Discarded oyster shells start new life

Last updated 09:22 06/06/2012
Graham Laidlaw and Murray Kerr

GOLDEN SHELLS: Bluff Sand Supply and Cartage company owner Graham Laidlaw, right, and employee Murray Kerr inspect the mountain of oyster shells waiting to be crushed.

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A Bluff businessman is turning a mountain of empty oyster shells into a growing enterprise.

Each year millions of oysters are opened in Southland and while most people enjoy what is inside, Graham Laidlaw is finding a way to savour the parts that get thrown away.

"When you eat an oyster, you don't think where shells go. I never did," Mr Laidlaw said.

"So processing oyster shells was something I didn't really know much about when I came to own the plant two and a half years ago.

"I bought the Bluff Sand Supply and Cartage company, a trucking company, and the plant was part of package.

"I really didn't know what I was going to do with it."

Just off Bluff Highway, six kilometres from Invercargill, is a modest processing plant and a mountain of oyster shells bleached and cleaned white by the elements.

The operation was run by one fulltime employee, Murray Kerr, and one part-timer, but it was now time to consider upgrading the facility, Mr Laidlaw said.

"The plant has been here long before I was around and belonged to poultry farmers who used to feed the calcium-rich product to their hens," he said.

"There hasn't really been an upgrade to the equipment in that time but with the demand for the product increasing that is the next step."

The raw product was piling up faster than it could be processed, Mr Laidlaw said.

The success of the plant, demand and good profit margins are all contributing to the need to look at increasing production, he said.

The oyster shells are collected from the oyster factories in the region and Mr Laidlaw admitted he could get the shells for almost nothing.

"It does help that the raw product is affordable and readily available," he said. "But if I don't take it, the factories would have to dispose of the shells themselves and would need resource consent."

Oyster shells are rich in calcium or lime and that was their key ingredient, Mr Laidlaw said.

Calcium has several uses and the small processing plant wholesales bags of crushed oyster shells for use in animal feed, especially for poultry in the production of eggs, stock feed and soil enrichment.

"We wholesale to companies and businesses across the country," Mr Laidlaw said.

In line with expanding the business, Mr Laidlaw said he was also eyeing to eventually export the crushed Bluff oysters to Asia.

"Oyster powder is very popular in China where it is used for medicinal purposes," he said.

"Exporting would be on the agenda once the plant is upgraded."

Mr Laidlaw said he was the only person in Southland who processed oyster shells.

"I think there is a company that crushes mussels in Nelson but other than that I'm the only one with a mountain of oyster shells on their property."


  • Shells are collected from oyster factories and placed in a stockpile.
  • Shells are exposed to sun, rain and wind for minimum of six months to be naturally cleaned.
  • Clean shells are loaded into a vibrating hopper and a controlled load is dropped into a tumbler.
  • The tumbler revolves, similar to a cement mixer, separating the shells before a diesel burner dries off any moisture. Dry shells are carried by an elevator up to the crusher and crushed into various sizes.
  • Crushed shells go back into a tumbler fitted with four different sized gratings to separate the crushed shells from fine powder to a course product.
  • A conveyor belt moves the selected product into a bagging machine.
  • Bags are filled and transported.

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- The Southland Times


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