Lake Biwa had eutrophicated till the 70s, but total phosphorus and chlorophyll a concentration began to improve around 1980 due to various efforts by the government and residents. Along with the decrease in chlorophyll a concentration, Secchi depth in Lake Biwa has been improved. It is expected that the decline in chlorophyll a concentration decrease primary productivity by phytoplankton. However, the phytoplankton community in Lake Biwa has also been changed along with the oligotrophication. Therefore, the response of the productivity against the change in chlorophyll a concentration may not be linear. In this research, areal primary productivity in the northern basin of Lake Biwa was estimated using phytoplankton census data and environmental data collected by Lake Biwa Environmental Research Institute from 1980 to 2008. Surprisingly, the estimated areal productivity tended to increase over time, whereas chlorophyll a showed a reverse trend. Two influential factors were deduced: the one was the expansion of euphotic zone with the improvement of Secchi depth and the other was the shift of phytoplankton to smaller species, which had higher productivity than larger ones. The latter had a stronger effect than the former. Thus, a change in phytoplankton community should be considered for the accurate evaluation of productivity.
Aluminum salt-based coagulants are widely used for fluoride removal in the world. However, there is little information about the mechanism of fluoride removal by aluminum salt. The present study aimed to elucidate the mechanism of fluoride removal using aluminum sulfate. The coagulation mechanism is generally composed of three types, clathration by aluminum hydroxide, chemisorption and physical adsorption by the Van der Waals force. Jar tests were performed under two conditions, with or without clathration, and then the residual fluoride concentration in treated water was analyzed. If fluoride ion formed clathrates with aluminum hydroxides, a difference of fluoride concentration in treated water under two conditions would be expected. However, no significant difference was observed in the experiments. Therefore, clathration was thought to be insignificant in fluoride removal by aluminum sulfate. In addition, X-ray diffraction analysis (XRD) was applied to the precipitates obtained from the jar tests, and revealed that the precipitates were amorphous. When chemisorption occurred, the generation of crystalline precipitates was expected. Accordingly, chemisorption was also inferred to be insignificant in fluoride removal. These results suggested that physical adsorption of fluoride onto aluminum hydroxide surface was responsible for fluoride removal using aluminum sulfate.
There has been little long-term environmental monitoring for specified chemicals and information on PRTR chemicals in the water environment is necessary in order to evaluate and manage environmental risks. In this study, river water was collected at eight sites of an urban river in each season from 2010 to 2013, and environmental monitoring was performed on 359 PRTR chemicals (388 including isomers) using GC/MS and LC/MS/MS. As a result, 232 PRTR chemicals were detected. Most of the chemicals detected were for industrial use, with very low concentrations (less than 0.1 μg/L), and low detection ratios. This is the first large-scale monitoring of PRTR chemicals in Japan, and the need for and usefulness of environmental monitoring of PRTR chemicals have been confirmed.
The enrichment of nitrifying bacteria was realized and sludge yield was calculated for the batch experiment period. The influence of four kinds of antimicrobials on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was investigated using batch experiments. The specific ammonia-oxidizing activity (SAA) was 0.44 gN/gVSS/d and the specific nitrite-oxidizing activity (SNA) was 0.64 gN/gVSS/d. Below 400 mg/L antimicrobials, Cefalexin (CLX) almost has no adverse effect on nitrification and the highest inhibition caused by Sulfamethoxazole (SMX) was 15.4% and 23.9% to SAA and SNA respectively. Azithromycin (AZI) exhibited the most intense inhibitory effect. The relative activity of AOB and NOB were 39.0% and 29.8% respectively when AZI was 400 mg/L. Due to the complexation of Tetracycline (TC) with Ca2+ and Mg2+, biomass showed obvious reduction with the foam on water surface. With the addition of 400 mg/L TC, only 76.9%, 13.7% and 8.1% of sludge remained when the substrate contained calcium or magnesium ions or both of them respectively.
A biofilm is an assembly of organisms attached to a surface and this feature is utilized in biofilm reactors to retain a high biomass concentration. Biofilm detachment, which is the release of biomass to the surrounding liquid, may significantly alter the performance. It is a local phenomenon which depends on the local shear stress and biofilm morphology. An empirical expression for the effect of morphology on fluid shear stress was constructed based on: (i) deviation of local biofilm thickness from its mean, (ii) from its maximum and (iii) a reference shear stress defined from flow conditions around the biofilm. The expression was calibrated with numerical results in literature obtained from computational fluid dynamics. The expression was integrated with an individual-based model platform where the biofilm morphology was determined by simulation of particles resembling individual bacteria that grow and divide. Biofilm detachment occurred locally where the shear stress exceeded biofilm cohesiveness, after which a new morphology was generated. The model developed was especially useful for predicting the detachment of biofilm when the shear stress suddenly changes. Biofilm detachment and sloughing were more pronounced in pulse shear conditions than biofilms under a constant shear stress.
Paddy-field areas are among the major non-point sources of phosphorus (P). Drainage canals can influence P concentration in drainage water because the sediments can absorb P and have large P buffering capacity. Assessment of the P buffering capacity and management of drainage canal sediments are important to reduce P effluent loadings from paddy-field areas. In this study, we investigated three paddy-field districts around Lake Biwa. Using adsorption and incubation experiments, we clarified the P adsorption and release characteristics of the sediments. The concentrations of total sedimentary P were highest in the surface layer of the sediments. The zero-equilibrium P concentrations of the sediments, estimated from the P adsorption experiment, varied widely among sites, and were similar to the peak concentrations of P released from the incubated sediments and the mean P concentrations in the drainage water (0.021 to 0.068 mgP/L). These results suggest that the sediments determine the concentrations of P in the overlying drainage water. Adsorption isotherms for dry sediments were described by a linear model with higher slope than wet sediments, indicating that drying drainage canals might enhance the P buffering capacity of sediments.
A stone-embedded fish passage (SEF) allows fish to pass a barrier by reducing the velocity in the slope. The efficiency of SEFs has however not been evaluated well and the design parameters are not clear. The efficiency of SEFs for fish therefore needs to be evaluated and analyzed. In this research, we attempted to develop a simple equation to estimate the passability of an SEF for Ayu (Plecoglossus altivelis), which is applicable in the SEF's designing stage. We reproduced the SEF conditions experimentally. The set-up consisted of a pool and a channel, and evaluated its passability based on physical conditions such as air bubbles, velocity, and depth. With the results, we developed a decision tree to explain the passability using design variables such as discharge, channel slope, and pool size and depth. Then, to estimate the whole SEF, we proposed an equation which calculated the average of the decision tree outputs throughout the SEF's whole ascending routes. Lastly, we verified the equation through field experiments. The equation showed good agreement with the observed fish ascent success rate. This technique could therefore be used to evaluate a SEF in its designing stage.
This study elucidated the energy budget in wastewater treatment streams at Tsumori, Ichioka, and Chishima wastewater treatment plants (WWTPs) in Osaka. At Tsumori WWTP, the primary sludge produced in primary settling tanks and excess sludge produced in secondary settling tanks of the three WWTPs were collected and then digested anaerobically to biogas for cogeneration. The energy content of raw sewage at Tsumori WWTP was 4.3 kJ/L. Those at Ichioka and Chishima WWTPs were 2.1 kJ/L. The respective energy contents of primary sludge of Tsumori, Ichioka, and Chishima WWTPs were 16.3, 7.6, and 10.2 kJ/g. Those of excess sludge were 14.6, 8.3, and 9.8 kJ/g, respectively. The total calorific inflow to the three WWTPs was 1.1 × 109 kJ/d. About 40% and 30% of the total calorific energy respectively becomes primary sludge and excess sludge. The remaining 30% is consumed in the aeration tanks. About 30 - 40% the total calorific energy is recovered as biogas by anaerobic digestion, which produces electricity at 1.6 × 108 kJ/d, corresponding respectively to 47% and 33% of the electricity consumption of Tsumori WWTP and the three WWTPs.