Cyanobacterial bloom has been considered as the issue in summer season because high water temperature is preferable for cyanobacteria. However, the occurrence of cyano bacterial bloom under low water temperature has been reported, indicating to control cyanobacterial biomass in low water temperature are also required to improve water quality. Here, we estimated the filtration rate and oxygen consumption rate of two bivalve species, Corbicula japonica and C. sandai. Experiments were conducted with natural lake water from Lake Hachiro under low water temperature condition. The filtration rates of C. japonica and C. sandai were estimated as 21.1 and 16.9 L kg－1 h－1, respectively, under 6.7～11.3℃. Oxygen consumption rates of C. japonica and C. sandai were 0.014 and 0.032 mgO2 g－1 h－1, respectively, under 5.4～11.4℃. Energy demand of both bivalves were also calculated based on the oxygen consumption rates to estimate the amount of dietary requirement during low water temperature season. C. japonica and C. sandai need to consume 0.032 and 0.073 m g－1 h－1 of algal dietary sources to meet their energy demand, respectively. These findings indicate that both bivalves can exert filtration and assimilation of suspended solids even low water temperature conditions.
In the present study, the effect of phosphorus removal pellets containing alum as a main component on the phosphorus removal efficiency in various on-site treatment systems for domestic wastewater was evaluated. When 400 g/week or 800 g/week of phosphorus removal pellets were put into the aeration tank and the raw water tank of three types of Johkasous (Tandoku-shori Johkasou, conventional Johkasou and nitrogen removal type Johkasou), total phosphorus (T－P) and phosphate phosphorus (PO4－P) in the effluent water were decreased after one week. In addition, there was no adverse effect of phosphorus removal pellets on the removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total nitrogen (T－N) in the effluent water. Depending on the conditions of the Johkasou, the T－P concentration tended to be higher when the suspended solids (SS) concentrations were increased. When the phosphorus removal pellet was applied to the aeration tank and the raw water tank of the Tandoku-shori Johkasou and the conventional Johkasou, the ratio of T－P concentration in each effluent water after addition of pellets to that before the pellets addition (T－P ratio) ranged from 0.3 to 0.6. In contrast, the phosphorus removal effect was low in the nitrogen removal type Johkasou, despite that pellets were put into the aeration tank, whereas when the pellets were put into the raw water tank, the T－P ratio was around 0.6.