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A local company has developed a ground-breaking new plant that can recycle excavation waste into reusable sand and aggregate, instead of dumping it in rural cleanfill sites.
Sustainable Sand and Stone founder Rob Southey, who lives at Snells Beach, says the new process has the potential to reduce demand for aggregate from sand mining and quarrying, both of which have a huge environmental impact and leave a significant carbon footprint.
The $7 million specially designed plant was imported from the UK and is based on machinery that is usually used to sort waste from street sweeping machines.
Southey said the idea of recycling the waste from his company’s hydro excavation fleet, which uses pressurised water jets for low-impact digging and trenching, was based on practical and environmental considerations.
Until recently, the muddy sludge byproduct from Southeys’ 20 trucks was taken to the former family farm at Waimauku, where it was dried and dumped in a 16-hectare cleanfill. However, after a more than a decade, the site was filling up and the Southeys realised it was time for change.
He said they thought about buying more land, but realised it made no sense to continue taking up time, energy and resources trucking waste out from Auckland, so general manager Kevin Chapman suggested looking into recycling, having seen machinery that he thought could be adapted in the UK.
After several Covid-induced delays in manufacturing, shipping and installation, the plant was finally up and running a few months ago, taking muddy slurry in at one end and producing two grades of sand and three sizes of chip and metal, all clean and ready to reuse in construction, at the other. The plant, which is in Mangere, also cleans and recycles all the water, too.
“We’re water positive,” Southey said. “We’re digging with it, sucking it back up, cleaning it and using it again and again.”
He said there was nothing else quite like the plant in New Zealand, due to its distinct design and patented process to separate, sort, grade and clean everything that goes through it to a high standard – “it does a lot more than just separate dirt and water”.
Southeys is currently in talks with major roading contractors, developers and councils, as well as going through the process of getting the quality recycled aggregate certified for sale and reuse.
Before expanding the family trucking and hydro excavation business, Southey was a dairy farmer at Whangaripo for 25 years. He was one of the first people in New Zealand to get into hydro excavation, importing a machine from the US in 2010, before working with Warkworth’s MS Engineering (now ITSS Engineering) on building an improved version.
We then went into partnership with director Hugh Harvey and formed Smart-Dig to build more machines. We’ve made about 80 since 2013 and Southeys use 20 of them,” he said.
Southey says the potential for the new waste recycling plant is huge, with scope to adapt it for other construction and excavation waste streams.
