The effect of C:N ratio on bench-scale composting of pulp and paper biosolids

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Larsen, Kevin Lee
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This study investigated the effect of C:N ratio on the composting of pulp and paper biosolids using bench-scale reactors, designed to simulate windrow composting. Four reactors (treatments) were run simultaneously, with C:N ratio's of 90:1 (control), 50:1, 30:1 and 20:1, each treatment was replicated three times. Each reactor was identical in mass, moisture content, particle size, amendments, loading, and aeration. Parameters that were monitored included compaction, temperature, and volatile solids reduction. It was found that an optimum C:N ratio (20:1) resulted in an increase in volatile solids reduction of 6% greater than the control (90:1), and showed similar temperature profiles The results suggest that the added cost of nitrogen fertilizer may not be justified for increased composting performance. The C:N ratio therefore is not that important with respect to composting performance and can save millions of dollars annually in fertilizer costs, however there is a stability issue. The marketability of compost requires nitrogen addition to satisfy CCME Guidelines for Compost Quality. Nitrogen addition required to meet these guidelines would cost approximately $628,200 annually. (Abstract shortened by UMI.)