A lab-scale anaerobic upflow fluidized bed reactor (FBR) was developed to treat synthetic wastewater containing antimony (Sb) and sulfate. The FBR was filled with polyvinyl alcohol (PVA) gel beads and inoculated with a Desulfovibrio sp. strain as a sulfate-reducing bacterium. Desulfovibrio sp. can dissimilatory reduce sulfate to sulfides. Sb(V) is then reduced to Sb(III) by the sulfide formed, which precipitates antimony trisulfide (Sb₂S₃). Wastewater contained 22.8 mg/L Sb, 98.6 mg/L sulfate, and 360 mg C/L lactate. The FBR was operated with hydraulic retention time (HRT) of 24 to 1 h at 28 ℃. The removal of sulfate and Sb decreased from 96.8% to 89.4% and from 93.7% to 49.0%, respectively, when the HRT was reduced from 24 h to 3 h. The maximum removal rate for sulfate and Sb was 68.6 mg/L/h at HRT of 1 h and 3.76 mg/L/h at HRT of 3 h, respectively. These results indicate that the rate-limiting step for Sb removal in the FBR is the chemical reduction of Sb(V) by sulfide rather than enzymatic sulfate reduction. The PVA gel beads and sludge accumulated in the FBR consisted mainly of Sb and sulfur, presumably Sb₂S₃. The Sb content in the PVA－gel beads and sludge increased up to 15.7 mg/g－dry and 109 mg/g－dry, respectively.

 The quality of secondary treated water and the removal performance of hygienically relevant microbes (HRM) during the changing operation from the standard activated sludge method to the stepwise advanced treatment method is unreported. Therefore, we clarified the secondary treated water quality (biochemical oxygen demand, total nitrogen, and total phosphorus) and removal performance of HRM (total coliforms, Escherichia coli, fecal streptococci, enterococcus form) in the changing operational process through one year of parallel operation with a stepwise advanced treatment control system. The secondary treated water in both systems consistently met the target water quality, verifying that the changing operation was appropriate. The total coliforms and E. coli in the experimental system converged to the control system concentration level, but the fecal streptococci, enterococcus form did not. The sludge return ratio correlated highly with the nitrification ratio in the reaction tank, temperature, and biodiversity index, and was useful as an indicator of the changing operational status. The logarithmic removal ratio of HRM was highly related, with the sludge return ratio > total nitrogen > Metazoans. We have clarified the notable points in the changing operation process, and the treated water quality and removal performance of HRM.

 Although total nitrogen (TN) and total phosphorus (TP) mass ratio (TN/TP mass ratio) has been recognized as an indicator of the cyanobacterial bloom occurrence, it has been still unclear whether the change in TN/TP mass ratio is a result or a cause of the blooms. This study examined how the TN/TP mass ratio changes accompanying the occurrence of Microcystis blooms via semi-continuous monoculture experiments. BG－11 medium was used with a fixed phosphorus concentration of 0.11 mg L^－1 and the initial TN/TP mass ratio varied in the range of 1 to 100. With the growth of Microcystis sp., the TN concentration showed a decreasing trend and the TP concentration exhibited an increasing trend, resulting in lowering TN/TP mass ratio. It was also indicated that Microcystis sp. was more likely to form blooms at the initial TN/TP mass ratios of 18 and 50. Furthermore, the TN/TP mass ratio was strongly influenced by increasing phosphorus-rich extracellular polysaccharides (EPS) and approaching the intracellular nitrogen and phosphorus mass ratio (N_c/P_c mass ratio) of 13.2－20.3 with the increase in Microcystis sp. cells. These results suggest that cyanobacterial blooms could be suppressed by controlling the TN/TP mass ratio to below 18 or above 50.