Life cycle assessment of powder and micro-grain activated carbon in a fluidized bed to remove micropollutants from wastewater and their comparison with ozonation

Francés. To tackle water micropollutant pollution, the development of an advanced wastewater treatment is necessary and should be supported by an environmental evaluation to guide decision-makers. Life cycle assessment (LCA) methodology has been applied in the literature for several technologies and highlighted the variability of results (e.g. site-specific conditions) and the limited (eco-)toxicity benefits compared to additional operating impacts. In this study, the LCA of an activated carbon (AC) adsorption process based on a fluidized bed (limiting AC usage) was performed to determine its optimal operating conditions (dosage, use of micro-grain - uGAC or powder - PAC) and environmental benefits compared to the common ozonation process. This study was based on pilot processes installed at the Seine Centre treatment plant (France), using sensitivity analyses to identify the conditions for choosing a technology. For the seven scenarios (fluidized bed with 10 and 20 mg/L, both for PAC and uGAC; ozonation with 0.6 and 0.9 gO3/gDOC; and pre-ozonation combined with uGAC), the operational impacts generated (energy and material use) and the impacts avoided (micropollutant removal) were evaluated for climate change, freshwater ecotoxicity and human toxicity (USEtox characterization factors for micropollutants complemented with literature data). The LCA results showed that the fluidized bed process should preferably be operated with uGAC rather than PAC. The advantage of uGAC adsorption compared to ozonation is negligible but could nevertheless be significant in European countries with a significant share of coal-based electricity (i.e. all countries except Sweden and France). As in most of the previous works, the (eco)toxicity impacts avoided were found to be negligible, but other substances, such as hormones and oxidation by-products, should be further considered and characterized to better represent the treatment performances. The combination of ozonation and uGAC adsorption on a fluidized bed is a promising option to efficiently remove micropollutants, as well as oxidation by-products, while keeping the impacts generated within a reasonable range. This paper presented valuable results to support the eco-design of advanced wastewater treatment (both in terms of operating conditions and targeted substances) but should be complemented with large-scale evaluations (e.g. using consequential LCA) and better impact characterization of micropollutants.