Formaldehyde removal from wastewater and air by using UV, ferrate(VI) and UV/ferrate(VI)

Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)-activated ferrate (Fe(vi)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(vi) could generate active species (Fe(v), Fe(iv), ˙OH and O2˙-) to degrade pollutants, while the in situ produced Fe(iii) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(vi) system, dissolved organic carbon was reduced by 49.38%, while UV254 was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J0 was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(vi) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.

Removal of Formaldehyde and Its Analogues Using a Hybrid Assembly of Pyrene-Modified Hydrazide and rGO: A Negative Carbon Emission and Green Chemical Decomposition Method

Indoor gaseous formaldehyde is the main environmental pollutant that can cause fatal threats to human health. A number of physical and chemical methods have been developed to tackle this issue. However, the existing methods are still unsatisfactory to meet the requirement of sustainable development owing to the flaws of low efficiency and reversible or second pollution. Herein, a chemical method based on a nucleophilic reaction between hydrazine and aldehyde that generates the only by-product of H₂O is designed for the removal of formaldehyde. 1-Pyrenebutyric hydrazide was synthesized by a simple esterification reaction and then self-assembled on reduced graphene oxide (rGO) with a large surface area by forming π-π stacking to obtain a composite for chemical removal of gaseous formaldehyde under ambient conditions. In a practical test, the formaldehyde removal rate could reach 91% of the theoretical value, which meets the requirement for commercial formaldehyde removal applications. After 10 times recycling, the formaldehyde removal rate still remains as high as 85%. Moreover, the composite could be regenerated in weak acidic media, which greatly reduce the manufacturing cost in practical applications.

The effect of disinfectants and antiseptics on co- and cross-selection of resistance to antibiotics in aquatic environments and wastewater treatment plants

The outbreak of the SARS-CoV-2 pandemic led to increased use of disinfectants and antiseptics (DAs), resulting in higher concentrations of these compounds in wastewaters, wastewater treatment plant (WWTP) effluents and receiving water bodies. Their constant presence in water bodies may lead to development and acquisition of resistance against the DAs. In addition, they may also promote antibiotic resistance (AR) due to cross- and co-selection of AR among bacteria that are exposed to the DAs, which is a highly important issue with regards to human and environmental health. This review addresses this issue and provides an overview of DAs structure together with their modes of action against microorganisms. Relevant examples of the most effective treatment techniques to increase the DAs removal efficiency from wastewater are discussed. Moreover, insight on the resistance mechanisms to DAs and the mechanism of DAs enhancement of cross- and co-selection of ARs are presented. Furthermore, this review discusses the impact of DAs on resistance against antibiotics, the occurrence of DAs in aquatic systems, and DA removal mechanisms in WWTPs, which in principle serve as the final barrier before releasing these compounds into the receiving environment. By recognition of important research gaps, research needs to determine the impact of the majority of DAs in WWTPs and the consequences of their presence and spread of antibiotic resistance were identified.

Effects of airflow rate and plant species on formaldehyde removal by active green walls

Formaldehyde is a hazardous volatile organic compound (VOC) listed as a Group 1 carcinogen by the International Agency for Research on Cancer. The active green wall system is a promising technology that utilizes active airflow passing through plants grown along a vertical alignment to increase their mass exposure to pollutants. However, few studies have investigated the effect of airflow rate on their efficacy for formaldehyde removal, and plant-mediated effects are unknown. This study assessed the formaldehyde removal ability of the active green wall using dynamic experiments. Three levels of airflow rate (30, 50, and 65 m³·h^-1) and inlet formaldehyde concentration (1.0, 2.0, and 3.5 mg·m^-3) were used and three plant species were investigated. The removal of formaldehyde by active green walls was significantly (P < 0.01) affected by the airflow rate, formaldehyde concentration, and plant species. The single pass removal efficiency varying from 38.18 to 94.42% decreased as the airflow rate and formaldehyde concentration increased. The elimination capacity varied from 189 to 1154 mg·m^-2·h^-1 and increased with the inlet formaldehyde loading rate. Significant differences in formaldehyde removal effectiveness among the plant species were observed with Chlorophytum comosum performing the best, followed by Schefflera octophylla, with Chamaedorea elegans being the worst.

Phytoremediation of indoor formaldehyde by plants and plant material

Formaldehyde evolves from various household items and is of environmental and public health concern. Removal of this contaminant from the indoor air is of utmost importance and currently, various practices are in the field. Among these practices, indoor plants are of particular importance because they help in controlling indoor temperature, moisture, and oxygen concentration. Plants and plant materials studied for the purpose have been reviewed hereunder. The main topics of the review are, mechanism of phytoremediation, plants and their benefits, plant material in formaldehyde remediation, and airtight environmental and health issues. Future research in the field is also highlighted which will help new researches to plan for the remediation of formaldehyde in indoor air. The remediation capacity of several plants has been tabulated and compared, which gives easy access to assess various plants for remediation of the target pollutant. Challenges and issues in the phytoremediation of formaldehyde are also discussed.Novelty statement: Phytoremediation is a well-known technique to mitigate various organic and inorganic pollutants. The technique has been used by various researchers for maintaining indoor air quality but its efficiency under real-world conditions and human activities is still a question and is vastly affected relative to laboratory conditions. Several modifications in the field are in progress, here in this review article we have summarized and highlighted new directions in the field which could be a better solution to the problem in the future.

Sustainable ferrate oxidation: Reaction chemistry, mechanisms and removal of pollutants in wastewater

This review is intended to evaluate the use of ferrate (Fe(VI)), being a green coagulant, sustainable and reactive oxidant, to remove micro pollutants especially pharmaceutical pollutants in contaminated water. After a brief description of advanced oxidation processes, fundamental dimensions regarding the nature, reactivity, and chemistry of this oxidant are summarized. The degradation of contaminants by Fe(VI) involves several mechanisms and reactive agents which are critically evaluated. The efficiency and chemistry of Fe(VI) oxidation differs according to the reaction conditions and activation agent, such as soluble Fe(VI) processes, which involve Fe(VI), UV light, and electro-Fe(VI) oxidation. Fe(VI) application methods (including single dose, multiple doses, chitosan coating etc), and Fe(VI) with activating agents (including sulfite, thiosulfate, and UV) are also described to degrade the micro pollutants. Besides, application of Fe(VI) to remove pharmaceuticals in wastewater are intensely studied. Electrochemical prepared Fe(VI) has more wide application than wet oxidation method. Meanwhile, we elaborated Fe(VI) performance, limitations, and proposed innovative aspects to improve its stability, such as the generation of Fe(III), synergetic effects, nanopores entrapment, and nanopores capsules. This study provides conclusive direction for synergetic oxidative technique to degrade the micro pollutants.

Water Purification of Classical and Emerging Organic Pollutants: An Extensive Review

The main techniques used for organic pollutant removal from water are adsorption, reductive and oxidative processes, phytoremediation, bioremediation, separation by membranes and liquid–liquid extraction. In this review, strengths and weaknesses of the different purification techniques are discussed, with particular attention to the newest results published in the scientific literature. This study highlighted that adsorption is the most frequently used method for water purification, since it can balance high organic pollutants removal efficiency, it has the possibility to treat a large quantity of water in semi-continuous way and has acceptable costs.

UV-activated permanganate process for micro-organic pollutant degradation: efficiency, mechanism and influencing factors

Ultraviolet-activated permanganate (UV/PM) process is a novel advanced oxidation process (AOP), but its application potential remains to be evaluated. This work investigates the degradation of refractory organic pollutant by UV/PM in terms of efficiency, mechanism, and influencing factors. The target compound benzoic acid (BA), which is a micro-organic pollutant and is resistant to PM and UV treatment, can be efficiently degraded by UV/PM. The electron paramagnetic resonance spectra directly supported the formation of hydroxyl radical (HO•) and superoxide radical (O₂^•-) from UV photolysis of PM. Competitive kinetics experiments verified that O₂^•- acted as precursor of HO• and the good degradation performance of BA was due to the involvement of HO• and manganese(V). The rate constants of BA degradation showed a positive linear relationship with PM dosage in the range of 0.5-20 mg·L^-1, and the degradation process was significantly influenced by solution pH and natural organic matters but insensitive to chloride and bicarbonate at environmentally relevant concentrations. Compared to the typical UV-based AOP UV/hydrogen peroxide, UV/PM is a little inferior, indicating that optimization and enhancement is needed for this process before its possible practical application.

Comparison of Azithromycin Removal from Water Using UV Radiation, Fe (VI) Oxidation Process and ZnO Nanoparticles

Antibiotics are resistant to biodegradation, and their removal by biological processes is difficult. The purpose of this study was to investigate the removal of azithromycin from water using ultraviolet radiation (UV), Fe (VI) oxidation process and ZnO nanoparticles. The effect of different parameters such as pH, temperature, hydraulic retention time (HRT), the concentration of Fe (VI) and ZnO nanoparticles and UV intensity on the removal of azithromycin from water was investigated. The optimal conditions for the removal of azithromycin were a pH of 2, a temperature of 25 °C, a HRT of 15 min, and a ratio of ZnO nanoparticles to the initial concentration of azithromycin (A/P) of 0.00009 which was fitted by Langmuir isotherm. In addition, the optimal conditions for the removal of azithromycin using UV radiation were a pH of 7, a temperature of 65 °C, a HRT of 60 min, and UV radiation power of 163 mW/cm2. For the Fe (VI) oxidation process, the optimal conditions were a pH of 2, a temperature of 50 °C and a HRT of 20 min. Also, the optimal ratio of Fe (VI) to the initial concentration of antibiotic was between 0.011 and 0.012. The results of this study showed that the Fe (VI) oxidation process, UV radiation, and ZnO nanoparticles were efficient methods for the removal of azithromycin from water.

Enhancing ferrate(VI) oxidation process to remove blue 203 from wastewater utilizing MgO nanoparticles

The aim of this study is to investigate the beneficial effect of utilizing MgO nanoparticles on the performance of ferrate(VI) oxidation process to remove blue-203 dye from wastewater. It was also made an attempt to assess the effects of pH, temperature, and MgO nanoparticle dosage on this oxidation process performance. Several sets of batch experiment were conducted to find out the effects of temperature ranging from 25 to 65 °C, pH ranging from 1.5 to 13, ferrate(VI) concentration ranging from 0.5 to 5.9 mg/L and MgO nanoparticles dosage ranging from 0.01 to 0.05 g in 150 mL solution on the removal efficiency. The results showed that adding MgO nanoparticles can improve the performance of ferrate(VI) oxidation removal method significantly, spec. at basic conditions. This synergistic effect can be attributed to the simultaneous adsorption of ferrate(VI) and dye molecules on the surface of nanoparticles. The results also revealed that the reaction between blue-203 dye and ferrate(VI) takes place rapidly at high mixing rate. It means that the required time to complete the removal process is controlled by mixing rate. It was finally concluded that adding MgO nanoparticles was an efficient means to enhance the performance of ferrate(VI) to oxidize blue-203 dye, esp. under basic conditions.