Study On Blue-green Algae Controlled By Carbon Dioxide

Eutrophication and algae bloom, often arose from anthropogenic pollution with nutrients in particular the release of sewage effluent and agricultural run-off carrying fertilizers into natural waters, have resulted in widespread reduction in the quality of surface water especially lakes and reservoirs. Blue-green algae, the most dominant in lake summer bloom, are the most dangerous algae species. Several attempts have been conducted and/or implemented to address algae bloom issue to date, including physical, chemical and biological treatments. Although these traditional approaches can efficiently remove blue-green algae from polluted surface water in short term, there are collateral ecosystem and economic limitations to the extent of long-time running, which are also the reasons why they were merely used as emergency solutions to algae blooms. Hence, additional research is urgently needed to develop a method controlling algae blooms with more efficiency, less environmental impact and long-term operation. In this study, unlike to traditional approaches, we used CO2 to lower water pH from alkaline to acid and investigated the effects of these various acid environments on the growth of blue-green algae.The role of pH adjusted by intermittently aerating carbon dioxides (CO2) was evaluated on the growth of two blue-green algae species (Microsystis aruginosa and Anabaena spiroides). All acid conditions (pH=5.5, 6.0 and 6.5) possess a significant inhibition effects on the growth of these two algae species when acidification treatment was started at the logarithmic phase. Differences in Chlorophyll a under three acid conditions were observed both in Microsystis aruginosa and Anabaena Spiroides. The maximum Chlorophyll a occurred at pH 6.5 while the least point at pH 5.5. Difference in inhibition influence of some definite acid condition was also existed between these two algae species. The effect of acid condition (pH=5.5, 6.0 and 6.5 respectively) on the growth of Anabaena Spiroides (growth rate: 0.1175d-1, 0.1334d-1, 0.1219d-1 respectively; and the maximum algae removal rate: 62.4%, 50.3%, 49.7%, respectively) was not as remarkable as Microsystis aruginosa (growth rate: 0.0030d-1, 0.0325d-1, 0.1105d-1 respectively; the maximum algae removal rate: 98.0%, 97.4%, 97.4%, respectively). The tolerance of Microsystis aruginosa to these acid conditions was also investigated in this study. The results indicated that Microsystis aruginosa was inhibited significantly but not died at pH 6.5, whereas died at pH 5.5 and 6.0. Additionally, all acid conditions (pH=5.5, 6.0 and 6.5) had different effects on the growth of Microsystis aruginosa when acidification treatment was started from stable breeding phase. The greatest inhibition effect occurred at pH 5.5 and no inhibition effect was found at pH 6.5, and the maximum algae removal rate at pH 5.5 and 6.0 were 24.0%, 9.8%, respectively.Moreover, to compare the effects CO2 with HCl on the growth of blue-green algae, the role of two acid conditions (pH=5.5, 6.5) adjusted by intermittently adding HCl was evaluated on the growth of Microsystis aruginosa. The results indicated that the effects of CO2 on the growth of Microsystis aruginosa were much better than that of HCl.