Grinding Mussel Shells Into Calcium Carbonate Offers High-value Waste Solution

A New Zealand company has cracked a way to turn thousands of tonnes of mussel shells dumped each year into calcium carbonate, a high-value product used in a range of industrial products.

Environmental Decontamination (NZ) Limited (EDL) is behind this breakthrough, with help from the Ministry for Primary Industries (MPI).

“In 2020 we partnered with EDL to develop mechanochemical technology to grind mussel shells into calcium carbonate powder,” says Steve Penno, MPI’s director of investment programmes.

“Calcium carbonate is a high-value ingredient that is in hot demand as it’s used in a range of industrial products – from concrete and paint to paper.

“The trials have been a resounding success, and they’ve demonstrated that the technology can be scaled up.”

EDL was granted $313,000 from MPI’s Sustainable Food and Fibre Futures fund to conduct pilot-scale trials. The company partnered with North Island Mussels Limited, who provided important market feedback and shells from their Tauranga facility.

“The technology offers an innovative solution to deal with the tonnes of mussel shells piling up,” says Mr Penno.

“The only other way to produce calcium carbonate is through mining, so this new technology represents a massive step towards more sustainable options. It also provides a local supply of calcium carbonate at a time when supply chains are a challenge worldwide.”

Dr Kapish Gobindlal, one of EDL’s directors and its chief scientist, is leading the project.

“Currently New Zealand mussel shells are disposed of in landfill or used as fill material on farmland, but the shells are classed as biowaste,” says Dr Gobindlal.

“We’re now looking at building a facility that aquaculture companies can send their shells to, and there’s potential to set up our grinding systems on site at mussel processing plants across the country as well.”

EDL already has interest from major aquaculture companies in New Zealand. Dr Gobindlal says several potential buyers of the end product are already involved in the project by testing and validating the technical properties of the calcium carbonate EDL is producing.

“Our testing and validation has confirmed that the technology we’ve developed produces high quality calcium carbonate, suitable for paint, construction, and other high value applications.”

Dr Gobindlal says New Zealand currently processes approximately 100,000 tonnes of green-lipped mussels for export and domestic supply per annum. This generates around 55,000 tonnes of mussel shells requiring disposal.

“Our aquaculture industry is projected to grow from NZ$600 million in 2019 to NZ$3 billion by 2035 so the issue of mussel shell waste is only going to grow.

“We’re pleased that this Sustainable Food and Fibre Futures funding has paid off – and we’ve proven that revenue can be generated from this waste stream.”

“New Zealand’s aquaculture sector aims to be the greenest in the world,” says Steve Penno.

“This project helps realise the goals of the sector and Government’s Fit for a Better World roadmap for the food and fibre sector, which aims to boost sustainability, productivity and jobs over 10 years. This includes a focus on turning waste streams into high-value products.

“This truly is Kiwi ingenuity at its best.”

Notes for editors

What are some common applications for calcium carbonate?

Calcium carbonate is used as an ingredient across many industries, including:

• Agriculture – soil pH stabiliser
• Construction – cement replacement and use in other cementitious products
• Paint – extender
• Life sciences – calcium source for humans and animals
• Water treatment – flocculent and contaminant removal
• Steel – removes impurities during the blast furnace phase of iron extraction
• Plastics – decreases surface energy, provides opacity, and surface gloss
• Paper – filler and coating pigment

How are the mussel shells crushed?

North Island Mussels Limited has produced a high-level conceptual design for a full-scale operational plant which is envisaged to be implemented at their Tauranga facility.

The major components of the proposed operational plant are listed below:

• Holding hopper. Temporary storage of mussel shells as they exit the production line.
• Shell washer. High-pressure water washer to remove residual meat and impurities.
• Shell dryer. Convection air dryer to reduce moisture content to <1%.
• Shell crusher. Preliminary crusher to reduce shells to 15-20 mm particles.
• MCD reactors. Dual cascading reactors to reduce / transform mussel shells into GCC.
• Packaging. Preparing the powdered product in accordance with customer requirements.

Which companies have been part of the market validation process?

Participating companies have included Stevenson Concrete (construction), Resene (paint), Ingredients+ (ingredient supplier – life sciences), Sanford (aquaculture), Farmlands Co-operative and Ravensdown Fertiliser Company (agrichemical suppliers).

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