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By Alice McFarlane

Pulp mill waste for fertilizer

Pulp mill waste could find new use as fertilizer

Dec 12, 2023 | 3:14 PM

Pulp mill waste heading for a landfill could have a second life as an organic fertilizer.

A University of Alberta research project suggested waste could help reduce the environmental impact of using conventional fertilizers while improving soil and tree growth.

A two-year study of a hybrid poplar tree plantation in northern Alberta showed that compared with using conventional fertilizers alone, adding wood and other fibers left over from pulp and paper production, reduced harmful greenhouse gas emissions from the soil.

Combining these biosolids and conventional fertilizer also improved soil fertility.

Scott Chang is the study’s lead author and a professor in the Faculty of Agricultural, Life and Environmental Sciences. He said the findings provide new insight into what effect biosolids could have if redirected for use on tree plantations that feed the forest industry.

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Conventional fertilizer, containing industrially produced urea, has been shown to stimulate greenhouse gas emissions from soil. Though pulp mill biosolids are generally rich in organic content and low in toxicity, it wasn’t known how they might also have an effect.

Chang said the results of the study show the potential for developing a strategy to manage pulp mill waste.

“Repurposing biosolids as an organic fertilizer, which may help reduce greenhouse gas emissions, could improve the sustainability of the pulp and paper industry,” Chang said.

On a 2.4-hectare test site of hybrid poplars, the researchers compared the effects of biosolids, conventional fertilizer and a combination of both on carbon dioxide, methane and nitrous oxide emissions from the soil. They also measured effects on the soil’s chemical and microbial properties.

They found that the conventional fertilizer increased soil carbon dioxide and nitrous oxide emissions by 30 and 83 per cent, respectively, while the addition of pulp mill biosolids alone increased those emissions by only 21 and 17 per cent.

Study co-author Xinli Chen said researchers were surprised to find the addition of the conventional fertilizer did not increase soil carbon dioxide emissions when biosolids were also applied.

“It’s possible that the applied biosolids absorb some of the mineral nitrogen in the soil initially and then later act as a slow-release fertilizer throughout the growing season,” Chen said. “That results in less pronounced effects on greenhouse gas emissions compared to conventional fertilizer application alone.”

The application of biosolids, both alone and with the conventional fertilizer, also proved generally beneficial to the soil for plant growth.

It also increased levels of dissolved organic carbon which is a type of carbon that is a vital part of carbon cycling and microbial biomass, made up of bacteria and fungi that decompose organic matter. Those changes help release nutrients into the soil.

Chen said the findings also suggest that soil micro-organisms play a key role in regulating greenhouse gas emissions, and how they could be an underlying mechanism in different fertilization scenarios which could lay the foundation for further research into improving environmental impact.

“Understanding their effect can help develop a strategy to mitigate the negative effects of conventional fertilization, such as by influencing some specific microbes in soils,” Chen said.

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alice.mcfarlane@pattisonmedia.com

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