Rethinking micropollutant removal assessment methods for wastewater treatment plants - how to get more robust data?

Hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane for ibuprofen removal

The investigations on the removal of ibuprofen (IBU) in a hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane are presented. The gaseous ozone into feed water in concentration of 11 g Nm^-3 was supplied. Positive influence of catalytic ozonation on ibuprofen decomposition was observed. The application of catalytic nanofiltration membrane led to the ibuprofen removal of 91% after the first 15 min from the beginning of the O₃/NF process, while at the same time, for the pristine membrane, it was equal to 76%. The investigations revealed incomplete degradation of drug under pH 3 after 2 h, i.e., 89%. On the other hand, the addition of inorganic salts did not affect the catalytic ibuprofen removal efficiency. Under acidic pH, the highest permeate flux decline (26%) was noted, whereas no differences between permeate flux measured under natural and alkaline conditions were observed. During the treatment process, three IBU by-products were detected, which significantly affected the permeate toxicity; however, after 2 h of catalytic nanofiltration, the product of treatment process was found as non-toxic.

Comparative Life Cycle Assessment of two advanced treatment steps for wastewater micropollutants: How to determine whole-system environmental benefits?

Advanced wastewater treatment (AWT) technologies are now considered to target urban micropollutants (MPs) before discharge into receiving water bodies and to comply with specific criteria for reuse. Extra energy and/or resources are necessary to achieve the elimination of MPs. Using the Life Cycle Assessment framework, this study assesses net environmental efficiencies for two AWTs (i) ozone systems (air-fed and pure oxygen-fed) and (ii) granular activated carbon filter. Sixty-five MPs with proven removal efficiency values and toxicity and/or ecotoxicity potentials were included in this study building on results from recent research. Consolidated Life Cycle Inventories with data quality and uncertainty characterization were produced with an emphasis on operational inputs. Results show that the direct water quality benefits obtained from AWT are outweighed by greater increases in indirect impacts from energy and resource demands. Future research should include water quality aspects not currently captured in life cycle impact assessment, such as endocrine disruption and whole-effluent toxicity, in order to assess the complete policy implications of MP removal strategies.

Fluorescence excitation/emission matrices as a tool to monitor the removal of organic micropollutants from wastewater effluents by adsorption onto activated carbon

Monitoring the removal of organic micropollutants (OMPs) in advanced wastewater treatment facilities requires expensive and time-consuming analytical methods that cannot be installed online. Spectroscopic techniques such as fluorescence excitation/emission spectroscopy were demonstrated to offer the potential for monitoring OMPs removal in conventional wastewater treatment plants or ozonation pilots but their application to activated carbon (AC) adsorption processes was only investigated at lab scale and not in real treatment facilities. In this study, indexes from fluorescence emission/excitation matrices (EEMs) were used to find correlations with the removal of 28 OMPs from a large-scale AC pilot in fluidized bed employed for wastewater advanced treatment, as well as from batch experiments. Differences in OMPs removal could be observed depending on the operational conditions (i.e. pilot or batch experiments, contact time, type of AC) and the physico-chemical properties of the molecules. 7 PARAFAC components were derived from the fluorescence EEMs of 60 samples obtained before and after adsorption. Positive correlations were obtained between the removal of fluorescence indexes and most OMPs, and correlation coefficients were much higher than the ones obtained with UV₂₅₄, confirming the interesting potential of fluorescence spectroscopy to accurately monitor adsorption performances at the industrial scale. The highest correlation coefficients were obtained for OMPs having the best removals while the ones that were refractory to adsorption, as well as to interactions with DOM, exhibited weak correlations. These results suggest that interactions between OMPs and fluorescing DOM and their subsequent co-adsorption onto AC were at the origin of the correlations found. Lower correlations were also found for the most biodegradable OMPs, which indicated that the occurrence of biological effects could make the monitoring of these compounds more challenging.

Benefits of ozonation before activated carbon adsorption for the removal of organic micropollutants from wastewater effluents

Advanced processes for the removal of organic micropollutants (OMPs) from wastewater effluents include adsorption onto activated carbon, ozonation, or a combination of both processes. The removal of 28 OMPs present in a real wastewater effluent was studied by ozonation coupled to activated carbon adsorption and compared to a sole adsorption. The influence of the specific ozone dose (0.09-1.29 gO₃/gDOC) and the influence of the powdered activated carbon (PAC) dose (2, 5 and 10 mg/L) were first studied separately. OMPs removal increased with both the specific ozone dose (up to 80% for a dose higher than 0.60 gO₃/gDOC) and the PAC dose. Ozonation performances decreased in presence of suspended solids, which were converted to dissolved organic carbon. A correction of the specific ozone dose according to the suspended solids levels, in addition to nitrite, should be considered. The influence of ozonation (0.09, 0.22, 0.94 and 1.29 gO₃/gDOC) on OMPs adsorption was then assessed. OMPs adsorption didn't change at low specific ozone doses but increased at higher specific ozone doses due to a decrease in DOM adsorption and competition with OMPs. At low ozone doses followed by adsorption (0.22 gO₃/gDOC and 10 mg/L PAC), the two processes appeared complementary as OMPs with a low reactivity toward ozone were well absorbed onto PAC while most OMPs refractory to adsorption were well eliminated by ozone. Improved removals were obtained for all compounds with these selected doses, reaching more than 80% removal for most OMPs while limiting the formation of bromate ion.

Influence of the properties of 7 micro-grain activated carbons on organic micropollutants removal from wastewater effluent

Most studies dedicated to organic micropollutants (OMPs) removal from wastewater effluents by adsorption onto activated carbon (AC) only consider a few conventional AC properties. The link between OMPs removal and these properties is often missing, which limits the understanding of the adsorption process and the interpretation of the results. The chemical, physical and textural properties of seven newly commercialized micro-grain activated carbons (μGACs) were determined to assess their influence on the removal of 28 OMPs. Conventional batch tests with wastewater effluent showed that a high percentage of microporous volume (>65%) was detrimental for the removal of 10 OMPs, probably due to a higher blockage of micropores by dissolved organic matter (DOM). The removal of 5 OMPs was correlated with μGACs surface chemistry properties (i.e. charge) which were potentially modified by DOM adsorption or inorganic species, thus favoring the adsorption of positively-charged compounds. A combination of OMPs properties including their charge, hydrophobicity and minimal projection area could explain their removal. Correlations were found between the removal of several OMPs and UV₂₅₄, suggesting that DOM and OMPs interacted with each other or followed similar adsorption mechanisms. A decrease in μGACs particle size had a positive impact on UV₂₅₄ removal under continuous-flow conditions in columns representative of a large-scale pilot due to better expansion.

Organic micropollutants in a large wastewater treatment plant: What are the benefits of an advanced treatment by activated carbon adsorption in comparison to conventional treatment?

Several advanced treatments, such as ozonation or activated carbon adsorption, are currently considered for the removal of organic micropollutants (OMPs) in wastewater treatment plants (WWTP). However, little is known on the overall performances of a WWTP upgraded with those processes and the benefits provided regarding the elimination of multiple families of OMPs. In this study, 5 sampling campaigns were performed to determine the removal of 48 OMPs in a WWTP followed by an activated carbon pilot. The primary treatment had no effect on OMPs (removals < 20%), whereas the biological treatment removed OMPs that can be easily sorbed onto sludges or biodegraded (>60%). The additional elimination provided by the advanced treatment was not significant (<10%) for OMPs already well removed in the WWTP) but was substantial (>30%) for recalcitrant OMPs. Removals higher than 60% were obtained for all OMPs (except azithromycin and sulfamethoxazole) over the WWTP and the activated carbon pilot. The adsorption conditions (10 g/m³ fresh activated carbon addition) were not sufficient to achieve the 80% removal targeted in Switzerland for compounds suggested as indicator substances for wastewater treatment. A higher dose of activated carbon or the combination with another advanced treatment should be used to achieve a satisfactory removal of those compounds.

Benchmarking Toronto wastewater treatment plants using DEA window and Tobit regression analysis with a dynamic efficiency perspective

The environmental-economic focus of wastewater treatment and management attracts growing attentions in recent years. The static efficiencies and their dynamic changes are helpful to systematically assess the environmental performance of the water agencies and wastewater treatment plants (WWTPs). Additionally, identifying key factors of efficiencies is critical to improve the operation of WWTPs. In this study, the window method of data envelopment analysis (DEA) was applied to estimate the annual efficiency for four Canadian WWTPs and to explore the variations of annual efficiency under different window lengths. Meanwhile, the Tobit regression analysis was developed to determine the driving forces for WWTPs' efficiency. The empirical results showed that: (i) the selected DEA window length remarkably affected both the average efficiency and the variations; however, it had no impact on the ranking of plants' efficiency; (ii) lower efficiencies were observed in plants with larger capacities due to higher infrastructure and operation investments involved; (iii) both the influent total phosphorus concentrations and influent flow rates had significant effects on the WWTPs' performance. Moreover, the staff and utility expenditures should be reduced to generate greater potential cost savings and efficiency improvement given the treatment technologies employed.