Nowadays, antibiotic residue in the aqueous environment is a critical issue that causes serious effects on human and ecological health. While the conventional treatment approaches cannot completely remove them from wastewater, photocatalytic materials have recently emerged as a promising strategy for antibiotic removal. Among them, graphitic carbon nitride (g-C₃N₄) has received great attention due to its metal-free, non-toxic, low-cost, and environmentally friendly characteristics. However, the photocatalytic efficiency of g-C₃N₄ is limited by its high charge carrier recombination rate. In this research, a heterojunction photocatalyst of g-C₃N₄/CoMoO₄ was synthesized by a hydrothermal-calcination method. The effect of g-C₃N₄/CoMoO₄ mass ratio, hydrothermal conditions, calcination conditions, pH, pollutant, and catalyst dose on photocatalytic degradation of tetracycline was investigated. The synthesized photocatalyst was characterized by scanning electron microscopy − energy dispersive X-ray (SEM-EDX), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The results showed that the composite photocatalyst synthesized with a 6:4 mass ratio of g-C₃N₄:CoMoO₄ for 6 h of hydrothermal treatment and calcination temperature of 500°C showed the highest removal efficiency of tetracycline at pH = 7.

Drinking water stagnation in premise plumbing leads to regrowth of microorganisms, including opportunistic pathogens. Although many studies have evaluated the changes in bacterial community structure, little data are available on the impact of water stagnation on antimicrobial resistance of bacterial communities. In this study, we collected drinking water samples before and after stagnation in premise plumbing in a building. After 24 h of stagnation, an increase in total cell count was observed with a simultaneous decrease in free chlorine residual. Bacterial communities before and after stagnation were incubated with serial dilutions of individual antimicrobial agents (ampicillin, cefotaxime, streptomycin, tetracycline, erythromycin, sulfamethoxazole, chloramphenicol, and ciprofloxacin) in R2A broth for three days to evaluate the antimicrobial resistance profiles. The minimal inhibitory concentrations of the antimicrobial agents against the bacterial communities increased after water stagnation. Community structure analysis revealed that Methylobacterium and Pseudoxanthomonas were dominant in enriched cultures with most antimicrobial agents before and after water stagnation, respectively. These results demonstrate that water stagnation in premise plumbing can affect the antimicrobial resistance profiles of bacterial communities.

Brilliant green (BG), a basic dye, is toxic to lung, eye, and skin. This study examines BG biosorption from aqueous solution using soybean milk residue (okara). A series of batch tests were conducted to explore influential factors including pH, biosorbent dose, initial BG concentration, contact time, and temperature. The isotherm data were fitted with Langmuir and Freundlich models. The kinetic data of BG biosorption by okara were analyzed using pseudo-first order and pseudo-second order models. The BG removal efficiency was enhanced at a higher biosorbent dose, contact time, and temperature. Contrarily, the greater BG initial concentration resulted in a decline in BG removal efficacy. In the pH range that BG dye was stable, the highest BG removal was attained at pH 5. The maximum BG adsorption capacity of okara was 64.33 mg/g. Langmuir model (R² = 0.98) was more appropriate than Freundlich model (R² = 0.93) in describing isotherm data. Kinetic data was well fitted with Pseudo-second order model (R² = 0.99). Thermodynamic results suggest the spontaneous and endothermic nature of the GB biosorption. The use of okara as a novel BG biosorbent can help not only wastewater decontamination but also recycling of okara in a green way.

This study aimed to control the buoyancy of Microcystis by increasing the growth rate and simultaneously reducing the cellular carbohydrate content under various light and temperature regimes. Microcystis was precultured in continuous dark (0 µmol·m⁻²·s⁻¹) or light conditions (135 µmol·m⁻²·s⁻¹) for 48 hours at 30°C and 35°C. After preculture, Microcystis was cultivated in a burette to observe the difference in the buoyancy. The buoyancy was evaluated by relative buoyancy of 25% (RB₂₅), defined as the percentage of Microcystis cell number in the upper 25% layer to the total cell number in the burette. The result showed that preculture under the dark condition at 30°C had higher RB₂₅ (43.8 ± 3.5%), than under the light condition (23.8 ± 2.8%). In addition, Microcystis precultured in the dark condition at 30°C also had the lowest cellular carbohydrate (3.1 ± 0.3 pg/cell). The reduction of cell ballast would promote the buoyancy of Microcystis. These results indicate that the buoyancy of Microcystis can be controlled by reducing cellular carbohydrate using preculture under the dark condition at high temperature. Thus, artificial control to increase Microcystis buoyancy could be a useful method for removal of Microcystis blooms, especially in water purification plants.

This study reports an intriguing observation regarding the betaproteobacterium Pelomonas saccharophila MRB3 (NITE P-01647), a candidate plant growth-promoting bacterium that accelerates biomass production of the aquatic plant, duckweed. In a series of experiments in which strain MRB3 cells were inoculated into duckweed cultures, MRB3 improved duckweed growth with decreasing cell density in the culture medium. By monitoring nutrient dynamics of plants and bacteria, we found that MRB3 exhibited spontaneous cell lysis and released NH₄⁺ and PO₄^3–, which were subsequently utilized for duckweed growth. Surprisingly, the amount of NH₄⁺ released by MRB3 corresponded to approximately half of the total nitrogen contained in the inoculated cells, notwithstanding the fact that the majority of nitrogen elements in bacterial cells should be present in plant-unavailable forms, such as proteins and nucleic acids. Spontaneous cell lysis, provision of macronutrients, and duckweed growth promotion by MRB3 were robustly observed in different inoculation amounts and growth media, including natural pond water. These observations indicated the possibility of utilizing autolytic bacteria as an alternative nutrient source in hydroponic cultivation of duckweeds and other plants.

This study focuses on the inactivation of methanogens under acidic environment that may arise due to overloading of anaerobic reactors. Two types of methanogen-enriched cultures were prepared in the lab-scale reactors using acetate and formate as substrate. Each culture was subsequently incubated in a batch reactor for 6 days under different pH conditions with one of the VFAs of formate, acetate, propionate, butyrate, valerate or phosphate buffer solution. Propidium-monoazide quantitative polymerase chain reaction (PMA-qPCR) analysis and the methane production test revealed that the methanogenic archaea were highly sensitive to the acidic environment. Under the moderate pH of 6.5–7.5, no significant change in cellular decay was observed. However, at pH below 6.5 the decay rate was accelerated leading to archaea’s inactivation. At pH 5.0, the archaeal specific decay rates were elevated as high as 40 times of that at pH 7.0. When the operational pH was the same in the experiments, the cellular decay rate was comparable between the batch test with VFA and that without VFA. These observations strongly suggest that the methanogen decay is caused by low pH rather than the elevated concentrations of VFA compounds (15–40 mM of undissociated VFA) during acidic failure of anaerobic digester.

The organic matter removal performance of a channel for enhanced sewer self-purification by porous media was investigated. The effect of temperature, within a range of about 10 to 28°C, on aerobic organic matter degradation was focused on, using real domestic wastewater as influent. A channel was observed for 96 days between the months of October to December, via a mass balance approach. Mass balance analysis revealed that organic matter removal mostly occurred via oxidation and that organic matter retention inside the channel was minimal. Using the oxygen consumption rate as a measure of organic matter removal, the evaluated removal performance was between 6.4–33.4 g O₂ m⁻² d⁻¹ expressed per area of porous sponge media. Oxygen consumption rates were observed to increase with increased temperature of the porous sponge media and was not affected by fluctuations in organic loading. The results highlighted that enhanced sewer self-purification by porous media is anticipated to perform well in regions with average temperatures above 20°C.

To attain effective utilization of water in different sectors, understanding and applying the new concept of water management tools like water footprint analysis is mandatory. Hence, this study aims to estimate green and blue water footprint for selected major cereal and vegetable crops in Salale Zone. Ten year (2011–2020) climatic, crop yield, and cultivated area data were collected. Green and blue water footprints (m³/ton), average water footprint per-kilogram of each crops product (m³/kg), and their Zonal level total water footprints (m³/ton) were estimated. The results indicated that both green and blue water footprint was greater than benchmark value for each considered crops though blue water was highly utilized in the Zone for production of vegetable crops than cereal. At Zonal level, average total water footprint for the major crops was estimated to 14,417.35 m³/ton from which 86% accounts for cereal. From the comparison of average Zonal water footprint with the benchmark, the estimated values for each crop was higher than the benchmark which indicated less efficient utilization of green and blue water. Hence, for effective management and utilization of water, applying the concept of water footprint is essential to account water use in production of a given crop.