Pulp sludge - Is there a best method for composting?

Quesnel River Pulp Company produces a clean organic sludge from its bleache d chemithermal-mechanical pulp mill. The sludge consists of approximately 8 0% primary clarifier sludge and 20% secondary clarifier sludge. The sludge has potential for use in agriculture, horticulture, nursery production, or forestry. The purpose of this research was to determine whether the pulp sl udge could be composted without bulking agent or fertilizer in an in-vessel compost facility. Trials were carried out in 200-L mini-composters and in 20-m(3) composting bays. The pulp sludge contained 72 to 79% moisture and h ad a C:N ratio of 50 to 60. Results from the mini-composting trial showed t hat the sludge could be successfully composted with a minimal amount of fer tilizer. Results from the larger-scale trials showed that the sludge compos ted well without any amendment or bulking agent. The composting process rea ched 50 degreesC within 1 and 10 days at sludge moisture contents of 72% an d 79%, respectively. Plant growth trials in the greenhouse demonstrated tha t plants did not grow well in raw pulp sludge. After four weeks of composti ng, plant growth was similar to that in regular growing media. In-vessel co mposting of pulp sludge to produce growing media ingredients is an economic ally feasible solution for chemi-thermal-mechanical pulp mills.