Valorisation of Oyster Shell and Wastes into valuable by-products

Improving the economic side streams from oyster processing and aquaculture industries

Pilot Background:

A Bord Iascaigh na Mhara (BIM) industry survey reports that Ireland produces 9,800 tonnes of marketable oysters annually from 128 Oyster farms (2018 estimates). Nationally this generates €58M from direct sales and contributes €37M to Gross Value Added (GVA) with an estimated €11M GVA and 249 jobs to the Donegal economy alone where Donegal Aquaculture Services Ltd (DAS) are located[2].

This pilot investigations that will be investigated in cooperation with the SYMBIOMA project seeks to enable DAS to implement a circular and bio-economy driven strategy for the calcium carbonate (CaCO3) rich oyster shell waste as well as other potential processing wastes which has not yet been exploited by the industry. Nationally, Oyster Shell waste accumulations report average stock mortalities of 20-30% per annum. A more fundamental challenge exists with the threat to the biological security of the sector resulting from pathogens (eg. Ostreid Herpes virus-1 (OsHV-1) which occur in 3-5 yearly cycles leading to mass stock mortalities of between 60-80% mortalities resulting in a significant waste issue for the industry, most recently experienced nationally in August 2019. Legislation safeguarding the sustainable disposal of waste accumulations in accordance with EU landfill directives has placed pressure, cost and onus on the industry to reduce organic waste volumes sent to landfill.

Donegal is the second largest Oyster producing county after Waterford and DAS commands a substantive share of output resulting from 3 harvesting sites/licences that we have spread along the Western- Northwestern (W/NW) coastline. The waste shell stock generated by DAS along with regional (NW) accumulations from other sites can range from 1000T-3000T /A.

DAS has been proactive over the last four years in researching the potential for converting shell waste into additional marketable revenue for the company through the establishment of an ancillary shell by-product processing facility that could operate sequentially alongside our existing primary Oyster production business.

Mollusc shells are viewed by the aquaculture and seafood industries as ‘nuisance waste’ and are largely disposed of in landfills. Not only is this an expensive (Increased levies for waste to landfill of €80-100/T) and ecologically harmful practice, it is a colossal waste of potentially useful biomaterials.

Calcium carbonate is a common ingredient with uses across multiple industries ranging from cement mix ingredient (construction) to treating wastewater (PH control). Unfortunately, the vast majority of the world’s calcium carbonate comes from ecologically harmful and unsustainable limestone mining. Reusing shell waste for such purposes is a perfect example of a circular economy, particularly as shells are a valuable biomaterial that can improve the sustainability of the aquaculture industry moving forward. Valorisation opportunities therefore exists for secondary economic benefits to be realised by DAS through the establishment of an ancillary waste shell processing facility.

Multiple uses ranging from low risk/low return (e.g. chicken feed, fertiliser products, landscaping), medium risk / medium return (e.g. use as an absorbent for volatile organic compounds (VOC’s) and sustainable bio-filtration products), and high risk/high return (e.g. ‘Functional Food & natural health supplements) products could be potentially obtainable from the industry wastes. Projected revenue’s average between €750-850/T for low -level by-products (i.e. egg chicken feed), €2k-3k /T for Mid-level, € 5K+ /T for High-end products.

Donegal Aquaculture Services Ltd harvesting and processing facilities

About DAS:

Donegal Aquaculture Services Ltd (DAS) was incorporated in 1999 by brothers Conor & Damien Reid. The company provides grading, packing and dispatch services to two large oyster farms, both owned by the company.  Both farms are based in inner Donegal Bay and have 15 full-time and 15 part-time employees. During the busy harvesting period this figure can increase by approximately 20%.

They process between 400 and 500 tonne of oysters per annum during which time an annual mortality rate of between 20% – 40% per annum can be expected. This figure can experience significant increases periodically as a result of the “red tide” pathogen. They are seeking to engage in a sustainable and responsible approach to off-setting waste shell sent to landfill. Current national and EU regulations and strategies on waste control necessitate the investigation of new opportunities in sustainable shellfish aquaculture. Such opportunities will encourage not only the application of environmental and sustainable technologies but also exploits waste oyster shell as a viable by-product resource which can generate extra income and create additional employment.