Public defence, Environmental Technology within Process Industry, MSc (Tech.) Juha Oksanen

Title of the thesis: Assessment of pulp and paper mill sludge utilisation options

Thesis defender: Juha Oksanen
Opponent: Prof. Mika Horttanainen, Lappeenranta-Lahti University of Technology LUT
Custos: Prof. Olli Dahl, Aalto University School of Chemical Engineering

Pulp and paper industry generates vast amounts of sludges as a result of effluent treatment processes. During the last decades the most common way to dispose the sludges has been co-combustion with bark or other biomass in biomass boilers. However, utilizing the sludge in agriculture is an interesting alternative to incineration and also other ways to valorise it have been studied intensively during the last decade. 

In this study two commercially available utilisation methods, incineration and land application, have been assessed, but in theoretical part of the study, other methods have been discussed too. From the sludge producer´s perspective it would be very essential to understand which way of the sludge utilisation is the most sustainable one.

The topic has been examined from three different perspectives. The first perspective was to investigate whether storing sludge together with bark has an effect on the heating value of the bark. The second perspective was to study the concentrations of harmful substances in the sludges and to assess their mobilization potential using a three-step sequential extraction procedure. The third perspective involved comparing the environmental impacts of sludge incineration and agricultural utilization through a life cycle assessment (LCA).

The results indicate that from the environmental perspective, agricultural utilization of pulp and paper industry wastewater sludge is favorable, at least when low-calorific sludge can be replaced with higher-calorific, non-fossil fuel and the use of fossil fuels can thereby be reduced. The climate impacts were smaller both for composted sludge and lime-stabilized sludge compared with the climate impact of sludge incineration. During storage, the sludge reduces the heating value of the biomass with which it is stored. However high concentrations of heavy metals, particularly cadmium, may restrict the use of sludge in agriculture.

Keywords: sludge, life cycle analysis, heating value, sequential extraction

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.

Contact information: 
juha.oksanen@aalto.fi 
+358405773498
https://www.linkedin.com/in/juha-oksanen-a1744245/