Agribusiness Report: Poo power - biogas from dairy effluent

Tank digester on the Landcorp farm at Eyrewell, North Canterbury. Photo / Natural Systems Ltd.

A prototype biogas system operating at a Landcorp-owned farm at Eyrewell, North Canterbury was well ahead of the curve.

In an early pilot study began around 2008, manure from the farm's cows was collected on a concrete pad outside the milking sheds, and pumped into a tank digester.

The gas produced was used to power a generator that provided around a third of the farm's energy requirements.

An arrangement with local retailer Genesis Energy meant that any excess electricity that is exported, got subtracted from the farm's overall consumption.

The BioGenCool™ system, designed and installed by Natural Systems Ltd, also instantly cooled the milk, which improves its quality and lowers power demand.

Natural Systems director Ian Bywater said the potential for biogas systems on dairy farms is growing fast, especially where farmers increasingly use barns to house cows during winter.
This not only boosts productivity by improving cows' welfare, it also enables 100 per cent of manure to be collected for energy generation during months that cows are inside.

There are environmental benefits to the biogas system also.

The digestate that comes out of the tank is very low in pathogens compared to raw manure, and is ready for use on paddocks as an effective biofertiliser.

This comes on top of the reduction in carbon emissions from using up methane.
"Farmers are realising that it's sensible to look at biogas energy generation — both to combat the environmental problems with dairy effluent, and because they're concerned with rising energy costs," said Bywater.

It's also a fast-developing trend in the United States, where biodigesters, use specialised bacteria to convert organic material — for example, cow poo — into biogas, a versatile fuel.

Once purified, this biomethane, also known as renewable natural gas, is chemically identical to the main ingredient in the fossil-based natural gas that comes out of your stove or heats your water.

Bovine waste is typically stored in vast open lagoons that emit methane—a greenhouse gas more than 80 times as potent as carbon dioxide over 20 years— making agricultural waste the single biggest contributor to total methane emissions from human activity.

Both biogas and fossil natural gas are mostly methane, and though they burn more cleanly than the megapolluter coal, they still emit carbon dioxide. But by diverting cow poo into biodigesters in the process of making RNG, gas companies argue, the effect is a net climate win.

Sources: ECCA and Bloomberg