به‌کار رفته در حذف یون‌های جیوه پیشنهاد می‌شود. از سوی دیگر، با توجه به پتانسیل مناسب نانوجاذب در حذف یون‌های جیوه و امکان استفاده‌ مجدد از آن به کمک فرآیندهای اسیدی، بازجذب نانوجاذب می‌تواند نقش موثری در کاهش پیامدهای محیط ‌زیستی داشته باشد.

life cycle assessment of mgo-nh2 nano-adsorbent disposal methods used for the removal of mercury ions from aqueous solutions

introduction heavy metals have posed significant threats to aquatic organisms and human health globally. mercury (hg (ii)) is of particular concern due to its persistence and harmful environmental properties. different physical and chemical separation approaches have been proposed to remove hg (ii) ions from water and wastewater. regarding the available adsorbents for the adsorption of toxic metal ions, nano-adsorbents are preferred due to their high adsorption capacity, low waste production, and simplicity in design and operation. among nano-adsorbents, functionalized graphene oxide (go) is the most applicable and widely used adsorbent for removing metal ions from aqueous solutions. meanwhile, the use of go is an emerging technology and is in the early stages of development and the environmental assessment of its application and disposal requires focused attention. life cycle assessment (lca) is an effective method for estimating the environmental impacts associated with the life cycle of a product or process from the early stage of production to its final disposal. hence, the lca of mgo-nh2 disposal, utilized for hg (ii) removal, was investigated in two scenarios including: desorption and landfill. materials and methods the lca of mgo-nh2 disposal was evaluated based on iso 14040:2006 standard, considering a functional unit of one kg of mgo-nh2 nano-adsorbent for mercury removal. the system boundary was based on two disposal scenarios including desorption and landfill from gate to grave. hcl, hno3, and h2so4 were utilized for the mercury desorption using mgo-nh2 nano-adsorbent to determine the efficient one. on the other hand, the recipe (h) 2016 midpoint and endpoint methods were applied to assess the environmental impacts of mgo-nh2 nano-adsorbent disposal using simapro 9.5.5.0 and the ecoinvent 3.4 datasets. the 18 midpoint impact categories were summarized into endpoint indicators such as damage to human health, ecosystem, and resources categories. meanwhile, the life cycle inventory was provided from experimental studies, and simapro databases. moreover, greenhouse gas (ghg) emissions during the disposal process were evaluated by greenhouse gas protocol (ggp). the ghg release was monitored from fossil fuel, biogenic, and land transformation. the energy flow was assessed in six impact categories including non-renewable fossil fuel, nuclear, biomass as well as renewable biomass, wind solar, and water resources using cumulative energy demand (ced). in addition, the ecological footprint (ef) of the disposal process was appraised in co2, nuclear, and land occupation categories. results and discussioncomparing the two disposal scenarios, the environmental impacts of the desorption scenario were significantly higher than the landfill scenario whereas the landfill scenario showed higher non-carcinogenic toxicity (9.29 kg 1, 4-dcb) than the desorption process with a value of 6.29 kg 1,4-dcb. evaluation of contributed parameters and processes in the environmental impact categories for the desorption scenario illustrated the significant role of electricity consumption. since electricity is produced from diesel and oil fuel in iran, it intensifies the environmental burdens, especially global warming. due to the substantial electricity required for nano-adsorbent synthesis and desorption, it increased the considered impacts compared to the landfill scenario. therefore, the electricity consumption during desorption process can be optimized by reducing the reaction time without altering the nano-adsorbent characteristics and its performance. the utilization of renewable energy sources in electricity generation can also reduce pollutant emissions. the assessment of endpoint impacts of nano-adsorbent disposal revealed notable effects of the desorption scenario on human health, ecosystems, and resources. the results of ced also indicated the highest share of fossil fuels with 94.29% and 90.50% contributions to desorption and landfill scenarios, respectively. meanwhile, the ggp index demonstrated a higher contribution of the desorption scenario to global warming potential, which was attributed to fossil fuel combustion. the amount of co2 release, land occupation, and nuclear energy derived from the ecological footprint analysis elucidated a much lower ecological footprint of the landfill scenario compared to the desorption scenario. conclusion the environmental impacts of the mgo-nh2 nano-adsorbent disposal used for the removal of hg (ii) ions were investigated to choose the appropriate method within desorption and landfill scenarios using lca. the comparison of two mgo-nh2 disposal scenarios indicated that the landfill scenario incurred lower environmental impacts compared to the desorption scenario. evaluation of the midpoint and endpoint impacts, ced, ggp, and ef highlighted the high environmental burdens of the desorption scenario concerning electricity consumption. moreover, the application of the landfill process can be restricted due to the lack of available land. on the other hand, due to the high cost of mgo-nh2 synthesis and also its suitable potential in hg (ii) ions removal, the possibility of mgo-nh2 desorption and reuse can reduce the environmental burdens compared to re-synthesis. furthermore, for desorption of mgo-nh2 nano-adsorbent on an industrial scale, electricity consumption should be optimized and supplied by renewable energy sources.