Author(s): Daiki Kakinuma, Tadashi Yamada
Linked Author(s): Daiki Kakinuma
Keywords: Closed water body, washout effect, growth rate, rotation rate, uncertainty
Abstract: An algal bloom is one of the problems in lakes and reservoirs worldwide. The reason why blue-green algae become a problem is that odors such as 2-methylisoborneol and geosmin can be generated, and water body turns into light blue and leads to landscape deterioration at the time of decomposition. In addition, it can be harmful to livestock and human health due to its liver poison. Blue-green algae occurs not only in lakes and reservoirs, but also in slow water flow rivers. Therefore, improvement of hydrophilicity and waterside is necessary, so river management considering water quality is very important at present. In this study, we assumed the environment has a lot of nutrients like nitrogen and phosphorous and propose a method to determine the volume of water conduction to prevent the occurrence of blue-green algae by numerical analysis and experiments. By adding a water conduction effect (referred to as washout effect) to the logistic equation, which describes the growth of an organism, the volume of water can be determined by the relation between the growth rate of algae and the rotation rate (Inverse of retention time). In other words, it is better to conduct water more quickly than the growth rate of blue-green algae. We investigated this relationship by indoor culture experiments with varying retention time and observation at Lake Tega-numa. Next, we proposed countermeasure for blue-green algae that contain uncertainty. The growth rate of algae uncertainty change depends on the light condition, water temperature, algae volume and cell condition. Thus, we proposed a new method that adds a washout effect term to a logistic equation and considering uncertainty into growth rate. We showed that it is possible to calculate the inflow discharge to flush out algae considering probability theory using new method
Year: 2017