VALORISATION OF PULP AND PAPER INDUSTRY RESIDUES TROUGH COMPOSTING

References: 12th International Multidisciplinary Scientific GeoConference, www.sgem.org, SGEM2012 Conference Proceedings/ ISSN 1314-2704, June 17-23, 2012, Vol. 4, 813 - 820 pp

ABSTRACT

The industrial production of pulp and paper generate large amounts of solid and liquid
residues, particularly sludge from wastewater treatment and ash from the biomass
furnace, requiring economical and environmental methods of disposal. These residues
are usually incinerated, landfilled or applied to soil, but other are uses are increasing in
Europe. Several studies have demonstrated that soil application in forestry is an
economically viable practice and promotes soil quality and forest productivity.
However, soil application must be done according to an implementation plan in the
order guarantee the best environmental practices and legal requirements, always taking
into consideration forest productivity. Composting of pulp and paper industry residues
is an environmental sound option to the direct application of those residues to the soil.
However, the costs of the composting process require a sustainable management plan.
This management plan must be based on field data, in order to determine composting
conditions requirements and the final compost quality. To obtain this data, a mix of
residues from pulp and paper industry using eucalyptus (Eucalyptus globulus Labill.)
was prepared with: primary sludge (46% v/v), secondary sludge (46% v/v), fly ashes
(2% v/v) and, as bulking agent, milled eucalyptus bark (6% v/v). This mix, with an
initial C/N ratio of 21, was composted in a 1.2m3 insulated plastic container, with
mechanical turning, to simulate the conditions normally occurring in a windrow
composting process. Temperature, moisture, pH and electrical conductivity were
regularly controlled. Mechanical turning provided aeration and the homogenization of
the mix. The raw materials, the composting mix and the final compost were chemically,
physically and biologically characterized. The composting process, carried out during 3
months, reduced the initial volume of the mix by roughly 60%. The mature compost
obtained showed no phytotoxicity or bad odor, was easier to handle than fresh sludge,
presented a low level of heavy metals, and showed good potential as organic fertilizer
(organic matter 44g 100 g-1; pH 7.6; electrical conductivity 0.54 dS m-1; total nitrogen
1.7 g 100 g-1, phosphor 1.0 g 100 g-1). An economical evaluation, comparing the
application of fresh residues to their compost to the soil, was developed for a region in
the southwest of Portugal (Palmela and Montijo). This study indicated that composting
is an economical option for pulp and paper industry residues treatment if the process
costs are below 8.05 € t-1. Moreover, composting increases the end uses of the residues
(more uses for compost than for the untreated residues) and reduces the possible adverse
environmental effects from fresh residues application, while reducing environmental
impacts associated to fossil fuels consumption for their transport and soil application.

Keywords: ashes, sludge, bark, fertilizer, eucalyptus, compost.