Degradation kinetics of target compounds and correlations with spectral indices during UV/H2O2 post-treatment of biologically treated acrylonitrile wastewater

Degradation behaviors of Nabumetone and its metabolite during UV/monochloramine process: Experimental and theoretical study

This study investigated degradation behaviors of a nonsteroidal anti-inflammatory drug Nabumetone (NMT) and its major metabolite 6-methoxy-2-naphthylacetic acid (MNA) in the coupling process of ultraviolet and monochloramine (UV/NH2Cl). The second-order rate constants of the contaminants reacting with reactive radicals (HO•, Cl•, Cl2•⁻, and CO3•⁻) were determined by laser flash photolysis experiments. HO• and Cl• contributed predominantly with 52.3% and 21.7% for NMT degradation and 60.8% and 22.3% for MNA degradation. The presence of chlorides retarded the degradation of NMT, while promoted the destruction of MNA, which was ascribed to the photosensitization effects of MNA under UV irradiation. Density functional theory (DFT) calculations revealed that radical adduct formation (RAF) was dominant pathway for both HO• and Cl• reacting with the contaminants, and hydrogen atom transfer (HAT) preferred to occur on side chains of NMT and MNA. NMT reacted with NO2• through single electron transfer (SET) with the second-order rate constant calculated to be 5.35 × 107 (mol/L)-1 sec-1, and the contribution of NO2• was predicted to be 13.0% of the total rate constant of NMT in pure water, which indicated that NO2• played a non-negligible role in the degradation of NMT. The acute toxicity and developmental toxicity of NMT were enhanced after UV/NH2Cl treatment, while those of MNA were alleviated. The transformation products of both NMT and MNA exhibited higher mutagenicity than their parent compounds. This study provides a deep understanding of the mechanism of radical degradation of NMT and MNA in the treatment of UV/NH2Cl.

Theoretical studies on the aqueous phase and graphene heterogeneous degradation of acrylamide and acrylonitrile by HO, ClO, and BrO radicals

The newly discovered ClO• and BrO• contribute to pollutant degradation in advanced oxidation processes, while acrylamide (AM) and acrylonitrile (ACN) are always the focus of scientists concerned due to their continuous production and highly toxic effects. Moreover, various particles with a graphene-like structure are the companions of AM/ACN in dry/wet sedimentation or aqueous phase existence, which play an important role in heterogeneous oxidation. Thus, this work focuses on the reaction mechanism and environmental effect of AM/ACN with ClO•/BrO•/HO• in the water environment under the influence of graphene (GP). The results show that although the reactivity sequence of AM and ACN takes the order of with HO• > with BrO• > with ClO•, the easiest channel always occurs at the same C-position of the two reactants. The reaction rate constants (k) of AM with three radicals are 2 times larger than that with ACN, and amide groups have a better ability to activate CC bonds than cyanide groups. The existence of GP can accelerate the target reaction, and the k increased by 9-13 orders of magnitude. The toxicity assessment results show that the toxic effect of most products is lower than that of parent compounds, but the environmental risk of products from ClO•/BrO•-adducts is higher than those from HO•-adducts. The oxidative degradation process based on ClO• and BrO• deserves special attention, and the catalytic effect of GP and its derivatives on the oxidation process is non-negligible.

Dynamic Modelling, Process Control, and Monitoring of Selected Biological and Advanced Oxidation Processes for Wastewater Treatment: A Review of Recent Developments

This review emphasizes the significance of formulating control strategies for biological and advanced oxidation process (AOP)-based wastewater treatment systems. The aim is to guarantee that the effluent quality continuously aligns with environmental regulations while operating costs are minimized. It highlights the significance of understanding the dynamic behaviour of the process in developing effective control schemes. The most common process control strategies in wastewater treatment plants (WWTPs) are explained and listed. It is emphasized that the proper control scheme should be selected based on the process dynamic behaviour and control goal. This study further discusses the challenges associated with the control of wastewater treatment processes, including inadequacies in developed models, the limitations of most control strategies to the simulation stage, the imperative requirement for real-time data, and the financial and technical intricacies associated with implementing advanced controller hardware. It is discussed that the necessity of the availability of real-time data to achieve reliable control can be achieved by implementing proper, accurate hardware sensors in suitable locations of the process or by developing and implementing soft sensors. This study recommends further investigation on available actuators and the criteria for choosing the most appropriate one to achieve robust and reliable control in WWTPs, especially for biological and AOP-based treatment approaches.

Characterizing dissolved organic matter in aquatic environments by size exclusion chromatography coupled with multiple detectors

Size exclusion chromatography (SEC) is one of the most commonly used techniques to detect the molecular weight (MW) of dissolved organic matter (DOM) in aquatic environments. The significant improvement and focus of this method have been the application of multiple detectors, which contribute to providing fundamental physicochemical properties of various MW fractions. This study has coupled SEC with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon, and dissolved organic nitrogen of different MW fractions. The detection limits for the organic carbon and nitrogen detectors were 0.20 μg C L^-1 and 0.14 μg N L^-1, respectively. Furthermore, we gave an interpretation of the nature and evolution of DOM in surface water based on the comparison and analyses of the combined chromatogram obtained from multiple detectors. Fractions assigned as hydrophobic humic-like substances, hydrophilic humic-like substances, low-MW microbial extracellular metabolites and low-MW hydrophobic protein-like substances were first established in this study and attributed to the presence of a fluorescence detector. We believe that the developed method provides in-depth knowledge of the structure and composition of DOM and could be used as a potential analytical tool in environmental organic chemistry, humus chemistry and supramolecular chemistry.