Alberta project turns manure into liquid gold

Researcher says liquid composting of manure is a viable on-farm process whose time has come

Nick Savidov doesn’t mince words when he talks about relying solely on synthetic fertilizer to feed the planet.

“The fact is that if we don’t learn how to recycle nutrients and water, we are doomed,” said the senior research scientist at the Bio-industrial Opportunities Branch of Alberta Agriculture and Forestry.

“We will start dying off from hunger. This is just one approach to prolong our existence on this planet.”

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Savidov is part of a team using a device called a bioreactor to extract nutrients from waste streams like animal manure. Described as ‘liquid composting,’ the bioreactor uses micro-organisms in an oxygen-rich environment to mineralize and dissolve the nutrients in a liquid solution. The nutrients can then be reused as plant food.

Recycling nutrients is critical because synthetic fertilizer sources are non-renewable, said Savidov. For example, 85 per cent of all phosphorus rock reserves on the planet are located in just one region (Morocco and the Western Sahara) while nitrogen synthetic fertilizers can only be produced using fossil fuels.

And recycled nutrients have an added benefit.

A demonstration project by Savidov, engineer and system designer Marc Legault, and their colleagues used the aerobic bioreactor to capture nutrients from raw poultry manure. They then used the dissolved organic fertilizer — or digestate — to produce vegetables and tree seedlings in a soilless growing environment.

“The results exceeded all our expectations,” said Savidov. “We demonstrated that we can produce vigorous growth of major nursery crops grown in Alberta and B.C. using poultry manure digestate.”

For example, greenhouse tomatoes grown with digestate had a 15 per cent higher yield than plants given synthetic fertilizer.

The reason?

Recycled organic fertilizers are biologically active with beneficial micro-organisms and this results in enhanced nutrient uptake by plants, said Savidov.

All types of manure can be used in the system, but poultry manure was chosen because it’s readily available, rich in nitrogen, and less fibrous than cattle manure. The latter is important because the more fibre, the longer the fermentation process in the bioreactor.

And speed is one of the selling points of this system.

Conventional composting of manure typically takes months, but liquid composting requires just two to three weeks. The method results in 100 per cent conversion of the raw manure to liquid plant food.

As well, an aerobic bioreactor is not expensive, space-age technology — it’s just a septic tank with a built-in agitator. Intense mixing of the three ingredients within the tank — manure, oxygen, and water — is critical to maintain consistent fermentation. And unlike septic tanks there’s no odour because oxygen reacts with foul-smelling compounds such as hydrogen sulphide.

After about three weeks, the bioreactor is stopped and the processed liquid is removed to a filtration tank, where any remaining solids are separated from the liquid and returned to the bioreactor for further fermentation, while the liquid stream is ready for use. The resulting liquid fertilizer has a low sodium content and a pH level within the tolerable range for plants.

The fermentation process also generates heat, which can be captured and used to heat buildings on the farm.

“To be honest, it’s not really an absolutely new system,” said Savidov. “It’s using bits and pieces of what is already used in the agriculture industry for manure treatment.”

Similar systems are already in use in Europe, and the hope is that the Alberta project will help aerobic fermentation of animal manure catch on here, too, he said.

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