In situ algal bloom control by the integration of ultrasonic radiation and jet circulation to flushing.

A novel strategy for in situ water bloom control was applied and evaluated in Lake Senba. The proposed strategy was to integrate ultrasonic radiation and water jet circulation to an existing flushing process for reducing the growth rate of cyanobacteria and to support the flushing process by providing efficient mixing. Ten units of the system, each consisting of an ultrasonication module and a water jet circulator module, were strategically situated on the lake, and the performance was monitored for 2 years. Water bloom occurrence reflected as chlorophyll a, SS, and transparency were controlled to lower levels when the integrated system was coupled with sufficient inflow water supply to achieve the target flushing rate. Also, an improvement in the water quality such as COD and phosphorus were observed. Based on linear regression analysis, relationships between water quality parameters and inflow water volume were discussed to evaluate the proposed strategy. Of the three major water quality parameters associated with water bloom, the integrated system contributed mainly to the reduction in SS and transparency compared to chlorophyll a reduction. Improved chlorophyll a reduction may be achieved by strategies that augment effective washout of cyanobacteria during flushing.