Advanced Oxidation Processes (AOP)

All advanced oxidation processes (AOP) are characterised by a common chemical feature: the capability of exploiting the high reactivity of HO radicals in driving oxidation processes which are suitable for achieving the complete abatement and through mineralization of even less reactive pollutants. The different AOP are considered and critically presented according to their specific features with reference, whenever possible, to their real applications for water pollution abatement. The experimental apparatus and working procedures which can be adopted for carrying out waste water treatments by AOP application are examined. Some remarks upon treatment economics are provided on the basis of the main parameters affecting the AOP costs.

Advanced Oxidation Processes (AOPs) are called to fill the gap between the treatability attained by conventional physico-chemical and biological treatments and the day-to-day more exigent limits fixed by environmental regulations. They are particularly important for the removal of anthropogenic pollutants and for this reason, they have been widely investigated in the last decades and even applied in the treatment of many industrial wastewater flows. However, despite the great development reached, AOPs cannot be considered mature yet and there are many new fields worthy of research. Some of them are going to be briefly introduced in this paper, including hybrid processes, heterogeneous semiconductor photocatalysis, sulphate-radical oxidation and electrochemical advanced oxidation for water/wastewater treatment. Moreover, the use of photoelectrochemical processes for energy production is discussed. The work ends with some perspectives that can be of interest for the ongoing and future research.

A wireless UV-A LEDs lab-scale reactor powered by a resonant inductive coupling (RLC) system was built to maximize the UV photon absorption of agro-industrial wastewaters. The UV-A LEDs (λ = 365 nm) energy was supplied through a magnetic field generated inside of the photoreactor by induction coils placed on the external wall made of polyvinyl chloride. Immersing the light sources in the wastewater increases the photon transfer efficiency and the reaction rate. Maximum magnetic field and optical irradiance were obtained at 26.8 and 27.0 kHz, respectively. As proof-of-concept, elderberry wastewater (EW), olive washing wastewater (OWW) and white and red winery wastewaters (WWW and RWW) were treated combining the wireless UV-A LEDs with the Advanced Oxidation Process (AOP) - Fenton reagent. Fenton experiments were performed using [Fe 2+ ] = 10 mg L -1 , [H 2 O 2 ] = 500 mg L -1 , pH = 3 and a reaction time of 4 h. With EW a DOC removal of 35% (k = 0.0696 h -1 ) was achieved, whereas adding the wireless UV-A LEDs (f = 26.8 kHz) 53% was attained (k = 0.1722 h -1 ). The Electric Energy per Order (E EO ) for the wireless UV-A LEDs consumption was calculated (E EO LEDs = 48.7 kWh m -3 ) and for all the remain equipment (air pump, RC box and power amplifier), E -1 ) and for all the remain equipment (air pump, RC box and power amplifier), E EO total = 495 kWh m -3 order -1 . Experiments with OWW presented a DOC removal of 62% and a E EO LEDs = 40.5 kWh m -3 order -1 ; RWW shown 40% of DOC removal and a E EO LEDs = 68.4 kWh m -3 order -1 , while with WWW 35% of DOC removal and a E EO LEDs = 79.8 kWh m -3 order -1 were obtained. This work shows that wireless UV-A LEDs can be a promising alternative to conventional UV lamps and wired LEDs in the treatment of real wastewaters. However, optimization of the induction system is still needed, as well as the number and wavelength of the LEDs (e.g. UV-C LEDs) to reduce the overall treatment costs.

Background: Due to contamination of the environment by pesticides and their mishandling, there is the need for treatment of contaminated sites and correct disposal of materials containing them. Thus, studies with advanced oxidation processes are expanding and can determine the rate constant of the hydroxyl radical with organic compounds of great importance in environmental contamination. In this context, the use of laser flash photolysis has been shown to be viable for the determination of these constants.
Results: The reaction rate constants of different pesticides with HO(•) in degassed acetonitrile have been determined. They were 1.6 × 10(9)  M(-1)  s(-1), 0.6 × 10(9)  M(-1)  s(-1), 1.2 × 10(9)  M(-1)  s(-1), 2.4 × 10(9)  M(-1)  s(-1) and 2.2 × 10(9)  M(-1)  s(-1) for the pesticides carbaryl, propoxur, fenoxycarb, ethoxysulfuron and chlorimuron-ethyl, respectively. These values are about an order of magnitude smaller than the diffusion controlled rate and correlate with the relative rates of disappearance of the pesticides in the photo-Fenton reaction in water.
Conclusion: The correlation of the relative rate constants determined by laser flash photolysis with the relative rates of photo-Fenton degradation of the pesticides is compelling evidence for the participation of the hydroxyl radical in the degradation of these pesticides in the latter system.

The paper industry is adopting zero liquid effluent technologies to reduce freshwater use and meet environmental regulations, which implies closure of water circuits and the progressive accumulation of pollutants that must be removed before water reuse and final wastewater discharge. The traditional water treatment technologies that are used in paper mills (such as dissolved air flotation or biological treatment) are not able to remove recalcitrant contaminants. Therefore, advanced water treatment technologies, such as advanced oxidation processes (AOPs), are being included in industrial wastewater treatment chains aiming to either improve water biodegradability or its final quality. A comprehensive review of the current state of the art regarding the use of AOPs for the treatment of the organic load of effluents from the paper industry is herein addressed considering mature and emerging treatments for a sustainable water use in this sector. Wastewater composition, which is highly dependent on the raw materials being used in the mills, the selected AOP itself, and its combination with other technologies, will determine the viability of the treatment. In general, all AOPs have been reported to achieve good organic removal efficiencies (COD removal >40 %, and about an extra 20 % if AOPs are combined with biological stages). Particularly, ozonation has been the most extensively reported and successfully implemented AOP at an industrial scale for effluent treatment or reuse within pulp and paper mills, although Fenton processes (photo-Fenton particularly) have actually addressed better oxidative results (COD removal ≈ 65–75 %) at a lab scale, but still need further development at a large scale.

Pharmaceuticals, which are frequently detected in natural and wastewater bodies as well as drinking water have attracted considerable attention, because they do not readily biodegrade and may persist and remain toxic. As a result, pharmaceutical residues pose on-going and potential health and environmental risks. To tackle these emerging contaminants, advanced oxidation processes (AOPs) such as photo-Fenton, sonolysis, electrochemical oxidation, radiation and ozonation etc. have been applied to remove pharmaceuticals. These processes utilize the high reactivity of hydroxyl radicals to progressively oxidize organic compounds to innocuous products. This review provides an overview of the findings from recent studies, which have applied AOPs to degrade pharmaceutical compounds. Included is a discussion that links various factors of TiO2-mediated photocatalytic treatment to its effectiveness in degrading pharmaceutical residues. This review furthermore highlights the success of AOPs in the removal of pharmaceuticals from different water matrices and recommendations for future studies are outlined.

Hospital effluents are the sources for complex high percentage of micropollutants and till date no specific treatment have been investigated for the removal of pollutants. These effluents and their complex characteristics pose resistance to unit operation which undergoes in hospital wastewater treatment plants (WWTPs). In other words such complex contaminants are unable to removed completely through conventional treatment processes. The pharmaceutical residues entering into the environment may pose a serious threat to the water resources around the world. In past few years environmental scientists are more concerned towards the effluent generated from medical care facilities, community health centers and hospitals. In this study, seven multi-specialty hospitals with non-identical pre-treatment were selected for 3-aspects i.e. conventional wastewater characteristics, high priority pharmaceuticals and microbial analyses. The present work is to evaluate efficacy of advanced wastewater treatment methods with regard to removal of these 3-aspects from hospital effluents before discharge into a sewage treatment plant (STP). Based on test results, two out of seven treatment technologies i.e. MBR and CW effectively reducing conventional parameters and pharmaceuticals from secondary and tertiary treatments except regeneration of microbes were observed in tertiary level by these two treatments. The result also suggests that, MBR exhibited 100% elimination of ibuprofen, carbamazepine, frusemide while CW indicated 100% elimination of ofloxacin. Furthermore, two combinations of advanced oxidation process viz. ozonation (O 3) and peroxone process (O 3 –H 2 O 2) were demonstrated to oxidize pharmaceuticals. The operational key factors for AOP involve pH, O 3 supply, contact time, and H 2 O 2 concentrations. Based on pharmaceuticals reduction efficiencies, the conventional O 3 alone is more efficient as compared to combine O 3 –H 2 O 2 treatment. Hence results confirmed that, MBR coupled with ozone process proved as an optimal technology among the seven technologies for the pre-treatment of hospital effluent. • MBR coupled ozonation process proved as an optimal technology among seven technologies for hospital effluent pre-treatment. • MBR technology exhibited 100% elimination of ibuprofen, carbamazepine, frusemide. • CW indicated 100% elimination of ofloxacin, followed by SAFF for 92% reduction of ofloxacin. • No significant improvements in elimination rates were observed by introducing peroxone process except diazepam. • CAR, DIA, DIC and FUR were completely reduced by ozonation and peroxone process for raw effluent. [ABSTRACT FROM AUTHOR]

Highlights •The influence of water matrix on the efficiency of AOTs is overviewed.•Photolysis, photocatalysis, UV/H2O2-, Fenton-, and O3-based processes are reviewed.•Dissolved organic matter and inorganics can act as inhibitors and/or promoters.•The effect results from the interplay of the co-existing substances.•The knowledge on the role of matrix constituents is crucial for installation of AOTs.

Hazardous organic wastes from industrial, military, and commercial activities represent one of the greatest challenges to human beings. Advanced oxidation processes (AOPs) are alternatives to the degradation of those organic wastes. However, the knowledge about the exact mechanisms of AOPs is still incomplete. Here we report a phenomenon in the AOPs: induced effects, which is a common property of combustion reaction. Through analysis EDTA oxidation processes by Fenton and UV-Fenton system, the results indicate that, just like combustion, AOPs are typical induction reactions. One most compelling example is that pre-feeding easily oxidizable organic matter can promote the oxidation of refractory organic compound when it was treated by AOPs. Connecting AOPs to combustion, it is possible to achieve some helpful enlightenment from combustion to analyze, predict and understand AOPs. In addition, we assume that maybe other oxidation reactions also have induced effects, such as corrosion, aging and passivation. Muchmore research is necessary to reveal the possibilities of induced effects in those fields. [ABSTRACT FROM AUTHOR]

Water pollution through natural and anthropogenic activities has become a global problem causing short-and long-term impact on human and ecosystems. Substantial quantity of individual or mixtures of organic pollutants enter the surface water via point and nonpoint sources and thus affect the quality of freshwater. These pollutants are known to be toxic and difficult to remove by mere biological treatment. To date, most researches on the removal of organic pollutants from wastewater were based on the exploitation of individual treatment process. This single-treatment technology has inherent challenges and shortcomings with respect to efficiency and economics. Thus, application of two advanced treatment technologies characterized with high efficiency with respect to removal of primary and disinfection by-products in wastewater is desirable. This review article focuses on the application of integrated technologies such as electrohydraulic discharge with heterogeneous photocatalysts or sonophotocatalysis to remove target pollutants. The information gathered from more than 100 published articles, mostly laboratories studies, shows that process integration effectively remove and degrade recalcitrant toxic contaminants in wastewater better than single-technology processing. This review recommends an improvement on this technology (integrated electrohydraulic discharge with heterogeneous photocatalysts) viz-a-vis cost reduction in order to make it accessible and available in the rural and semi-urban settlement. Further recommendation includes development of an economic model to establish the cost implications of the combined technology. Proper monitoring, enforcement of the existing environmental regulations, and upgrading of current wastewater treatment plants with additional treatment steps such as photocatalysis and ozonation will greatly assist in the removal of environmental toxicants.