Global Fisheries and Aquaculture Production

Fisheries and Aquaculture Production

• The total world fisheries and aquaculture production showed a 41% growth from 2000 to 2019, reaching 178 million tons in 2019.
• Molluscs comprised 13% of the total production, while crustaceans comprised 9%.

Shell Waste Generation and Composition

• Close to 8 million tons of waste crab, shrimp, and lobster shells are produced globally each year, comprising up to 60% of overall crab mass.
• Over 10 million tons of mollusc shells are produced annually, with over 70% represented by oyster, clam, scallop, and mussel shells.
• Shell waste accounts for 65-90% of live weight, depending on the species.
• Mussels have the greatest increase in production and shell contribution compared to other shellfish species.

Shell Waste Disposal and Environmental Impacts

• Disposed shells are primarily dumped at sea or sent to landfills, causing environmental damage.
• Shell waste can lead to decomposition of residual tissues, foul odors, and visual pollution.
• Shell waste is generated at various locations, including fisheries, aquaculture, processing companies, restaurants, and individual consumers.

Chemical Composition of Shells

• Shells are composed mainly of calcium carbonate (CaCO3).
• The decomposition of shells requires high temperatures of over 1000°C, resulting in high energy consumption and greenhouse gas emissions.

Valorization of Shell Waste

• Shell waste can be valorized through various applications, including agriculture, medicine, chemical production, construction, environmental protection, and cosmetics.
• The valorization of shells and the unlocking of markets for new products is essential for sustainable waste management.

Cleaning and Preparation of Shells

• Shells need to be cleaned prior to industrial use.
• Cleaning methods include washing with freshwater, heating at 500°C to burn off residual organic material, and enzymatic cleaning.

Environmental Applications of Shell Waste

• Shell waste can be used for water purification and bio-filters, particularly in wastewater treatment and phosphate removal.
• Calcined shells can be used for heavy metal removal from water and wastewater.
• Shell waste can be used for soil remediation, acid mine drainage treatment, and ocean deacidification.

Sustainability Challenges

• Cleaning shells with freshwater is water-intensive, and the use of enzymes is costly.
• The calcination of shells requires high temperatures, resulting in energy consumption and greenhouse gas emissions.### Sensitivity to Ocean Acidification
• Shellfish are more sensitive to ocean acidification at the larval stage than at the adult stage
• Ocean acidification can negatively impact shellfish production
• Increasing seawater alkalinity can help mitigate the effects of ocean acidification
• Restoration of macroalgae and seagrass beds can remove CO2 from seawater during photosynthesis

Use of Waste Shells

• Waste shells can be used to buffer decreases in seawater carbonate due to ocean acidification
• Placing shell reefs adjacent to shellfish farms can improve pH and carbonate geochemical conditions
• Waste shells can control benthic acidity, prevent heavy metal speciation, and reduce eutrophication
• Waste shells can serve as settlement substrates for free-living shellfish larvae and as shelter for other aquatic organisms

Flue Gas Treatment

• Calcined shell waste can be used as an excellent biosorbent material to remove pollutants like SO2, SO3, H2S, and NOx
• Calcined oyster shells can be used to prepare CaO adsorbent for CO2 sequestration

Road De-icing

• Crushed freshwater bivalve shells can be used as an alternative to sodium chloride (NaCl) for road de-icing
• Calcium-magnesium acetate or calcium acetate derivatives can be used as environmentally friendly road de-icers

Green Roofing

• Mollusc shells can be used as a material for green roofing structures, such as drainage layers, or to help neutralize acid rain
• Shells have bioremediation potential and can be used to reduce runoff water

Sustainability Challenges

• Calcination of waste shells requires high temperatures and special machinery, making it a non-sustainable solution
• Using raw shells as bio-filters can be a more sustainable solution, but requires careful consideration of instability in acidic waters and sludge formation

Food and Feed Additives; Nutraceuticals

• Waste shells can be used to produce natural shell powder, a relevant source of calcium for the food and nutraceutical industry
• Chitin is widely used to immobilize enzymes and whole cells in the food industry
• Chitosan is used as a preservative, thickener, and stabilizer in food products

Calcium Supplement

• Calcium supplementation from shell powders can improve bone health, blood circulation, and eggshell quality in livestock

Protein Supplement

• Meals derived from crustacean shell waste are usable feed ingredients, rich in essential amino acids
• Shell fermentation products can be used as a feed ingredient in the aquaculture industry

Antibacterials for Food

• Macromolecular chitosan has powerful antibacterial properties, inhibiting bacterial growth on surfaces of aquatic and meat products

Bioactive Molecules/Antioxidants

• Chitosan and chitosan oligosaccharides act as potent antioxidants, scavenging free radicals and preventing oxidative sequences

Bioactive Molecules/Cholesterol Reduction

• Chitosan acts as a hypocholesterolemic agent, reducing LDL-cholesterol levels and increasing HDL-cholesterol levels

Bioactive Molecules/Blood Pressure Reduction

• Chitosan oligosaccharides have angiotensin-converting-enzyme (ACE) inhibitory activity, reducing peripheral blood pressure and having an anti-hypertensive effect

Sustainability Challenges

• Extracting chemicals from waste crustacean shells is destructive and expensive, requiring fractionation and the use of hazardous chemicals
• A sustainable fractionation method to separate proteins, CaCO3, and chitin without hazardous chemicals is needed

Biomaterials

• Shells of both crustaceans and molluscs have potential applications in biofuels, flavors, fragrances, pharmaceuticals, industrial chemicals, and biomaterials
• Chitin and chitosan can be used as chemical building blocks for various biomedical applications

Bone Tissue Regeneration/Bioceramic

• Powdered oyster nacre can stimulate bone cell differentiation and bone formation in vitro and in vivo
• Oyster shell powder can be used as an injectable osteogenic biomaterial for treating vertebral bone loss

Cosmetics

• Clam shell powder has potential as a new biomaterial with high calcium, phosphate, chitin, and protein content
• Hydroxyapatite from shells can be used as an additive in sunscreen lotions, substituting oxybenzone, zinc oxide, and titanium dioxide

Wound Healing

• Chitin film and fiber can be used as a wound-dressing material, exhibiting bacteriostatic and fungistatic properties

Biocomposites/Biofillers

• Calcined, powdered mollusc shells can be used as additives for polyesters, endowing antibacterial properties to biocomposites

Biopackaging

• Biopolymers deriving from waste shells can be used to manufacture eco-friendly bioplastics for biomedical, industrial, and household applications### Antimicrobial Biopackaging
• Chitosan, derived from shell waste, is a promising active packaging material developed in the last decade.
• However, its stability is lower due to its hydrophilic character and pH sensitivity, making it imperative to investigate its bioactivities and develop new separation and enrichment technologies.

Sustainability Challenges

• Shell waste biomaterials are only developed as niche applications or tested in laboratory scales, not yet realized in production.
• To commercialize these biomaterials, it is necessary to consider their overall performance, chemical stability, reusability, economic, and environmental values for maintaining sustainability.

Construction

• Shells have been used in houses and walls as path aggregates and mortar mixes.
• Mollusc shells can be used as cement additives or aggregates to replace conventional aggregates in concrete, reducing production costs.
• Incorporating mollusc shell ash/powder for cement partial replacement results in reduced early compressive strength, but increases with age due to hydration of calcium oxide.
• The use of waste shell powder can possibly supplement non-renewable limestone powder in cement-based materials.

Shell Waste Repurposing

• Shell waste repurposing and valorization are important for determining strategies to make them a standard valuable resource for various applications.
• Bivalve aquaculture has the potential to act as a carbon sink, sequestering several million metric tons of CO2 per year globally.
• However, most aqua-cultured bivalves and crustaceans are traded fresh, and their shells are disposed of as domestic waste, releasing trapped CO2 back to the atmosphere during incineration.
• To upgrade waste shells, they should be collected in an organized manner, and their quantities estimated, ensuring a stable supply for large-scale applications.

Environmental Impact

• The repurposing of waste shells should reduce environmental impact, particularly in terms of energy and water demand.
• The use of cleaner energy sources could ameliorate the environmental impact of repurposing operations.
• The reuse and valorization of waste shells must consider collection, cleaning, storage, transport, and utilization costs, as well as economic value and impact.