Composting Pulp and Paper Mill Sludge - Effect of Temperature and Nutrient Addition Method

Pulp and paper mill sludges (PMS) are a significant by-product of the paper making industry world-wide, and composting with mineral nutrients in Tasmania is viewed as the most environmentally suitable method to convert this material into a horticultural product, thus eliminating the need for landfilling. The major control variables for composting PMS with a high C:N ratio are nutrient and temperature management. Addition of the nutrient requirement prior to composting can result in significant nutrient loss by leaching and may lead to ground water pollution. Alternatively, the nutrient requirement may be added incrementally during composting, thereby decreasing the risk of nutrient loss. Control of temperature is also important as this affects the metabolic activity of microorganisms and may determine the rate at which a cured compost can be produced. This study therefore examined the relationship between the method of nutrient addition and temperature on composting of PMS, using small-scale reactors designed to simulate conditions in a large-scale mechanically turned windrow. The rate of PMS decomposition as determined by the rate of CO 2 production and O 2 consumption was higher at 55°C than at 35°C. The time to produce a cured compost could be shortened by 30-50 days if composting was undertaken at the higher temperature. The method of nutrient addition had no effect on the respiratory activities of compost microbiota or rates of decomposition, but had a major influence on pH which determined the intensity and period of ammonia volatilization. If pH was controlled, then incremental nutrient addition could be advantageous from the perspective of nutrient conservation.