Centralized anaerobic digestion of dewatered sludge from small scale wastewater treatment plants and other waste biomass such as kitchen garbage is a promising energy recovery technology. Anaerobic digestion at lower temperatures reduces operational cost, while hyperthermophilic pretreatment upgrades anaerobic digestion performance. The applicability of dewatered sewage sludge from an oxidation ditch process to anaerobic digestion was investigated by continuous and batch experiments under combined different temperature conditions. Dewatered sewage sludge was diluted to total solids 5% before feeding. When the organic loading rate was 0.94 kg volatile solids (VS)/(m3·d), biogas production from dewatered sewage sludge at a mesophilic condition (35°C) was 0.20 NL/gVS-added. Under anaerobic digestion conditions at 25, 30 and 35°C with hyperthermophilic pretreatment at 80°C for 24 h, biogas production was higher than 0.20 NL/gVS-added. Effect of different temperatures on digestate characteristics and microbial communities were revealed. An ammonia concentration of the digested sludge with pretreatment was higher than that of the digested sludge without pretreatment. These results proved that the combination of pretreatment and psychrophilic anaerobic digestion is applicable for sludge management in local cities with decentralized small facilities.
In the construction or renovation of settling tanks for water treatment systems, installing lamella baffles is a promising alternative to reduce the footprint. Conventionally, the increasing flow rate in a lamella settling tank is calculated based on the contribution of the entire projected area of inclined plates to lamella settler capacity. However, this design criterion is not fully verified. In this study, computational fluid dynamics (CFD) was used to simulate the sedimentation tank and lamella settling tank under different flow rates. Simulation results indicated that, at the targeted suspended solids (SS) removal efficiency of 82%, which corresponded to the original linear velocity of 1 m3/(m2·h), a 1.5-fold increase in flow rate required no less than a 6.2-fold increase in settling area using inclined plates. The actual effectiveness of baffles (α) on increased flow rate was estimated to be a maximum of 7.9%. Inclined plates had different influences on the SS removal efficiency of each particle group. Further, the baffle configuration was proven to influence the flow pattern and therefore the performance of the tanks. Using CFD, the SS removal efficiency in settling tanks and lamella setting tanks could be predicted accurately and their design could be significantly optimized.
Biological filtration plays an important role in a sustainable recirculating aquaculture system. To provide the appropriate conditions for biofilter acclimation, the effects of the salinity and acclimation period on nitrogen removal and microbial diversity were evaluated. Nitrification rate (NR) of the shrimp tank biofilter increased during the first 4 weeks and decreased thereafter. The highest NR was found in the 5 PSU salinity tank at week 2, whereas in the other salinities (15 and 25 PSU) the highest NR was observed at week 4. Meanwhile, the denitrification rate (DNR) increased significantly on week 8 and the highest DNRs were obtained after switching from an aerobic to an anoxic condition with methanol supplement. Under this anoxic condition the biofilter acclimated in seawater had the highest DNR. Changes in the microbial community during immobilization were monitored using Illumina MiSeq DNA sequencing. Proteobacteria and Bacteriodetes were the most abundant phyla found in this study. For nitrifiers, Nitrosomonadaceae were found from the first week of acclimation, while only one operational taxonomic unit (OTU) of Nitrospiraceae was observed. Under the anoxic condition at the end of the shrimp culture, two OTUs of Nitrospiraceae were found in both the 15 and 25 PSU tanks.
As a method for raising the electric power of microbial fuel cells (MFC), we have noticed that repeat of discharge (closed circuit: CC) and charge (open circuit: OC) produces higher electric power than continuous CC. We tried to find the best interval time for the electric power generation of MFC using compost by experiments and model simulations. As a result of the experiment, the interval time of CC and OC, which was less than 60 seconds, produced about 1.2 times-higher electric power output than the continuous CC. In addition, as for the fixed interval time of CC, which was 30 s, the longer time of OC produced higher power. It is difficult to keep the same condition on the MFC, because each experiment uses the power of the MFC, and then the voltage decreases. Therefore, we simulated the experiments by making a mathematical model for estimating the electric power. The model was based on variation of the concentration of organic compounds, which are consumed by electric current and supplied by diffusion. As a result of the calculation, the effective interval time of CC and OC is less than 15 s. As for the fixed time of CC, the model shows the longer time of OC generates the higher power; however, as the time efficiency, the shorter time of OC is preferable. Therefore, the time efficiency should be considered for practical use of the MFC.
A DNA microarray analysis targeting nitrogen-cycling functional genes was applied to monitor sediment microbes in the Juso Lagoon (brackish area) and the Shirokita Wando (freshwater area) along the Yodo River in Japan in 2014–2015. The microarray contained 905 oligonucleotide probes for the nif, amo, hao/hzo, nap, nar, nirK, nirS, nrf, cnor, qnor, and nos genes. Diverse genes were detected in the sediment samples. Especially in the summer brackish area, about 70 probes were detected, 26–31, 11–12, and 31–32 of which targeted genes on nitrogen-fixation, nitrification, and denitrification, respectively. Canonical correspondence analysis showed that the nitrogen-cycling functional gene profiles of the sediment microbes were characterized by nitrification activity, denitrification activity, conductivity, pH, temperature, and vegetation of their habitats.
The brackish and marine amphipod Grandidierella japonica is an organism well-suited to sediment toxicity testing in Japan, where no other sentinel amphipod species are found. To provide the application example of toxicity testing using G. japonica in Japan, we performed 10-day whole sediment toxicity tests of six estuarine sediment samples collected from estuaries and tidal rivers flowing into Tokyo Bay. While all the tested sediment samples were not lethally toxic to this species, the body length increment of surviving amphipods was significantly different among sediment samples. To verify that the observed growth inhibition was caused not by large proportions of fine particles but by chemical contamination, additional 10-day tests using formulated sediment with different particle size distributions were performed. As the result, sediment containing more than 25% of < 63 μm particles could reduce the body length, but the reduced body length in the sediment collected from Heisei bridge (S3) was demonstrated to be due to chemical contamination, not due to fine particles. The species characteristics and test results presented in this study provide fundamental information to interpret the results of whole sediment toxicity tests.