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To overcome the problems of high excess sludge yield and poor nitrogen removal efficiency in traditional biological treatment processes, a multi‐stage A/O biofilm reactor was developed by combining the multi‐stage A/O process with novel floating spherical carriers, resulting in repeated coupling of anoxic and aerobic environments. Results showed that the system achieved COD, NH4+-N, and TN removal efficiencies of 93.8%, 84.5%, and 75.7%, respectively, with average effluent concentrations lower than: 29.8 COD mg/L, 4.3 NH4+-N mg/L, and 13.2 TN mg/L. The observed sludge yield was 0.139 g MLSS/g COD, which was lower than that of the conventional activated sludge process. Microbial analysis showed that the community structure and cell morphology of microorganisms changed greatly with alternating aerobic–anoxic condition; high‐throughput sequencing results proved that functional microorganisms can be enriched on the surface of the carries and therefore improved the nitrogen removal efficiency and meanwhile minimize the sludge yield within the system. Practitioner points: The research innovatively developed a novel floating spherical carrier and coupled it with multi‐stage A/O process.The complex redox environments inside the floating spherical carriers improves the nitrogen removal efficiency and the sludge reduction effect.Nitrospirae, Hydrogenophaga promoted the nitrogen removal, Firmicutes, Bacteroidetes and Dechloromonas promoted the in‐situ sludge reduction of the system. [ABSTRACT FROM AUTHOR]

As a green advanced process for drinking water treatment, the UV/hydrogen peroxide (UV/H2O2) process has been gradually applied in China. To study the effect and mechanism of organic matter removal and the development of microbial communities in the UV/H2O2-biological activated carbon (UV/H2O2-BAC) process, a pilot-scale UV/H2O2-BAC system was built and operated over one year. Low water temperature affects the UV/H2O2 process efficiency, the biofilms in the BAC system were mature and stable after 240 days, and the contribution rate of BAC adsorption to dissolved organic carbon (DOC) removal was approximately 14.2% after one year of operation. The liquid chromatography-organic carbon detection (LC-OCD) analysis shows that UV/H2O2 process can increase the amounts of Low Molecular Weight (LMW) neutrals, and the specific UV absorbance (SUVA254) value is not suitable for predicting Trihalomethanes (THMs) precursor contents in water after UV/H2O2 treatment. High-throughput sequencing results prove that microbial species in the middle section are the most abundant compared to those in the influent and effluent sections, hydrogen peroxide has lower inhibition on the development of microbial community than ozone and the low concentration of hydrogen peroxide (<0.25 mg/L) promotes the development of the microbial communities, hydrogen peroxide can reduce Proteobacteria abundance by inhibiting the growth of anaerobes. Acidobacteria may have a certain contribution to the degradation of soil organic matter (SOM), and the effluent section of BAC with low DOC concentration cannot form the dominant species of Rhodobacter. [ABSTRACT FROM AUTHOR]

Identification and characterization of disinfection by-product (DBP) precursors could help optimize drinking water treatment processes and improve the quality of finished water. This study comprehensively investigated the characteristics of dissolved organic matter (DOM), the hydrophilicity and molecule weight (MW) of DBP precursor and DBP-associated toxicity along the typical full-scale treatment processes. The results showed that dissolved organic carbon and dissolved organic nitrogen content, the fluorescence intensity and the SUVA 254 value in raw water significantly decreased after the whole treatment processes. Conventional treatment processes were in favor of the removal of high-MW and hydrophobic DOM, which are important precursors of trihalomethane and haloacetic acid. Compared with conventional treatment processes, Ozone integrated with biological activated carbon (O 3 -BAC) processes enhanced the removal efficiencies of DOM with different MW and hydrophobic fractions, leading to a further decrease in almost all DBP formation potential and DBP-associated toxicity. However, almost 50% of the detected DBP precursors in raw water has not been removed after the coagulation-sedimentation-filtration integrated with O 3 -BAC advanced treatment processes. These remaining precursors were found to be mainly hydrophilic and low-MW (< 1.0 kDa) organics. Moreover, they would largely contribute to the formation of haloacetaldehydes and haloacetonitriles, which dominated the calculated cytotoxicity. Since current drinking water treatment process could not effectively control the highly toxic DBPs, the removal of hydrophilic and low-MW organics in drinking water treatment plants should be focused on in the future., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H 2 O 2 /O 3 was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H 2 O 2 /O 3 is higher than by UV/H 2 O 2 or UV/O 3 which can reach 95% at the UV dose of 400 mJ/cm 2 . An alkaline environment reduces the oxidation efficiency of UV/H 2 O 2 /O 3 technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO 3 - , SO 4 2- , Cl - and NO 3 - are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H 2 O 2 /O 3 is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H 2 O 2 /O 3 was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled “Using UV/H(2)O(2)/O(3) technology to control N-nitrosodimethylamine precursor release from AOM: formation characteristics, water matrix effects and degradation pathway”., (Copyright © 2021. Published by Elsevier B.V.)