Eco-efficiency: putting chelating agents on test

Using the EEA methodology practiced at AkzoNobel, Tobias Borén, Kjerstin Ludvig, Karin Andersson Halldé & Jan Seetz demonstrate why GLDA, which is a biodegradable, phosphorous-free and based on a renewable raw material, is the most environmentally benign chelating agent

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Using the EEA methodology practiced at AkzoNobel, Tobias Borén, Kjerstin Ludvig, Karin Andersson Halldé & Jan Seetz demonstrate why GLDA, which is a biodegradable, phosphorous-free and based on a renewable raw material, is the most environmentally benign chelating agent

Chelating agents are widely used in detergents and cleaners to improve detergency power. The chelating agents bind hard water ions (calcium and magnesium) firmly in complexes, thus softening the water so that these ions cannot interfere with the cleaning action of the detergent and less detergent needs to be used to achieve the required cleaning effect.

With the purpose of assessing different chelating agents from an environmental and financial perspective an eco-efficiency analysis was carried out for European conditions. In this study GLDA was compared with its main alternatives EDTA, NTA and STPP. The chelating agents were compared on an equal weight basis in order to make the study independent of the exact amounts used in the many detergent recipes possible.

ECO-EFFICIENCY ANALYSIS (EEA) METHODOLOGY

An EEA assesses the ecological impact and cost structure of competing products, processes or services delivering the same customer benefit and identifies the best alternative. It includes all steps along the value chain. The general procedure for carrying out the EEA is presented in figure 1, modified from Rudenauer et al.

The eco-efficiency methodology is based on a combination of a Life Cycle Assessment (LCA) according to ISO 14040+14044 and an assessment of the Life Cycle Costing (LCC). ISO standards on LCA methodology have been prepared for harmonisation of LCA procedures and for credibility reasons. The grey shaded steps in figure 1 can be found in the LCA standards. The LCA is also complemented with an analysis of the alternatives’ toxicity potential and risk potential. The eco-efficiency method used by AkzoNobel is also used by BASF and many other corporations and institutes.

The goal definition states the purpose of the study and the intended use of the results. The scope definition includes a description of the function and product to be studied and a functional unit which is a measure of the system’s performance and function which satisfies a need. Also included in the scope definition is a definition of the environmental and technical time perspective of the study, and of geographical and technical (against nature and other product lifecycles) system boundaries. This defines which processes to include in the EEA.

ECONOMY: LIFE CYCLE

COSTING (LCC)

The focus of life cycle costing is adapted according to the goal and scope of the study. The LCC is actor specific, ie all costs for a certain actor that are associated with a given alternative over the whole period of ownership or stewardship are taken into account. The actor to focus the LCC around is given by the goal and scope definition. Often the actor is the purchaser of a product and the purpose of the LCC result is to communicate how future costs of the product will affect the economy of the purchaser. External costs are not covered by the LCC since by definition external costs are borne by society and reflect environmental aspects of the system under study. These aspects are covered by the LCA steps.

ECOLOGY: LIFE CYCLE INVENTORY (LCI)

The life cycle inventory step involves quantification of inflows and outflows of material and energy over the defined system boundaries of the lifecycle. It includes flows related to raw material extraction, processing of raw materials, manufacturing, use, maintenance, recycling/reuse, waste management and transportation (figure 2). Each process requires material and/or energy inflow and produces different kinds of emissions and waste. The LCI results in a long list of different environmental interventions.

ECOLOGY: LIFE CYCLE IMPACT ASSESSMENT (LCIA)

The vast amount of data produced by the LCI, and the complexity of the cause and effect of different environmental interventions, make it hard to identify which data are important from an environmental point of view. For interpretation and communication purposes, methods have been designed to aggregate the LCI data to fewer digits, representing either different impact categories (characterisation) or the total environmental load of the system (weighting). In this way the environmental hot spots of the life cycle can more readily be identified. The LCIA encompasses three parts: classification, characterisation and weighting (figure 3).

In the classification phase inventory data is sorted into environmental impact categories. The classification is based on scientific cause-effect relations, hence one substance can be assigned to more than one environmental impact category. In the characterisation process the inventory data is multiplied with a characterisation factor which is specific for each data and environmental impact category. In this way, for each category, the potential environmental impact of all substances in the category is summed up and represented by one index.

The impact categories that were considered in the EEA and were applied on different chelating agents are primary energy consumption, resource depletion, area use, emissions, human toxicity and risk. The impact category ‘emissions’ is further subdivided into other impact categories.

In a further weighting process the impact category results are aggregated into a single indication or statement of the total strain put on the environment. In the ISO standards the weighting is an optional step of the LCA and no specific weighting methodology is recommended. However, weighting is often a necessary step to simplify communication and decision making and is therefore widely used within industry. In the EEA method, a weight is assigned to each impact category which expresses the environmental importance of that impact category relative to the other impact categories.

These weighting factors are the geometric means of impact category specific ‘relevance factors’ and ‘societal factors’. To derive the relevance factor, the result of the alternative with the highest impact in that category is normalised against the total load of the same category in a specific region. This is merely a normalisation step which yields the relative significance of the different impact category results. The societal factors, on the other hand, express the severity of each item relative to the other impact categories as perceived by a group of people. The societal factors are based on the opinions of people in the same region as were chosen for the derivation of the relevance factors. The societal factors have been presented by BASF and were derived through a public opinion poll.

In this way the weighting step combines all environmental loads and impact categories and makes it possible to assess the relative contribution of different data to the total strain. This facilitates effective communication and interpretation of the results and provides a better overview of a complex system. When performing an EEA the need for weighting is high otherwise each of the various environmental impacts would have to be compared with the cost side individually.

ASSESSMENT, EVALUATION & INTERPRETATION

The eco-efficiency method includes a weighting of environmental impact and costs resulting in displaying the most eco-efficient alternative in a two-dimensional diagram (figure 4). The axes in the diagram are inverted so that the alternative that has the lowest sum of environmental and financial performance is found closer to the upper right corner. This alternative is termed the most eco-efficient alternative and is therefore favoured from an eco-efficiency perspective.

The purpose of the interpretation phase is to analyse the results of the study, evaluate and explain its limitations and generate conclusions and recommendations. The robustness of the results can be assessed with a sensitivity analysis of the effects that chosen methods and data have on the result of the study.

It is clear that a trade off between different kinds of environmental impacts is needed in order to generate a priority list of the different chelating agents from a holistic environmental perspective. This trade off is done via the weighting step.

The result of the weighting is illustrated in the bar chart and table in figure 5. They show the weighted values for each impact category and alternative chelating agent, with the top of the bars denoting the total and final environmental results that were integrated with economic data in the complete EEA.

DISCUSSIONS & CONCLUSIONS

The result of this study puts GLDA scores best or second best in all impact categories except ‘area use’ and ‘acidification’. However figure 5 reveals the small relevance of ‘area use’ in this assessment. Even though GLDA requires more land than its alternatives since it is based on renewable raw materials, the land use is small on an absolute basis and therefore not a key criterion in an environmental assessment of different chelating agents. In fact in this study emissions to water is the most important environmental aspect, according to the applied weighting methodology, followed by toxicity, risk and global warming potential.

GLDA performs well in all important aspects compared to the other alternatives, mainly because it is based on renewable raw materials and is readily biodegradable. Another advantage of GLDA is that (unlike STPP) it does not give rise to any phosphorous emissions to water and hence the eutrophication potential of GLDA is insignificant. With respect to the toxicity potential, GLDA scores much better than especially NTA for which there is limited evidence of carcinogenic effects from exposure (R40 label). For these reasons it can be concluded that on an equal mass basis GLDA is the most environmentally benign chelating agent. A sensitivity analysis also showed that this result is robust with regard to the region (continent) chosen for the weighting.

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