Solar Bee pilot project at Rietvlei Dam

Leanne Coetzee Deputy Director: Scientific Services,
Bulk Water Supply, City of Tshwane
Rietvlei Water Works and Purification
Plant
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Rietvlei Dam has been utilized
by the City of Tshwane for
drinking water, since 1934
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The Rietvlei WTW purifies
approx 36 ML/day, 365 days a
year (±6% of CoT water
requirements)
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Rietvlei Nature Reserve
surrounds the Rietvlei dam
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Recreational use for
Pretoria Sailing Club
Canoe Club
Anglers
Friends of Rietvlei
Rietvlei Dam and Water Works
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Problems especially in summer
but also in spring and autumn
due to :-
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Taste and odors caused by
blue-green algae – MIB /
Geosmin
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Toxin production (Microcystin)
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Heavy metals (anaerobic)
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Water quality variation (hourly)
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Filter clogging
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Increased backwashing
Eutrophication is the problem…
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Eutrophication is caused by enrichment of
water (N,P)
– and causes plants, especially algae, to
proliferate - blooms
Harmful algal blooms (HAB) require
nutrients (N,P), suitable temperatures, light
for photosynthesis and prefer stagnant
water
Blue-green algae establish themselves –
Microcystis species - dominant in summer
Dinoflagellates in autumn and spring Ceratium hirundinella
– Rietvlei dam is classed as severely
eutrophic
Cyanobacteria aka “Blue-green
algae”
Significant impacts on water resources and are able to outcompete other algae
Competitive advantage due to:¾ Gas vesicles to regulate their buoyancy
¾ Some species fix atmospheric Nitrogen
¾ Toxin production
¾ Not very palatable for fish and zooplankton
Management Approaches
In lake management approaches have been used to manage
cyanobacterial blooms include:• Copper sulphate
• Alum addition – P binding
• Aeration
• -grid powered fountains,
• -diffusers
• Barley straw
• Catchment Management
• Habitat disturbance
• Long distance solarpowered reservoir
circulator
• Circulates up to 40,000
liters/minute
• 316 Stainless steel
construction
• On board battery system
• Brushless motor
• 80 Watt PV panels
• SCADA output
• 25 year performance
warranty
Shallow Hose Setting
Intake hose set deep for
hypolimnetic oxygenation
Consumption versus Decomposition – Algal Pathways
N + P + Sunlight + Warm temperatures
Edible green algae
Consumption
Non-edible blue
green algae
Decomposition
PROPOSED SOLARBEE PLACEMENT OPTIONS FOR
RIETVLEI DAM
Option
Location
No of
SolarBees
A
Whole
Lake
B
Partial
Tower
C
Partial SE
area +
Tower
D
E
Partial
Partial
North West North
Central
F
No SolarBee
16
6
6
4
3
0
Improvement
(treated
area)
>95%
± 80%
± 80%
± 70%
± 70%
0%
Improvement
(whole lake)
>95%
± 80%
± 80%
0%
0%
0%
Option A
Whole lake treatment for controlling
harmful algal blooms that cause taste and
odor and impair recreational activities
Option B
Partial lake treatment for controlling algal
blooms to treat area in front of the dam
and tower to WTP. Wind conditions may
be a factor
Option C
Partial lake treatment for controlling
harmful algal blooms . 5 Units for treating
the South East tributary responsible for the
most nutrient loading and likely site for
HAB generation and 1 unit at tower for
WTP
Option D
Partial lake treatment for controlling algal
blooms – 4 units for demonstration
purposes only – no anticipated benefit to
WTP or whole lake
Option E
Partial lake treatment – 3 SolarBee units
for demonstration purposes only – there
would be no anticipated benefit for
improving the water
Feasibility / Cost benefits of the SolarBee
Algal activity and chlorophyll a
Low
Low
High
Approximate days per year
200
200
165
Chemical cost per kilogram
R1.41
R9.26
R9.26
% expected reduction in dosing
rate due to SolarBee
0
30
30
R3981.80
R7963.60
Cost per day without SolarBee
Cost per day with SolarBee
R1087.47
R3981.80
R4379.98
Annual Cost without SolarBee
R217
494.00
R796
360.00
R796
360.00
R1 313 944.00
Annual Cost with SolarBee
Projected annual Cost Saving
with SolarBee
R722 696.70
R591 297.30
SolarBee installation
SolarBee installation on 7-9 July 2008
SolarBee technician from the USA installed 6
SB 12000 units
Each unit is capable of treating 12- 14
hectares of dam surface area
Monitoring at 3 different points in the dam
every 2 weeks
Pole
Sampling
point
Dam Wall
sampling
point
Buoy No 5
sampling
point
Anticipated Benefits of SolarBee
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Control of harmful algal blooms
Reduction / elimination of odors
Improved water clarity
Reduction / elimination of seasonal fish kills
Improvement in spawning, zooplankton no’s ↑
Dissolved oxygen levels ↑ pH ↓ ammonia ↓
Reduction of heavy metals released into water
Substantial economic savings in chemicals, H2O,
energy
• Enhances food web -improvement in species
diversity
Monitoring of Rietvlei dam
Parameters
TP and Ortho -P
TN /NH3/ NO3
Algal Identification
Secchi disc
Chlorophyll a
Dissolved Oxygen/Temp
pH, EC
COD
TOC
Average values 2007/8
0.89 / 0.349 mg/L
2.4 / 0.38 /1.22 mg/L
Ceratium / Microcystis
0.4m - 3.4m
84.9ug/L
Up to 11.79mg/L O2
8.63 / 51.2mS/m
37
8-12mg/L
Secchi Disc Readings Sept 2007 - Sept 2008
4.00
3.50
3.00
Buoy No. 5
2.00
Dam Wall
Pole
1.50
1.00
0.50
Date
2008/09/20
2008/07/20
2008/05/20
2008/03/20
2008/01/20
2007/11/20
0.00
2007/09/20
Meters
2.50
Current Status
• During winter Ceratium
species were always
present (Chl a 14-34ug/L
on average)
• Ceratium bloom 200- 487
ug/L chl a(August/September 2008)
• No evidence of
Microcystis or other
Cyanobacteria at present
• Dam stratified for summer
SolarBee maintenance
Lake Palmdale, California
Surface area: 234 acres
(95ha)
• Depth max. ~ 25 ft (7.6m)
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Blue-green algae (BGA)
• Taste and odor associated to BGA
• High chemical treatment costs
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7 SolarBees installed in June 2003
Palmdale Lake
Zooplankton Contents (2002-2003)
Copepoda
SolarBees installed
Cladocera
Total
Palmdale Lake: Data Summary
Average
Minimum
Maximum
2002 – No lake circulation
pH
8.79
8.24
9.12
Temperature oC
19.1
12.6
24.8
Turbidity, NTU
6.66
2.7
9.3
Chlorophyll a
13.5
5.3
24.9
TSI (Chl a)
56
47
62
Trophic State
Eutrophic
Mesotrophic
Eutrophic
Secchi depth, ft
3
3
4
2003 – Lake circulation with SolarBees
pH
8.46
8.13
8.97
Temperature oC
20.3
13.6
25.6
Turbidity, NTU
5.21
0.7
12
Chlorophyll a
66
2
20 1
Note: 2005 chlorophyll a concentrations remained about 3 ug/L
Grasmere Lake, CO,
before SolarBee
Grasmere Lake after
9 weeks
Thank you