Composting by-products from a bleached kraft pulping process: Effect of type and amount of nitrogen amendments

Over 70% of solid wastes (by-products) generated in the manufacture of pape r pulp are presently disposed of in landfills. Most of these by-products ar e compostable and reusable in horticulture, landscaping and agriculture. Th is work addresses the questions of nitrogen amendments required for compost ing a mix of four bleached kraft pulp mill by-products - namely, primary sl udge, bark, grit and ash. Two nitrogen amendments, ammonium nitrate and chi cken litter were compared to determine which provided a more rapid mass red uction and stabilization. Different amounts of ammonium nitrate addition we re evaluated to determine if decreasing the C:N ratio of the initial mix (f rom 130.9 to 28.3) resulted in more rapid composting. A blend of sludge, gr it, bark and ash in dry weight percentages of 56, 25, 6 and 13% respectivel y, stabilized (measured using oxygen respirometry) in a period of 28 days. Although in the initial stages of composting there were differences resulti ng from the effect of the two types of nitrogen amendments, at the 28th day no significant difference was observed. It was also found that decreasing the ON ratio did not accelerate the composting process. A composting mix wi th a ON ratio of 130.9 had similar mass reduction compared to others with C :N of 95.3, 79.5 and 28.3. Lower C:N ratios were in fact less preferable be cause of high soluble salt content and greater amendment requirements.