The Direct Blue 71 (DB71) dye can pose risks to the life of aquatic flora, fauna, and human beings, owing to its toxic, carcinogenic, and mutagenic nature. Hence, this study fabricated and applied acid-activated shrimp shell-derived hydrochar (A-WSH) for the adsorptive removal of anionic DB71 from aqueous solutions. The effects of adsorption conditions on DB71 sequestration by A-WSH were evaluated. Characterization and modeling methods were utilized to elucidate the DB71 adsorption behaviors and mechanisms of A-WSH. Results showed that DB71 adsorption by A-WSH was optimized at pH 6.78, contact time of 4 h, adsorbent dose of 1 g/L, room temperature of 300 K, and shaking speed of 120 rpm. The isotherm data were best described by the Langmuir model with the DB71 maximum adsorption capacity of 156.25 mg/g. The kinetic data were more satisfactorily represented by Pseudo-second-order model than the Pseudo-first-order model. Thermodynamic and characterization results revealed that DB71 adsorption by A-WSH was endothermic and chemisorption. The A-WSH can be a promising DB71 adsorbent, thanks to high adsorption capacity, short equilibrium time, and no pH adjustment requirement. This study has opened up a novel pathway for the valorization of shrimp shells and remediation of DB71-contaminated aqueous solutions.

Cyanobacterial blooms often cause water treatment disturbance problems such as unfavorable odor and taste in tap water and leakage from filter beds. It has been pointed out that blooming cyanobacteria are less susceptible to photoinhibition due to their buoyant nature, which may give them an advantage in light competition against non-buoyant phytoplankton in turbid environments. However, such indications are based on field observations, and there is no study that have demonstrated the superiority of blooming cyanobacteria in turbid environments through culture experiments. In this study, we conducted static mixed cultures of a buoyant cyanobacterium, Microcystis wesenbergii, and a non-buoyant phytoplankton, Staurastrum dorsidentiferum, isolated from Lake Biwa and evaluated the effect of turbidity on the dominance of M. wesenbergii. Although M. wesenbergii was inhibited by turbidity of 100 kaolin turbidity unit (inhibition rate: 47–49%), the inhibition rate was lower than that of S. dorsidentiferum (inhibition rate: 77%). Moreover, the mixed culture did not inhibit the growth of M. wesenbergii. On the other hand, S. dorsidentiferum was significantly inhibited by mixed culture (inhibition rate: 78%). Thus, experimental results demonstrated that M. wesenbergii is more likely to dominate over non-buoyant phytoplankton due to the shading effects of turbidity and surface accumulation.

Improper treatment of antibiotics in wastewater has led to the spread of antimicrobial resistance. One of the solutions to this global problem is the Bio-Fenton reaction, which is effective in removing antibiotics. To stimulate Bio-Fenton reaction, magnetite fine particles are employed in the advanced activated sludge process. While combining the activated sludge process with membrane filtration can be more efficient, membrane bioreactors (MBRs) require frequent cleaning to prevent membrane fouling, inducing chemical and energy costs. To address this issue, a magnetic filter to capture activated sludge flocs with the magnetic particles was equipped near the MF (microfiltration) membrane surface to mitigate membrane fouling. The objective of this study is to assess the effectiveness of the magnetic filter in a lab-scale advanced Bio-Fenton MBR system. Transmembrane pressure (TMP) was measured as an indicator of the fouling extent, and the effect of the magnetic filter was evaluated by examining TMP change, supported by SEM (Scanning electron microscopy) analysis of foulant composition. Results showed lower TMPs and less Fe composition in the foulants with magnetic filter across various conditions. From the results, we concluded that the magnetic filter was effective for alleviating membrane fouling in the advanced Bio-Fenton MBR system.

Taste and odor are common problems in water supplies worldwide. While many treatments have been applied, biological drinking water treatment has attracted attention for removing 2-methylisoborneol (MIB). However, the potential mechanism of MIB removal via biological drinking water treatment has not yet been characterized. This study aimed to determine the MIB removal potential of biological active carbon (BAC) using a laboratory-scale one-path column assay system. Sodium azide was used to discriminate between adsorption removal and biodegradation of BAC. Volumetric removal potential of BAC collected from a pilot-scale up-flow biological filter placed before coagulation/sedimentation (BAC-UF, n = 2) showed 5.8–7.2 mg MIB/m³ BAC/h, while that of BAC collected from a full-scale BAC filter placed after ozone oxidation (BAC-OZ, n = 1) was 2.2 mg MIB/m³ BAC/h. Biodegradation accounted for 23% of the volumetric removal rate of BAC-UF, whereas almost 100% of the removal was attributed to adsorption for BAC-OZ. Although the copy numbers of prokaryotic 16S rRNA genes of BAC-UF and BAC-OZ were similar, the 16S rRNA copy numbers of BAC-UF (1.6 × 10¹¹–1.1 × 10¹² copies/g dry BAC) were higher than those of BAC-OZ (2.7 × 10¹⁰ copies/g dry BAC). The abundance of active microbes may be related to differences in the biological removal potential.

The chemical forms of iron significantly influence the dynamics of nutrients and biological productivity in the water environment. The most common oxidized form of iron, Fe(III), forms insoluble compounds such as goethite (α-FeOOH) in its oxidized state. Especially, Fe(III) compounds readily adsorb phosphate ions, effectively preventing phosphorus from dissolving into the water. Conversely, in a reductive environment, the reduction of Fe(III) to Fe(II) can release previously adsorbed phosphorus. These interactions are considered crucial for proper water quality management and environmental conservation, with a focus on the chemical forms of iron. In this study, highly sensitive methods for analyzing the chemical forms of iron using X-ray absorption fine structure (XAFS) measurements were developed. Four pretreatment methods were evaluated, and anaerobic drying was found to most effectively preserve the reduced iron state. Pattern fitting techniques were applied to sediment samples, and it was shown that the method could accurately describe the iron forms in these samples. These findings are considered to contribute to the understanding of iron’s role in nutrient cycling and its broader impact on water environments.