Development of Water Pollution Control System for Urban Lakes using Algae Trap

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Accumulations of floating algae, known as water-blooms, cause nuisances in lakes and other water impoundments because of their unsightly appearances and the release of noxious taste and odors as they decompose. This is called water pollution by eutrophication. A few methods exist such as application of copper ions, but they cause secondary water pollutions like massive fish-kills.We developed a harvesting system named algae trap. It consists of a weir as an inlet and a separation tank with outlet. Floating algae are accumulated by wind. By setting the trap on the lee-ward shore, we can harvest them in high density without any energy because they are carried into the trap by overtopping wave and then separated from water in separation tank by autofloatation.We carried out on-site and model experiments on trapping. The results of onsite experiments show the system can harvest water-blooms effectively at low cost.It is very interesting that the result of model experiments showed that floating particles flowed into the trap as several times much as ones predicted by potential analysis. The SMAC method was modified to solve navierstorks equation with the surface tension. This analysis showed that marangoni effect acceralated the particle flow.Vertical migration speeds of water-blooms were measured to design the separation tank. After that densities of reflaoted algae were measured to know the efficiency of separation. Specific filtration resistances of algae were also measured. These results show that it is easy to separate algae from water but some pre-treatment may be need to filtrate refloated algae for resources recovery.