How serial inventor Coll Bell’s wastewater system could revolutionise the dairy industry


He blew up his first methane tank, built a boat in the shape of a saucer, and helped to design a super-efficient water blaster, but Coll Bell’s favourite inventions involve manure, and the more, the better.

Words  Images: Kathy Hunter

Additional images: Coll Bell

Coll Bell is an inventor, the proper, old-fashioned type who’s never happier than when tinkering in his capacious shed. His favourite line is “I’ve got a cunning plan!” and one of his most profitable cunning plans to date is in our back garden, full of busy worms composting everything we flush down our loo. He’s also invented the perfect ‘short drop’ loo, a sailing saucer, and an ark-shaped sleep-out that’s bigger than 10m² but doesn’t require council permission.  But it’s his latest wastewater project that may be a game-changer and a way for dairy farmers to help save the planet.


Cleaning down the test cow shed on the neighbour’s farm

Coll (65) is fairly well known in the poo business. His first experiments in trying to make something positive out of ones and twos dates back to the late 1980s. He had the idea of harvesting methane gas for his self-sufficient lifestyle and created a polystyrene tank coated in concrete which was connected to the toilet. But one dark and stormy night there was an almighty explosion and a terrible smell. The less said, the better says Coll. Undeterred, he tried again. The catalyst this time was that his home was at the bottom of a cliff and to pump poo up it to the town supply sewage system was a pain. He figured out a way to separate solids from liquids and just pumped the dirty water up the cliff, while worms dealt to the solids. This formed the basis of his first commercial product, the Natural Flow system, which he built up and then sold.


Water and manure are washed into decanting tanks.

He’s run his latest company, Simple Waste Water Solutions, for the past 10 years and his latest alternative to the septic tank is the end product of his years of experience in sustainable waste management. In his humble opinion, it’s pretty perfect. The system comprises three components. The first is a solid waste digester, a 1.2m moulded plastic tank where a colony of tiger worms recline on a bed of bark and sawdust, ready to munch through kitchen and toilet waste. The digester is easily cleaned out, about every two years for a family of four. Grey water from the shower, bath and washing machine goes straight into a much smaller mixing tank where it meets any black water that comes through the solid waste digester. The combined water is then returned to an aerobic state by filtering it through the second component, a series of bark and sawdust-filled tubs planted with a variety of greenery, including native grasses such as Carex virgata. The root systems of the plants grow good bacteria, and the bark and sawdust suck up nitrogen.


The Clean Cow system’s main tanks on Coll’s trial farm – the clear tanks to the left are being used as tunnel houses to grow plants which filter the decanted water.

The filtered water that comes out at the end of this process goes into a small dosing tank, the third and final component. This simply regulates the discharge, and can be attached to a hydroponic tunnel house which ensures nil discharge of the treated water. You can also opt for a slow release scenario, drip-feeding it around your garden if it’s on a bit of a slope. If not, a solar-powered pump can move things along. Selling and installing this system keeps him and his son-in-law pretty busy for most of the year, but Coll isn’t satisfied with small scale projects. The logical extension is found at the busy heart of the dairy farms that surround him on his small block north of Auckland. Every cowshed produces a huge amount of wastewater every day, and Coll’s Clean Cow dairy effluent disposal system is nothing less than his water-saving vision for the future of the dairy industry.


Coll has spent years developing successful plant filters which use native grasses.

In developing his newest invention, Coll looked at the amount of water used during a typical milking, the run-off into streams, and the need to recycle a cleaner product (and a valuable by-product) back into the environment.


Coll’s poly house uses plants to filter water, which then feeds his garden.

Clean Cow’s concept is the same as the one for his septic tanks, but it’s bigger. A lot bigger. Coll used outside funding to set up a trial on a neighbour’s dairy farm. It has 230 milking cows, and there was enough room for Coll to work around the existing set-up. A mate who runs a rotational plastics business created a 1.6m radius quarter-tank mould which can be clear or dark green. As with many of Coll’s inventions, it works on a number of levels:

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• when lying flat, it is the Clean Cow decanting tanks;
• when cut in half, it can become a solid waste digester;
• clear ones on their sides can be used as tunnel houses.

The water used to wash down the cowshed is directed into the decanting tanks on a rotating basis. Once it settles, liquid is drained off to the plant filters. Any other water bypasses the decanting tanks and goes straight to the filters. The filtered water, full of nutrients, can be stored and sprayed on to the paddocks. The solids caught by the filter are processed by tiger worms which produce a rich, crumbly vermicast compost, which can be bagged and sold.

A close-up of one of the quarter-tanks being used as a tunnel house.

A close-up of one of thequarter-tanks being used as a tunnel house.

Part of the success of this plant is due to a cowshed-customised water blaster Coll has designed with a German company which makes significant water savings. The water blaster is not compulsory for the Clean Cow system, however projected future droughts mean every drop in future will become more precious. There’s also the possibility that any permitted activity in a waterway with a meter that’s overused will incur fines, so there will soon be a monetary incentive to save water.


Coll’s test farmer was a convert, using it to wash down the plant, and the tractor and ride-on. The results were just what Coll was hoping for: water usage went from 10,000 litres per milking, down to just over 2000 litres, a 75% saving. The trial set-up was also used to gauge how much liquid and solids a herd of 230 cows can produce in a standard herringbone shed over the course of a few months. As a result, Coll redesigned the system to have a 2.4m radius quarter tank, with four of them giving a farmer a 32,000 litre capacity decanting tank. However, Coll’s system is flexible so a farmer can add in as many tanks as required for the number of milking cows on a farm. Like all inventions, it’s going to require more money, so Coll is now looking for someone to both invest and run the business side of things so he can concentrate on getting the formula right. As well as getting on with his next invention, of course.

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Coll was brought up as an inventive and independent young chap. His parents owned the campground at Waipu Cove, a beautiful surfing mecca an hour and a half north of Auckland. He says he experienced a pretty perfect childhood there, but when it was time to decide what to do for a living he was a bit stumped. After a number of doubtful diversions, he joined the NZ Army, staying for four years. In 2012 he wrote a memoir about his experiences entitled The Green Machine.

“From what I could gather you got fed, somewhere to sleep – not always indoors – heaps of toys and a chance to play cowboys and indians all day. The bonus was you got paid. This sounded too good to be true until (a friend) mentioned that part of the deal was that you had to go to Vietnam and get shot at. “All-in-all though, the pros outweighed the cons and the whole business came across as a pretty good deal.”

After leaving the army, Coll was given a book called How to Build a Boat and a couple of years later he was the proud owner of a 46’ ketch. He funded his boat by driving a bread truck, running a lawn mowing round, and working at the Auckland Artificial Limb Centre building hydraulic limbs. “Facilitating the ambulation of monopedes,” as he puts it.

He was good enough for it to become his career but it wasn’t to be the life-long passion he envisaged. Then, at the age of 55, he was diagnosed with Parkinson’s Disease. This has slowed Coll down a little, but not much. His left arm likes to go its own way on occasion and he often needs an early night, but his energy levels are pretty formidable – with three grown-up daughters and a tribe of grandchildren, he says he needs all the energy he can get – and there is none of the trademark head tremor known as dyskinesia.

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Dyskinesia is caused by the very drug that treats the symptoms of PD. The drug is Levodopa or L-Dopa which helps to restore levels of dopamine, a chemical in the brain responsible for coordinated movement and other cognitive functions. Coll was prescribed these drugs, but was dismayed by the side effects, the worst of which for him was depression.“I’d never felt depressed in my life, and I decided the disease itself was the lesser of the two evils.”

He began his own research into other options and his efforts soon uncovered a natural remedy which had garnered some positive results, a sub-tropical bean plant called Mucuna pruriens. Coll stopped taking his prescription drugs and started experimenting on himself. Mucuna, or velvet bean, contains a natural form of L-Dopa and it has worked well for Coll. He sources it in capsule form from a company in Nelson called Shaman’s Garden and combines it with rest, exercise, humour and stress reduction techniques which when combined produce very good relief for him from the symptoms of PD.

Warning: Natural treatment options may be appealing but they can sometimes bring other risks, especially if combined with existing pharmaceuticals. It’s best to talk with your doctor before trying anything new for yourself.



This is a perfectly round vessel with a fixed sail and a keel that can move around 360 degrees. Coll says it never really had a fair whack at the marketing machine and now languishes on the backburner.

This has garnered a fair bit of interest. Coll has an acute allergy to council rules and he had a nasty flare-up when he wanted to build a sleep-out that was bigger than the standard 10m². He was quoted the costs for the consent process and reeled back in horror.

Armed with the knowledge that a floating or otherwise movable home did not incur the same expensive red tape, he built an ark, a beautifully-designed, nautical-styled cabin complete with mezzanine sleeping platform, galley and heads, that rests on wheels and has pontoons. No consent necessary.
“The Ark is on the move right now,” says Coll. He’s built four this year and has a waiting list.

This is a no-smell composting loo, attractively housed in a tall, plastic-moulded tank, a no-flush, no-power alternative to the hideous ‘long drop’. The deluxe option includes a rainwater collection tank, guttering, hand basin and foot pump.

Liquids are processed via a single bin containing bark that can be planted with either native grasses or other specific plants which work as filters via transpiration and evaporation. Tiger worms in the waste digester under the loo seat break down solid material.


Seawater or greywater is boiled in a vacuum – working in a vacuum makes water boil at much lower temperatures – and then distilled. Although not drinkable, it can be used for showering and laundry purposes

NZ Lifestyle Block This article first appeared in NZ Lifestyle Block Magazine.
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