Biopolymer from industrial residues: Life cycle assessment of poly(hydroxyalkanoates) from whey

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Abstract

Life cycle assessment (LCA) has turned into a powerful tool to critically and straightforward assess the holistic impact of bio-based plastics and other bio-based products. In order to assure at the same time ecological soundness and to support the economical success of a bioproduct, an early assessment already in the stage of product development is needed. This strategy helps to identify and subsequently to avoid ecological “hot spots”. Assessment by using the sustainable process index (SPI), a member of the ecological footprint family, is considered as an especially viable strategy to realize this goal. The software SPIonExcel was developed to make the assessment methodology easily applicable and operator-friendly.

During the process of development for archaebacterial production of poly(hydroxyalkanoate) (PHA) biopolyesters from the industrial surplus material whey, a SPI assessment was accomplished to optimize the process in terms of ecological sustainability. As the major outcome, the resulting ecological footprint was comparable with that of competing fossil plastics. Additionally, optimization potentials to further increase the ecological competitiveness were highlighted and quantified. In addition, the developed PHA production process was compared with production of whey powder as the competing, conventional application of surplus whey. Also in this case, the novel PHA production process was superior according to the SPI calculations.

Highlights

► Viability of value-added conversion of whey to PHA is demonstrated by the sustainable process index (SPI). ► Suitability of SPIonExcel for process development is demonstrated. ► Superiority of PHA bioplastics to common plastics in terms of SPI is demonstrated. ► Optimization steps for conversion of whey are identified and quantified.

Introduction

Since the early 1990s, significant industrial and academic efforts are dedicated globally to the development of process design strategies aiming at energy conservation and waste reduction for a broad range of industrial processes (Dunn and Bush, 2001, Stöglehner, 2003, Fijał, 2007, Merrild et al., 2008). Such endeavors are politically supported by the willingness of most nations to forcefully foster the market penetration of bio-based and biocompatible materials that are independent from the availability of fossil resources. These meritorious intentions are documented by the outcomes and conventions at the Earth Summit in Rio de Janeiro in 1992, the Kyoto Protocol to the United Nations Framework Convention on Climate Change (2005), or, more recently, at the Durban Climate Change Conference (2011) (Koller et al., 2012a).

Regarding the contemporary sustainability discourse, the application of renewable raw materials in processes currently based on fossil feed stocks is generally recognized as an important strategy toward sustainability (Dovì et al., 2009). This switch to new raw materials is of paramount importance especially in the area of such goods exerting considerable ecological pressures like bulk chemicals and here, most of all, those that are applied as plastic materials.

The industrial application of processes based on “renewables” and biocatalysts nowadays is well-known as “White Biotechnology”. In this context it has to be emphasized that the utilization of renewable resources does not only require novel and innovative technologies, but will fundamentally change the global industrial structures (Gwehenberger and Narodoslawsky, 2008, Narodoslawsky, 2010). However, it has to be considered that products from natural resources, especially bio-based plastics, are not a priori superior to their fossil counterparts in terms of sustainability (Kurdikar et al., 2000). Therefore the ecological process evaluation already early during the stage of process or product development is not only an environmental but also an economical necessity to prevent dead ends and unexpected obstacles on the long and often cumbersome way to the product's final market launch (Narodoslawsky and Krotscheck, 2004). Minimizing the environmental impact must be taken into account during the technological development phase to the same extent as to decreasing costs for achieving economic competitiveness. Such “double optimization” in terms of ecological and economic benefit is shaping technology and influencing important engineering decisions. This concerns the choice of raw and auxiliary materials, the selection of process steps and equipment and the logistics along the entire life cycle of a product or service chain (Krotscheck et al., 2000, Narodoslawsky and Krotscheck, 2000).

A complete life cycle analysis (LCA) for ecological assessment of processes is usually connected to large efforts to collect the necessary data and analyzing the impacts of a given technology. Moreover, the problem oriented approach that constitutes the base of conventional LCA (EN ISO 14040, 1997, Guinée, 2002) does not render itself easily to technological optimization: the work of engineers usually is concerned with finding viable compromises that, in many cases, merely shift impacts across environmental problems, e.g. by considerably reducing the greenhouse gas emissions while, at the same time, aggravating other negative impacts of the process. Therefore, development tools are required that, on the one hand, offer comparability of different impacts with a data requirement reduced to an absolute minimum while still considering the whole life cycle and, on the other hand, are compatible with the results of well-known in-depth LCA. The software SPIonExcel constitutes a tool meeting these challenges; it is based on the sustainable process index (SPI) methodology. This software was developed to enable engineers and industrial decision makers to optimize life cycle impacts already during technological development and also for existing processes (Sandholzer et al., 2005a, Sandholzer et al., 2005b, Sandholzer and Narodoslawsky, 2007).

Regarding the work at hand, the applicability of SPIonExcel to “real world” process development was demonstrated in the case of the process development to obtain poly(hydroxyalkanoate) (PHA) bio-based plastics from whey by the archaeal production strain Haloferax mediterranei DSM 1411. An ecological assessment using this software has been carried out in order to identify ecological “hot spots” and to provide decision support for process alternatives already early in the development phase. Due to the fact that not too many reliable commercial data are reported for large scale PHA production, complete and well-grounded LCA studies analyzing the entire environmental impact of PHAs are rather scare in literature. Some laudable attempts to quantify the environmental impact of PHA production via the tools of LCA are reported; unfortunately, they are mainly focusing on isolated aspects of the entire process like merely the polymer production itself, raw material aspects, CO2 emissions or energy requirements (Gerngross, 1999, Gerngross and Slater, 2000, Harding et al., 2007, Pietrini et al., 2007).

Whey constitutes a surplus material from dairy and cheese industries. During cheese production, it accrues in a ratio of approximately 9 t of whey to 1 t of cheese. Reported amounts of whey that are produced globally vary from 1.15 * 108 t (Peters, 2006) to 1.40 * 108 t (Audic et al., 2003) per year. OECD and FAO even estimate 1.60 * 108 t with an annual increase of 1–2% (values for 2008; Guimarães et al., 2010). Mainly in North America and Europe, huge quantities of whey are available; in 2008, the estimated accruing values are reported with 4 * 107 t for the USA, and 5 * 107 t for the EU-27. At present, the major part of whey is used to produce whey powder for human or animal nutrition. Other applications of whey, e.g. for pharmaceutical purposes or production of bioethanol, only amount to a minor extent. The quantities of whey produced nowadays, especially in the Northern hemisphere, surpass by far the requirements for production of whey powder. Hence, at the moment, whey constitutes a surplus material even causing severe disposal problems for dairy industry.

The process for production of whey powder requires high amounts of energy for concentrating the whey by evaporation, with the modest result of producing a good of exceptionally low market value. Due to this fact the process is highly uneconomic and should be regarded rather as a waste treatment as whey should not be committed to sewage in an untreated form because of its high biological oxygen demand (BOD5 of 34,000 mg/kg) (Kim et al., 1995). Therefore, contemporarily a huge amount of whey just “vanishes” somewhere in the ecosphere, often in marine environments (Koller et al., 2007).

A growing demand in proteins, e.g. the pharmaceutically significant compounds lactoferrin or lactoferricin, recently led to additional amounts of whey that were processed (Koller et al., 2012b), resulting in large amounts of lactose-rich whey retentate remaining after removal of the said proteins. Hence, an even larger surplus exists and has to be treated as waste material. This constitutes the economic and ecologic background of the presented work.

Section snippets

Materials and methods

The standardized approach to life cycle analysis (LCA) is defined in the norm series ISO 14000 and constitutes the base to assess and compare industrial activities in terms of their sustainability (EN ISO 14040, 1997). A LCA gives detailed information on a given product, process, or service chain. However, in order to achieve this goal, considerable effort is necessary and ISO 14000 often is applied only after a product or process has already been introduced to the market. The development of

Calculation

Any LCA has to be defined in terms of the system boundaries which in turn is already a normative step and dependent on the question the LCA has to answer. This means that the evaluation with the SPI during design has also to take system boundaries into account that represent a reasonable life cycle. Evaluation in the current study is based on the following assumptions:

  • Whey is a by-product of a process serving a different sector (food production) and will be produced regardless if it is

Results

The results of a SPI analysis contain diverse information. The atot as calculated by Eq. (4) gives an indication of the “cost” in terms of ecological sustainability of a given product or service. The partial areas in Eq. (1), (2), (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 identifying the most problematic step in the life cycle from

Discussion and conclusion

At the present stage of development the process of producing PHA bio-based plastics from whey still has a high impact on the environment. This is due to the fact that the process is not yet completely optimized.

As the main reasons for the high impact, the high mechanical energy requirement for the fermentation process and a low amount of PHA output per kg whey input can be pointed out. These are the two most obvious process optimization potentials. Achieving optimal values in both directions,

Acknowledgements

The authors gratefully acknowledge the support of the European Commission by granting the project s WHEYPOL (FP5; GRD2-2000-30385) and ANIMPOL (FP7; Contract No. 245084)

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