Sustainable? Processes from Renewable Resources

נשלח 19 באוק׳ 2011, 12:41 על ידי Sustainability Org   [ עודכן 19 באוק׳ 2011, 12:41 ]

D. Sandholzer, M. Narodoslawsky

Graz University of Technology, Institute for Resource Efficient and Sustainable Systems, Inffeldgasse 21/B, 8010 Graz, Austria

Tel. +43 316873 7977, e-mail:sandholzer@arena-research.at, fax: +43 316873 7963


 

Abstract

As fossil resources become more expensive scientific research and process development concentrated in the last years on renewable resources as production feedstock. New products were introduced into the scientific community but only a few made it into the markets. A reason for many of these products to fail was the very reason they had been developed: a lack of sustainability.

To avoid developing unsustainable and therefore unsuccessful products from renewable resources life cycle assessment already during development phase is essential. Although such assessment has to be done for each single process some general conclusions regarding renewable resource processes can be drawn by past developments. These heuristics help process developers to keep an eye on common ecological “hot spots” for renewable resource processes.

 

Introduction

Today much attention is given to the use of renewable resources as a way to achieve sustainability. These topics are discussed widely not only inside the scientific community but in politics and industry too. Technology based on renewables is believed as a sure bet to contribute and achieve sustainability of future mankind.

The experiences of the past decades (oil crisis and continually rising prices) have shown the vulnerability of the fossil based economy. The number of years that these resources are believed to last varies greatly, depending on the person asked. Nonetheless it is a fact that someday we will run out of crude oil and natural gas.

The remaining deposits are concentrated in politically unstable regions, leading to unsure provision of fossil feedstock. The effect of this can be seen in the increasing of numbers and intensity of conflicts in such regions.

Besides the primarily economic and political issues the ecologic consequences of the use of fossil resources must also be considered. Here two main areas of can be discerned. The influence of fossil CO2 on the climate change and the influence of fossil based agriculture on the environment.

The impacts of the unchecked consumption of fossil resources can be perceived clearly. Environmental effects as eutrophication, acidification, ozone depletion and climate change have been influenced by human activities stronger than ever.

More extreme temperatures in summer and winter were measured in many regions of the world and the increasing numbers of floods, draughts, hurricanes and other natural disasters have additionally heated the discussion of our role in the change of the earth.

Scientists are warning now that we move toward a “point of no return” in climate change, polluting the natural compartments with too many emissions. The only chance to avert crossing this point would be a massive decrease of fossil resource usage. The logical alternative is a change to renewable resources. However, this may lead to further intensifying of cultivation practices in agriculture and the agricultural sector itself is critical from an ecologic standpoint.

Mankind depends on the management and harvest of biological resources. Therefore, their habitats have always been influenced by the conversion of ecosphere into cultivatable land and still are. This conversion has been the most evident change on our planets surface, leading to the fact that at the beginning of this century mankind has put about half of the planets surface to their service. This was accomplished by massive land degradation and loss of biodiversity worldwide.

However, not the amount of land use itself led to these results but the kind of cultivation is the problematic point. Industrialized societies developed a way to breach the limitations of biological resources by utilizing fossil feedstock. Due to this fact mankind was able to decouple industrial activities from biological productivity. Renewable resources as feedstock lost importance in many sectors to be replaced by fossil ones. A whole new industry branch, the petrochemical industry, arose from these circumstances. This industrial sector creates synthetic materials and fossil based chemicals that were able to compete with and often outperform goods from renewables. This change also influenced the agricultural sector where the intensity of cultivation was increased by applying synthetic fertilizers and pesticides along extensive use of machinery.

Due to these facts there exist two groups promoting the feedstock change from fossil to renewable resources. One group argues from an economic point of view with the goal of breaking the dependency from a feedstock that gets scarcer and more contentious. The other group acts from an ecological viewpoint to ensure that earth is habitable in the future. Regardless their reasoning, both groups propose a feedstock change to renewable resources. This shall solve the problems of present and future generations.

The question is if this change alone will really lead to a more sustainable industry and lessen our environmental problems?

 

Ecological Assessment for Process Development

When a change in feedstock to renewables is to be implemented many actors have to act in unison: e.g. agriculture, forestry, industry, transportation. A main challenge will be to change the processes itself according to demands of the new feedstock.

Processes on the base of renewable resources always have an “intrinsic” perception of being environmentally friendly and sustainable. As this property is a major selling point for products generated by these processes there is a necessity to prove their sustainability credentials in a rigorous manner that can withstand the scrutiny of a competitive market.

Here engineers and process developers will play a key role on the way in realizing these processes. To ensure sustainable processes and sustainable industry it is therefore, necessary to equip process developers for this task – regarding the background as well as working tools.

Measurement of environmental sustainability of technological processes and goods is necessary to provide support for decisions regarding ecological problems. The challenge is to translate matters of ecological sustainability into the language of engineers neither limiting the field of application in terms of variety of technologies nor disregarding ecological interrelations on which sustainable concepts are based.

Life cycle assessment (LCA) is a good basis for product and process evaluation as was shown due to many studies. It is able to account for all environmental impacts incurred by the provision of the good in question. Strict standards for LCA are laid down in the ISO standards of the 14.00X family [1].

The ISO standard divides the Life Cycle Assessment in four phases (Figure 1). In the first phase a goal and scope definition has to be done. This includes the definition of system boundaries which clarifies the content of the life cycle assessment.

fig1

Figure 1: Structure of a Life Cycle Assessment according to the ISO 1400x norm

In the second phase data is collected and related to the process steps in question. Eco-inventories including all relevant input and output data of a process are assembled. If a process produces more than one product allocation methods have to be chosen.

In the following impact assessment phase the data is assessed according to the chosen methodology to obtain evaluation results. These results are then interpreted.

During the life cycle assessment results may be obtained that may propose a revision of prior phases, e.g. the system boundaries if a process has been excluded that now seems to be important. Therefore, LCA has to be seen as iterative process.

However, these standards only provide a guide how to proceed in the evaluation and do not prescribe a fixed evaluation method. In case of assessment of processes from renewable resources LCAs are further complicated as they face special methodological challenges. Firstly, many industrial renewable raw materials are by-products or surplus products from agricultural activities leading to other (more valuable) products. This leads to the fact that in contrast to conventional resources we face not linear value chains but more complex production networks. With multi-output processes the general problem of allocating the pressures of the agricultural sector arise (as agricultural production is not driven by generating the by product that is utilized). This may considerably influence the outcome of any assessment. In some cases the raw materials are even streams that are considered as waste, which makes a prudent valuation even more complicated.

The second challenge that has to be faced is the sustainability evaluation of processes leading to the same sort of goods on the base of different raw materials. This valuation must account for the different impacts from different raw material generations. Especially the difference between renewable and depletable raw material systems must be evaluated.

Next to these methodological challenges further requirements have to be met by ecological assessment for processes from renewable resources. It is a fact that a process will never be an ultimate solution and continuous optimization is necessary. This task contains making compromises as in improvements on one front often lead to disadvantages in others. When economical considerations are the basis of process development such decisions between benefits and drawbacks can be calculated easily as such tools have been provided and used constantly in the past decades. Comparing alternatives on ecological basis is much more difficult for an engineer as there exist many different problem fields where ecology is affected by processes, e.g. climate, health.

Most of the LCA are based on the problem oriented approach to impact assessment (Centrum vor Milieukunde Leiden, CML-method) [2],[3] resulting in various impact categories. They provide a reasonable communication and discussion tool for questions like which environmental problems are caused to which extent over the life cycle of a product. But in many “real world cases” improvements on one front, like reduction of greenhouse gas emissions, tend to lead to disadvantages in other areas. How to weight an increase in greenhouse gas emissions against a decrease in acidification potential?

Ecological assessment for process development has therefore, to lead to a highly aggregated number which can be compared easily. In order to be of interest for a process developer this aggregated number will have to be sound from a scientific vantage point of view as this is the basis for engineering. Instead of eco-indicators (e.g. EcoIndicator 99 [4][5]) that are based on weighing factors set by experts that are thus not undisputable, a tool for engineering puposes must have a more generally acceptable methodological base.

The Sustainable Process Index, which will be explained in detail in the next chapter, fulfills all the above mentioned demands.

The Sustainable Process Index

Energy which is consumed inside a system has to be renewed by provision from outside. This also holds true for the earth, a system of its own. The energy source here is the solar radiation. As society is highly dependent on energy as it is the driver of all life on earth the definition of a sustainable society has to be based on a sustainable energy provision.

Therefore, energy emitted from the sun represents the only energy source for a sustainable society.  This energy is used by many natural processes which in themselves are sustainable. To collect and utilize this solar energy e.g. in form of photosynthesis, surface area is needed. This also holds true for anthropogenic utilization of solar radiation like photovoltaic panels.

Although available practically indefinitely solar radiation is a limited flow as it is received by our planets finite surface. Therefore, all natural as well as anthropogenic activities compete for surface to utilize the limited flux of solar energy that they need for sustaining themselves.

This concept was developed in parallel from two different points of departure. Rees and Wackernagel looked at the problem from the economical point of view whereas Narodoslawsky and Krotscheck focused on the engineering perspective. These approaches led to the "ecological footprint" [6] and the Sustainable Process Index (SPI) [7].

The Sustainable Process Index focuses on aspects of environmental sustainability for engineers and the factors they can influence most effectively. These factors are material and energy flows that processes exchange with their environments.

The SPI uses a concept for environmental sustainability taking into account the limitation in the natural income for setting criteria for the exchange of material flows between anthroposphere and the environment.

These criteria were developed by SUSTAIN [8]. The criteria are:

·         Human activities must not alter long term storage compartments of global material cycles in quality as well as in quantity. If this principle is not adhered to resources will be depleted and substances accumulated in ecosphere, overstraining the natural cycles.

·         Flows to local ecosphere have to be kept within the qualitative and quantitative range of natural variations in environmental compartments. If such flows exceed the amount a compartment can integrate the accumulating substances will alter the compartment. This alteration can lead to a local environment that is no longer able to sustain flora and fauna.

·         Also preservation of a variety of species, landscapes and habitats has to be preserved or increased. Variety is an important factor for flexible response of natural systems to pressures. ,

 

Human activities exert impacts on the environment in different ways. On the one hand they need resources, energy, manpower and area for installations. On the other hand besides to the intended goods they produce emissions and waste. Consequently the SPI includes all these different aspects of ecological pressure on the environment. Therefore the total area Atot for sustainable embedding of human activities sustainable into the ecosphere is calculated by (eq. 1).

 
equation 1

  [m2]     (1)
 
Equation 2

 [m2]     (2)
 
Equation 3

[m2]     (3)


The areas on the right hand side are the “partial areas” that refer to the impacts of the different productive aspects. AR, the area required for the production of raw materials, is the sum (eq. 2) of the areas to provide renewable raw material (ARR), fossil raw material (ARF) and non-renewable raw material (ARN). AE is the area necessary to provide process energy including electricity. AI, the area to provide the installation for the process, is the sum (eq. 3) of the direct use of land area (AID) and the area for provision of buildings and process installations (AII). AS is the area required for support of staff and AP is the area for sustainable dissipation of emissions and waste products into the ecosphere.

For some resource flows like area consumption or the cultivation of renewable resources ARR the conversion is easy. Area consumption is based on the amount of area needed for growing a certain renewable resource, which is well known. The assumption here is that in a sustainable agriculture the process of growth and harvest closes the global cycles (e.g. the carbon cycle) on the field without changing local environmental compartments. However the effort for the activities of agriculture (energy and material input for planting, cultivating, harvesting and storing) has to be factored in order to take into account the whole life cycle.

The area needed for fossil resource provision is based on the first principle as well, meaning that these flows are linked to the process of replenishing long term storage of carbon. The SPI method here takes into account the process of sedimentation in oceans, as this process takes out carbon from the dynamic global cycle into a long term storage compartment.

The conversion of non renewable resources to area is more difficult. Because no global cycles exist for non renewables, their use is inherently dissipative. Therefore the impact for these materials is generally separated into two parts: the provision of the material and the dissipation of the resulting emissions and wastes. The provision is taken into account within the raw material area ARN. It takes into account the impact of the whole life cycle to provide a non renewable material to the factory gate. Wherever no full life cycle for these materials is available, the energy input for mining and refining (as this usually provides the largest impact) is taken as a proxy. If even that is unknown, a first estimation of consumed area is made via the retropagatoric method. This uses the ratio of product value to energy input to estimate the ecological impact.

The conversion of emission of processes in air, water and soil are calculated using the second principle. For most substances their existing concentration in (ground) water and soil is known. For these two compartments a replenishment rate can be defined, for ground water this is the seepage rate (depending on local precipitation). For soil the replenishment by decomposition of biomass to humus (best measured by the production of compost by biomass) is taken as a measure of renewal of this compartment. So area for "sustainable dissipation" of emissions is calculated by the amount of area needed to replenish enough ground water or soil that is able to absorb the amount of a given substance in the emission flow of a process without exceeding its natural concentration level in the respective compartment.

Emissions to the compartment air are treated slightly different, as there is no natural replenishment rate for this compartment. Here the natural exchange of substances between forests and air per unit area (which is known for most airborne substances) is taken as a base of comparison between natural and anthropogenic flows.

For a given emission flow (e.g. the gas effluent from a stack) all dissipation areas for the constituent substances flows to their final compartment are calculated. Only the largest of these dissipation areas however is taken into account, because all emissions with lower area consumption may be dissipated in this area without violating the second principle stated above in any other compartment.

For the purpose of technological optimization the impact per good or service unit is of interest. This is represented by the overall footprint of a product atot (eq. 4).


 
Equation 4

 [m2 /unit a-1]    (4)

NP is the number of goods or services supplied by the process in question for a reference period. In general this reference period will be one year, as most natural and engineering flow data are available on a yearly base, leading to a unit for NP depending on the good or service of unit.a-1. [15].

The area derived from a specific process to provide a specific good or service can be related to the area that is statistically available to a person. This relation represents the "cost" in terms of ecologic sustainability of this particular good or service, the SPI (eq. 5)

 
Equation 5

 [cap/unit]         (5)
 

where ain is the area per inhabitant in a given region. The lower the SPI the lower is the ecological impact of providing the good or service on the ecosphere.

The engineering data needed for calculating the SPI are the energy and mass flows of a process. The corresponding data for natural systems are the sedimentation rate of carbon in oceans, the natural concentrations of substances in soil and water, the exchange rates per area unit of airborne pollutants between forests and air and the replenishment rates for soil and water. Most of the natural flow and quality data allow a certain "regionalisation" of the SPI wherever that is needed.

The results of a SPI analysis contain diverse information. The SPI as calculated by eq. (5) gives an indication of the "cost" in terms of ecological sustainability of a given product or service. The SPI number indicates what fraction of the overall "ecological budget" of a person is used to provide this good or service.

The partial areas in eq. (1) to (3) allow the identification of the largest contribution to the overall impact in terms of impact categories. The evaluation of the contribution of different steps to the overall footprint in eq. (4) allows to identify the step in the life cycle that is the most problematic from the view point of sustainable development and that is the premium target for technological optimisation. Finally the inspection of the largest partial area caused by any step in the life cycle offers the possibility to identify optimisation potential in an in-depth technological optimisation.

Heuristics for Renewable Resources Processes

Ecological assessment of different processes from renewable resources was done in our working group with the SPI [10]. During this work problematic areas of such processes have been identified. Most prominent among them are energy input, chemicals and feedstock from agricultural production.

Energy

Energy is in almost all processes the largest contributor to the ecological pressure. However, energy is a very general term summarizing different subcategories. For a better understanding of the ecological implication of energy we have to discern between two energy categories used in industries: electricity and process heat.

Electricity is used mostly for running pumps, agitators and other machinery. Especially biotechnology uses much mechanical energy. Electricity is produced from different sources: nuclear fission, fossil resources like oil or natural gas, coal and renewables like wind, water or biomass.

Process heat in form of direct heat or steam is often used to maintain elevated temperatures for reactions, for separating processes like distillation or drying. It is mostly produced from hard coal, fuel oil or natural gas.

Figure 2 show exemplary results of the contribution of electricity and heat for processes from renewable resources discussed in the Case Studies Chapters. As some processes use the same process data they are shown summarized.

Figure 2: Distribution of energy input for production of renewable products

Figure 2: Distribution of energy input for production of exemplary renewable products

It can be seen that in most processes electricity plays a major role. Nonetheless process heat is an important factor, too.

Electricity is needed in almost all industrial processes, often in large amounts. Nonetheless in most processes it is not seen as critical factor for economical competitiveness. This derives from the fact that electricity is usually a “cheap” input compared to process chemicals and raw material.

Renewable resource based processes seem to be especially electricity intensive. This fact arises on the one hand from the development phase those processes are in as most of them are either in an early development stage or have just been applied in industries in the last couple of years. Such processes are usually not optimized to their full extend yet and even when optimization has taken place, electricity optimization is not a priority. On the other hand renewable resource processing does need inherently more energy than comparable synthetic processes on fossil base. The reason for this is the fact that much more masses have to be processed when dealing with renewables and in case of fermentations this may also take much more time for reacting leading to a higher electricity demand as large fermenters have to be operated for long time.

Different kinds of electricity production cause different ecological pressure. In Figure 4 can be seen that the provision systems span a wide range of ecological pressure whereas the renewable electricity production systems lie at the lower end. The ecological footprints of the provision type can be related to its percentage of the electricity mix [9].

figure 3

Figure 3: The EU25 electricity mix

It becomes apparent that the provision types that exert the largest pressures on environment are most prominent ones in the electricity mix. The only exception is hydro power that plays a major role in some European countries (e.g. Austria, Norway).

Figure 4

Figure 4: Ecological footprints of 1kWh electricity produced by different systems

This fact leads to the conclusion that electricity consumption itself is not the problem. Problematic is the provision of this electricity in the current energy system. That a change to sustainable provision systems is possible was pointed out by different studies, e.g. by Zachhuber [11]. Additionally utilizing a sustainable electricity provision would lead to a further decrease of the environmental pressure as the provision and production systems are iteratively linked. So electricity from biomass would lower the ecological footprint of its biomass feedstock supply chain and vice versa.

Concerning process heat the picture is less diverse as heat is almost exclusively produced from fossil resources. Some factories utilize alternative heat production like burning of waste obtained during processing but this currently only covers a small fraction.

As the amount of process heat needed in industries is large optimization is already advanced here. Via heat exchanger lot of energy demand can be saved and the engineering methods for this optimization are commonly known.

What can be deducted from these results is the fact that not only the energy consumption of a process itself has to be considered during development of sustainable processes. The energy provision itself will have to change if sustainable industry has to be achieved.

How would the picture change if these energy systems are altered to sustainable systems? In order to estimate such a scenario a sustainable electricity and process heat mix has been assembled consisting only of processes from renewable resources [11]. The data for the energy provision processes was taken from this work too, based on an energy system that is feasible for Austria. Other countries may have different mixes due to Austria’s large availability of hydro power. It has to be clarified that these mixes are only assumptions for future energy generation systems and shall only show the potentials of such an energy change for processes based on renewables from an ecological viewpoint.

Electricity is provided by solar power plants, biogas plants and combined heat and power generation plants (cogeneration) besides the traditional processes of hydro, wind and biomass power.  The assumed electricity mix is shown in Figure 5.

fi

Figure 5: Sustainable electricity mix

The ecological footprint for such an electricity mix would be 4.53m2/kWh a-1. Compared to this the footprint of electricity for the EU25 countries at the moment is 552.95m2/kWh a-1. This means a change to a sustainable electricity mix would decrease the pressure on environment from this input category by about 99%. The reason for this tremendous decrease is that even the electricity provision inflicting the largest pressure on environment in this mix, photovoltaic, has only a footprint of 35.06m2/kWh a-1 whereas the least unsustainable electricity generation from fossil resources, natural gas, accumulates 147.65m2/kWh a-1.

In the case of process heat the energy mix assumed is shown in Figure 6. Most of the process heat here is provided by thermal utilization of wood chips. The remaining heat demand is covered by cogenerated heat from combined heat and electricity as well as biogas plants.
Figure 6

Figure 6: Sustainable process heat mix

The ecological footprint of the resulting process heat would be 4.02m2/MJ a-1. Comparing this value with the footprints of process heat from fossil resources e.g. 44.45m2/MJ  a-1 produced from hard coal and 19.58m2/MJ a-1 from natural gas a substantial decrease can be achieved.

Comparing the decrease of the pressure on environment for electricity and process heat it strikes out that electricity is able to lessen its footprint much more than process heat. The reason for this is that in the case of process heat the really unsustainable types of energy generation, nuclear power and lignite, are not applied and the still problematic one, hard coal, seldom. So process heat is mostly generated by the combustion of oil or gas, which inflicts relatively low pressure on environment compared to the other types. In electricity generation this trend is just the other way round. Here the “unclean” provision types produce most of the energy.

When this sustainable energy mixes are applied the footprints of renewable based products decrease dramatically leading in all cases to products more sustainable than their fossil counterparts. This holds true even if fossil goods are produced with this sustainable energy mix too, meaning that in this case only the feedstock derives from fossil sources.

In the shown results only the energy input for the processes were changed to the renewable energy mix. The specific footprints of all intermediates used in this processes are still based on the unsustainable energy mixes reflecting the present situation.

The effect of this will be addressed in the next Chapter.

Feedstock

Feedstock also plays a major role for processes from renewable resources. However, this effect does not always arise, depending on the kind of feedstock. If the feedstock is a waste or low value product it does not influence the ecological footprint prominently.

However, many processes utilize feedstock cultivated solely for this process. This cultivation is mainly done by agriculture to a lesser extend by forestry and aquaculture.

The origin of industrial renewable feedstock is almost always conventional agriculture (except for pulp and paper industry) which inflicts high pressure on environment. To grow agricultural crops with the maximum feasible yield, large amounts of fertilizer have to be used as the soil is not able to provide the nutrients needed. This comes from the fact that yield has surpassed the natural biological productivity by far. Additionally farmers often overstrain the soil by cultivating similar agricultural crops successive instead of rotating the cultivated crop in a way that allows the soil to regenerate. That leads to still higher fertilization demand creating a vicious circle especially for monocultures.

Due to large areas in which the same goods are cultivated they are more susceptible for fungal decay and pest. This leads to additional inputs of pesticides in conventional agriculture weakening the capacity of the soil further as benevolent insects and fungi are killed too. The high intensity of cultivation created a high demand of machining mostly in form of agricultural machines like tractors and combine harvesters. This machination need consumes large amounts of (diesel) fuel.

Figure 7 shows the fraction the agricultural inputs described above hold on the overall footprint of exemplary agricultural crops [13].
Figure 7

Figure 7: Distribution of the ecological footprint along the inputs of conventional cultivation

The distribution shows that fertilizer input is the main contributor to the ecological pressure during conventional cultivation. Machine use also inflicts high pressure on environment. Pesticides in contrary don’t generally have such a great influence on the environment. The area needed for cultivation and the production of the seeds are small in comparison.

A possibility to lower the pressure on environment is a change in cultivation from conventional practice to organic farming. Organic cultivation means abandoning synthetic fertilizers and pesticides. Figure 8 shows the footprint distribution of organic cultivation along the input categories.

fig8

Figure 8: Distribution of the ecological footprint along the inputs of organic cultivation

When organic cultivation is applied, the ecological footprint decreases and the distribution shifts. This shift is most noticeable in the decrease of the influence of fertilization. That is obtained due to the low fertilizer input allowed in organic cultivation. The largest contributor in organic cultivation due to this shift is the machine use. The influence of seed production rises as the overall footprint decreases and cultivation area plays also a bigger role as organic agriculture has a lower yield and therefore, needs more area per unit of produced good compared to conventional agriculture.

The main pressure agricultural machine use exerts on environment is due to the fossil diesel consumption. Therefore, a fuel change would ease the ecological pressure accumulated in agriculture considerably and would benefit especially organic cultivation. To estimate the decrease in the footprint when fossil diesel is replaced in agricultural machines the fuel provision was assumed to be false flax oil. The change of fuel leads to a decrease of 60% in the area of machine use and therefore, lowers the ecological footprint substantially. Figure 9 shows the decrease from conventional agriculture to organic agriculture and organic agriculture utilizing false flax oil as feedstock.

figure 9

Figure 9: Decrease of the ecological footprint utilizing different cultivation methods

In some cases this must be calculated in an iterative manner as the product of a process and feedstock production may be linked together. Utilizing organically grown sunflower seed for biodiesel production would lead to a more sustainable biodiesel. Applying this in agriculture would lead to a more sustainable sunflower cultivation and so on.

Chemicals

Chemicals may be a problematic factor from an ecological point of view. Some processes like the transesterification processes in biodiesel production utilize large amounts of chemicals (in the processes in question methanol). As this methanol is produced from fossil resources which inflict large pressure on environment and is utilized in large amounts the resulting partial footprint has a large influence on the overall footprint.

In such cases the chemical input plays an important role. Here process developers will have to minimize the input need and additionally look for more sustainable alternatives of process chemicals. In case of methanol this could be bio-methanol obtained from fermentation processes or gasification of biomass. Such change in the provision system of chemicals will lead to a decrease that can be substantial and ensure ecological sustainability.

As no data was available for production of bio-methanol assumptions for a comparison have to be made. These assumptions will lead to very rough results but they point out the alteration of the ecological pressure that can be expected of a chemical input change. Therefore, it is assumed that the bio-methanol can be substituted by bio-ethanol for first estimations. The data for bio-ethanol production comes from EdZ [12]. For the energy input biogas was utilized.

The production of bio-ethanol results in a footprint of 206,23m2/kg a-1. The ecological footprint of fossil methanol is 543.42m2/kg a-1. If bio-ethanol is applied to the transesterification step instead of fossil methanol the overall well to wheel footprint of engine output utilizing biodiesel from rape seed oil decreases to 51.05m2/MJ a-1. This is a decrease of 4%.

This shows that the change as well as an optimization of the chemical input of a process will not lead to a reduction of the footprint on the same scale as the energy and feedstock inputs.

Conclusions

Three major factors contribute to the ecological pressure of processes from renewable resources. These are energy, agricultural feedstock and chemicals.

Of these three chemicals usually have the smallest influence. A change in chemicals may lead to a decrease of the overall ecological footprint of the obtained product. However, this decrease tends to be small.

Agricultural feedstock has a much larger influence on the sustainability of a process especially if the feedstock is cultivated solely for the process. The kind of cultivation plays a major role. Therefore, the selection of this feedstock and its provision has to be done carefully. In conventional agriculture the input of fertilizer and the extensive use of agricultural machines exert a high pressure in the supply chain of the process feedstock. This pressure can be decreased by applying alternative cultivation methods like organic or semi-natural farming. Additionally the commonly used synthetic fertilizers can be substituted by organic ones.

With cultivation comes a high demand on machine use. This cannot be reduced much even in organic cultivation. What can be done is to apply renewable fuels to agriculture machinery. This could be vegetable oils or biodiesel.

A further possibility is semi-natural agriculture which does not apply any fertilization and reduces machinery input to a minimum [14]

Energy is the most prominent of the three factors from an ecological point of view. This holds especially true for processes from renewable resources as they consume much energy.

The energy consumption of such processes can therefore be seen as problematic point in renewable processes and has to be regarded already during process development.

Especially electricity provision is presently unsustainable. The potential decrease of the ecological footprint of almost all processes (even those utilizing fossil resources) by sustainable electricity provision is tremendous. Due to these facts engineers are required to optimize the energy consumptions of processes early in development. Nonetheless energy optimization will not suffice as its provision especially for electricity inflicts high pressure on environment. Therefore, energy systems will have to be changed to sustainable energy generation from renewable resources in order to make a step forward on the way to reach sustainable industry.

However, this is a task that process developers do not have the power to influence. This has to be taken up by politics and society in a general way in order to achieve sustainability.


Heuristics

Summarizing these results the following heuristics regarding process development for renewable resources can be stated:

  • Processes from renewable resources are not inherently more sustainable than their fossil counterparts. Therefore, a process has to be assessed already during development phase.
  • Energy consumption, especially electricity need, is a major factor for sustainability of the process. This factor is not only related to the amount of energy utilized by the process but also by the manner of its provision. The more sustainable energy is provided the less influence this input will have.
  • Feedstock has to be chosen carefully as it may shift a process from superiority compared to fossil alternatives to inferiority from a sustainable viewpoint. If possible the feedstock should be a waste or surplus material. Such utilization will not only increase sustainability of the process but of the whole system as waste materials are reintegrated in anthropogenic material cycles and processed to value products.
  • If the feedstock is from agriculture it is preferable to cultivate it organically or even semi-natural. Conventionally grown feedstock inflicts large environmental pressures already by its provision and will burden each following process step.
  • The role of chemicals for sustainability varies from process to process. If chemicals can be derived from renewable resources they should be favored. Other issues like energy optimization and careful selection of the feedstock should be treated first by process developers.
  • Processes from renewable resources exert most ecological benefit when embedded in sustainable systems (e.g. for energy provision) as the contribution of the process itself in reaching sustainability is limited by its industrial surroundings.

References

 

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   [7]        Narodoslawsky M, Krotscheck C. The sustainable process index (SPI): evaluating processes according to environmental compatibility. Journal of Hazardous Materials 1995; 41(2-3): 383

   [8]        SUSTAIN. Forschungs- und Entwicklungsbedarf für den Übergang zu einer nachhaltigen Wirtschaftsweise in Österreich. 1994

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