60ª Reunião Anual da SBPC

INTRODUÇÃO:

As Peak Oil and Global Warming become topics of main ecological concerns, biofuels get increasing importance as an alternative energy. Usually biofuels are presented as suitable option for energy supply, considering that if adequately supported, they could replace a portion of fossil fuels. The main reasons presented to promote biofuels production are: (a) they are “green”, because are produced from renewable natural sources and, therefore, could supply a virtually infinite amount of energy for an infinite period of time; (b) biofuels, by replacing oil, would allow reducing GHG emissions; (c) biofuels are noticed as a good strategy for rural development. However, biofuel production requires the use of fossil fuel energy, as fertilizers, agrochemicals, machinery for both agricultural and industrial phases, as well as transportation of raw materials, inputs and distribution of biofuel. Moreover, depending on the biomass used, biofuels processing could require huge amount of fossil fuel. Biofuel production, as it is conceived nowadays, promote social exclusion and increase biodiversity loss and global warming. This study discusses biofuels renewability and examine the environmental feasibility of large-scale biofuel production.

METODOLOGIA:

In this work three different methodologies were used to make system diagnosis: Embodied Energy Analysis (EEA) method accounts the amount of commercial energy that is required directly and indirectly by the process of making a good or a service (Slesser, 1974; Herendeen, 1998). All the material and energy inputs are multiplied by appropriate oil equivalent factors (kg oil/unit) and converted to energy units using the standard calorific value of oil fuel. After that, energy output is compared with energy input. Emergy Accounting (EA) looks at the environmental performance of the system, taking into account the free environmental inputs such as sunlight, wind, rain, which are not usually included in EEA. Emergy is defined as the amount of solar available energy that was directly or indirectly required to make a given good or service and it is measured in solar equivalent Joules (seJ). The Ecological Footprint (EF) is an accounting tool that makes possible to estimate the resource consumption and waste assimilation requirements of a defined human population or economy sector in terms of corresponding productive area (Wackernagel and Rees, 1995).

RESULTADOS:

The EEA of biodiesel from soybean shows that 2.34 Joules of biodiesel are produced per Joule of fossil fuel used. For sugarcane ethanol this value is 8.2. Fossil fuels present much higher energy return, between 10-15 (Ulgiati, 2001). Considering this approach, we realize that biofuels use high amounts of fossil fuel energy in agricultural and industrial conversion stages. In some cases, fossil fuel energy used for biofuel production overcomes the energy available in the biofuel delivered, as for corn and cellulose ethanol produced in USA (Pimentel and Patzek, 2005). Considering EA, results showed that only 25% of the resources used to produce biofuel from soybean are renewable. Ethanol from corn uses 9%, and sugarcane ethanol, 30% in conventional systems. EF indicate that, in a scenario where all Brazilian automobiles use ethanol, required forest area to absorb the CO2 emitted would be 6.08 million ha smaller than if they use fossil fuel, but the amount of additional area required to counterbalance erosion and secure biodiversity would be 34.40 million ha. Comparing sugarcane plantation and native forest ecosystem services, results showed that sugarcane reduces the capacity of water percolation and lead to high losses of nitrogen fertilizer by leaching and runoff processes.

CONCLUSÕES:

Emergy Accounting and Ecological Footprint Assessment showed quantitatively that biofuels produced nowadays couldn’t be considered as renewable energy sources. When crop production and industrial conversion to biofuel are supported by fossil fuels in the form of chemicals, goods, and process energy, the fraction of biofuel that is actually renewable is very low. The future of biofuels is very likely to be linked to the ability of clustering biofuel production with other agro-industrial activities at an appropriate scale and mode of production to take advantage of the potential supply of valuable co-products. If the biofuel production systems are not carefully designed as diversified small-medium scale integrated systems (that produces food, energy and environmental services), for example using the “eco-unit” perspective (Gunther, 2004), the intensive exploration of land and fossil fuel use for biofuels production is more likely to result in green deserts and social damages than to become a renewable energy source to society. Some possibilities exist and are being used in small scale, but we need efficient Public Policies to make them concrete measures in large scales.

Instituição de fomento: The authors wish to acknowledge the financial support from Capes, CNPq and Fapesp.

Palavras-chave: Food, Energy, Ecosystem Services

E-mail para contato: ortega@fea.unicamp.br