1.1.1 Green chemistry

Green chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances (Anastas et al., 2000). The concept emerged 20 years ago with the introduction by Paul T. Anastas and J. C. Warner of the 12 principles of green chemistry (see Table 1.1). The subject continues to develop strongly around these principles (Anastas and Warner, 1998). Green chemistry aims to achieve (Clark and Macquarrie, 2002):

Efficiency is the key, and green chemistry has continued developing around the principles, which guide both academia and industry in their pursuit of more sustainable processes. In an ideal case, according to these principles, a reaction would only produce useful material. Waste and pollutants would be prevented, improving the reaction yield and reducing losses, thus improving the overall economics of a process. Since our society and industries are governed by increasing efficiency and profit, green chemistry therefore theoretically fits the agendas of most manufacturing companies these days, not only appealing to chemical producers.

Today, 20 years after their publication, the 12 principles of green chemistry are as meaningful as ever in the light of the increasing interest the area attracts due to concerns over sustainability (Anastas and Kirchoff, 2002). Misunderstandings have arisen due to the attractiveness of the area to sectors dealing directly with public demands for ‘greener and more environmentally friendly’ products. It is therefore of vital importance that the message is not distorted by common misconceptions over what is or is not ‘green’, thus altering their original goal: to aim towards safer and cleaner chemistry.

The implementation of REACH (Registration, Evaluation, Authori- zation and Restriction of Chemicals), or Directive (EC 1907/2006), ROHS (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) or Directive 2003/108/EC, and other initiatives highlighting the hazardous character of some chemicals used in day-to-day consumer products, such as the SIN list (n.d.) , are pushing hard for their replacement to avoid further risks to human and/or environmental health. However, we should make sure the substitutes used are genuinely safer across the whole life cycle and as effective as what they are replacing. Investing in R&D focused on finding truly greener alternatives, thus eliminating rushed and weak substitutions that can even increase the number of components present in formulations when ingredients are added to compensate for a lack of performance in the ‘greener’ formulation, is important. The same applies to the substitution of fossil-derived chemicals with more sustainable bio-derived chemicals: when using renewable feedstocks such as biomass, we have to use clean and efficient synthetic routes, minimizing the amount of unwanted by-products and the use of scarce resources (i.e., scarce metals).

Scarce metals are increasingly used in clean alternative energy-producing technologies. Their reserves are sometimes only estimated to last another 50 years, or even less for key elements such as indium (a key component in solar panels) (Dodson et al., 2012) and we must take this into account when modifying our energy and manufacturing infrastructure, taking advantage of the whole periodic table. This is especially relevant to the area of catalysis: re-usable catalytic metals are seen as better reagents than hazardous reagents such as AlCl₃ . But many of the most interesting catalytic metals are also becoming scarce and their production process can be resource intensive and wasteful, making their recovery and reuse essential. Water is increasingly seen as a scarce resource too in certain areas of our planet, but its use as a green solvent is increasingly envisaged due to its non-toxicity compared to hydrocarbon-based solvents (Simon and Li, 2012). Nevertheless, contaminated water is difficult and expensive to treat and re-use. Another alternative to VOC solvents are involatile solvents such as ionic liquids designed to eliminate air-borne emissions. Ionic liquids are used in phase transfer catalysis for example (Welton, 2004), but their non-emissions are counteracted by their toxicity and their environmental impact when prepared, used and separated for end-use.

Biodegradability is an important sought-after characteristic for ‘greener’ products, but increasing the life-time of a molecule to promote its re-use could be another strategy. Heavily halogenated compounds are poorly degradable and there are some large volume halogenated compounds that need to be phased out (e.g., the solvent dichloromethane). But we must not bundle all halogenated compounds in the same ‘red’ basket. Nature turns over enormous quantities of organohalogen compounds and we need to learn from nature and avoid, as much as possible, those compounds that it cannot deal with (e.g., perhalogenated compounds).

Food waste is a feedstock rich in functionalized molecules, and although it is biodegradable, it should be valorized for new applications as a raw material for renewable chemicals, materials and bio-fuels, leading us towards waste minimization and waste valorization. Wasting resources should be avoided in any optimized process. However, waste can also represent an opportunity as we can no longer afford the luxury of waste.

This past paragraph shows you how tightly knit these issues are, illustrating how important it is to assess the greenness of a process through each of its steps, from the use of raw materials to end-use through manufacturing and use. One change can affect several steps and it is important to assess a process through its full life cycle even though it is time-consuming and its quality is dependent on the data used. Such a tool can help us assess the use of bio-processes versus chemo-processes, for example. Many believe bio-processes are preferable to chemo-processes as they are superior in terms of environmental impact, since they use non-toxic components to selectively yield the targeted product. But as they are time-consuming and expensive, it is unrealistic to believe that chemo-processes will be entirely replaced by natural organism catalysed processes in the foreseeable future.

1.1.2 Drivers for change

Our society faces a new challenge: as the current consumption model dominated by market demand is running out of breath, our society needs to adopt a more realistic and sustainable model based on the efficient and sustainable use of natural resources in order to sustain emerging economies at the standard established in the West over the last century.

Current manufacturing practices are strained by the increasing price of feedstocks such as oil and consequently of energy and petrochemicals, increasing waste cost (treatment or disposal) together with the increasing impact of legislation affecting almost all aspects of its operations (e.g., supply of raw material, manufacturing, end-use and disposal).

Legislation has had a dramatic impact on product manufacturing since human and environmental safety have attracted increased concern follow- ing publications of traces of chemicals in animal and human tissue in the 1970s and 1980s (e.g., dioxins) (Schecter, 1998). Legislation now has an influence on the type of process, process steps, emissions, end treatment of waste, illustrating how every stage of the supply chain of a chemical product has to be the least polluting possible (i.e., Integrated Pollution Prevention and Control legislation, IPPC) (Lancaster, 2010). With new regulations such as REACH and ROHS (Restriction of Hazardous Substances), an important number of chemicals will have to be replaced by less harmful substitutes, shaking to the core industrial sectors like home and personal care products, the pharmaceutical industry and the agricultural sector.

Resource is a stage in the product life cycle where green chemistry can have a major impact in the future. The use of renewable, typically biomass for carbon, instead of finite resources is becoming more economically and environmentally sound, being one of the main areas of research in green chemistry along with clean synthesis, greener solvents and renewable materials. Biomass is also a resource which can be renewed within a time interval relevant to our resource consumption (see Fig. 1.1), biomass being a ‘biological material derived from living, or recently living organisms’.

The emergence of EU standards for bio-based products (Mandate M/429; see Section 1.3.1) will, in the near future, embrace life cycle considerations and introduce specifications along the whole supply chain for new and existing products on biomass content, and will further discourage the use of fossil resources in favour of renewable feedstocks such as biomass including bio-wastes.

The public and consequently the retail sector have been increasingly aware of the dangers of some unsafe practices in industry and unsafe chemicals in consumer product formulations. They are now asking manu- facturers to produce bio-derived chemicals and question the environmental impact of their production, driving the market towards green and renewable alternatives in many sectors, especially in home and personal care products.

In line with the EU’s innovation strategy and following the initiation of a new policy in 2006 aiming to support the development of high economic and societal value markets, the European Commission proposed further steps for the creation of lead markets. Bio-based products are the subject of one of the identified lead markets and fall into this category for several reasons (European Commission, 2007, 2009):

A recent study estimates that, by 2025, over 15% of the US$3 trillion global chemical market will be derived from bio-derived sources (Vijayendran, 2010). Yet another study highlights the technical feasibility of over 90% of the annual global plastic production of 270 Mt being substituted by bioplastics. In 2005, bio-based products already accounted for 7% of global sales and around €77 billion in value in the chemical sector. EU industry accounted for approximately 30% of this value. Estimates of the ad hoc advisory group for bio-based products have identified active pharmaceutical ingredients, polymers, cosmetics, lubricants and solvents as the most important sub-segments (Commission, 2009). Active pharmaceutical ingredients in particular, with 33.7% of global chemical sales, are expected to be the chemical segment with the highest percentage sales of products produced using biotechnological processes. It is predicted that Europe will be strong in sales in the following sub-segments: active pharmaceutical ingredients, polymers and fibres, cosmetics, solvents and synthetic organic compounds.

1.1.3 Product substitution

The use of renewable feedstock is one of the cornerstones of modern green chemistry. Non-renewable fossil resources supply 86% of our energy and 96% of organic chemicals (Binder and Raines, 2009). But fossil resources are not renewed in a time interval relevant to our resource consumption: according to our actual consumption, the future petroleum production is unlikely to meet our society’s growing needs: by 2025, our energy demands are expected to increase by 50% (Ragauskas et al., 2006). Other drivers are pushing for the substitution of chemicals used daily in consumer products: safety concerns for both humans and the natural environment. Volatile chlorinated compounds used in dry cleaning, sulphonated surfactants, and polybrominated compounds in flame retardants are compounds used in formulations and processes for which replacement molecules would be preferred. Research on the production of cost-effective alternatives derived from renewable resources is an area of primary importance if we want to satisfy the requirement for green and sustainable chemicals and products. Green chemistry now embraces the whole life cycle of a product (see Fig. 1.2), rather than just focusing on the production stage. Upstream and downstream stages of the production, including the raw material employed, its use, end-use and disposal, are included, guaranteeing the true sustainability of a product (Anastas and Lankey, 2000).

Improvements in today’s modern formulating-based industries at the production stage of the life cycle, are restricted (although moving towards renewable energy and zero waste is important and not trivial). The use of renewable feedstocks could offer an important margin for progress, especially for companies, such as consumer goods manufacturers, keen to dramatically improve the environmental performance (decrease the CO₂ emissions) of their products.

1.1.4 From petro-refineries to bio-refineries

It is important to ensure that both the resource and the process technology used as well as the products made are environmentally acceptable. The twentieth century saw the development of processes designed for the production of energy and organic chemicals based on the oil refinery. The twenty-first century must see the development of similar processes based on the biorefinery. The aim is to design an integrated process capable of generating a cost-effective source of energy and chemical feedstocks using biomass as a raw material. The key is to find alternative sources of carbon to oil, available in high quantities and process them using green chemical technologies, ensuring products obtained are truly green as well as sustainable. Technologies used should ideally be flexible enough to accommodate the natural variation of biomass associated with seasonal or variety change (Clark et al., 2009 ). The efficiency of the process needs to be maximal: ideally every output has to have a use and a value/market. We can no longer afford the luxury of waste. Practices based on industrial symbiosis looking at re-using the waste produced by one process to feed another, or converting waste into a useful by-product with a marketable value need to be developed. The aim would be to achieve a zero waste biorefinery able to compete economically with existing systems used to produce energy and chemicals, an objective increasingly pushed by EU regulations (see Section 1.3.1).

Adding value to every output of the biorefinery can be achieved by combining several technologies together, using a sequential approach to extract chemicals before biomass is converted to energy. The main green extraction processes used to extract valuable compounds from biomass include liquid and supercritical CO₂, ultrasonic or microwave-assisted extraction and accelerated extraction. Microwave-assisted extraction is a commercial reality with Crodarom using this technique to extract purer and more degradation stable plant materials (Crodarom, n.d.). The extraction can be followed by biochemical or thermochemical processes and internal recycling of energy and waste gases. This approach ideally constitutes the basis of an economically sound starting point for the design of a biorefinery and is illustrated in Fig. 1.3. The integration of technologies for the biorefinery takes into account the complex nature of lignocellulosic biomass, in order to produce several products and render the biorefinery concept cost-effective.

Biomass contains an array of functionalized molecules, with many of them having a market value. Compounds such as natural dyes or colorants (e.g., carotenoids), polyphenols, sterols, waxes, nonacosanol or flavonoids (e.g., hesperidin), amino acids, and fatty acid derivatives can be extracted selectively using clean extraction techniques prior to the treatment of biomass by biochemical and thermochemical processes. These compounds have uses in cosmetics, as nutraceutical or semiochemicals (Clark et al., 2006; Deswarte et al., 2006). Often, secondary metabolites are extracted using volatile organic solvents, but clean extraction techniques such as liquid and supercritical CO. are very selective, allowing fractionation of extracted mixtures and have the advantage of being allowed for processing raw materials, foodstuffs, food components and food ingredients (together with ethanol and water) according to Directive 2009/32/EC of the European Parliament on extraction solvents used in the production of foodstuffs and food ingredients. This technique also does not leave any residues (Budarin et al., 2011), allowing it to be used for pharmaceutical, food and cosmetic applications and compensating for both high technology capital cost and energy consumption. The polarity of CO₂ can also be fine-tuned using co-solvents such as methanol or ethanol (Sahena et al., 2009). As a matter of comparison, the polarity of supercritical CO₂ can be compared to that of hexane (Deye et al., 1990). Although energy requirements of supercritical CO₂ are high, the technology has been commercially used for hop extraction, decaffeination of coffee and dry cleaning (Arshadi et al., 2012 ).

Biochemical and thermochemical processes complement each other well, the former being very selective but slow compared to the latter. Biochemical processes require low temperatures but pre-treatments are often required (e.g., ammonia fibre expansion or AFEX, dilute acid hydrolysis) to open up biomass’s fibre structure and yield fuels and chemical intermediates used for further downstream processing (Eggeman and Elander, 2005; Tao et al., 2011). Processing times and space-time yields are high compared to thermochemical processes, but they are less energy intensive (Kamm and Kamm, 2004). Thermochemical processes, which include gasification, pyrolysis and direct combustion (see Table 1.2), usually operate above 500°C and are much less selective, yielding oils, gas, chars and ash (Fernandez et al., 2011).

Biomass with a high acid, alkali metal and water content can be difficult to use in conventional thermal treatments: the high water content can render pyrolysis or gasification processes very difficult and the acidity of the feedstock can limit the applications of the pyrolysis oil obtained, for example.

Microwave technology has been studied for the pyrolysis of straw. This technology was proven to improve the quality of bio-oils obtained at lower temperatures (typically under 200°C), yielding oils with properties outperforming commercial fuel additives: bio-oils produced have a lower oxygen, alkali, acid and sulphur content (Budarin et al., 2009).

The properties of the oil obtained could also be modified by using additives during the heating phase, showing how microwave technology is versatile and can offer an alternative to conventional thermal processes. Microwave technology has an added advantage compared to conventional thermal heating: it activates cellulose at a temperature of 180°C, helping the conversion process (Budarin et al., 2010). It has been reported that at this precise point and under microwave heating conditions, the rate of decomposition of the amorphous part of cellulose increases due to in-situ pseudo acid catalysis, yielding a char and bio-oil of superior properties compared to those produced when using conventional heating methods.

1.2.1 Defining biorefineries and bio-processing

In addition to the definition of green chemistry given previously in Section 1.1.1, two additional definitions need to be highlighted in this chapter: the term ‘biorefinery’ and the term ‘bioprocessing’.

A biorefinery is an analogue to the current petro-refinery, in the sense it produces energy and chemicals. The major difference lies in the raw material it will use, ranging from biomass to waste. The use of clean technology is another imperative for the biorefinery, ensuring its output(s) are truly sustainable. The IEA Bioenergy Task 42 defines biorefining as ‘the sustainable processing of biomass into a spectrum of bio-based products (food, feed, chemicals and/or materials) and bioenergy (biofuels, power and/or heat)’ (IEA, 2009). Various biorefinery designs of varying size and output number will emerge commercially in the future (Cherubini, 2010), taking advantage of flexible technology, helping the concept of a biorefinery to process locally available biomass to its fullest in an integrated fuel- chemical-material-power cycle, improving cost-efficiency, the quality of life of the local population and lowering the environmental impact governed by the three dimensions of sustainability (environmental protection, social progress and economic development; see Fig. 1.4). Networks of biorefineries are to be considered too, for maximum resource efficiency.

Bio-refining should not be confused with bioprocessing. A bioprocess is any process which uses biological organisms (e.g., enzymes) to carry out targeted chemical or physical transformations. A bioprocess can be used as part of the conversion process in a biorefinery along with other low environmental impact technologies such as microwave chemistry or aqueous phase catalysis processing. This illustrates how important it is to interconnect different disciplines such as chemistry, chemical engineering, biotechnology and biology together with techno-economic and sustainability assessment, as they are crucial for the development of a successful fully integrated biorefinery. Biomass is a term applied which includes a great variety of different and often complex plant components embedded in a matrix that differs according to the origin of the biomass used. A multi-disciplinary approach is therefore necessary to maximize the value of the products obtained while using green chemistry technology.

1.2.2 Biorefinery types and product areas as defined by feedstocks and waste streams

There are three biomass feedstocks: carbohydrate (starch, cellulose and hemicellulose) and lignin from lignocellulosic biomass, triglycerides (soybean, palm, rapeseed, sunflower oil) and mixed organic residues. Ligno- cellulosic feedstocks can be obtained through the production of dedicated crops such as miscanthus or short rotation woody crops such as willow or poplar. Agricultural residues such as rice or wheat straw and paper pulp from the paper industry are other examples of sources of lign- ocellulosic material. Figure 1.5 shows the two main types of biomass feedstocks.

Biorefineries can be subdivided via over simplification into biorefineries of phase I, II and III according to the feedstock and process used, as well as product targeted (chemicals or energy) (Cherubini et al., 2009; Kamm and Kamm, 2004). A table listing examples of different technological processes to be used in a biorefinery are listed in Table 1.3.

Phase I biorefineries focus on the conversion of one feedstock, using one process and targeting one product. A biodiesel production plant would be a good example of a phase I biorefinery: rapeseed or sunflower is used for oil extraction, which is subsequently transesterified to produce fatty acid methyl esters or biodiesel using methanol and a catalyst (Shahid and Jamal, 2011).

Phase II biorefineries differ from phase I biorefineries by the number of outputs they can produce. A typical example of a phase II biorefinery is the production of starch, ethanol and lactic acid together with high fructose syrup, corn syrup, corn oil and corn meal from corn wet mil operations (EPA, 2011).

Phase III biorefineries allow for a wider range of technologies, to be combined (e.g., supercritical CO₂ extraction followed by biological transformation), in comparison to phase I and II biorefineries. They also allow for a higher number of valorized outputs since several constituents of the feedstock used can be treated separately. Biorefineries falling into that category can also be called ‘product-driven biorefineries’. They generate two or more bio-based products and the residue is used to produce energy (either fuel, power and/or heat). Examples of phase III biorefineries include whole crop biorefineries which make use of several agricultural by-products originating from the same crop. Phase III biorefineries are typically the ones targeting the production of chemicals and fuels. Sub-categories also exist according to the type of technology used (thermo-chemical or biochemical biorefineries).

Another classification has now been adopted by the IEA Bioenergy Task in 2010 to take into account the complexity of the biorefinery concept and its future developments around new technologies. It is based around the four cornerstones of the biorefinery concept: feedstock used (i.e., dedicated crop, process or agricultural residue, algae), platform products obtained (i.e., C5 sugars, pyrolysis oil or syngas), final products obtained (energy or chemicals) and process used (Cherubini et al., 2009 ). This classification has the advantage of accounting for the need to apply a given technology to different feedstocks and will therefore include biorefineries developed in the future. Biorefineries should not be designed in a generic way but should be adapted to the best technology and the best feedstock available in the geographical location chosen.

1.3.1 Drivers for change

The EU has recognized that, in order to sustain our demands in energy, chemicals and food, while addressing environmental issues, we need to substantially reduce our dependence on oil by establishing a bio-based economy. The European Commission recently issued Mandate M/429 (European Commission, 2011) to develop a standardization programme for bio-based products, raising the general public’ s awareness for bio-based products (since no external, perceptible characteristics differentiate them from oil-derived products). It was developed with the contribution of industry, research organizations, sector associations and standardization bodies and is anticipated to take a life cycle approach to evaluation and be sensitive to eco-system issues which have become so evident in the bio-fuels arena. Critical issues will include moving away from first generation feedstocks, increasing use of wastes, and ensuring the use of sustainable and low environmental impact technologies throughout the supply chain alongside a consequent reduction in wastes in new feedstock industries.

Early research on renewable resources focused heavily on crops such as rapeseed, corn or sugar cane. However, the controversial competition between food and non-food uses of biomass had an negative effect on crop prices as well as on press feedback concerning biofuels (OECD, 2008). Other sources of biomass are now studied and waste is increasingly considered as another renewable feedstock for the production of bio- derived chemicals, materials and fuels.

In times which increasingly value resource efficiency, waste has become a luxury. DEFRA, the Department of Environment, Food and Rural Affairs in the UK, has estimated that businesses could save up to £23 billion by re-using resources more efficiently (DEFRA, 2012). In the EU, Council Directive 99/31/EC, better known as the Landfill Directive, will drastically reduce the amount of landfill space available as the amount of biodegradable waste sent to landfill in member countries by 2016 will have to reach 35% of the 1995 level. As a result, landfill gate fee has increased from £40-£74 to £68—£111 (including landfill tax) in the UK between 2009 and 2011 (WRAP, 2009, 2011). Policy makers support alternatives to landfill (e.g., value recovery from waste), especially in the context of achieving a zero waste economy and the vision of the European Bioeconomy 2030 (European Commission, n.d.). At the same time, our society faces a huge looming crisis of resources. Globally, ‘30% fewer resources [are needed] to produce one Euro or Dollar of GDP than 30 years ago; however, overall resource use is still increasing […] as we consume growing amounts of products and services’ (Giljum et al., 2009 ). As traditional resources such as oil and minerals become scarcer, their availability will become more politically controlled leaving them vulnerable to highly politicized negotiations and pricing.

Waste valorization represents a promising research topic from both environmental and economic points of view as ‘there is a considerable emphasis on the recovery, recycling and upgrading of wastes’ (Laufenberg et al., 2003). Current management practices of waste should be replaced by strategies which have a lower environmental impact and which allow the recovery of marketable products for existing or new markets, thus offering added revenues for companies. Valorizing our waste also has the potential to reduce a process’s carbon footprint and dependence on fossil resources, increase its efficiency and cost-effectiveness and moving towards ‘closed loop manufacturing’, one of the EU’s clear future strategies, highlighted in the Europe 2020 strategy document (European Commission, 2010). The use of renewables in consumer products is especially relevant at a time when public awareness of environmental issues and cradle-to-grave concerns is growing, leading to industry’s increasing concern over their ‘green’ credentials and environmental performance.

1.3.2 Concept of a waste biorefinery

There is a growing recognition that the twin problems of waste management and resource depletion can be solved together through the utilization of waste as a resource. Some initiatives looking at the re-use of waste already exist, like in Spain for example, where the environmental complex of Montalban, Spain (Epremasa, Complejo Medioambiantale de Montalban), is a unique example of integrated waste management (EPREMASA, n.d.). It was built to meet the new EU directives regarding waste management; concentrating, recovering and valorizing waste in order to avoid landfilling as much as possible. The company is responsible for waste management operations in the province of Cordoba, Andalusia. It provides home collection of municipal solid waste (household waste, paper, cardboard, glass and electric appliances), transportation, processing and landfill management for 74 municipalities (approximately 475,500 inhabitants). This strategy and the scale of operations allows the facility to be cost-effective with more flexible working procedures and a rationalization of human and material resources involved in the cycle.

The complex is an integrated facility which combines high efficiency waste scanning and segregation, recycling, composting, electricity generation and landfilling activities on the same site. The complex is able to produce high quality recycled plastic by sacrificing 40% of the organic waste through the use of a more rigorous process. Its efficiency is around 90% as only 10% of the plastic arriving at the facility is landfilled (mainly plastic contained in Tetrapack® packaging). As a result, the higher quality plastic meets the specifications for being used in further plastic packaging applications which, up to now, was limited. In addition, compost is commercially produced from organic waste, as well as 1.2 MW of electricity as the composters are connected to a biogas plant.

This process illustrates how the valorization of waste can provide first generation waste-derived feedstocks (recycled plastic, compost, biogas/energy) as an alternative source of carbon. Such applications reduce the need to use virgin land and finite resources such as oil.

1.3.3 Opportunities offered by the use of food supply chain waste

Waste biomass from the food supply chain (i.e., agricultural residues such as wheat straw, rice husks, waste cooking oil or food manufacturing waste such as tomato peels) are an ideal renewable material as they do not compete with the food and feed industries for land. An FAO report issued in 2011, estimates that ‘one-third of food produced for human consumption is lost or wasted globally, which amounts to about 1.3 billion tons per year’ (Gustavsson et al., 2011). It is important to note the difference between food waste and food loss, the latter being food lost due to the use of poor technological means or diseases affecting crops, for example (Parfitt et al., 2010 ).

The agro-food supply chain includes a broad variety of manufacturing processes producing consequent cumulative quantities of different wastes, especially organic residues at every step of the supply chain (Goméz et al., 2010; Laufenberg et al., 2003). The increasing demand for chemicals and fuel together with other drivers are encouraging the re-use and valorization of organic waste from the food supply chain for the production of novel added-value bio-derived sustainable products. A description of a food supply chain is given in Fig. 1.6.

Food waste encompasses domestic waste produced by individuals in their homes. This represents a logistical problem as it would be difficult to collect and concentrate in one place, except in large housing complexes. On the other hand, it might be argued that if the waste produced by the agricultural and processing sectors before it reaches the consumer is generated in a more concentrate manner, it would be easier to collect and valorize. The problems associated with these wastes are:

Current practices for the management of food waste include:

Composting is a popular re-use practice as it lowers waste management costs, diverts waste from landfill and reduces waste disposal costs (Schaub and Leonard, 1996), but composting is also ‘time consuming, location dependent and subject to contamination’ (Davis, 2008).

While progress is being made in using anaerobic digestion to both treat food waste and provide some energy value, the chemical and material potential of food supply chain waste is such that we should also quickly move to realizing that potential through the use of other green chemical technologies. There are five reasons to develop the valorization of residues and by-products of food waste: they are a rich source of functionalized molecules (i.e., biopolymers, protein, carbohydrates), abundant, readily available, under-utilized and renewable. Many waste streams even contain compounds such as antioxidants which could be recovered, concentrated and re-used in functional food and lubricant additives (Peschel et al., 2006 ). Such applications solve both a resource problem and waste management problem as the issues associated with agro-food waste are important. Other than decreasing landfill options, when landfilled, waste is a source of pollution: municipal solid waste for example can produce uncontrolled GHG emissions and contaminate water supplies through leaching of inorganic matter (Cheng and Hu, 2010). Incineration is energy intensive, emits CO₂ and toxins and is sensitive to the waste’s moisture content. The scale at which waste from the food supply chain is generated is significant. In the United States, USDA calculated that US$ 50 million could be saved annually if 5% of the waste generated by the processing, retail and service sectors together with consumer food losses were recovered (Laufenberg et al., 2003).

This type of waste represents a valuable and sustainable source of useful products that could be used by other industries, especially the chemical industry, as shown in Fig. 1.7 . Novel strategies and technologies for waste valorization can potentially have a global impact on the chemical and biotechnological industries and waste management regulations in the years to come. However, despite the clear benefits, the utilization of food waste represents a challenge. A regular and consistent supply chain is important for the successful realization of a biorefinery. But high cumulative volumes of waste are often generated intermittently, over a period of a couple of months in a year, affecting the year-round availability of chemicals and materials produced from food supply chain by-products and residues. The large volumes of food supply chain by-products available are illustrated in Table 1.4 .

Although the availability of some food supply chain by-products is clearly an advantage regarding security of supply, several limitations exist and need to be taken into account as part of the logistics needed to valorize this resource. Food supply chain waste can be/can have:

At a European level, research is being promoted via the Framework VII KBBE (Knowledge-Based Bio-economy) theme. In the UK, a number of food supply chain waste related research projects are being carried out in collaboration with industry on, for example, the use of supercritical carbon dioxide to extract chemicals from cereal straws and also the use of starch- rich wastes to make adhesives for carpet tiles and other consumer goods. In the Review of Waste Policy issued by DEFRA in June 2011, launching a zero waste economy plan, the UK Government announced it will work with industry to drive innovation in reuse and recycling for materials, such as metals, textiles and all biodegradable waste (DEFRA, 2011). The EU issued new FP7 funding calls for 2012 mentioning that ‘research is needed to develop innovative concepts and practical approaches that would add value to and find markets for food waste of plant and dairy origin’ (CORDIS, 2011).

In France, work on the valorization of oil crop by-products is now being supported by the French government-funded ‘project PIVERT’. In Spain, a research team in Barcelona is studying the use of amino acids derived from food supply chain residues for the synthesis of amino-acid derived surfactants such as ethyl-N-lauroyl-L- arginate HCl or LAE, which have been successfully commercialized (Infante et al., 1992). Waste cooking oil and citrus waste produced from the juicing industry are also being studied in Spain as raw materials for the production of bio-diesel and bio-ethanol/D-limonene extraction, respectively (Kulkarni and Dalai, 2006; Sunde et al., 2011). In Greece, whey is being explored as feedstock for microbial oil production that could be used for oleochemical synthesis (Vamvakaki et al., 2010 ).

The topic is gaining increased attention worldwide: the NAMASTE project (EU–India) is directed at the valorization of selected by-products, such as fruit and cereal processing residues, for the global food and drink industry. In the United States, the Center for Crop Utilization Research at Iowa State University is focusing on adding value to Midwest crop (i.e., soy, corn) by-products to increase the value of the food supply chain. Scientists at the American company Cardolite have succeeded in producing thermosetting binder resins for use in the transportation and brake industries from cashew nutshell liquid (highly thermostable, impermeable and durable) (Cardolite, n.d.).

1.3.4 From first generation waste re-use to second generation waste re-use

The example given in Section 1.3.2 shows how one step change in a process can avoid further fossil resource deletion by recycling waste. But there are smarter ways of using food supply chain waste: this type of co-product is rich in chemical compounds and it is important to take advantage of that resource before using it for energy generation. The food supply chain generates a high amount of waste, even at a pre-consumer stage. Around 89 million tons of food waste is generated every year in the EU-27 (Bio Intelligence Service, 2010). Some 38% is generated by the manufacturing sector, 42% by the household sector (other sectors: 19%). First generation food supply chain waste re-use such as anaerobic digestion, composting, or conversion to animal feed only has marginal economic value compared to the revenue that could be generated from the production of pectin (10–12 £/kg) from citrus peels, for example.

In addition, when using waste, several criteria need to be considered in order to make sure the feedstock chosen is going to be used over the long term. Volumes available, occurrence in several geographical locations, guaranteeing a regular supply throughout the year, chemical functionalities present, extractables recoverable and their value as well as fitting the feedstock with appropriate green chemical technologies are all important parameters to consider when selecting a waste by-product for valorization.

Wheat straw is a major by-product of the agricultural sector. It is estimated that in the UK alone, 6.3 million tonnes of wheat straw was generated in 2007 (NNFCC, 2008), with a net surplus over livestock demand of 5.7 million tonnes in 2007. In the context of the UK Government’s new targets on biomass generated heat and power (5% by 2020) (HM Government, 2009), wheat straw represents a good choice of feedstock for combustion for heat and power generation. However, available valuable chemical functionalities should be recovered before any thermo- or biochemical processes are applied to wheat straw for conversion to energy. Two valorization routes have been demonstrated (see Fig. 1.8): the combustion of wheat straw and subsequent valorization of the slag and fly ash produced and supercritical CO₂ extraction of waxes followed by char production from wheat straw by microwave pyrolysis. Both approaches are aiming for the development of a close to zero integrated wheat straw biorefinery. The first one valorizes the by-product of the combustion of wheat straw: the high content of alkalis (chloride, K₂O and SiO₂) can be extracted by water at room temperature. Up to 30% of the silica present in the ash (wheat straw ash contains 44.25% silica on a dry weight basis) can be extracted at room temperature in the form of a bio-silicate solution by using wheat straw’s own alkali content. Silicates are studied as an alternative to formaldehyde- based adhesives in entirely bio-derived, fire resistant, moisture resistant construction boards and have the potential to improve the cost-effectiveness of energy producing technologies such as combustion and help the direct production of materials from agricultural biomass (Dodson et al., 2011).

The second approach takes advantage of the combination of two green technologies: supercritical CO₂ extraction and low temperature microwave pyrolysis, benefiting from the financial return offered by the extraction of phytochemicals prior to the production of char by microwave pyrolysis at 180°C. The first step is the extraction of the wax coating the wheat straw: between 0.9 and 1.1 wt% at 32°C and 100°C, respectively, which is comparable to hexane. The added advantage associated with using supercritical CO₂ over hexane is that unwanted components such as pigments, free sugars and polar lipids are less soluble in supercritical CO₂ than in hexane. Compounds found in the extracted wax range from 6,10,14-trimethyl 2-pentadecanone used in detergents, to nonacosane, a bio-derived type of paraffin wax, and octadecanal, an aldehyde used as a flavouring additive in foods. The de-waxed wheat straw is then pyrolysed using microwaves as a heating method, producing five fractions. They are described as follows:

It should be noted that both technologies are scalable and are commercially used by the food industry and yield several useful marketable products in the context of a wheat straw biorefinery. Microwave technology is less sensitive to water content than conventional convection heating. The use of biomass with a high water content can prove to be advantageous as water can dissociate at higher temperatures under microwave conditions (Vaks et al., 1994) and can generate an in-situ acidic pseudo catalysis process benefiting the targeted process (extraction, chemical reaction). Furthermore it is portable, tuneable (additive, temperature, pressure, power) and fast, proving to be applicable to a variety of feedstocks, or feedstock agnostic. In terms of energy consumption, the described process only requires 1.8 kJ/g of energy compared to 2.7 kJ/g when using convection heating for the pyrolysis stage (Budarin et al., 2011 ). Supercritical CO 2 may require a very high capital investment, but on a large scale, it has been proven to be more cost-competitive than using hexane (List et al’, 1989), as this technique is virtually residue-free, requiring less downstream separation to achieve high purity of the extracted compounds.

Straw represents 50% of the yield of a cereal crop (Clynes, 2009) and with 650,881,002 tonnes of wheat produced in the world in 2010, wheat straw represents an important agricultural by-product occurring on every continent on the planet, with Europe, Asia and North America being the largest wheat producers. In conclusion, by integrating just two green processes, several products can be obtained starting from a unique feedstock available worldwide.