Sludge" is the name given to primary and secondary waste water residuals . It can also include power boiler ash, waste from chemical processing, waste fibre, and other sources.
Pulp mill sludge is, by nature, a complex mix of compounds, including some well known contaminants such as heavy metals, dioxins, organochlorines, and nonylphenols.
Secondary sludge is a byproduct of biological treatment. It is far more difficult than primary sludge to de-water and dispose of.
Many mills in Canada currently de-water their sludge and burn it, but are eager to spread it on forest, park, and farm land as "fertilizer." Unfortunately, there has been no scientific analysis of pulp mill sludge. There has also been no definitive study of compounds created by bacterial activity in the secondary treatment ponds.
Catalyst is permitted to burn their effluent treatment sludge.
Recently, the Ministry of Environment approved a regulation for the land spreading of sludge as a "soil amendment". Concerns about this practice include the potential for water, soil, and organism contamination and bioaccumulation of heavy metals and other toxins.
The financial need to expedite disposal of industrial waste may eclipse the overall intention of sludge application as a "soil amendment" or "soil enhancement". Careful consideration is needed for the delicately balanced systems of soil, including its hydrology, chemistry, tilth, and propensity, as with other biological systems, for the bioaccumulation of toxins.