Application of photocatalysts is among the most promising methods to eliminate organic pollutants in wastewater. A photocatalytic reaction, which involves the generation of reactive radicals from the reaction on the photocatalyst’s surface and their interaction with organic molecules, can degrade organic pollutants. Titanium dioxide (TiO₂) is a well-known photocatalyst because it has low toxicity and cost including high chemical stability. However, it cannot be efficiently activated in water because of the difficulty in adsorbing ultraviolet light. In this work, a floating photocatalyst was prepared by combining TiO₂, Ni-P plating, and a polypropylene (PP) hollow ball substrate. An Ni-P coating was electrolessly deposited on the PP hollow ball in the presence of TiO₂. The prepared photocatalyst was characterized using X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The PP hollow ball substrate was sufficiently covered with the Ni-P coating and Ti was confirmed to be contained in the Ni-P coating. The obtained specimen floated when placed in aqueous solutions and its photocatalytic activity was confirmed through degradation of methylene blue. In addition, the Ni-P plating was found to protect PP from degrading by photocatalytic activity of the TiO₂.

The seawater exchange is closely related to the spreading of pollutant and the water quality in coastal seas. The Seto Inland Sea is a semi-enclosed coastal sea which has a series of broad basins and narrow straits, and the along-channel outflows from the strait located at the center of the channel toward east and west may play an important role in seawater exchange. In this study, flows along the boundary between Bisan Seto which is located at the center of the Seto Inland Sea and the adjacent basin called Harima Nada were measured using a ship-mounted Acoustic Doppler Current Profiler and residual flows were obtained by removing tidal currents. The survey results showed significant volume flux of the along-channel outflows from Bisan Seto toward Harima Nada. A numerical model based on Princeton Ocean Model was also used in order to analyze the driving forces of the along-channel outflow. The outflow was well reproduced using the model which was driven by tide and horizontal density gradient between the strait and basin, suggesting that these possibly induce the seawater exchange in the Seto Inland Sea.

Environmental DNA (eDNA) is a non-invasive and less labor-intensive tool for biological survey. The advantages enable more frequent sampling work, but there is a lack of fundamental field data on the variation of eDNA in sediment in different timescales. We conducted a yearlong sampling at two marine parks of Tokyo Bay (Odaiba Marine Park and Kasai Marine Park) to investigate the temporal variation of sediment eDNA at scales of one year, one month and one tidal period. Grandidierella japonica, an indicator benthic species of water quality in Japan and also an invasive species in other countries, was chosen as target species. In yearlong scales, the total eDNA content and the copy number of the amphipod eDNA in both parks showed a seasonal variation pattern as low in cold season (89 ± 14 ng DNA/g sediment, 583 ± 64 copies/g sediment) and high in warm season (884 ± 97 ng DNA/g sediment, 9,501 ± 3,553 copies/g sediment). In scales shorter than one month, eDNA kept stable and did not show clear variation. The results indicated that eDNA in sediment is useful for biological survey by reflecting the well-averaged state of the species abundance in the environment and not showing the erroneous sudden variation in a short timescale.

In order to establish infrastructure relating to domestic wastewater collection and treatment according to the Sewerage Master Plan, Ho Chi Minh City, Vietnam, is in need of large capital investment. The increase in contribution from users is one of the prerequisites for ensuring financial sustainability; however, it is essential to investigate and understand the users’ preferences and willingness-to-pay (WTP). The study aims to investigate factors affecting respondent’s WTP a premium for improved wastewater services in Ho Chi Minh City. Double-bounded questions for the contingent valuation method were used for analysis, based on the interview data collected randomly from 431 households in 2017. The study, which applied Logit model, found, in regression results, that bid level, a respondent opinion of 10% of environmental protection fee for wastewater that is currently applied, respondent knowledge on operated wastewater treatment plants in city, prior information on the plans of wastewater treatment plants, marital status, and first and second choice variables were associated with respondents’ WTP for the improved sewerage services. However, according to the single-bounded model, water payment, gender, household income, and house ownership played a role in households’ WTP.

In this study, various pretreatments were applied to spent mushroom substrate (SMS) for the methane gas production by anaerobic digestion. Hydrothermal treatment, acid treatment using H₂SO₄, and alkali treatment using NaOH or KOH were applied and evaluated as pretreatment of SMS before anaerobic digestion. The methane gas produced was 119.1 mL/g-dry weight (D.W.) with untreated SMS, 55.5 mL/g-D.W. with hydrothermal treated SMS, 22.5 mL /g-D.W. with acid treated SMS, and 219.1 mL/g-D.W. with alkali treated SMS. These results demonstrated that the alkali treatment showed the largest amount of methane gas production between these pretreatments of SMS. Alkali treatment combined with heating did not show significantly affect the amount of methane gas production. Also, there was no significant difference in the amount of methane gas production between NaOH treatment and KOH treatment. These results indicated that optimum pretreatment for the methane gas production of SMS is alkaline treatment. It was also suggested that the no necessary for heat pretreatment of SMS and alkaline treatment such as KOH is most effective method of SMS pretreatment for the methane gas production by anaerobic digestion.

The physicochemical analysis of surface water of Mooi and Vaal rivers network indicated that the concentration of iron was far above the required limit by the South Africa water regulation. In this study, brewing waste was used as biosorbent for the removal of iron from synthetic solution to develop strategies for remediation of Mooi and Vaal rivers network pollution. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), were used for the characterisation of the sorbent. BET was calculated using nitrogen and carbon dioxide adsorption data. Batch tests were conducted to evaluate the influence of sorbent concentration and pre-treatment on the iron removal. The brewing waste showed a removal percentage of 93% with residual iron concentration of 2.6 mg L⁻¹ while the acid pre-treated brewing waste indicated 98% removal and 0.6 mg L⁻¹ residual iron concentration. The adsorption equilibrium, based on correlation coefficients, was best described by Dubinin-Radushkevich and Langmuir, for raw and acid pre-treated brewing waste, respectively. The kinetic data were best described by pseudo-first-order with correlation coefficients (R²) of 0.9898 and 0.9968 for both raw and acid pre-treated brewing waste, respectively. The mass transfer coefficient indicates the intraparticle diffusion controls the rate of sorption of iron in this study.

16S rRNA gene copy numbers and bacterial counts in the permeate from different microfiltration membranes installed in membrane bioreactors (MBRs) were measured in order to provide information on the selection of suitable membrane for wastewater reclamation and reuse. 16S rRNA gene copy numbers in the MBR effluent (10⁵ − 10⁷ gene copies / mL) were 1/5 to 1/500 of those in the centrifugal supernatant of the mixed liquor. High bacterial counts and high gene copies were observed in the permeate of the membranes at the beginning of the filtration stage. The permeate contained bacteria without exceptions by using a 0.4 µm or larger pore size membrane, although the passage of bacteria was sporadic by the use of a membrane with cylindrical pores of 0.2 µm diameter. Acinetobacter junii and Microbacterium fluvii were identified in the permeate of the 0.2 µm pore size membrane based on the closest match of 16S rRNA gene sequence. The possibility of selective passage of small size bacteria in the mixed liquor of activated sludge through the membrane was suggested.