Scarcity of water and concerns about the ecotoxicity of micro-contaminants are driving an interest in the use of advanced tertiary processes in wastewater treatment plants. However, the life cycle environmental implications of these treatments remain uncertain. To address this knowledge gap, this study evaluates through life cycle assessment the following four advanced process options for removal of micro-contaminants from real effluents: i) solar photo-Fenton (SPF) operating at acidic pH; ii) acidic SPF coupled with nanofiltration (NF); iii) SPF operating at neutral pH; and iv) neutral SPF coupled with NF. The results show that acidic SPF coupled with NF is the best option for all 15 impacts considered. For example, its climate change potential is almost three times lower than that of the neutral SPF process (311 vs 928 kg CO2 eq./1000 m3 of treated effluent). The latter is the worst option for 12 impact categories. For the remaining three impacts (acidification, depletion of metals and particulate matter formation), acidic SPF without NF is least sustainable; it is also the second worst option for seven other impacts. Neutral SPF with NF is the second worst technology for climate change, ozone and fossil fuel depletion as well as marine eutrophication. In summary, both types of SPF perform better environmentally with than without NF and the acidic SPF treatment is more sustainable than the neutral version. Thus, the results of this work suggest that ongoing efforts on developing neutral SPF should instead be focused on further improvements of its acidic equivalent coupled with NF. These results can also be used to inform future development of policy related to the removal of micro-contaminants from wastewater.

A new model is proposed for the photo-Fenton oxidation of water contaminants including the effect of photon absorption (volumetric rate of photon absorption, VRPA), the effect of the geometry of the reactor and the illuminated volume to total volume ratio (Ri) in the reaction system. Fe(III) was found to be the main species in the aqueous solution responsible for photon absorption provided that hydrogen peroxide was not totally consumed. Paracetamol was used as model pollutant at a concentration of 1 mM to validate the model. The illuminated part of the raceway reactor configuration (total length of 80 cm) was operated at two liquid depths (5.0 and 2.5 cm) equivalent to two irradiated reactor volumes (2 and 1 L) and using Ri ratios in the range 0.30–0.65, which changed the dark reactor volume. These values are commonly found in photo-Fenton pilot plants for water treatment and purification. The model successfully fitted the temporal evolution of the dissolved oxygen (O2) and the hydrogen peroxide (H2O2) concentrations and the evolution of the total organic carbon (TOC) in solution in both reactor geometries and for different illuminated volume to total volume ratios. The model can be easily extended to model other water contaminants and provides a robust method for process design, process control and optimization