The development of activated sludge （AS） process over the past 100 years have been passed. I have read the original papers of Mrs. Ardern & Lockett, who are widely recognized as the “discoverer” and “inventors” of the AS process. From numerous books, papers and reports, I felt that there was an interesting drama in the early days of the AS process development. Therefore, I will outline the dawn of the AS process and its introduction into Japan. I introduced with personal interest its historical developments such as “intellectual property right and AS process” and “prohibition law and AS bulking”.

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are an emerging contaminant of concern. However, the present sewage treatment plants (STPs) are not designed with treatment units for direct removal of ARB and ARGs. STPs are considered to be hotspots of horizontal gene transfer of ARGs as well as a major source of their emissions in the aquatic environments. In order to mitigate the risk of infection by ARB and ARGs, their reduction in STPs needs to be fully understood. This review focused on disinfection, the tertiary treatment of the sewage treatment process, and discussed the advantages, limitations, and improvements in the process using each disinfection technology, with the aim of identifying treatment strategies and further research directions for future ARB and ARGs in reducing emissions into the environment.

Bioreactors with manganese (Mn)-oxidizing microorganisms are potent tools for removing Mn from pH-neutral mine drainages, based on their ability to form insoluble Mn oxides. We examined the effects of loadings of Mn and zinc (Zn) ions on the removal of these metals from synthetic mine drainages by a laboratory mini-size bioreactor, which was packed with limestones encrusted with Mn oxides and a Mn(II)-oxidizing bacterial community. The initial influent Mn(II) concentration and hydraulic retention time were set at 10 mg L^-1 and 24 h, respectively. The results showed that the Mn(II) removal rate was dependent on the amount of Mn oxide precipitates associated with the limestone and was not largely lowered even if the Mn(II) concentration was gradually increased to six times or soluble Zn(II) coexisted at 6 mg L^-1. The effluent Mn(II) concentrations met the effluent standard in Japan (< 10 mg L^-1) when Mn(II) was loaded up to 28 mg L^-1 bioreactor d^-1. The bioreactor also effectively removed dissolved Zn(II). The bacterial community structures of the Mn precipitates in the bioreactors consisted of diverse heterotrophs mainly belonging to Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, and Bacteroidetes. The bacterial communities also included species closely related to known Mn(II)-oxidizing heterotrophs. The results demonstrate that the bacterial communities with Mn(II)-oxidizing activity can be maintained under organic substrate-poor conditions, further supporting the usefulness of Mn(II)-oxidizing bioreactors in mine drainage remediation.

Image analysis was applied for the non-destructive measurement of the respective frond areas of three duckweed species. The dry biomass (y, mg) was found to be proportional to the frond area (x, cm²) measured by image analysis, y = 1.99x － 0.24 for lesser duckweed Lemna aoukikusa, y = 2.36x － 3.22 for giant duckweed Spirodela polyrhiza, and y = 1.17x + 0.91 for rootless duckweed Wolffia globosa. These duckweed species were cultivated separately for 7 days in the modified Hoagland medium under laboratory batch conditions. Biomass growth and nitrogen and phosphorus removal in the medium could be well predicted from change of the frond area and from typical biomass yields on nutrients without disturbing batch operations.

The production of NO₂^－－N from NH₄⁺－N via partial nitrification is necessary for anaerobic ammonium oxidation (anammox). This study investigated partial nitrification using a dropping reactor that comprised a hanging 10 × 10 × 10 mm polyolefin sponge cube with an effective length of 30 cm. In this present study, a dropping reactor was proposed for the partial nitrification. This configuration simulated a down－flow hanging sponge reactor. The synthetic NH₄⁺－N contaminated groundwater (40 mg/L) was fed at a 1.0－5.0 mL/min flow rate for 287 d. We found that the efficiency of the partial nitrification method increased with an increase in the synthetic groundwater flow rate. The partial nitrification percentage (NO₂^－－N in effluent) was 11.0－59.5% at 4.0－5.0 mL/min. The amoA gene of ammonia-oxidizing bacteria (AOB) and nxrA gene of nitrite-oxidizing bacteria (NOB) and 16S rRNA genes of Nitrosomonas (AOB) Nitrobacter and Nitrospira (NOB) were detected in the sponge material of the partial nitrification reactor. The AOB and NOB might have contributed to partial and complete nitrification. The results suggested that the proposed partial nitrification method effectively produced NO₂^－ from NH₄⁺ in the contaminated groundwater without the high cost of aeration. Therefore, this new method could cost-effectively provide the NO₂^－ required for anammox.