Fuels, Chemicals and Materials from the Oceans and Aquatic Sources

Fuels, Chemicals and Materials from the Oceans and Aquatic Sources provides a holistic view of fuels, chemicals and materials from renewable sources in the oceans and other aquatic media. It presents established and recent results regarding the use of water-based biomass, both plants and animals,for value-added applications beyond food.

The book begins with an introductory chapter which provides an overview of ocean and aquatic sources for the production of chemicals and materials. Subsequent chapters focus on the use of various ocean bioresources and feedstocks, including microalgae, macroalgae, and waste from aquaculture and fishing industries, including fish oils, crustacean and mollusc shells.

Fuels, Chemicals and Materials from the Oceans and Aquatic Sources serves as a valuable reference for academic and industrial professionals working on the production of chemicals, materials and fuels from renewable feedstocks. It will also prove useful for researchers in the fields of green and sustainable chemistry, marine sciences and biotechnology.

Topics covered include:
• Production and conversion of green macroalgae
• Marine macroalgal biomass as an energy feedstock
• Microalgae bioproduction
• Bioproduction and utilization of chitin and chitosan
• Applications of mollusc shells
• Crude fish oil as a potential fuel

• Language: English
• Publisher: Wiley
• Release date: May 30, 2017
• ISBN: 9781119117186

Book preview

List of Contributors

Ibraheem Adeoti Department of Process Engineering, Memorial University of Newfoundland, Canada

Ravi S. Baghel Marine Biotechnology and Ecology Division, CSIR – Central Salt & Marine Chemicals Research Institute, India; Academy of Scientific and Innovative Research (AcSIR), Central Salt & Marine Chemicals Research Institute, India

Kelly Hawboldt Department of Process Engineering, Memorial University of Newfoundland, Canada

Masanori Hiraoka Usa Marine Biological Institute, Kōchi University, Japan

Francesca M. Kerton Department of Chemistry, Memorial University of Newfoundland, Canada

Bin Li CAS Key Laboratory of Bio-Based Material, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, China

Kevan L. Main Marine & Freshwater Aquaculture Research Program, Mote Marine Laboratory, USA

Vaibhav A. Mantri Marine Biotechnology and Ecology Division, CSIR – Central Salt & Marine Chemicals Research Institute, India; Academy of Scientific and Innovative Research (AcSIR), Central Salt & Marine Chemicals Research Institute, India

Heather Manuel Centre for Aquaculture and Seafood Development, Fisheries and Marine Institute of Memorial University of Newfoundland, Canada

Clifford R. Merz University of South Florida, College of Marine Science, USA

Dibyendu Mondal Natural Products & Green Chemistry Division, CSIR – Central Salt and Marine Chemicals Research Institute, India; Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Portugal

Xindong Mu CAS Key Laboratory of Bio-Based Material, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, China

Jennifer N. Murphy Department of Chemistry, Memorial University of Newfoundland, Canada

Kamalesh Prasad Natural Products & Green Chemistry Division, CSIR – Central Salt and Marine Chemicals Research Institute, India; AcSIR – Central Salt & Marine Chemicals Research Institute, India

C.R.K. Reddy Marine Biotechnology and Ecology Division, CSIR – Central Salt & Marine Chemicals Research Institute, India; Academy of Scientific and Innovative Research (AcSIR), Central Salt & Marine Chemicals Research Institute, India

Shuntaro Tsubaki Department of Applied Chemistry, Graduate School of Science and Engineering Tokyo Institute of Technology, Japan

Ning Yan Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore

Wenrong Zhu Graduate School of Kuroshio Science, Kōchi University, Japan

Series Preface

Renewable resources, their use, and modification are involved in a multitude of important processes with a major influence on our everyday lives. Applications can be found in the energy sector, paints and coatings, and the chemical, pharmaceutical, and textile industry, to name but a few.

The area interconnects several scientific disciplines (agriculture, biochemistry, chemistry, technology, environmental sciences, forestry, etc.), which makes it very difficult to have an expert view on the complicated interaction. Therefore, the idea to create a series of scientific books that will focus on specific topics concerning renewable resources has been very opportune and can help to clarify some of the underlying connections in this area.

In a very fast-changing world, trends are not only characteristic for fashion and political standpoints; science is also not free from hypes and buzzwords. The use of renewable resources is again more important nowadays; however, it is not part of a hype or a fashion. As the lively discussions among scientists continue about how many years we will still be able to use fossil fuels—opinions ranging from 50 to 500 years—they do agree that the reserve is limited and that it is essential not only to search for new energy carriers but also for new material sources.

In this respect, renewable resources are a crucial area in the search for alternatives for fossil-based raw materials and energy. In the field of energy supply, biomass and renewable-based resources will be part of the solution alongside other alternatives such as solar energy, wind energy, hydraulic power, hydrogen technology, and nuclear energy.

In the field of material sciences, the impact of renewable resources will probably be even bigger. Integral utilization of crops and the use of waste streams in certain industries will grow in importance, leading to a more sustainable way of producing materials.

Although our society was much more (almost exclusively) based on renewable resources centuries ago, this disappeared in the Western world in the nineteenth century. Now it is time to focus again on this field of research. However, it should not mean a retour á la nature, but it should be a multidisciplinary effort on a highly technological level to perform research toward new opportunities, to develop new crops and products from renewable resources. This will be essential to guarantee a level of comfort for a growing number of people living on our planet. It is the challenge for the coming generations of scientists to develop more sustainable ways to create prosperity and to fight poverty and hunger in the world. A global approach is certainly favored.

This challenge can only be dealt with if scientists are attracted to this area and are recognized for their efforts in this interdisciplinary field. It is, therefore, also essential that consumers recognize the fate of renewable resources in a number of products.

Furthermore, scientists do need to communicate and discuss the relevance of their work. The use and modification of renewable resources may not follow the path of the genetic engineering concept in view of consumer acceptance in Europe. Related to this aspect, the series will certainly help to increase the visibility of the importance of renewable resources. Being convinced of the value of the renewables approach for the industrial world, as well as for developing countries, I was myself delighted to collaborate on this series of books focusing on different aspects of renewable resources. I hope that readers become aware of the complexity, the interaction and interconnections, and the challenges of this field and that they will help to communicate on the importance of renewable resources.

I certainly want to thank the people of Wiley's Chichester office, especially David Hughes, Jenny Cossham, and Lyn Roberts, in seeing the need for such a series of books on renewable resources, for initiating and supporting it, and for helping to carry the project to the end.

Last, but not least, I want to thank my family, especially my wife Hilde and children Paulien and Pieter-Jan, for their patience and for giving me the time to work on the series when other activities seemed to be more inviting.

Christian V. Stevens

Faculty of Bioscience Engineering

Ghent University, Belgium

Series Editor Renewable Resources

June 2005

Preface

This book provides a holistic view on fuels, chemicals and materials from renewable sources in the oceans and other aquatic media. To our knowledge, it is the first of its kind to cover water-based biomass—both plants and animals—for value-added applications beyond food, despite the fact that there are previously published books focused on more specialized sources (such as algae).

The concept of biorefinery, referring to processes that convert biomass into fuels, chemicals and materials, has received wide awareness and acknowledgement in the new century. The first-generation biorefinery uses sugar- or starch-rich crops, associated with the issue of food security, while the second-generation biorefinery is based on cellulosic materials. In both cases, however, land scarcity sometimes becomes a limiting factor. In this context, oceans and other aquatic media, which account for over 2.5 times more area than land on Earth, appear to be a complementary source of feedstocks for biorefineries.

We realized the underestimated potential of a great variety of water-based biomass resources years back. Together with other researchers around the world, we have strived to extend the concept of biorefinery to include diversified biomass resources from the ocean. For instance, F. Kerton and coworkers proposed and practiced the concept of ‘Marine Biorefinery’, taking fishery by-products and transforming them into a range of value-added products in Newfoundland, Canada, while N. Yan proposed and practiced the concept of ‘Shell Biorefinery’, in which waste crustacean shells are fractionated into three major components and further upgraded for a range of applications.

To date, research and development toward this sort of biorefinery are still in a nascent state, with most work only demonstrated in the lab while large-scale commercial productions may be years ahead. However, there is a consensus being reached around the globe that the valorization of ocean biomass could nicely complement the existing biorefinery, to help avoid the compromise of food security and land use for human beings. Ocean biomass also features unique components and structures enabling the production of high-value chemicals and materials that are difficult to be obtained from other biomass resources or fossil fuels.

These promising aspects made us come together and organize this book, covering various aspects of ocean-biomass-based biorefinery. The book is structured in the following manner: Chapter 1 provides an overview of ocean and aquatic sources for chemicals and materials. Chapters 2–4 describe the production, harvesting and conversion of marine macroalgae into fuels and other compounds. Chapter 5 switches to the topic of microalgae, reviewing its transformation into feeds, foods, nutraceuticals and polymers. Chapters 6 and 7 are focused on crustacean shells, with the Chapter 6 providing recent developments in fractionation of shells into chitin, while Chapter 7 summarizes a broad range of applications of chitin in chemical production and materials science. The final two chapters (Chapters 8 and 9) describe the utilization of waste streams from mollusc and finfish industries, respectively.

This book should be able to serve as a valuable reference for academic and industrial professionals in research and development sectors in renewable fuels, chemicals and materials. Most chapters are written at an introductory level but with sufficient details to serve both undergraduate and graduate students majoring in chemistry, chemical engineering, marine sciences and biotechnology and beyond.

Finally, the editors would like to express their gratitude to all the chapter authors for their invaluable time and contribution to the book and our colleagues, students and family for their patience while we worked on it.

Francesca M. Kerton

Memorial University of Newfoundland, St. John's, Canada

Ning Yan

National University of Singapore, Singapore

October 2016

Chapter 1

Overview of Ocean and Aquatic Sources for the Production of Chemicals and Materials

Francesca M. Kerton¹ and Ning Yan²

¹Department of Chemistry, Memorial University of Newfoundland, Canada

²Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore

1.1 Introduction

The Earth is a watery planet—about 71% of its surface is covered by water [1]. Among all liquid water resources, less than 1% is freshwater, and over 99% is salty seawater. Freshwater in lakes and rivers, despite being in a very small percentage, has shaped our civilizations since the beginning of humankind. On the other hand, people's perspective towards the ocean has been changing over time. In the old days, the oceans served for trade, adventure and discovery, as it set different civilizations apart. At present, the oceans are widely regarded as one of Earth's most valuable natural resources for food, various minerals, crude oil and natural gas.

As there is an increasing concern regarding sustainability, human beings currently strive for a paradigm shift of obtaining resources from renewable feedstocks instead of non-renewable, depleting ones. More than 150,000 animals and 100,000 plants can be found in the oceans, all of which are renewable organic species. Sea plants can be divided into microalgae and macroalgae, whereas sea animals can be broadly categorized into three main types, namely fish, crustaceans and molluscs (Figure 1.1). Unfortunately, the huge potential of the oceans and other aquatic sources to provide renewable organic carbon, hydrogen, nitrogen and other elements as starting materials for chemicals and materials appears to be underestimated. Indeed, according to the data from Web of Science in 2015, of the total relevant papers on renewable feedstocks, only 2.3% were concerned with algae or oceanic biorefinery [2].

Illustration of the animal and plant resources from the ocean and other aquatic sources: microalgae, macroalgae, fish, crustaceans and molluscs.

Figure 1.1 Overview of the animal and plant resources from the ocean and other aquatic sources: microalgae, macroalgae, fish, crustaceans and molluscs.

In fact, compared to conventional land-based biomass, aquatic (in particular, oceanic) biomass has several advantages [3]. First of all, a majority of seaweeds and fishery waste are not consumed as human food, and as such, there are no ethical issues of compromised food supply due to chemical and material production. At the same time, the development of ocean-based biorefinery can release the land area constrains, which are a serious problem in some countries such as Japan and Singapore. Many areas in the world are short of fertile soil for the generation of land-based biomass, and through the development of ocean-sourced feedstocks, people in these regions would utilize renewable materials without costly land-based agriculture. Last but not least, certain oceanic biomass species have intrinsic advantages over land-based resources, such as faster growth rate, less demanding growth conditions, more enriching components and so on.

People have achieved remarkable success in harnessing land-based biomass—starch, woody biomass and vegetable oils—for fuels and chemicals. A landmark event was the opening of the world largest cellulose bioethanol refinery plant with an annual productivity of 30 million gallons by DuPont in November 2015 [4]. Woody biomass, consisting primarily of cellulose, hemicellulose and lignin, enters the biorefinery to be separated and further converted into a wide scope of valuable products [5, 6]. We could anticipate similar concepts towards valorization of aquatic-source-based biomass feedstocks. In the aquatic biomass refinery, ‘wastes’ could be fractionated through an array of processes into different components and further transformed into end products via physical, chemical and biological treatments. Once these objectives are met, new opportunities for building waste industries from ocean-based feedstock will arise. To achieve that, strong supports from research institutes, governments, organizations, companies and the public are integral. In particular, groundbreaking fundamental research from researchers worldwide is crucially required to conquer the technical barriers for integrated, value-added applications of oceanic biomass.

In this chapter, we aim to provide an overview of various feedstocks from ocean and other aquatic sources, including sea-plant-based biomass, finfish-based biomass and shellfish-based biomass. The chemical component, current production scale, utilization and potential application and/or upgrading of each of these are summarized in separate sections.

1.2 Shellfish-Based Biomass

1.2.1 Crustacean Shells

Global shellfish production, such as crabs, shrimps and lobsters, reached around 12 million tons in 2014 [7]. With such massive production, and due to the significant shell content (e.g. the shell of a crab can account for 60% of its weight), tremendous amounts of waste are generated from these crustacean species every year. As an estimation, astonishing 6–8 million tons of waste from crustaceans are produced annually [8].

Long before the modern era, shells were used as currency and regarded as a symbol of wealth. Later on, they were gradually substituted with other materials and became useless. Nowadays, there has been essentially no satisfactory solution to utilize the crustacean shells. Raw shells, such as dried shrimp shell or crab shell powder, have very low monetary value. Newport International, a seafood company partnering with co-packing plants in many Southeast Asian countries, including Indonesia, Vietnam, Thailand and Philippines, sells the by-product of dried shrimp shells at merely US$ 100–120 per ton. The price is commensurable with wheat straws and corn stover, which are agricultural wastes typically sold at US$ 50–90 per ton [9]. Due to the very low profitability, a vast majority of waste shells are disposed or landfilled without use. In developing countries that lack regulations, waste shells are often directly discarded, posing environmental concern. In developed countries, disposal can be costly—for instance, as high as US$ 150 per ton can be charged in Australia and Canada.

Crustacean shells constitute 15–40% chitin, 20–40% protein and 20–50% calcium carbonate [10]. With several million tons of shells generated worldwide each year, the huge potential value of such shells is currently wasted. It is crucial to reconsider how to utilize such an abundant and cheap renewable resource, rather than continue treating it as waste. Further details on the processing of crustacean shells and utilization of chitin and chitosan can be found in Chapters 6 and 7 of this book.

The protein in shells is a good nutrient for animal feed. For example, the protein from Penaeus shrimp shell is a complete protein food as it contains all the essential amino acids. The ratio of essential amino acids to total amino acids is 0.4; the nutrient value is comparable with that of soybean meals [11]. The market demand for protein meal continues to increase due to the rapid growth in livestock breeding. If all the protein from crustacean waste shells from Southeast Asia is extracted as animal feed, an annual market value of over US$ 100 million could be expected even based on the most conservative estimation [12].

Calcium carbonate is widely applied in construction, pharmaceutical, agricultural and paper industries. Current production of calcium carbonate mainly comes from geological sources such as marble and chalk. Ground calcium carbonate, being the major product, has a market price based on a particle size, which ranges from US$ 60–66 per ton for coarse particles to US$ 230–280 per ton for fine particles [13]. Ultrafine particles can reach an astonishing US$ 14,000 per ton. Provided that the calcium carbonate from crustacean shells can only be made into coarse particles, an annual market value of up to US$ 45 million could be estimated from Southeast Asian countries. Due to its bio-origin, calcium carbonate from waste shells is superior to that from marble and limestone for applications involving human consumption, such as calcium carbonate tablets.

The last major component, chitin, is a linear polymer of β(1→4)-linked 2-acetamido-2-deoxy-d-glucopyranose [14]. The structure of chitin is similar to that of cellulose, but chitin has an amide or an amine group instead of a hydroxyl group on the C2 carbon in the repeating unit. Aside from being one of the major components in crustacean shells, chitin is widely present in the exoskeleton of insects, fungi and plankton, making it the second most abundant biopolymer around the world, with approximately 100 billion tons produced per year [15]. Chitin and chitosan (the water-soluble derivative) have been identified as useful functional polymers in several niche applications, including cosmetics, water treatment and biomedicals [16]. However, the current utilization of chitin neither matches its abundance nor fully harnesses its structural uniqueness.

Chitin serves as a major renewable feedstock that simultaneously offers organic carbon and organic nitrogen elements. While a consensus has been reached on the importance of renewable organic carbon, not much has been emphasized on renewable organic nitrogen resources. The necessity is not obvious—after all, nitrogen is the dominant fraction in the Earth's atmosphere. However, nitrogen gas has to be converted into ammonia prior to application or further transformations. Ammonia synthesis is undesirable for the low efficiency that this single process accounts for 2–3% global energy consumption [17]. In addition, three moles of hydrogen gas, which is currently produced from fossil fuels, are consumed for every mole of nitrogen gas. The chemical industry cannot claim to be sustainable without addressing the sustainability issue of the nitrogen source in its products.

Chitin appears to be more suitable for the production of some nitrogen-containing compounds. The major elements required—organic carbon, nitrogen and oxygen—are already in place. Chitin is also enriched with functional groups, thus requiring fewer derivatization steps when used as a raw material compared with fossil fuels. Effective valorization of chitin into chemicals may represent a ‘Game-Changing Innovation’ by bringing substantial benefits for both the economy and environment.

Valorization of shells from crustacean species is not easy. First and foremost, fractionation is needed for further physical, chemical or biochemical processing. However, the current commercialized route to fractionate crustacean shells is associated with serious environmental and economic issues. Two key steps in the process include the removal of protein from the shell by sodium hydroxide solution and the digestion of calcium carbonate by hydrochloric acid. If chitosan is the final product, an additional step of treating chitin with 40% concentrated sodium hydroxide solution is required.

The entire process is destructive, wasteful and expensive—protein and calcium carbonate fractions are currently destroyed and never recovered; sodium hydroxide and hydrochloric acid are highly corrosive and hazardous; production of 1 ton chitosan from crustacean shells needs more than 10 tons water. All these factors lead to negative environmental impacts and high capital costs. As a result, the price of good-quality chitin is as high as US$ 200 per kilogram, although the starting material is not costly. Due to the high price, global industrial use of chitin is estimated to be only 10,000 tons annually [15]. The lack of competitive pricing of chitin in the market, in turn, limits its production scale, forming a ‘high cost/low demand/low production’ pattern. Economically and ecologically unfavourable, chitin production plants are absent in many developed countries and only exist on a small scale in countries such as Thailand and Indonesia.

There are considerable challenges in the post-fractionation steps as well. While the utilization of calcium carbonate and proteins is comparatively easier, the transformation of chitin to value-added, nitrogen-containing chemicals is a critical problem. We envisage that the major obstacles in valorizing chitin to be similar to those in woody biomass valorization. Unlike fossil fuels, biomass feedstocks such as chitin and cellulose are highly functionalized, oxygen-enriched polymers. Side reactions occur easily, leading to the formation of a variety of complicated compounds under severe reaction conditions. In addition, natural chitin is a highly crystallized biomass that impedes accessibility of reagents to the polymer chains. Finally, it is often challenging to separate these bio-based products from the reaction system in a cost-effective way.

To establish a new profitable industry with crustacean shell waste, creative solutions have to be developed for both upstream and downstream sectors. In the upstream sector, the key issue is enabling manufacturing competitiveness to lessen production cost and environmental impact; in the downstream sector, the key issue is establishing economic sustainability via integrated, value-added applications of each component.

A revolutionary fractionation method to separate chitin, calcium carbonate and proteins is highly desirable (Figure 1.2). For an ideal protocol, the following characteristics should apply: (i) all three major components are processed into separate fractions; (ii) strongly corrosive or hazardous reagents are avoided; and (iii) waste generation is minimized. Fortunately, new technologies that partially satisfy these criteria are emerging. For example, lactic acid fermentation has been developed for chitin production both on a lab scale and a pilot-plant scale [18]. The process adopts blended bacteria to simultaneously consume proteins and decompose calcium carbonate. Protein hydrolysate and calcium lactate can be recovered after chitin separation.

Illustration of The concept of waste-shell refinery for various useful chemicals and materials.

Figure 1.2 The concept of waste-shell refinery for various useful chemicals and materials (diagram based on the concept presented in Ref. [8]). (Source: Data taken from Yan and Chen 2015 [8].)

Another method is to utilize specific ionic liquids, which can remarkably dissolve carbohydrate polymers and thus extract chitin from waste shells [19]. In this way, the produced chitin has high molecular weight and is thus suitable for processing into fibres and films. In addition to these, we propose exploring the possibility of shell fractionation via physical methods more intensively. Ball mill and steam explosion may be effective in separating the major components in the shells. Finally, a process combining chemical force and mechanical force might prove to be advantageous, since synergistic effects may lead to unprecedented performance. To exemplify a scenario, combined use of ball mill and a small amount of acid catalyst leads to a complete degradation of wood without extra heating. A similar strategy could be applicable to shells, enabling a highly effective, solvent-free approach for fractionation.

In the downstream sector, diversified utilization of each component is essential. While calcium carbonate and proteins can find direct applications, there is an untapped potential towards chitin utilization. The transformation of chitin into functional polymers and a series of value-added chemicals is a promising direction. There have been decades of research on chitin conversion to polymer derivatives for distinct applications. Conversion of chitin into small nitrogen-containing chemicals is also developing very fast, although it is still at a very early stage. A nitrogen-containing furan derivative was obtained directly from chitin via boric-acid-catalyzed depolymerization and dehydration [20, 21]. Recently, a number of other value-added chemicals have also been produced from chitin or chitin monomer on the lab scale [22–25]. Future investigation should be focused on the following: (i) exploration of new routes from chitin to other potentially related chemicals; (ii) enhanced product yield via improved catalysis and/or chitin pretreatment; and (iii) facile separation of products, such as membrane-based pervaporation technique.

1.2.2 Mollusc Shells

As described in Chapter 8 of this book, in 2013, over 18 million tons of molluscs were harvested, which amounted to 11% of the world's fisheries, and they were mainly produced via aquaculture [7]. In addition to being a valuable source of protein in our diets, molluscs have the benefits of being able to reach maturity in only 2–3 years and are filter feeders, so they do not need to be fed by the farmer. Waste materials, which could be valorized, are produced at a number of stages during harvesting and processing this food. For example, some molluscs will be dead when harvested, die during harvesting or are damaged during the harvesting process (e.g. cracked shells). These wastes can be used to supply biorenewable calcium carbonate and possibly protein product streams (Figure 1.3). The protein can be used in a similar way to that obtained from crustacean shells as described earlier, that is, as a feed or fertilizer. More recently, there has been interest in the use of mussel protein as a nutritional supplement because it contains components that have the potential to treat obesity [26]. Therefore, we expect enhanced interest in mollusc production in the coming years, which could lead to more waste being produced. Furthermore, if the mollusc is processed before being marketed as a food (e.g. canned)—the meat will be removed from the shell, but the shell will often still contain residual protein (i.e. the adductor muscle of the mollusc). The waste streams from mollusc production, if not handled correctly, can be a biohazard, and if the waste is not used, it must be disposed of at specialist landfill sites with associated tipping costs of approximately US$ 150 per ton. This leads to an added incentive for farmers to explore alternative waste disposal/processing options as described as follows.

Illustration of Potential products and applications of materials from a mollusc-based waste utilization process.

Figure 1.3 Potential products and applications of materials from a mollusc-based waste utilization process.

There are two main processes that have been explored for cleaning mollusc shells in order to eliminate the biohazard risk and produce value-added materials. The first process involves burning off residual protein and organic matter by heating the shells to 500 °C. This has been explored on a pilot-plant scale in the region of Galicia, Spain [27]. Various challenges were encountered during this scale-up, for example, SO2 and NO2 emissions when oil was used in the heating process. Furthermore, in such a process, the protein stream is wasted. From a sustainability perspective, biocatalytic (enzymatic) cleaning processes are perhaps more promising. Enzymatic proteolysis of finfish and crustacean by-products has been studied extensively, but there are few examples of its application to mollusc and mollusc shell processing. In most examples, only a small amount of the catalytic protease enzyme is needed, and temperatures are not much higher than room temperature (40–70 °C) [28]. As with most enzymatic processes, the pH of the process must be monitored in order to prevent deactivation of the enzyme. The protein hydrolysate stream produced via such hydrolysis reactions has potential uses in flavourings or supplements within the food industry. Further hydrolysis and separations could yield amino acids, which could be used as chemical building blocks to build up more complex structures such as bioactive compounds (pharmaceuticals).

Although less extensively studied compared to crustacean waste streams described in Section 1.2.1, applications of mollusc shells in a range of areas have been proposed and investigated on a lab scale. The calcium-carbonate-rich shells produced by molluscs have the potential to become high-value, low-volume products (e.g. cosmetics or medicine) or low-value, high-volume products (e.g. soil amendment or building materials). Applications of mollusc shells include the following: feed additives for poultry, soil amendment, treatment for acid mine drainage, water purification, additive for building materials (e.g. concrete) and lime (calcium oxide) production. Additonally, it is worth noting that the structure of biogenic calcium carbonate [29, 30] is significantly different from that of quarried calcium carbonate, and this may lead to additional value to end users. For example, in Thailand, a range of different shells were studied as cost-effective replacements for Portland cement in the production of plastering cement [31].

It is also worth noting that molluscs can play an important role in integrated multi-trophic aquaculture (IMTA) that is being explored worldwide as a method of sustainable farming. In such approaches, different organisms are grown/farmed in close proximity in an attempt to mimic natural aquatic ecosystems and prevent pollution of the oceans nearby. For example, a pilot project has been studied in the Bay of Fundy, New Brunswick, Canada [32]. Seaweed (Kelp), mussels and Atlantic salmon were grown nearby, uneaten salmon feed and faeces provided nutrients to the mussels and excess dissolved nitrogen and phosphorus produced during the salmon farming were taken up by the seaweed. It is hoped that such practices will prevent hypernutrification and eutrophication of coastal waters around finfish farms. If IMTA becomes a well-established way to reduce environmental impacts of finfish farming, levels of mollusc production will likely increase as the aquaculture industry continues to grow to meet the needs of a growing global population [7].

1.3 Finfish-Based Biomass

About 580 species of fish, including finfish and shellfish, are farmed worldwide, and production from wild capture and aquaculture exceeded 160 million tons in 2013, with aquaculture contributing 70 million tons [7]. The most important farmed finfish species are carp, tilapia, catfish and salmon. The amount and type of fish farmed often depend on the location and climate. For example, the major producers of farmed salmon are Chile, Norway, Scotland and Canada. Finfish farming can occur in cages at sea or on land. Research is ongoing towards development of farming sites further out at sea, as, at present, most of them are normally situated in sheltered, coastal locations. However, there is interest in developing multi-platform sites where IMTA (described earlier) can be pursued and monitored alongside off-shore wind-farm platforms so that food and power would be generated at a single site and costs of manpower and transport could be shared.

The typical stages in finfish farming are outlined in Figure 1.4. Upon harvesting, fish frequently undergo primary processing where they are decapitated and gutted and often fileted. The fish may then undergo secondary processing such as smoking or salting. During processing, significant quantities of waste are produced: heads, viscera (guts), belly flaps, frames (bones), skin, gills and blood water [33]. Approximately 70 million tons of fish per year are processed worldwide by filleting, freezing, canning or curing, and these activities generate 30–50%