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St. Marys is a ground wood pulp and paper mill located in Sault Ste. Marie, Ontario, Canada, which produces combined primary and secondary biosolids at a rate of 7000 m3 per month. Currently the mill has developed alternative waste management strategies to avoid ultimate disposal of the waste by exercising reuse opportunities.

Characterization of the biosolids has shown that it poses little threat of environmental contamination. Metal levels have also been consistently below regulatory guidelines for land application. With the exception of a high carbon to nitrogen ratio, characterization suggests that the biosolids have macro and micro nutrient levels well suited for use as an organic soil medium or amendment.

The biosolids material has been used to successfully cap a dozen different landfills in the local area over the past eight years. Soil testing at each of the sites has revealed low metal concentrations and neutral pH pore water. Vegetation has successfully reestablished itself at each of the sites within two years of date of application.

St. Marys has also successfully used their biosolids to reclaim uranium and copper acid generating mine tailings at a site where conventional reclamation means had failed. When the mine site closed in 1972, lime and fertilizer were initially applied to encourage re-vegetation. Though this showed promise during the first two growth seasons, the acidity eventually resurfaced and the vegetation died off. The site reverted back to its barren state. The die off was attributed to lack of organic matter, acidity, and the poor physical and nutrient quality of the soil.

In 1998, reclamation efforts recommenced with the addition of lime and 30 cm of pulp and paper mill biosolids supplied by St. Marys Paper Ltd. to 13 hectares of tailings. Data collected revealed that the biosolids successfully sustained vegetation re-growth. The biosolids reduced erosion and improved groundwater quality in the area. Acidification was also shown to be absent from the biosolids layer. For the past six years, the biosolids have been able to sustain healthy, diverse vegetation over the entirety of the receiving area.

Greenhouse studies however have revealed that the undiluted fresh biosolids are not well suited to supporting vegetation as a growth medium. The carbon to nitrogen ratio of the biosolids is too high to encourage immediate plant growth. The material requires stabilization before it can perform adequately as a soil alternative. These findings are consistent with historical findings at the landfill sites which have previously received biosolids. Significant vegetation growth has occurred after the initial growth season.

The greenhouse studies however revealed that fresh biosolids were better suited as an organic additive rather than a soil alternative and improved the growth of jack pine seedlings. A mix of 50% fresh biosolids and 50% potting soil yielded plants with a higher dry mass than those grown in potting soil alone.

In order to provide the necessary stabilization required for the biosolids stream, in-vessel composting is being investigated. This processing step will lower the carbon to nitrogen ratio through biodegradation and improve the physical characteristics of the material. If the compost meets regulations, it offers a way of reclassifying the “waste” stream into a “product” which is not subject to public use restrictions. Developing this composting technology is a step towards beneficial re-use which not only provides a way of recycling organic matter back into the growth cycle but also the potential for financial gain and new business opportunity.
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Document Type: Research Article

Publication date: 2005-01-01

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