Disease outbreaks attributed to monsoon flood-induced pathogen exposure are frequently reported, especially in developing cities with poor sanitation. Contamination levels have been monitored in past studies, yet the sources, routes, and extents of contamination are not always clear. We evaluated pollution from municipal wastewater (MWW) discharge and investigated fecal contamination by Escherichia coli (E. coli) in three agricultural fields on the outskirts of Hue City, Vietnam. After E. coli concentration was determined in irrigation water (IRW), MWW, soil, vegetables (VEG), and manure, its dispersion from MWW was tracked using multilocus sequence typing (MLST) and phylogenetic analyses during the wet and dry seasons. IRW was severely contaminated; 94% of the samples were positive with E. coli exceeding the stipulated standards, while VEG contamination was very low in both seasons. The confirmed total number of isolates was comparable between the seasons; however, results from MLST and phylogenetic clustering revealed more links between the sites and samples to MWW during the wet season. The wet season had four mixed clusters of E. coli isolates from multiple locations and samples linked to MWW, while only one mixed cluster also linking MWW to IRW was observed during the dry season. The most prevalent sequence type (ST) complex 10 and two others (40 and 155) have been associated with disease outbreaks, while other STs have links to major pathotypes. Irrigation canals are significant routes for E. coli dispersion through direct links to the urban drainage-infested river. This study clarified the genotype of E. coli in Hue city, and the numerous links between the samples and sites revealed MWW discharge as the source of E. coli contamination that was enhanced by flooding.

Soil dispersion induces soil erosion and colloidal leaching. Nutrients are lost at the same time and this causes water contamination. Phosphate is an essential element for living organisms. Because phosphate influences soil dispersion and it is an important limited resource, this influence must be evaluated well in order to diminish negative effects on soil structure. In this paper, we firstly evaluated the influence of phosphate sorption on soil dispersion by calculating repulsive potential energy between soil particles. Ferralsol, which is a typical soil in rainy tropical regions, was used as the material. The dispersion-flocculation phenomena were investigated with absorbance of soil suspension under different pH, phosphate adsorption and electrolyte concentration in an Na-NO₃-PO₄ system. The repulsive potential energy was calculated based on the diffuse double layer theory and the measured zeta potential. We indicated that the measured absorbance increased with the increase of the repulsive potential energy. The repulsive potential energy increased with increasing phosphate sorption up to about 5 to 20 mmol kg⁻¹ at all pH, and it induced the soil dispersion, because phosphate sorption increased the negative charge of the soil. After its peak, it decreased with increasing phosphate sorption because the electrolyte concentration increased and the electrolyte screened the electric field near the soil surface. The repulsive potential energy also increased with increasing pH because of the increase of the negative charge of the soil. Even at low pH, after a certain amount of phosphate sorption, the soil dispersed due to the increase of repulsive potential energy, although the soil flocculated before phosphate application. Because the soil dispersion causes soil and phosphorus loss, the influence of soil pH and phosphate sorption on the soil dispersion should be considered for good soil management.

Odor problems in treated municipal wastewater are a concern, yet the sources and formation dynamics of these compounds within sewerage systems remain unclear. 2,4,6-trichloroanisole (2,4,6-TCA) is a key odorant in the effluents of municipal wastewater treatment plants (WWTPs). This study investigates the formation of 2,4,6-TCA through the conversion of its precursor, 2,4,6-trichlorophenol (2,4,6-TCP). The concentrations of both compounds were quantified across a step-feed anaerobic-anoxic-oxic (A₂O) process over multiple seasons. Effluent concentrations of 2,4,6-TCA consistently exceeded its odor threshold. Inverse correlations between 2,4,6-TCP and 2,4,6-TCA concentrations within the aerobic zones supported the biological transformation. In the anaerobic zones, 2,4,6-TCA also increased only during winter, suggesting a seasonal contribution to elevated 2,4,6-TCA concentrations in effluent during this time. Amplicon sequencing of the activated sludge samples revealed the presence of the bacterial and fungal genera previously associated with methylation of 2,4,6-TCP. Additionally, wastewater samples were collected from multiple WWTPs and pump stations to determine the source of 2,4,6-TCP within the sewerage system. Wastewater from commercial areas exhibited higher 2,4,6-TCP concentrations compared to that from residential areas, suggesting greater contributions from commercial sources. Furthermore, batch experiments suggested that reactions between chlorine and phenolic compounds in wastewater contribute to 2,4,6-TCP formation. These findings highlight the importance of source control of phenolic compounds and chlorine, as well as operational optimization, such as dynamic aeration, to mitigate 2,4,6-TCA formation in wastewater treatment systems.

Reclaimed wastewater (RWW) has been used globally for centuries, though its application in aquaculture is less extensive. Limited study has addressed impacts of RWW-derived volatile odour compounds (VOCs), such as 2,4,6-trichloroanisole (TCA), 2-methylisoborneol (MIB), and geosmin (GSM), on fish quality. This study aims to (1) assess the feasibility of reusing secondary effluent from a municipal wastewater treatment plant (WWTP) for Plecoglossus altivelis aquaculture in a land-based flow-through system and (2) evaluate the sensory effects of selected VOCs on fish quality. Results showed that increased temperature and ammonia levels in summer RWW negatively affected fish growth, while autumn RWW did not. Heavy metals in fish did not cause health issues. TCA, MIB, and GSM concentrations in fish tissues were 4.7–5.7, 0.3–40.5, and 1.1–1.9 mg kg−1, respectively. TCA emerged as the most concerning odorant, with higher relative odour intensity than MIB and GSM in RWW-cultured fish, regardless of seasonal change. This study is the first to report on a self-constructed aquaculture system using RWW at a WWTP, recommending effective VOC and ammonia removal for sustainable RWW use in aquaculture. Additionally, the study highlighted TCA's impact as an anthropogenic indicator in aquatic environments amid increasing WWTP prevalence in developed cities.