Modelling industrial symbiosis of biogas production and industrial wastewater treatment plants

Important results from the project

The overall project goal was to develop a mathematical model for an industrial symbiosis that integrates wastewater treatment of a pulp and paper mill with biogas production from waste streams generated in food production. The symbiosis includes a high-rate anaerobic reactor, an active sludge plant and a biogas plant, where the biosludge is co-digested with nutrient- and energy-rich organic waste. The model should include the dynamics between the different units including turnover of organic material, biogas production and release of nutrients.

Expected long term effects

Analyses show that the developed model can predict dynamic processes that occur during planned changes but also from process disturbances in the wastewater treatment or biogas plant and their impact on the integrated system. The model can also predict the release of nutrients in the co-digestion plant, its return to and subsequent consumption in the water treatment. The overall model is thereby a tool that, after adaptation, can predict the effects of the concept on other facilities and is thus useful as a decision support for continued implementation.

Approach and implementation

The project began with a literature review to identify useful sub-models for integration and find a suitable modelling tool. Collection/sampling and analysis from before the implementation of the symbiosis concept was made and the model of the original wastewater treatment was calibrated against these data. When the symbiosis was implemented, additional data were collected, the models for the digestion processes were evaluated and the system of wastewater treatment, digestion processes and stream recirculation were linked together. A number of scenarios were set up and tested.