Light-Assisted Advanced Oxidation Processes for the Elimination of Chemical and Microbiological Pollution of Wastewaters in Developed and Developing Countries

Abstract

In this work, the issue of hospital and urban wastewater treatment is studied in two different contexts, in Switzerland and in developing countries (Ivory Coast and Colombia). For this purpose, the treatment of municipal wastewater effluents is studied, simulating the developed countries' context, while cheap and sustainable solutions are proposed for the developing countries, to form a barrier between effluents and receiving water bodies. In order to propose proper methods for each case, the characteristics of the matrices and the targets are described here in detail. In both contexts, the use of Advanced Oxidation Processes (AOPs) is implemented, focusing on UV-based and solar-supported ones, in the respective target areas. A list of emerging contaminants and bacteria are firstly studied to provide operational and engineering details on their removal by AOPs. Fundamental mechanistic insights are also provided on the degradation of the effluent wastewater organic matter. The use of viruses and yeasts as potential model pathogens is also accounted for, treated by the photo-Fenton process. In addition, two pharmaceutically active compound (PhAC) models of hospital and/or industrial origin are studied in wastewater and urine, treated by all accounted AOPs, as a proposed method to effectively control concentrated point-source pollution from hospital wastewaters. Their elimination was modeled and the degradation pathway was elucidated by the use of state-of-the-art analytical techniques. In conclusion, the use of light-supported AOPs was proven to be effective in degrading the respective target and further insights were provided by each application, which could facilitate their divulgation and potential application in the field.

Keywords: E. coli; MS2 coliphage; UV/H2O2; emerging contaminants; micropollutants; pathogen microorganisms; photo-Fenton; saccharomyces cerevisiae; urban and hospital wastewater; urine treatment.

Figure 1

Schematic representation: Treatment focus, strategy and targets of WWTP by light-assisted AOPs in developing countries. Switzerland and its motion of upgrading the WWTPs is studied, presenting solutions based on the application of mainly UV-based AOPs, compared with the solar photo-Fenton. The targets are the micropollutants chosen by the Swiss evolution of control policy and the indigenous population of bacterial microorganisms present in WW.

Figure 2

Degradation of chemical and microbiological contaminants in MWW. (a) Weighted average removal of seven selected micropollutants by the UV/H₂O₂ process (ng/L initial MP content and 25 mg/L H₂O₂); and (b) reduction of bacteria contained in WW by the UV/H₂O₂ (continuous trace) and the solar photo-Fenton process (dashed line). The colors correspond to the previous secondary treatment (blue: Activated Sludge, red: Moving Bed BioReactors, green: Coagulation-Flocculation). More details on the micropollutants’ initial content, experimental configuration and wastewater characteristics can be found in [78,79].

Figure 3

Schematic representation: Using the photo-Fenton as a disinfection method in developing countries. The application of Fenton reagents, aided by the numerous sunny days in the circum-Equatorial regions, which coincide with the geographical distribution of developing countries, was assessed on their virucidal and fungal inactivation capacities, using bacteriophages and common yeasts as proxies, while assessing the important role of dissolved organic matter and iron.

Figure 4

Stepwise construction of the solar photo-Fenton process. Effects of solar light, solar/H₂O₂, solar/Fe and solar photo-Fenton in viral (MS2) infectivity in simulated secondary wastewater, as in [87]. Note the difference inflicted by the initial speciation of iron in the solution.

Figure 5

Internal and external damages during Saccharomyces cerevisiae inactivation by the photo-Fenton process at near-neutral pH. The panels indicate the external and two types of internal damage inflicted to the model yeast pathogen: cell wall proteins, genome and cytoplasmic proteins, respectively.

Figure 6

Schematic representation: Treatment of hospital and highly concentrated flows of PhACs. The treatment methods were associated with the concentration of the matrix (urine), hence UV-based solutions were sought, or the WW flows, allowing the assessment of photo-Fenton as a viable solution.

Figure 7

ICM Iohexol degradation by UV-based AOPs in: (a) water; (b) wastewater; and (c) urine. H₂O₂ addition and Fe-assisted experiments, aided by acidification of the matrix hold minor improvement in degradation kinetics.

Figure 8

Antidepressant Venlafaxine degradation in MQ water. (a) UV/H₂O₂ mediated degradation and kinetic evaluation of H₂O₂ incremental addition; and (b) solar photo-Fenton at acidic pH, with the optimal degradation areas (light color contour).