The green microalgae Chlorella vulgaris, which is known to accumulate valuable substrates, are one of the promising bio-resources. To achieve the mass cultivation of microalgae, anaerobic digestion supernatant was applied as cultivation media in membrane photobioreactor system. In the experiment, the synthesized anaerobic digestion supernatant mimicked from activated sludge collected from an actual wastewater treatment plant in Ishikawa, Japan, was used as cultivation media. In the point of view of nutrient loading, the diluted digestion supernatant satisfied the level for growth. Especially, N/P ratio was 3.8 with high concentration of P, which was previously reported as limiting factor when treated sewage was used as media. Although the maximum biomass productivity (5.58 mg/L/day) was below the previously reported data with treated sewage, the high P concentration in anaerobic digestion supernatant could be utilized as a “supplement” in media.

A double-chamber microbial fuel cell (MFC) using ferric-EDTA chelates (Fe (III)-EDTA) as electron acceptors was developed and a dialysis-based system was introduced into the catholyte pH control in this research. In the developed MFC system, Fe (III)-EDTA was transformed into ferrous-EDTA (Fe (II)-EDTA) at cathodes, which was reused as electron acceptors after re-oxidation to Fe (III)-EDTA with a trickling filter-type oxidation column. The MFC operation using a pre-sedimented municipal wastewater revealed that the observed current density of the MFC using Fe (III)-EDTA reached 144 − 192 mA/m² that was much higher than that of the control using dissolved oxygen electron acceptors. The higher current density was attributed to the higher density of electron acceptors in the catholyte. The average coulombic efficiency of the MFC using Fe (III)-EDTA was 8.2%. When a conventional reagent-based pH control was applied, the electricity production of the MFC was deteriorated because of both the low temperature and the salt accumulation in catholyte derived from acid for pH control. On the contrary, the dialysis-based pH control successfully prevented the salt accumulation and maintained the higher current density. Thus, the introduction of Fe (III)-EDTA electron acceptors and the dialysis-based pH control system for catholyte was thought to be useful for operating the double-chamber MFC without any noble catalyst.

Conventional wastewater analysis based on on-site sampling holds a limitation of accuracy because of fluctuation of influent composition in time and its corruptible nature in organics. To cope with the problem, this study aimed at developing an alternative method using on-site lab-scale activated sludge reactors, where a set of mean influent material concentrations was calculated from the analysis of activated sludge constituents of which fluctuation was damped due to long sludge retention time. Focusing on the activated sludge collected from the reactor having a primary settling tank, the soluble biodegradable material concentrations in the influent were calculated using IWA Activated Sludge Model. Similarly the concentrations of inert and biodegradable particulates in the influent were obtained from the increment of activated sludge constituents between the reactor without a primary settling tank and that with a primary settling tank. The specific decay rate of the activated sludge, which was an influential kinetic parameter on the mathematical calculation, was also regularly monitored. According to the statistical analysis, 6 collection frequencies seemed to be enough to grab the parameter. This new method required noticeably low manpower to estimate particulate BOD, soluble BOD, SS and VSS in the wastewater compared to the conventional techniques.

Bacillus species is an important microbial species in the activated sludge process. Some researchers reported that the predominance of Bacillus spp. improves treatment performance and good sludge settleability. The viable count of Bacillus spp. is usually measured by the plate culture method. Recently developed massive sequence technology has been applied to activated sludge samples; this technique provides more detailed information on its microbial community. However, the relationship between the number of Bacillus spp. and microbial compositions is not yet well understood. In order to elucidate this relationship, microbial community analyses based on 16S rRNA gene sequence and cell count of Bacillus spp. were conducted. Activated sludge samples, including those from conventional activated sludge, sequencing batch, and oxidation ditch processes, were collected and subjected to analysis. The results of microbial community analysis revealed that Proteobacteria and Bacteroides were the predominant bacterial phyla and overall community compositions resembled each other at the phylum level. The detection ratio for Bacillus spp. was 0–0.33%, and the number of Bacillus spp. ranged from 10⁵ to more than 10⁸ colonies/g-MLSS. The results showed that the number of Bacillus spp. and detection ratio showed a similar trend, and thus, these analyses could be complementary to each other.

Wastewater discharged from the coagulation process of natural rubber contains high concentrations of organic compounds, mainly formic or acetic acid, and residual rubber particles. These compounds pose serious issues during the high-rate anaerobic digestion without pH adjustment and solid removal in advance. In this study, an anaerobic baffled reactor (ABR, working volume of 68 L, ten compartments) was investigated for the treatment of such wastewater with a HRT of 3.5 ± 0.9 days. The performance of the ABR was evaluated with the stepwise increase in COD influent during a period 224 days. The microbial community in the sludge from each compartment of the ABR on the 143rd day was analyzed. Under an OLR of 1.4 ± 0.3 kg-COD/(m³·day), the highest COD and total suspended solid removal efficiency of 92.3 ± 6.3% and 90.0 ± 5.6%, respectively, were observed. Sequencing of 16S rRNA genes using MiSeq revealed the difference acetogen communities in each compartment. Most of the methanogens, particularly acetate-utilizing methanogens, were predominantly distributed in the 3rd, 4th, and 5th compartments, where volatile fatty acid concentration considerably decreased and the highest biogas production was observed. These results indicated that the ABR is a potential alternative for the treatment of this wastewater.