Microplastics in the sediments of small-scale Japanese rivers: Abundance and distribution, characterization, sources-to-sink, and ecological risks.

Microplastic pollution in small-scale river sediments remains mostly unknown. This study explored microplastics in the sediments of four small-scale Japanese rivers in Yamaguchi Prefecture: the Awano, Ayaragi, Asa, and Majime. Sediment samples (n = 23) were collected from the selected stations. Density separation and wet peroxidation methods were applied to extract microplastics. Polymers were detected through attenuated total reflectance-Fourier transform infrared spectroscopy. Microplastic abundance indicated relatively moderate values in the small-scale Japanese rivers compared to other rivers around the world. Large microplastics (1-5 mm) in size, fragments in shape, and high-density particles of diverse polymers dominated. Polyvinyl chloride, polyethylene, and polypropylene were the major polymers. The polymers-polyvinyl chloride, polymethylmethacrylate, polyurethane, fluorinated ethylene propylene, and polybutylene in sediments were distinct from those detected in surface water, as were the predominance of large-size (1-5 mm) and fragment-shape microplastics. In contrast to surface water, sediments preserved both common and distinctive microplastics. Thus, the riverine sediment compartment acted as microplastic sink. Scanning electron microscopic (SEM) analysis suggested the presence of weathered microplastics in sediments. Energy dispersive X-ray spectroscopic analysis (EDX) revealed metal contaminants on the microplastic surfaces, indicating synergistic hazard potentials in the riverine ecosystems. Ecological risk assessment results suggested low to very high risks of microplastic pollution for the rivers. The higher abundances of microplastics and highly toxic polymers contributed to the elevated ecological risks. Polyvinyl chloride, acrylonitrile butadiene styrene, polyurethane, and polymethylmethacrylate were the detected highly toxic polymers. The urban and residential areas affected stations ranked high to very high ecological risks. The sites posing very high ecological risks were regarded as pollution hotspots. Overall, this study developed new insights into microplastic pollution in the small-scale rivers and ecological risks for riverine environments, as well as providing a baseline for more comprehensive risk assessments and developing pollution control and management strategies.

Assessing small-scale freshwater microplastics pollution, land-use, source-to-sink conduits, and pollution risks: Perspectives from Japanese rivers polluted with microplastics.

Rivers are vital for understanding freshwater microplastics pollution, along with the conduits from land-sources to marine-sinks. In this study, we investigated microplastics in the small-scale Awano and Ayaragi rivers, which flow into the Sea of Japan (SJ), and the Asa and Majime rivers, which flow into the Seto Inland Sea (SIS) in Yamaguchi Prefecture, Japan. Surface water samples were collected from 29 stations. Filtration, wet peroxidation, and density separation methods were employed to extract microplastics. Polymers were identified via attenuated total reflectance-Fourier transform infrared spectroscopy. Microplastics abundances and comparisons among different rivers revealed that these small-scale rivers were highly polluted than others around the world. Characterization demonstrated that small microplastics (<1000 µm) in size, fibers and fragments in shape and the polymers-polyethylene, polypropylene, vinylon, polyethylene terephthalate, and polystyrene were dominant. These small-scale rivers emitted substantially higher quantities of Japan land-sourced microplastics (0.4-154.27 billions/day and 0.01-17.55 tons/day) into the SJ and SIS environments than larger rivers in other countries compared to basin areas. The pollution load index indicated that all the river stations were polluted with microplastics. An assessment of the polymeric and pollution risks revealed variably low to high risks. The higher were the abundances of microplastics and toxic polymers, the higher were the pollution level and risks. The sites at high risk of pollution were regarded as hotspots. Both point and non-point land-uses sources of pollution could release microplastics into the river freshwater environments, affected posing high risks and hotspots. Moreover, the pollution characteristics (shapes-sizes-polymers) indicated serious ecotoxicological threats to these rivers and their downstream environments. This study provided new insights into river microplastics pollution and revealed small-scale rivers to be prominent source-to-sink microplastics conduits. Risk assessments provided a baseline for future comprehensive assessments and developing practical approaches to wards setting water quality criteria, pollution control and management.

Fish habitat evaluation based on width-to-depth ratio and eco-environmental diversity index in small rivers.

We estimated the performance of river fish habitat evaluation using width-to-depth ratio (WDR) in comparison with eco-environmental diversity (EED) to propose an inexpensive and easy-to-use habitat evaluation procedure, which is applicable to small river construction works. WDR calculation costs less than that of EED. For verification, 25 stations in eight rivers were selected and fish were captured using electrofishing. pH, electrical conductivity, turbidity, dissolved oxygen (DO), water temperature, fraction of forest, farmland, and residential area in each basin were measured to examine possible influence of water quality. Results show that there is no major water quality issue in the target rivers. Although fish habitat is classified as good when WDR is higher than 6, it cannot be evaluated by WDR when it is lower than 6. EED has positive relationship with fish habitat for any WDR value. Thus, if a river geometry design in a river work results in WDR higher than 6, no measures need to be taken regarding fish habitat condition; however, if it is less than 6, it is necessary to examine whether the construction work lowers the EED or not.

Influence of water-film-forming-unit on the enhanced removal of carbon dioxide from mixed gas using water absorption apparatus.

This research uses tap water to absorb carbon dioxide from mixed gas (N2 and CO2) in an absorption apparatus coupled with a water-film-forming-unit (WFFU). The objective is to assess the benefits of using a WFFU to enhance CO2 removal efficiency at low pressure conditions. Based on our results, the WFFU significantly improves CO2 capture at 0.30 MPa in a water absorption system with two WFFUs. The CO2 removal efficiency was 20% greater than for systems without WFFUs. Moreover, statistical data attained by the Taguchi analysis method showed that the number of WFFUs used in the absorption system has the greatest influence on CO2 removal efficiency (contribution percentage = 50.65%) compared to gas pressure, initial CO2 concentration, gas-to-liquid ratio, and liquid temperature. We also thoroughly investigated the effects of these factors on CO2 removal performance. The optimum conditions for CO2 removal efficiency in a system equipped with two WFFUs are low temperature, low gas-to-liquid ratio, low gas pressure (0.25-0.30 MPa), and high inlet CO2 concentration. These findings could provide an effective method for capturing CO2 from exhaust gases, and thus help mitigate global warming.

Response surface method for modeling the removal of carbon dioxide from a simulated gas using water absorption enhanced with a liquid-film-forming device.

This paper presents the results from using a physical absorption process to absorb gaseous CO2 mixed with N2 using water by producing tiny bubbles via a liquid-film-forming device (LFFD) that improves the solubility of CO2 in water. The influence of various parameters-pressure, initial CO2 concentration, gas-to-liquid ratios, and temperature-on the CO2 removal efficiency and its absorption rate in water were investigated and estimated thoroughly by statistical polynomial models obtained by the utilization of the response surface method (RSM) with a central composite design (CCD). Based on the analysis, a high efficiency of CO2 capture can be reached in conditions such as low pressure, high CO2 concentration at the inlet, low gas/liquid ratio, and low temperature. For instance, the highest removal efficiency in the RSM-CCD experimental matrix of nearly 80% occurred for run number 20, which was conducted at 0.30MPa, CO2 concentration of 35%, gas/liquid ratio of 0.71, and temperature of 15°C. Furthermore, the coefficients of determination, R2, were 0.996 for the removal rate and 0.982 for the absorption rate, implying that the predicted values computed by the constructed models correlate strongly and fit well with the experimental values. The results obtained provide essential information for implementing this method properly and effectively and contribute a promising approach to the problem of CO2 capture in air pollution treatment.

Synergistic effect of pressurized carbon dioxide and sodium hypochlorite on the inactivation of Enterococcus sp. in seawater.

This study investigated the effect of combined treatments using pressurized carbon dioxide (PCD) and sodium hypochlorite (NaOCl) on the inactivation of Enterococcus sp. in artificial seawater. Bacterial inactivation was conducted in a liquid-film-forming apparatus with various pressure conditions, CO2 supply rates, and chlorine dosages. Combined PCD/chlorine treatments resulted in greater disinfection efficiency than those for the two individual treatments. Synergy values were correlated with pressure and CO2 concentrations (p < 0.001). Combination of 0.9 MPa PCD (various CO2 supply rates: 25% CO2 + 75% N2, 50% CO2 + 50% N2, and 100% CO2) and chlorine (0.20 mg L-1) yielded average synergy values of 4.9, 5.2, and 4.4 log, respectively, within 3 min. Combined treatment with PCD (100% CO2, 0.3 MPa, and 20 °C) and chlorine (0.20-0.22 mg L-1) achieved an average synergy value of 4.6 log and complete inactivation (5.2-5.5 log reductions) of Enterococcus sp. within 4 min. In contrast, when the two individual treatments (PCD and chlorine) were used, only 3.7 and 1.8-2.3 log reductions, respectively, were achieved after 25 min. These findings suggest that the combined PCD/chlorine treatment has synergistic benefits and provides a promising method for the disinfection of ballast water.

Effects of pressure and pressure cycling on disinfection of Enterococcus sp. in seawater using pressurized carbon dioxide with different content rates.

Interest is growing in a disinfection technique for water treatment without disinfection byproducts. This study presents the result of using a liquid-film-forming apparatus at less than 1.0 MPa for disinfection of seawater. The sensitivity of Enterococcus sp. (ATCC 202155) to the pressurized carbon dioxide (CO2) was examined under various conditions of pressure cycling, pressure, working volume ratio (WVR), and CO2 content rate. The key influences on frequency and magnitude of pressure cycling in enhancing Enterococcus sp. inactivation are elucidated. The results reveal strong correlation between pressure cycling and inactivation efficiency (P-value < 0.001). The outcome of linear regression model analysis suggests that the model can explain 93%, 85%, and 89% of the inactivation efficiency of (25% CO2 + 75% N2), (50% CO2 + 50% N2), and 100% CO2, respectively. The predicted value was fit with experimental results (p-value <0.05). Under identical treatment conditions (pressure = 0.9 MPa, ΔP = 0.14 MPa, 70% WVR, and 20 ± 1°C), treatment with pressurized CO2 (100% purity) resulted in complete inactivation 5.2 log of Enterococcus sp. after 70 cycles within 20 min. The Enterococcus sp. inactivation of pressurized CO2 followed first-order reaction kinetics. The smallest D-value (largest k-value) was induced by pressurized CO2 (100% purity) at 0.9 MPa, which was obtained at 3.85 min (0.5988 min(-1), R(2) ≥ 0.95). The findings could provide an effective method for enhanced bactericidal performance of pressurized CO2, to address recently emerging problems in water disinfection.

Potential bioremediation of mercury-contaminated substrate using filamentous fungi isolated from forest soil.

The use of filamentous fungi in bioremediation of heavy metal contamination has been developed recently. This research aims to observe the capability of filamentous fungi isolated from forest soil for bioremediation of mercury contamination in a substrate. Six fungal strains were selected based on their capability to grow in 25 mg/L Hg(2+)-contaminated potato dextrose agar plates. Fungal strain KRP1 showed the highest ratio of growth diameter, 0.831, thus was chosen for further observation. Identification based on colony and cell morphology carried out by 18S rRNA analysis gave a 98% match to Aspergillus flavus strain KRP1. The fungal characteristics in mercury(II) contamination such as range of optimum pH, optimum temperature and tolerance level were 5.5-7 and 25-35°C and 100 mg/L respectively. The concentration of mercury in the media affected fungal growth during lag phases. The capability of the fungal strain to remove the mercury(II) contaminant was evaluated in 100 mL sterile 10 mg/L Hg(2+)-contaminated potato dextrose broth media in 250 mL Erlenmeyer flasks inoculated with 10(8) spore/mL fungal spore suspension and incubation at 30°C for 7 days. The mercury(II) utilization was observed for flasks shaken in a 130 r/min orbital shaker (shaken) and non-shaken flasks (static) treatments. Flasks containing contaminated media with no fungal spores were also provided as control. All treatments were done in triplicate. The strain was able to remove 97.50% and 98.73% mercury from shaken and static systems respectively. A. flavus strain KRP1 seems to have potential use in bioremediation of aqueous substrates containing mercury(II) through a biosorption mechanism.

Inactivation effect of pressurized carbon dioxide on bacteriophage Qß and ΦX174 as a novel disinfectant for water treatment.

The inactivation effects of pressurized CO2 against bacteriophage Qß and ΦX174 were investigated under the pressure of 0.3-0.9 MPa, initial concentration of 10(7)-10(9) PFU/mL, and temperature of 17.8°C-27.2°C. The optimum conditions were found to be 0.7 MPa and an exposure time of 25 min. Under identical treatment conditions, a greater than 3.3-log reduction in bacteriophage Qß was achieved by CO2, while a nearly 3.0 log reduction was observed for phage ΦX174. The viricidal effects of N2O (an inactivation gas with similar characteristics to CO2), normal acid (HCl), and CO2 treatment with phosphate buffered saline affirmed the chemical nature of CO2 treatment. The pumping cycle, depressurization rate, and release of intracellular substances caused by CO2 were its viricidal mechanisms. The results indicate that CO2 has the potential for use as a disinfectant without forming disinfection by-products.

Delignification of disposable wooden chopsticks waste for fermentative hydrogen production by an enriched culture from a hot spring.

Hydrogen (H2) production from lignocellulosic materials may be enhanced by removing lignin and increasing the porosity of the material prior to enzymatic hydrolysis. Alkaline pretreatment conditions, used to delignify disposable wooden chopsticks (DWC) waste, were investigated. The effects of NaOH concentration, temperature and retention time were examined and it was found that retention time had no effect on lignin removal or carbohydrate released in enzymatic hydrolysate. The highest percentage of lignin removal (41%) was obtained with 2% NaOH at 100°C, correlated with the highest carbohydrate released (67 mg/g pretreated DWC) in the hydrolysate. An enriched culture from a hot spring was used as inoculum for fermentative H2 production, and its optimum initial pH and temperature were determined to be 7.0 and 50°C, respectively. Furthermore, enzymatic hydrolysate from pretreated DWC was successfully demonstrated as a substrate for fermentative H2 production by the enriched culture. The maximum H2 yield and production rate were achieved at 195 mL H2/g total sugars consumed and 116 mL H2/(L·day), respectively.

Effect of different carbon sources on the biological phosphorus removal by a sequencing batch reactor using pressurized pure oxygen.

The effect of different carbon source on the efficiency of enhanced biological phosphorus removal (EBPR) from synthetic wastewater with acetate and two ratios of acetate/starch as a carbon source was investigated. Three pressurized pure oxygen sequencing batch reactor (POSBR) experiments were operated. The reactors (POSBR1, POSBR2 and POSBR3) were developed and studied at different carbon source ratios of 100% acetate, 75% acetate plus 25% starch and 50% acetate plus 50% starch, respectively. The results showed that POSBR1 had a higher phosphate release-to-uptake ratio and, respectively, in a much higher phosphorus removal efficiency (93.8%) than POSBR2 (84.7%) and POSBR3 (77.3%) within 30 days of operation. This indicated that the phosphorus removal efficiency decreased the higher the starch concentration was. It was also found that POSBR1 produced more polyhydroxyalkanoates (PHAs) than the other reactors. Based on the effect of the carbon source on the PHA concentration and consumption, the conditions of POSBR1 were favourable for the growth of polyphosphate-accumulating organisms and therefore, beneficial for the biological phosphorus removal process.

Comparison of disinfection effect of pressurized gases of CO2, N2O, and N2 on Escherichia coli.

Based on the production of gas bubbles with the support of a liquid film-forming apparatus, a device inducing contact between gas and water was used to inactivate pathogens for water disinfection. In this study, the inactivation effect of CO2 against Escherichia coli was investigated and compared with the effects of N2O and N2 under the same pressure (0.3-0.9 MPa), initial concentration, and temperature. The optimum conditions were found to be 0.7 MPa and an exposure time of 25 min. Under identical treatment conditions, a greater than 5.0-log reduction in E. coli was achieved by CO2, while 3.3 log and 2.4 log reductions were observed when N2O and N2 were used, respectively. Observation under scanning electron microscopy and measurement of bacterial cell substances by UV-absorbance revealed greater cell rupture of E. coli following treatment with CO2 than when treatment was conducted using N2O, N2 and untreated water. The physical effects of the pump, acidified characteristics and the release of intracellular substances caused by CO2 were bactericidal mechanism of this process. Overall, the results of this study indicate that CO2 has the disinfection potential without undesired by-product forming.