Environmental comparison between activated carbon and biochar for tertiary wastewater treatment

Wastewater facilities are adding treatment for removing micropollutants (e.g., antibiotics, endocrine disrupting compounds) to reduce environmental and human health impacts. Powdered activated carbon (PAC) adsorption is effective, but PAC production is energy intensive and expensive. Biochar is a low cost adsorbent with the potential benefit of being carbon sequestering. However, micropollutant sorption capacity of biochar ranges from negligible to similar to PAC, depending upon solution characteristics and biochar production conditions. Lower adsorption capacity translates into higher adsorbent use rates, which affects process cost effectiveness and environmental impacts. To evaluate relative environmental costs and benefits, life cycle assessment (LCA) was used to compare the production and use of a coal-derived PAC, wood biochar, and biosolids biochar for sulfamethoxazole (SMX) removal in tertiary wastewater treatment. Wood biochar had the lowest environmental impacts, primarily deriving from energy co-production during pyrolysis and the potential for carbon sequestration. Biochar net environmental impact depends on adsorption capacity. Wood biochar with high adsorption capacity exhibited smaller negative environmental impacts than PAC across all impact categories. Use of biochars with lower adsorption capacity resulted in environmental tradeoffs when compared to PAC. Onsite production of biosolids biochar resulted in an insufficient adsorbent quantity. Biosolids biochar supplemented with wood biochar or PAC resulted in the higher environmental impacts than wood biochar or PAC alone. This presentation will report LCA results and highlight salient environmental impacts of using PAC and biochars to achieve 75% reduction of SMX in wastewater effluent.