Removal of Micropollutants from Wastewater : evaluation of effect of upgrading ozonation to electro-peroxone

Abstract: The United Nations (UN) has adopted 17 “Sustainable Development Goals” (SDGs) to achieve a clean, better and sustainable future. SDG 6 is to ensure that everyone has access to clean water and sanitation by 2030. According to the UN Educational, Scientific and Cultural Organization (UNESCO), more than 80% of wastewater produced from human actions is discharged into rivers or seas without any pollution removal. Thus, the presence of micropollutants (MPs: including, inter alia, pharmaceuticals, biocides and personal care products) in wastewaters is a major challenge that poses potential threats not only to aquatic system but also to humans due to their potential toxicity and potential to induce antibiotic resistance. Wastewater treatment plants (WWTPs) are considered hotspots for release of MPs as the current treatment processes are not designed to remove them. This thesis is based on studies described in four appended papers (Papers I-IV) designed to help efforts to solve these problems by investigating the factors involved and developing advanced treatment processes for removing MPs.Ozonation is one of the most intensively studied and widely used advanced treatment processes for removing MPs. However, due to ozone’s (O3) chemical selectivity, it cannot remove resistant MPs so its use (without additional treatments) results in their release into the environment. Thus, key objectives were to evaluate effects of switching to a new emerging process called electro-peroxone (E-peroxone) on MPs’ removal, by inserting two electrodes into an ozonation reactor. Its potential utility for other applications were also investigated.Paper I addresses effects of upgrading from ozonation to E-peroxone on pharmaceuticals’ removal at lab-scale, using a quantitative structure-activity relationship (QSAR) model. For this purpose, the relationship between QSAR model-predicted second-order rate constants of ozone’s reactions with pharmaceuticals (kO3 values) and ratios of experimentally determined pseudo-first order rate constants of E-peroxone and ozonation (kEP/kOZ values) was examined. Results showed that E-peroxone accelerated the removal of O3-resistant pharmaceuticals. In addition, the QSAR model predicted kO3 values for 491 pharmaceuticals, which suggested that large numbers of pharmaceuticals have high O3 resistance. Paper II addresses the removal of antimicrobials, including biocides and antibiotics, by E-peroxone and ozonation in relation to the water matrix. The results indicated that all studied antibiotics were effectively removed by both processes. In contrast, most of the biocides were at most moderately reactive with ozone, so their removal rate by ozonation was lower. The E-peroxone process increased their removal rate (i.e. removed them much more rapidly) by enhancing formation of hydroxyl radicals (•OH). Paper III reports the design, construction and tests of a pilot-scale mobile E-peroxone and ozonation system for removing naturally occurring MPs in secondary wastewater effluents. The tests included assessments of a new, scalable graphene modified carbon brush cathode for the E-peroxone process, which was found to enhance removal of moderately O3-reactive MPs significantly, and O3-resistant MPs moderately, while consuming similar amounts of electrical energy, or even less, for removing most of the MPs used in the experiments. Paper IV describes the regeneration of spent activated carbon, used for removing ionic MPs, by E-peroxone and ozonation. Both processes restored the activated carbon’s sorption efficiency to similar (or even higher) levels than that of virgin activated carbon, for all tested MPs except perfluorooctanoic acid (PFOA). It was concluded that sorption of MPs on regenerated activated carbon is mainly driven by interactions between ionic forms of the MPs with activated carbon’s charged surfaces rather than their interactions with pores in the activated carbon.