Biomass. What is it?
Sludge, often referred to as
biomass, is solid material—such as wood fibre, dirt, clay and microorganisms from secondary effluent treatment—which can be separated from
effluent. Pulp and paper mills produce three types of biomass: primary, secondary and recycle biomass.
Primary biomass is the material that can be removed from pulp and paper mill effluent using gravity to settle it out. This is usually carried out in a primary treatment process, where solid particles are given time to sink to the bottom of a tank (called a
clarifier) before being collected and removed from the effluent.
Secondary biomass is the material that is separated from effluent during secondary treatment. The secondary effluent treatment process uses microorganisms to break down the dissolved organic material in the effluent. When the microorganisms have completed their work, they are removed from the treated wastewater in a clarifier. These settled microorganisms are called secondary biomass.
Recycle biomass is the material that results from the reuse of post-consumer paper and includes fibre and filler materials such as clay. This type of biomass is also recovered through settling by gravity in a clarifier.
What do we do with it?
Primary and secondary biomass is combined, and then excess water is removed from the mixture. Recycle biomass is de-watered separately.
De-watered biomass has several uses. Primary and Secondary Biomass is de-watered and used for fuel in #6 Power Boiler, along with bark and other wood waste, to generate steam and electricity for the mill. Recycle Biomass is used beneficially as daily cover at the local municipal landfill. In some cases it is sent to landfill. Alternative uses for biomass are emerging as a result of the material’s highly valuable properties. Some of these uses include soil fertilization/enhancement, composting, insulation or hydro seeding.