IMPROVING LAKE WATER QUALITY BY SOLAR POWERED CIRCULATION

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IMPROVING LAKE WATER QUALITY BY SOLAR POWERED
CIRCULATION

• Bo Labisi, P.E
• Palmdale Water District
• blabisi_at_palmdalewater.org

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INTRODUCTION

• Palmdale is located in the high desert community
  of Antelope Valley, NE of LA County
• Lake surface elevation is 2812.5ft
• Average depth is 17.6ft
• Maximum depth is 25ft
• Surface area is 234 Acres
• Capacity is 4129AF
• Lake is supplied mostly from CA SWP (Aqueduct).
  Can be supplied from Littlerock Dam

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LAKE TROPHIC STATE (Carlson, 1977)

• TSI 60 14.4 ln (SD) (Eqn. 1).
• TSI 9.81 ln (CHL) 30.6 (Eqn. 2)
• TSI 14.42 ln (TP) 4.15 (Eqn. 3)
• TSI Trophic State Index
• SD Secchi Depth, meters (Palmdale Lake, 0.91m)
• CHL Chlorophyll a, µg/L (Palmdale Lake Min.
  5.3, Ave. 13.5, Max. 24.9)
• TP Total Phosphorus, µg/L (Palmdale Lake Range
  8.75 400)
• Palmdale Lake TSI ranged from 47 to 62 based on
  Chlorophyll a concentration in 2002. It is
  eutrophic on the average.

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TROPHIC STATE INDEX - 2002
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ALGAE BLOOM

• OCCURS IN SUMMER AS A RESULT OF
• Flow pattern and restriction
• High temperature
• Availability of light for photosynthesis
• Nutrient supply (Eutrophic lake) mainly
  phosphorus

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PROBLEMS FROM ALGAE BLOOM

• Unsightly lake condition
• Taste and Odor
• Inadequate settling

• Filter breakthrough
• Filter clogging
• Toxins

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LAKE TREATMENT

• Prior to 2003, lake was treated aggressively with
  copper sulfate in summer
• Weekly treatment amounts to big dollars
• Copper has secondary MCL of 1ppm and AL of 1.5ppm
  under lead and copper rule
• Copper is regarded as toxic element not to be
  discharged into US waterways
• Application of copper during high concentration
  algae bloom may lead to release of intracellular
  taste and odor causing compounds and cyanotoxins.

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LOCATIONS OF SEVEN SOLAR POWERED CIRCULATION
DEVICE
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LAKE MONITORING

• Five spots on the lake
• Identified with anchored buoys
• Parameters measured with SONDE twice a month
  March to September and once a month October to
  February
• Parameters are pH, DO, turbidity, temperature,
  and chlorophyll a from each site
• Composite samples for algae and zooplankton
  analysis, phosphorus analysis and mathematical
  model

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ALGAE ENUMERATION Taste Odor algae, toxin
producers, filter cloggers (excluding diatoms),
and pollution indicators.

• Average monthly population in the lake epilimnion
  between March and August 2002 was 1323 units/mL
  with weekly copper treatment (total of 27,250Ibs
  and 258 gallons)
• For the same period in 2003, when solar powered
  circulation device was in operation, the number
  was 2120 units/mL and major copper treatment was
  done twice (total of 7,000Ibs and 60 gallons)

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TOTAL ALGAE
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Diatoms and Zooplankton

• March August 2002
• Diatoms - 1820 units/mL
• Zooplankton 220 /mm3
• March August 2003
• Diatoms - 6131 units/mL
• Zooplankton 737 /mm3
• Circulation encourages proliferation of diatoms
  and zooplankton and promotes competition for
  limited nutrients among all species

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Diatoms Proliferation
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Zooplankton Proliferation
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Chlorophyll a Level

• A threshold level of 15µg/L was chosen
• This level coincides with observed poor lake
  aesthetic conditions and increased pH that
  compromises the ability of aluminum sulfate to
  perform as coagulant in the treatment process
• The lake is eutrophic at the threshold
  chlorophyll a concentration

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Chlorophyll a levels (2002 2003)

• Before lake circulation, chlorophyll a was
  consistently above the threshold in summer (2002)
• After installation of solar powered circulation
  device, chlorophyll a level stayed below the
  threshold value all summer (2003) despite higher
  temperature that summer compared to 2002

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Chlorophyll a Temperature
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Nutrient Supply

• Nutrient supply to the lake is naturally
  curtailed by denitrifying bacteria (Pseudomonas
  aeruginosa) therefore phosphorus is the limiting
  nutrient. Phosphorus levels vary widely based on
  the Aqueduct levels
• A mathematical model was used to calculate
  phosphorus loading to the lake. The loading range
  was 8.75 400µg/L in 2002 and 2 275 µg/L in
  2003
• Phosphorus as low as 20µg/L will encourage the
  growth of algae

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Mathematical Model Phosphorus or Chlorophyll a
Estimation

• C 10 (exp(pH0.05))(1.6806 x 10-4) ?1/T ln
  (TPI)
• where
• C Chlorophyll a, µg/L
• pH pH of lake water, units
• T Temperature of lake water, oC
• TPI Total Phosphorus Index
• Accuracy within 10 for Chlorophyll a
• Accuracy within a range of 0 - 2.5µg/L or 0 -
  50µg/L depending on phosphorus concentration
  between 2 and 400µg/L

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Total Phosphorus Index
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Example - Model Calculation

• Phosphate loading to the lake is 98µg/L. Lake
  temperature is 21.68oC and the pH is 8.32. What
  is chlorophyll a concentration in µg/L?
• C 10 (exp(pH0.05))(1.6806 x 10-4) ?1/T
  ln (TPI)
• exp(pH0.05) 4315.6
• 10 (exp(pH0.05))(1.6806 x 10-4) 5.31
• ?1/T 3.1421/21.68 1.054
• ln (TPI) ln 3 1.0986
• Predicted chlorophyll a, C 5.31 1.054
  1.0986 7.46µg/L
• Actual chlorophyll a 7.1µg/L
• Difference 5

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Phosphorus Loading
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Lake Phosphorus Levels

• Pre-circulation lake phosphorus level ranged from
  lt10µg/L to 100 of input concentration.
• Post-circulation lake phosphorus level ranged
  from lt10µg/L to 50 of input concentration.

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pH

• Average lake surface pH between March and August
  2002 was 8.79. For the same period in 2003, it
  was 8.46
• When pH reaches 8.9 and above, it gets difficult
  for aluminum sulfate, the coagulant used in
  treatment, to perform effectively especially at
  flow rates near the plant design capacity (28MGD)
  prevalent in summer months
• pH peaked at gt8.9 several times between May and
  July in 2002 while there was just one such
  incidence in 2003 (March 27, 2003)
• Lower pH level in 2003 is tied to less algal
  activity because of lake circulation despite
  higher average lake temperature in 2003

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pH Chart
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pH Chlorophyll a Trend
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Lake Stratification

• Daily summer temperature difference between the
  epilimnion and hypolimnion is above 1oC on a
  regular basis hence lake stratification occurs
  most of summer
• Lake epilimnion temperature can reach 26.5oC and
  ambient temperature gets to 110oF (29oC) in
  summer
• Device cannot operate without solar energy
  therefore there is virtually no circulation at
  night
• With lake circulation, thermocline layer is
  disrupted continuously preventing constant
  stratification
• Lack of fixed warm layer reduces plankton
  activities

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Lake Stratification
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LAKE TEMPERATURE
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DISSOLVED OXYGEN

• DO distribution is more uniform with lake
  circulation
• March October 2002 (No circulation)
  Epilimnion/Hypolimnion
• Average difference 2.74mg/L
• Maximum difference 7.56mg/L
• Minimum DO 2.67mg/L
• March October 2003 (Lake circulation)
  Epilimnion/Hypolimnion
• Average difference 1.65mg/L
• Maximum difference 5.99mg/L
• Minimum DO 3.86mg/L

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DO CHART
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DATA SUMMARY
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CONCLUSIONS

• Forced lake circulation using solar powered
  device was effective in controlling the incidence
  of algal bloom in Lake Palmdale during the summer
  of 2003
• Substantially less quantity of chemicals was used
  to treat the lake in 2003 because of lake
  circulation resulting in significant savings
• Water quality parameters like DO, pH, Secchi
  transparency depth, turbidity and chlorophyll a
  improved noticeably with lake circulation
• Irrespective of nutrient loading, algae and
  zooplankton proliferation was curtailed because
  circulation exposed available nutrient to all
  species stimulating much higher food demand than
  supply therefore forcing quicker die off

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RECOMMENDATION

• While it typically does not rain in summer in
  Southern California, the influence of spring
  showers on summer algal bloom with or without
  lake circulation could not be assessed for the
  two-year study period. Total rainfall from
  February to April 2003 in Palmdale was 5.56
  inches while for the same period in 2002, 0.18
  inch was recorded
• Effect of the amount of annual rainfall on algal
  activities on the lake needs to be investigated
  however modest improvement in water quality with
  circulation is expected even in dry years
• http//newweb.wrh.noaa.gov/climate/index.php?wf
  olox

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REFERENCE

• Water and Wastewater Calculations Manual, Shun
  Dar Lin McGraw-Hill-2001. ISBN 0-07-137195-8
  156-159.

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ACKNOWLEDGEMENT

• Chris Ehlers Zone 7 Water Agency, Pleasanton,
  CA. Lake Circulation Device Installation and
  Operation.
• Chris Brundage Palmdale Water District, CA.
  Sonde and data logging, sampling and sample
  analysis.
• Chris Bones Palmdale Water District, CA. Boat
  Operation and sampling.
• Dr. Judy Westrick Lake Superior State
  University, MI. Arranging plankton analysis.
• Robin Root Northern Kentucky University, KY.
  Algae analysis.
• Dr. Richard Back Lake Superior State
  University, MI. Crustecean zooplankton analysis.
• Lake Circulation Device (Solarbees) manufactured
  by Pump Systems, Inc. Dickinson, ND.

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• THANK YOU