تولید اتانول زیستی از کاغذهای باطله: امکان سنجی اقتصادی و حساسیت تجزیه و تحلیل

As a significant fraction of municipal solid waste, waste paper is a potential source for producing bioethanol. In the present paper, bioethanol production from various waste papers (newspaper, office paper, cardboard and magazine) using an enzyme complex (Cellic Ctec 1) was evaluated from an economic standpoint. Four bases cases without pre-treatment and two state-of-the-art cases (including dilute acid pre-treatment for office paper and oxidative lime pre-treatment for newspaper) were constructed using laboratory experimental data, literature values, expert consultations and simulation using AspenPlus™. Several scenarios were also carried out to assess the sensitivity of various technology parameters (i.e. solids loading in saccharification, anaerobic digestion and fermentation efficiency, and sugar yields in pre-treatment). The sensitivity analysis suggested that the economic performance of bioethanol produced from waste paper could be improved significantly with an up to 25% reduction in minimum ethanol selling price (MESP) by increasing solids loading in saccharification and with a 6% reduction in MESP by enhancing fermentation efficiency. The comparison of the bioethanol selling price at pump (reference year 2009) and the petrol price showed bioethanol produced from newspaper, office paper and cardboard were economically competitive with petrol.

Concerns over climate change effects and energy security have become prominent in public life in recent years. World energy consumption is predicted to increase by 50% to 2030 according to a prediction from the United States Energy Information Agency [1] and US retail gasoline prices have soared from 0.83 $/gallon in 2000 to 3.49 $/gallon in 2011 [2]. Such factors have stimulated the search for viable, alternative transport fuels. The UK is the third largest consumer of energy amongst the EU 27 countries, albeit with a relatively low dependency (25%) on energy imports in 2010 due to its large domestic energy production (mainly oil and gas) [3] and [4]. However, the share of renewable energy in the total energy consumption for the UK is relatively low as 3.3% in 2010 though progresses has been made toward the EU’s Renewable Energy Directive (RED) target of 15% by 2020 [5]. Compared with the first generation (1G) biofuel produced from food crops, second generation (2G) biofuels from lignocellulosic biomass or agricultural wastes have many advantages. For instance, most second generation biofuels are considered to be able to deliver substantial GHG emissions reductions when compared with petrol [6] and [7]. However, the development of 2G biofuels is also challenging, for example securing a low-cost and stable feedstocks, minimising land use changes caused by demand for biomass feedstocks and optimising bioethanol production technologies. Considering these challenges, waste papers as part of the degradable fraction in municipal solid waste (MSW) have potential to be a promising feedstock for bioethanol production. The reasons for this include: (1) waste papers are relatively abundant in the UK, reaching 8.8 million tons in 2008 due to reasonably efficient MSW collection and sorting systems, (2) they are economically competitive with other biomass feestocks because of the relatively low costs (average £40/ton), (3) they contain relatively high levels of carbohydrates that are potential convertible to bioethanol, (4) they are likely to be easily digestible without aggressive physical or chemical pre-treatments, (5) utilisation of waste papers for bioethanol production may offer a useful and valuable alternative route to managing these papers in addition to/as a complement to recycling. There is also a potentially available resource of waste papers in the UK because only 45% of recovered papers were recycled domestically while the remaining were exported overseas (in 2008) and in parallel the UK imported approximately 4.9 million tonnes of pulp and paper products. This reflects the fact that not all recovered paper is demanded by UK paper mills because paper quality specifications mean there are limits to increasing the recycled content in paper products [8] and, furthermore, (6) paper recycling technology itself has limitations, for example, effective deinking technology is needed to produce high quality paper products, paper fibres can only be recycled through a limited number of cycles and recycling to paper is very difficult for waste paper that has been mixed with other ‘organic’ waste (kitchen/garden waste etc.). Economic analysis has been used as a promising tool to assist the biofuels research community in identifying key cost drivers, evaluating novel technologies and assessing new process configurations. The National Renewable Energy Laboratory (NREL) in the US has developed a detailed techno-economic model for corn stover-based bioethanol production process design, to evaluate new developments and technologies [9], [10] and [11]. The NREL model has been adapted in several studies, including the present research [12], [13], [14], [15], [16], [17] and [18]. In a previous study, we reported composition and high-solids loading saccharification results for various waste papers [18]. These laboratory-derived primary data have been used here to adapt the NREL corn stover-based model to a suitable process design for bioethanol production from waste papers [18]. The effects of varied feedstock, process and technology parameters on the economic analysis of ethanol from waste papers as reflected in the calculated minimum ethanol selling price (MESP) are investigated in the present study. This work aims to provide a detailed economic assessment for waste papers-derived bioethanol production with sensitivity analysis and discussion on the robustness of this approach to biofuel production.

Economic analyses of bioethanol production from various waste papers were conducted using experimentally generated data, literature data and AspenPlusTM simulation. It is concluded that, with the exception of magazine paper, bioethanol produced from newspaper, office paper and cardboard can be economically superior to petrol at pump prices. In addition, DA and OL pre-treatments can improve the economic feasibility of office paper-to-bioethanol and newspaper-to-bioethanol supply chains. A series of sensitivity analysis suggests that biomass feedstock cost, capital costs and surplus electricity selling price are dominant factors affecting the MESP. Therefore, securing a feedstock source at relatively low prices, reducing capital investment, and selling surplus electricity at high price can improve the economic performance of waste papers-to-bioethanol supply chains. The sensitivity analysis also suggests that increasing the solids loading in saccharification and enhancing fermentation efficiency can reduce the minimum ethanol selling price. Overall, this work suggests that there is considerable potential from an economic perspective for using waste paper as feedstock for bioethanol production. These analyses provide an economic rationale and incentive for further environmental impact studies such as those of Shi et al. [42] and Wang et al. [43] and [44] (including consequential effects such as diversion, increased recovery in paper recycling etc.) on the potential for using waste papers as feedstocks for biofuel production.