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].

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 ß(14)-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...