From pulp sludge to super fertilizer

Mar. 23, 2012 – Once thought of as a waste product from the mechanical pulping process in pulp and paper industries destined for incineration and landfilling, but now thanks to the 20 years of research in mechanical pulp sludge utilization on both agricultural and forest soils in Alberta, mechanical pulp sludge has re-invented itself as a “super fertilizer.”

This work was first initiated in 1992 under the collaboration of the Alberta Research Council (now part of Alberta Innovates – Technology Futures), Alberta Newsprint Company (ANC), Millar Western Forest Products, and Slave Lake Pulp (SLP).

The first experiment conducted through the Mechanical Pulp and Paper Consortium was a land-spreading field trial involving forest cut-block field locations to determine the impact of different application rates of the conventional and de-ink sludge on soils and trees. Subsequent trials involved sludge application on juvenile trees, seedling/sucker trials, spreading sludge without incorporation on various slope and aspect positions, sludge application on both frozen and snow covered soils, thinning trails, operational spreading trials and equipment evaluation.

Growth response of different treatments were evaluated using several techniques including height and diameter comparison and projections, survival rates, the age-shift method – which quantifies how much sooner a particular size is reached due to treatment effect, and growth multipliers – which represent the treatment effect as the ratio of treated to untreated.

The results from these long term experiments indicate that sludge application in the forest had an overwhelmingly positive effect on tree volume, with the largest projected gain in stemwood volume on balsam poplar and aspen species at age 25. The greatest benefit comes from applying sludge in marginal soils to stimulate tree growth; while juvenile trees are best candidates for sludge application as they are able to achieve more volume production than seedlings.

Results suggest sludge application rate should be at 50 t/ha or less to reduce herbaceous competition. The value of pulp sludge will continue to grow as the industry looks for other potential uses for what was once thought of as “waste” product.

For more information on the sludge research please go to www.SmartSludge.com.