Life cycle assessment of biochar filters for on-site wastewater treatment

Biochar is a promising filter material for wastewater treatment. This study evaluated the environmental (climate, eutrophication, acidification) impacts of biochar filters for onsite wastewater treatment and compared them with those of a conventional sand filter. Using a parameterised life cycle assessment (LCA) approach, these three impact categories were quantified for two designs of biochar filter and a sand filter, used in normal and sensitive areas as defined by Swedish government recommendations. Different scenarios for the biochar filters, with different combinations of biochar supply chain, biochar end-of-life and energy system, were simulated and analysed. The eutrophication impact of the biochar filters was similar to that of the sand filter, while the acidification impact was generally slightly higher than that of the sand filter in sensitive areas, and lower in normal areas. The climate impact of the biochar filter varied considerably, from substantially higher to lower than that of the sand filter, depending on specific scenario. A few scenarios in which biochar filters had lower overall impacts than the sand filter were identified. In general, the biochar filters had lower environmental impacts in a renewable energy context than in a fossil fuel context. Using biochar in landscaping soil was a better end-of-life alternative than combustion. Biochar from syngas-heated pyrolysis performed considerably better than biochar from electricity-heated pyrolysis in a fossil energy context. Direct emissions to air and water from the wastewater treatment process, production of biochar and biochar end-of-life contributed most to the total impacts and variation in these for all biochar systems.