Industrial Wastewater Will Provide More Biogas

A new research project being executed at Karlstad University in Sweden will validate a way that maximises biogas production from forest industrial sewage sludge, while reducing electricity and chemical consumption. 

Energy-efficient purification of forest industrial wastewater is a key issue for the pulp and paper industry. To achieve energy efficiency, treatment processes and sludge management need to be handled holistically. Most Swedish mills treat their wastewater by applying energy-intensive aerobic biological methods. Some add a chemical treatment, which is energy-efficient, but adds a cost for precipitation chemicals and produces large quantities of sludge. An alternative is anaerobic digestion, which uses forest industry sludge to produce energy as biogas.

The research project will lead to increased knowledge of energy-efficient wastewater treatment with biogas production and chemical recovery from pulp and paper mills.

"This project is mostly performed in order to validate previous findings by including more mills. However, this is the first time that we’re working on recovering chemicals from wastewater treatment. Hopefully, we will find that we can in fact recover some of these chemicals, because that would have a great effect seen from both a financial and an environmental point of view," says COWI Specialist Alina Hagelqvist.

Directly applicable research 
COWI will contribute expertise for the experimental setup and visualisation of the process as well as financial calculations for the project. Four Swedish pulp and paper mills are also involved in the project. One of the mills has already applied some of the preliminary research results to their wastewater treatment, and the chemical recovery data are designed to be applied right away by the industry.

"The greater aim of the project is to produce as much biogas as possible, using as little electricity as possible in the wastewater treatment and sludge management combined. The main gain is to provide more biogas, which can replace petrol as vehicle fuel," says Hagelqvist. 

The project costs more than SEK 2 million and is entirely funded by the Thermal Engineering Research Institute in Sweden.