Comparative life cycle assessment of co-pyrolysing sewage sludge and wastewater-grown microalgae for biofuel production

Using available data, we analysed the biofuel production via pyrolysis of sewage sludge (SS) and microalgae grown in wastewater, either alone or at mass ratios of 1:1, 1:2, and 2:1. The life cycle assessment (LCA), global warming potential (GWP), energy recovery, and economic feasibility were compared. GWP was 36-44% lower for the co-pyrolysis scenarios than for SS alone. For energy recovery from pyrolysis gases, a gas turbine was more effective than gas heating, compensating for up to 28% of the pyrolysis energy requirement for all five scenarios. The drying process accounted for 69-88% of the total energy consumption, indicating that the dewatering process should be improved to maximise sustainability and profitability. All scenarios were profitable; the 1:1 mixture gave the highest net profit (9% more than that of SS). To conclude, co-pyrolysis of SS and microalgae is environmentally and financially viable for biowaste management in municipal wastewater treatment plants.

Automated summary

This study compared the life cycle assessment, global warming potential, energy recovery, and economic feasibility of biofuel production via pyrolysis of sewage sludge and microalgae alone or at different ratios. The co-pyrolysis scenarios showed 36-44% lower global warming potential compared to sewage sludge alone. Gas turbine was found to be more effective for energy recovery from pyrolysis gases, compensating for up to 28% of the energy requirement. The drying process accounted for the majority of energy consumption, highlighting the need for improved dewatering process for sustainability and profitability.