Pilot-scale and mechanistic study of the degradation of typical odors and organic compounds in drinking water by a combined UV/H2O2-BAC process

Quenching residual H2O2 from UV/H2O2 with granular activated carbon: A significant impact of bicarbonate

UV/H2O2 has been used as an advanced oxidation process to remove organic micropollutants from drinking water. It is essential to quench residual H2O2 to prevent increased chlorine demand during chlorination/chloramination and within distribution systems. Granular activated carbon (GAC) filter can quench the residual oxidant and eliminate some of the dissolved organic matter. However, knowledge on the kinetics and governing factors of GAC quenching of residual H2O2 from UV/H2O2 and the mechanism underlying the enhancement of the process by HCO3- is limited. Therefore, this study aimed to analyse the kinetics and influential factors, particularly the significant impact of bicarbonate (HCO3-). H2O2 decomposition by GAC followed first-order kinetics, and the rate constants normalised by the GAC dosage (kn) were steady (1.6 × 10-3 L g-1 min-1) with variations in the GAC dosage and initial H2O2 concentration. Alkaline conditions favour H2O2 quenching. The content of basic groups exhibited a stronger correlation with the efficiency of GAC in quenching H₂O₂ than did the acidic groups， with their specific kn values being 8.9 and 2.4 min-1 M-1, respectively. The presence of chloride, sulfate, nitrate, and dissolved organic matter inhibited H2O2 quenching, while HCO3- promoted it. The interfacial hydroxyl radical (HO•) zones were visualised on the GAC surface, and HCO3- addition increased the HO• concentration. HCO3- increased the concentration of persistent free radicals (PFRs) on the GAC surface, which mainly contributed to HO• generation. A significant enhancement of HCO3- on H2O2 quenching by GAC was also verified in real water. This study revealed the synergistic mechanism of HCO3- and GAC on H2O2 quenching and presents the potential applications of residual H2O2 in the H2O2-based oxidation processes.

A Bibliometric Analysis of Geosmin Removal and Treatment Technologies using Web of Science Database and VOSviewer

In the last few years, the presence of geosmin (GEO) in water bodies has caused serious problems related to water consumption by the population. Many studies focus on its occurrence and detection, but little is discussed about the technologies for treatment and removal of this contaminant. In this way, the present work aims to present a bibliographic search and a bibliometric analysis carried out in the Web of Science database and in VOSviewer software about geosmin remediation, in the last 10 years. 100 articles were found, of which only one, from 2021, was a review. It was possible to assess that the subject has gained greater notoriety in the last 7 years, since the year 2016 marked the increase of publications on the subject, as well as an increasing number of citations. Among the most published countries is the People's Republic of China, with 53% of publications. Bibliometric analysis showed that GEO is directly related to 2-methylisoborneol (2-MIB), since both occur simultaneously in water bodies. In addition, it was possible to identify that adsorptive processes are the most used in the removal of these contaminants, followed by advanced oxidative processes and biological processes, in that order.

The analytic hierarchy process method to design applicable decision making for the effective removal of 2-MIB and geosmin in water sources

Numerous utilities encounter issues with taste and odor that alter the public's impression of the safety of drinking water. The creation of certain components in water naturally due to global climate change is another source of taste and odor components, in addition to industrial emissions. Geosmin and 2-methylisoborneol (2-MIB), both of which are generated by blue-green algae and actinomycetes, are two substances that contribute to the musty and earthy smells in drinking water sources. Unfortunately, current conventional treatment plants only partially remove 2-MIB and geosmin. Therefore, to protect the environment and public health, more up-to-date or optimized treatment methods should be applied to outdated treatment facilities. Best treatment practices, evaluation standards, and decision-making approaches, however, are still shrouded in mystery. The goal of this study was to identify the most effective treatment options for 2-MIB and geosmin. By using the analytical hierarchy process (AHP), a total of 22 assessment criteria were found and prioritized. A thorough literature search led to the identification of potential treatment options, and their effectiveness was evaluated. These options and priority rankings were decided upon using AHP in the decision-making process. Advanced oxidation techniques came out on top in the final priority ranking, followed by membrane filtering, adsorption, oxidation, hybrid processes, and traditional treatment methods. The applied analytical decision techniques may also be used to choose the optimal treatment options, even though the results are particular to 2-MIB and geosmin.

Degradation of mixed typical odour gases via non-thermal plasma catalysis

The simultaneous treatment of H₂S and NH₃ typical odours by plasma was investigated and the co-treatment of both was found to have a facilitating effect the conversion. The degradation efficiency and by-product emissions of single plasma technology and plasma co-catalytic two-stage technology were compared and the degradation mechanism was further analyzed. The results show that in the single plasma technology conversion experiment, the conversion rate of the treated odours mixture is higher than that of the treated single odours, and the by-product emissions of SO₂ and NO_x are also reduced due to the reaction of intermediate products and by-products during the reaction process. The absolute removal of the odours mixture is optimal when treating at a gas flow rate of 6 L/min, a voltage of 16 kV and a frequency of 200 Hz. The M(Ce,Cu)-Mn/13X loaded catalyst was synthesized by co-precipitation method. Under the conditions of gas flow rate of 3-7 L/min, the efficiency of H₂S and NH₃ removal and the reduction of by-product emission were ranked as: uncatalyzed > Cu-Mn/13X > Ce-Mn/13X, which proved that Ce-Mn/13X showed better catalytic activity and application value.