Marine Pollution : New Zealand: Waste mussel shells to filter rivers and streams
Scientists in New Zealand have discovered a low-tech way to filter nutrients from groundwater.
The possible solution to target the contamination of waterways in the country involves the use of waste seashells.
Green-lipped mussels (GLM) are the most important aquaculture species in New Zealand. Their use-both in the food as well as the bio-pharmaceutical and health industry- serves to generate NZ $300 million per year.
Yet, according to Associate Professor Aisling O’Sullivan, one of the academics from the University of Canterbury Department of Civil and Natural Resources Engineering investigating the filtration potential of waste seashells, the farming of green-lipped mussels is responsible for the annual proliferation of 90,000 tonnes worth of shell waste.
“When the meat is taken out, the shell becomes waste material. Approximately half of these shells go to landfill. We started looking at using those shells as an active substrate that we could put into something like a filter and treat the water as it passes through.”
GLM shells contain calcium carbonate, which can be used to remove organic pollutants from acid rain and wastewater. This eco-friendly filtration material is also considered more effective in eliminating contaminants from wastewater than conventionally mined limestone.
Professor Aisling O’Sullivan and Professor Tom Cochrane previously used seashells in 2006 to treat mine drainage and remove metals. Called project ‘Storminator’, their award-winning and patented innovation was intended to reduce heavy metal rates such as that of zinc and copper from roof stormwater in urban areas.
Filtering nutrients such as nitrates and phosphates from waterways represents the next developmental stage of the pair’s bespoke filtration method.
Nitrate leaching is a major issue within the agricultural sector.
It occurs when there is more fertiliser (which contains nitrate) in the soil than crops can use, resulting in the ‘leaching’ of nitrates into groundwater or other waterways.
Using mussel shells would not only reduce soil nitrate levels but also eliminate the need for nitrate rich fertilisers as GLM’s make for natural lime fertilisers and soil enhancers.
“We believe this solution will have a reduced carbon footprint because we’re diverting waste from landfill and at the same time reducing the need for imported and synthetic fertiliser currently used on farms. Our solution is a regenerative approach that supports a circular economy,” Associate Professor O’Sullivan said.
“It’s low-tech, green technology that is reusing waste that would otherwise go to landfill, it is economically viable, and it could be reused after it’s captured the nutrients. All these aspects make it highly attractive to develop and implement.”
The new technology does not only take recent freshwater reforms into account but could also help farmers meet the country’s nitrate reduction goals by 2025. The potential for its large-scale adoption is vast, seeing as alternative filtration systems come with ‘unintended consequences’, as Professor O’Sullivan terms it.
“There are constructed wetlands or permeable reactor barriers that target nitrate in agricultural settings, but they’re quite expensive to construct, they’re limited in terms of how much nitrate they can remove, and their performance is lower in cooler months. We’re looking at overcoming those limitations with our design”, he added.
After their potential use via drainage pipes, the used shells-turned-filters could either be ‘regenerated’ to enable their further use for filtration purposes or they could be crushed so as to derive an organic fertiliser that can be used for farming.