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The aroma at 90 Hunua Rd, Papakura, on this bright, cold morning is that hot vomit stench you get from the depths of your rubbish bin, magnified by a hundred.

Andrew Fisher, who greets us with enthusiasm at the gates, describes it as “rich”.

To Fisher, the tonnes of household food waste giving off this distinctive smell are a previously disregarded goldmine.

He’s pioneering – taking it from landfill and turning it variously into fertiliser, heat for growing hothouse tomatoes and gas for the national grid – and if you live in Auckland, you’re along for the ride.

Since Auckland Council launched a food scraps recycling programme, complete with mantras about ‘kai to kai’ and adverts featuring an oversized fairy, I’ve been a diligent part of Fisher’s experiment.

I dutifully fill a small plastic caddy on my kitchen bench with eggshells, potato peels and uneaten school lunch sandwiches. I decant it in pink compostable bags into a larger plastic bin. I ignore the plaintive complaints on my local Facebook page and leave it on the kerbside for its weekly collection.

Now, I’d like to see what happens next.

The first step

The journey begins when my kumara peelings are collected from the kerbside in a truck driven by Amandeep Singh. He leaves Smart Environmental’s yard at 6am and picks up the first of about 800 bins on this lower North Shore run at 7am. He reckons about half the houses leave their bins out. “I don’t need to go to the gym after this,” he says. “I’ve already lost 11kg in six months.”

Singh tips my bin into a purpose-built hopper which takes up to 150kg of food waste before it’s drawn into the truck body (which in turn accommodates up to 3.5 tonnes), by an augur designed not to compress it so it still retains the liquid content. Cameras on the hopper can help spot any contamination by non-food waste (the rate is about 4 per cent, lower than for regular recycling bins). The council intends all these trucks will eventually be electric.

Singh’s load, and those of trucks from routes around Auckland are consolidated at an old polystyrene plant in an industrial estate in Papakura, in the city’s south.

And that’s why we’re there at 7.30am to get the guided tour from Fisher, a gregarious former Army engineer and SAS officer, who is now a biowaste evangelist, given to enthusiastic statements about “New Zealand catching up with the rest of the world”.

He owns 15 per cent of Ecogas, which holds the contract for Auckland’s food waste; the philanthropic Central Lakes Trust has the other 85 per cent through its renewable power provider Pioneer Energy.

Inside, piles of pink bags are mounded in those big concrete bays usually filled with sand or gravel at garden centres.

A substantial portion of the waste processed here comes from the commercial sector, with out-of-date, spoiled, retained samples and end-of-line leftovers. Buying up these leftovers to turn them into animal feed was Fisher’s introduction to the sector.

A truck arrives full of rejected chicken and pallets of recalled frozen raspberries (they’ve got 2,000 to work their way through) are stacked in a corner. Fisher says in the bad old days, they would simply have been tipped into landfill, packaging and all. This way, the pallets and cardboard can be reused and the berries thrown into the mix.

They have a machine to “pre-break” loads – and to let them have a look at what might have snuck in. So far, they’ve had lawnmower blades, knives and even an engine block; one UK plant Fisher visited had a trophy room with a stag’s head and a bowling ball.

But otherwise, says Fisher, this clean, tidy, organised warehouse is “just a railway station” – most waste lingers less than six hours before being collated and heading south.

Outside, one truck is being weighed (38 tonnes) as it departs. Driver Zoe Henderson is waiting to take the next load. She’s driven up from Taupō with an empty truck this morning, but Fisher assures us they usually piggyback off loads of building aggregate coming north that would otherwise return unladen – part of a plan to combat criticisms that the scraps’ journey creates unnecessary carbon emissions. We will catch up with Henderson at the other end.

A shiny slice of the future

Three hours south, in a flat paddock outside the Waikato town of Reporoa sits Ecogas’ biowaste plant, a shiny, purpose-built slice of the future.

There’s thousands of these places all over Europe, Fisher assures us, but this is the first in New Zealand and he has lots of nice things to say about Auckland Council’s vision in backing it. “Kiwis, we are s… at inventing stuff, but we are great at grabbing something and going on with it,” he says.

By the time we arrive via a couple of coffee stops, Henderson has already driven her truck inside the main building, offloaded, hosed it down and is ready to leave. She assures us she no longer notices the smell, but makes sure she keeps her boots outside the cab so it doesn’t accompany her.

Inside, a mound of tomato vines has joined the familiar pile of pink bags and raspberries and is already being attacked by a forklift, scooping them into a large hopper. Fisher looks on in delight. “This would all have gone to landfill. But this is a resource. This is gold.” He laughs. “You just can’t see it.”

I won’t quite pretend to understand the next bit well enough to explain it with any level of technical detail, but one machine strips and compacts any plastics left in the waste (processing about 22 tonnes an hour), which Fisher uses to make plastic roading blocks at another pilot plant. Another machine crushes the food into a thick – and thanks to the raspberries – dark purple liquid, which looks like a smoothie if you can ignore the brown crust floating on top.

From there, it runs, with an audible chugging noise, through various pipes out of the main building and into a series of giant steel tanks. I realise this all sounds a bit like the Wonka chocolate factory.

Outside, as a cat from the neighbouring farm strolls past, Fisher shows me a control room full of computers and screens which, he says, can be monitored from overseas when nobody’s there and ensures the tanks are maintained at the right chemical balance. Various bugs work away at the soup as it rotates between the tanks, and after about 70 days, during which it is acid-shocked, pasteurised and finally fed through a one millimetre screen to pick up any remaining impurities, it’s ready to use, or as Fisher puts it: “It’s gone from a thick spirulina to a strong black Turkish coffee.”

Ecogas general manager Alzbeta Bouskova says that the recipe in the tanks remains quite constant – although much higher in protein than at European plants. She attributes that to many Aucklanders composting their fruit and veg, and sending their meat and milk to foodscraps. Even 200 tonnes of raspberries arriving at once would have little impact on the mix when there’s 10,000 tonnes of waste in the tanks.

As well as the fertiliser, the process produces a biogas, used to create electricity for the site.

A water jacket captures the heat produced by that process. The heated water runs through steel pipes from the plant’s back fence to warm the neighbouring Turners and Growers’ immaculate tomato hothouse, where about 1.15 million tomato plants march in neat hundred metre rows into the distance.

The plants are stripped back to reduce the risk of mould and insect infestation, while outside, a truck of discarded vines is about to make the short journey back to Ecogas to join the sludge. The heated water also returns, going back along the pipes at a reduced temperature to be used in the pasteurisation process. Soon, says Fisher, enough gas will be produced to return some to the national grid.

The great debate

Whether they use their food scraps bin or not, every Auckland ratepayer is contributing $71.20 a year to this new programme.

That decision has kept individual costs low, but fuelled some simmering rage on local Facebook groups. Among those irritated are the diligent citizens who already compost, those who think the environmental benefits are marginal and one erudite contributor who wrote: “Stick it up your a…, council, I am not paying for that s…, so f… off”.

On the morning of our visit, Bouskova had logged on to her local community page in Māngere Bridge to engage in debate with cost-conscious naysayers. She reckons it’s more than worth a buck twenty a week.

The Czech-born Bouskova seems the perfect foil to Fisher’s Tiggerish temperament. With a masters and a PhD in anaerobic digestion – “so this is my thing” – she was involved as a consultant in the project’s early days a decade ago, then reviewed the final design before ending up here full-time.

“This generation will be okay,” says Fisher, who is playing a very long game. “We’ve got to get through the next 10 years and normalise it for the next one.”

He’s just announced a new plant in Christchurch and has plans for another north of Auckland, as Supercity residents become more accustomed to the scheme.

Auckland Council first began talking about a food scraps programme in 2010. Officials visited plants in Australia and the UK and considered two bids before agreeing to a 20-year deal, with a 10-year renewal, with Ecogas. Other councils, such as Hamilton and New Plymouth, were already collecting and composting food waste, but Auckland is the first to try anaerobic digestion.

The early take-up rate is about 30 per cent, says council’s Elise O’Brien, “but we want that to be way higher… we see huge environmental benefits and the more people that use it, the higher the benefits”. O’Brien and the other official leading the project, Terry Coe, happen to be on a certification trip to the plant on the same day we visit.

The early indications, says Coe, is there’s been a decline in waste going to landfills in the north and west of the city, which helps council with rising government levies on landfill use.

The medium-term goal is to deliver 40,000 tonnes of food waste per year, and council plans to shift rubbish collections from weekly to fortnightly could lift that higher.

Coe sees the public in three camps – the enthusiasts, those who see the benefits and so engage grudgingly, and those for whom it’s too much effort. “People have a lot to think about these days,” he says gently. “This is an added thing, and it isn’t high on their priority list.”

Fisher is completely convinced anaerobic digestion is the future, both environmentally and financially. “You can’t be green and bleed red… the council are not paying a premium, we had to be cheaper than landfill,” he says.

He shrugs off any critics, such as Waste Management chemical engineer Timothy Brake who told BusinessDesk earlier this year it was “subsidised greenwashing”, which gently amused Coe and annoyed Fisher.

Fisher says, “I know Tim, I know Tim very well… They are upset they didn’t do this first.”

Brake’s argument was that food “rots away to nothing” in landfill, and when the methane it releases is captured, it generates sustainable electricity, while the food scraps programme generates carbon emissions through the transport of waste. “Our grandchildren will not thank us,” Brake said. “It just doesn’t matter.” He was even less impressed by composting programmes.

Maria Gutierrez-Gines, who leads the biowaste team at the Crown Research Institute ESR says anaerobic digestion isn’t new – sewage works have used it to treat their brown water for years and, overseas, it’s also been used to deal with animal manure.

In broad terms, she says, there are three ways to deal with food waste: landfill may give you some recoverable methane, but that’s it; composting offers a good end product, but up to half of the matter can be lost by respiration, so anaerobic digestion is the most efficient technique. But there’s a caveat: she’s concerned about the miles the food travels, and says those transport emissions may change the equation substantially.

It explains why Fisher is so particular about using trucks that would otherwise be travelling empty.

A heady bouquet

The finished product sits in giant inflatable tanks, like those jumping pillows at campgrounds, where it is tapped off into waiting tankers. Fourteen local farms take the fertiliser, and one around the corner has just received a delivery, where, as our final, satisfying act, we watch a contractor spraying it across a paddock.

Just before we depart, Bouskova taps off a jerrycan of the final product for me to take home. Fisher reckons it will be dynamite on my struggling back lawn. As a test, I decant some on to my garden beds. It’s impossible, of course, to know whether a few molecules of my kumara peel have thus made the entire 555 kilometre roundtrip, but I’d like to think so.

After I’ve carefully poured the sludge on the fruit trees and the clivias, I go inside to find my partner has examined the underwear of both younger children, assuming from the odour that one has soiled themselves.