As far as rubbish goes, it smells pretty good.

Former barista Ninna Larsen wheels a common rubbish bin forward, opens the lid and dumps a full load of coffee grounds.

Next to the pile of dark brown and black grounds is another, bigger mound, consisting of animal faeces, food waste and plant matter. This one smells less appealing.

Ms Larsen has another nine bins full of coffee grounds in the back of her van to be unloaded at Melbourne Zoo and sit right next to the zoo’s organic waste dump.

“We have a partnership with around 400 cafes around Melbourne,” she tells the ABC between loads.

“We collect around 1.2 tonnes of coffee per run and we have about two to three runs a day, so significant amounts of coffee a day.”

Reground aims to transform coffee grounds into compost to help reduce greenhouse gas emissions. (ABC News: Iskhandar Razak)

Eleven years ago, Ms Larsen started Reground, a social enterprise that collects coffee waste to be reused.

She did it after finding out how much environmental harm Melbourne’s love affair with lattes, long blacks and flat whites can cause.

“In landfill, coffee grounds emit a lot of toxic gases,” she said.

The emissions include methane gas.

And Matt Genever, the CEO of Sustainability Victoria, said those emissions were a national problem — especially because Australia generated about 75,000 tonnes of ground coffee waste every year.

Reground’s Ninna Larsen worked with Sustainability Victoria CEO Matt Genever to help turn the coffee grounds into compost. (ABC News: Iskhandar Razak )

But environmental groups have come up with an ingenious solution.

Sustainability Victoria has granted Reground more than $400,000 in recent years to help turn the grounds into compost, which doesn’t emit harmful gases.

Coffee grounds on their own are too acidic to be used in a garden.

But if properly mixed with organic matter like animal waste, they can be highly effective fertilisers because they are high in potassium and nitrogen.

And one partner with an ample and never-ending supply of animal waste ready to be transformed is Zoos Victoria.

750 kilograms of animal waste

Melbourne Zoo has hundreds of animals creating waste every day.

Then there are food scraps from animals and visitors alike, as well as plant litter from dozens of gardens and enclosures.

“We produce about 1,000 tonnes a year of organic waste, Sarah Larkin from the zoo’s sustainability team said.

“So that equates to 3,000 kilograms a day.”

Of that, about 750 kilograms are daily animal waste.

Giraffes are contributing more waste to the compost program than any other animal at Melbourne Zoo. (Supplied: Zoos Victoria)

“The giraffes are the biggest contributors and now we have a new calf, we’ll get even more from them,” Ms Larkin said.

All of this organic waste is put through what’s known as the “Hot Rot”.

It is a 10-metre-long machine that mulches and churns organic waste into compost — including the coffee leftovers from Reground.

“Everything goes into it,” Ms Larkin said.

“We have tigers and lions, so carcasses go into it. Bone is in there. Fruit from all of our animals. All sorts of organic rich material.

“It’s already nutrient-dense.

“But it is a more nutrient-rich product with the coffee. And Reground drops off three-times a week.”

Millions of kilograms of coffee grounds diverted

Once churned, the Hot Rot material comes out a very dark brown.

But despite the volume of excrement, once it is mixed and churned, the end product doesn’t stink.

Instead, it has an earthy odour.

Melbourne Zoo is one of the zoos using the recycled compost in its gardens. (ABC News: Iskhandar Razak)

The zoo previously sold its compost to the public, but now only uses it on its own premises.

However, there are plans make it available to the community again soon.

Ms Larsen is quick to quote her enterprise’s environmental impact.

“We have diverted 2 million kilos of coffee grounds — which is the same as 58 million café lattes,” she said.

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