The following paper on controlling blue-green algae (cyanobacteria) in reservoirs and lakes was presented in an international meeting in Japan.
Eliminating Cyanobacteria in Reservoirs and Lakes
6th International Conference on the Conservation and management of Lakes – Kasumigaura, Japan 1995.
Reduce algae in lakes, ponds, rivers and reservoirs using inversion and aeration with bacteria and non-pesticidal chemicals.
Robert L. LAING
Cyanobacteria (blue-green algae) in reservoirs are a primary cause of unfavorable taste and odor in drinking water. This paper presents a history of studies showing less blue-green algae in lakes and reservoirs using combinations of continuous laminar flow inversion and buffered alum. Continuous laminar flow inversion and buffered alum do not affect blue-green algae in any way. They simply reduce the nutrients that produce blue-green algae growth. Inversion takes blue-green algae to the bottom of lakes and reservoirs, where they cannot receive sunlight.
Mitsui Engineering & Shipbuilding (MES) and CLEAN-FLO (CFL) extensively studied results of the CLEAN-FLO process on several lakes and reservoirs. Results of the process on Cyanobacteria control were of particular interest because of the prevalent problems with taste and odor in drinking water and aesthetic quality of scenic water.
After studying lakes already treated, MES then studied the CLEAN-FLO process in detail for two years at Shinobazu-Ike Lake, Ueno, Tokyo, to compare cyanobacteria growth with initial conditions. This is a 3-ha, 1.4 m average depth lake with considerable cyanophyceae growth. It has thousands of waterfowl and fish. Visitors throw huge quantities of food into the water. Such an environment is ideal for cyanobacteria growth.
Water quality of Shinobazu-Ike was tested from July 1988 to March 1991. MES installed the CLEAN-FLO system, and compared monthly tests for two years after. Eight 0.4 kw oilless compressors were placed on the shore, and connected via tee-fittings to sixteen self-sinking air lines. The air lines passed along the lake bottom to sixteen microporous ceramic air diffusers, approximately evenly spaced. The system was turned on in March 1991. CLEAN-FLO buffered alum was added nine times during the two-year period, at two or three-month intervals.
Shinobazu-Boat Lake had improvement in water quality, Figures 1 – 6. Phosphorus and nitrogen declined, dissolved oxygen increased, and pH stabilized between 7.0 and 8.0. Average thickness of organic sediment at thirty test sites showed 15 cm decrease due to aerobic biodegradation, physical compaction, etc.
From August 1990 to August 1992, total cyanobacteria cells in Shinobazu-Ike declined from 89 percent of total algae cells to 17 percent, Figure 7. Microcystis sp. declined from 91 percent of cyanobacteria cells to 2 percent. Total algae cells declined from 98,350 cells/100 ml to 47,040 cells/100 ml, Figure 8. Periodic influent nutrient loads, such as heavy rain runoff sometimes temporarily increased the total number of alga cells. Species of phytoplankton remained improved during these setbacks. Complete data is available from MES.
Results have been published since 1971 showing CLEAN-FLO continuous laminar flow inversion/oxygenation and CLEAN-FLO buffered alum are both effective in reducing aquatic plant nutrients. Cyanobacteria cannot grow in nutrient deficient water. (Tables 1, 2 and 3)
The lakes studied by Beduhn, 1994 were under-aerated because of budgetary limitations by private lakeshore owners. These projects were not government-funded. As a result, Beduhn’s report shows that water quality may not have improved as much as fully aerated projects. Beduhn only tested the lakes during one post-aeration season. Pre-treatment data was not taken for a comparison. The tests showed that the five aerated lakes had 67% less cyanobacteria than six lakes that did not need treatment.
The city of Kaohsiung, Taiwan solved their low oxygen, high ammonia, blue-green algae and bad taste and odor problems in their city drinking water with the CLEAN-FLO process in Feng-Shan Water Reservoir in 1992 (a report will be published). Feng-Shan Water Reservoir is 50-ha, 25 meters deep, with maximum volume 8,400,000 m3. Retention time is 1 – 7 days.
The Taiwan Water Supply Company reported to CFL that Cyanobacteria were much less, resulting in a reduction of chlorine consumption in the water treatment plant from 50 mg/l to 9- 10 mg/l. Taste and odor problems disappeared. Bottom dissolved oxygen increased from 0.0 mg/l to 3.6 mg/l average. Reservoir outlet ammonia decreased an average of 2.5 mg/l. Also in 1992, the city of Fourmies, France received the two highest environmental awards for restoration of the Helpe Mineure River using the CLEAN-FLO process, and Ridgegate Reservoir (Macclesfield, U.K.) and Worsbough Reservoir (Yorkshire, U.K.) were successfully treated.
In 1992, a team of MES and CFL engineers and scientists tested and studied twenty U.S. lakes. All lakes received the CLEAN-FLO process. In the twenty lakes studied in Minnesota and Wisconsin, all lakes had good water quality, and a significant lack of cyanobacteria. Space does not allow publishing this data.
Cyanobacteria were much less abundant when either buffered alum or continuous laminar flow inversion was used. Buffered alum may help improve non-flowing lakes, or small lakes. For drinking water reservoirs, buffered alum is expensive, and may be flushed out due to short hydraulic retention time. Continuous laminar flow inversion is an economical way to remove factors that produce Cyanobacteria in drinking water reservoirs before the water is treated in potable water treatment plants. This will greatly reduce or eliminate taste and odor problems in the drinking water.
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Beduhn, Robert J., 1994. The effects of destratification aeration on five Minnesota lakes. Lake and Reservoir Management, 9(1): 105-110. Proc. North American Lake Management Society, Seattle, WA Nov. 1993.
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