How affects the choice of primary treatment the biogas potential of primary sludge?

The primary settling tank (PST) at municipal wastewater treatment plants (WWTP) is most often the first treatment step after screens, and fat and sand traps. The PST should reduce the organic load to the subsequent biological treatment step. Filtration, e.g. with rotating belt filters (RBF) or drum filters, is a high-rate alternative to PST due to its limiting spatial footprint. Chemically enhanced primary treatment (CEPT) by addition of coagulants and/or flocculants, is often also introduced for maximising removal of organics.

It has been stated that RBF sludge has a higher biogas production potential than PST sludge (Paulsrud et al., 2014). This is not hypothesised only due to better removal of organics in RBFs but also due to removal of certain kinds of organics generating more biogas, i.e. increased removal of cellulose. However, there are no studies making comparisons between sludge produced by the same influent wastewater.


The main objective of this project is to study biogas production potentials in between different primary sludge produced from different primary treatment methods.


The bio-methane potential (BMP) tests are performed in the laboratory at the Department of Chemical Engineering. RBF sludge is received from a pilot plant at Källby WWTP in Lund. PST sludge from Källby and other WWTPs in the neighbourhood will be tested as well. Also the influent wastewater to Källby will be treated in lab-scale with different flocculants to see the effect on different primary treatment methods.

Project supervisors

David Gustavsson, research leader, VA SYD/Sweden Water Research (

Åsa Davidsson, senior lecturer, Lund University (