Solar-powered Circulators Improve Lake Houston Water Quality

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					    Solar-powered Circulators Improve Lake Houston Water Quality
               Dannelle Belhateche(1), Mike Turco(2), Yong Wang(1), Joel Bleth(3)
   (1) City of Houston Public Works & Engineering Department, (2) United States Geological Survey,
   (3) SolarBee, Inc.

ABSTRACT

        The City of Houston (COH) is the fourth-largest city, and tenth largest
metropolitan area in the United States. Lake Houston is the major surface-water supply,
supplying approximately 30% of the city’s total drinking water source, and provides a
recreation place for the Houston metropolitan area. Beginning in 1983, the U.S.
Geological Survey (USGS), in cooperation with the City of Houston (COH) Department
of Public Works and Engineering, has collected water-quality data at Lake Houston, as
well as water-quality and discharge data for its major tributaries.

        In August 2005, the Northeast Water Purification Plant (NEWPP), which is
located in the southwestern quadrant of Lake Houston, was put in service to supply
drinking water to north and northwest area of the COH. The firm capacity of the
NEWPP is 80 MGD, while its daily average flowrate is approximately 30 MGD. In its
first year service, the NEWPP was experienced with several taste and odor events. The
cause of the taste and odor appears to have been MIB (2-methylisoboneol) and geosmin
produced by blue-green algae (cyanobacteria), and possibly some sulfides produced by
algae or other decaying organic material at the bottom of the lake.

        To eliminate the taste and odor events in the NEWPP source water, twenty(20)
solar-powered circulators were installed near the NEWPP intake in April 2006. The
COH and the USGS also initiated a water quality study to evaluate the effects of
localized changes in circulation on water quality of Lake Houston. Three(3) real-time
monitoring stations with vertical profiling capabilities have been installed since August
2006. Each monitoring station consists of were a floating platform anchored in place on
the lake, which includes a gage house, solar panels, 12-volt batteries and omni-directional
antennae. Each gage house contains a multi-parameter instrument the collects data from
4 different water depths once an hour. Parameters being monitored at four depths
included water temperature, specific conductance, dissolved oxygen, pH, turbidity, and
chlorophyll a. The data from each depth are transmitted hourly through the NOAA
GOES network, transferred into the USGS database, and displayed on the website of the
USGS.

        In addition, two existing USGS stream gage houses, located at upstream of the
Lake Houston, Spring Creek and New Caney, were also used for this study. Similarly,
the multi-parameter instrument at the gage house automatically collects the hourly
samples. Parameters such as discharge flow, turbidity, water temperature, pH, and
specific conductance are sent to the USGS database through the NOAA GOES network,
and indicated in its website. These real-time raw water quality monitoring stations, as the
early warning system, are also being beneficial to the NEWPP personnel to have enough




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time to adjust the plant treatment processes for dealing with the raw water quality
changes.

KEY WORDS

MIB Geosmin        Blue-Green Algae      Lake Houston               Solar-powered
Circulators Real-time Monitoring Station

INTRODUCTION
        The City of Houston (COH) is the fourth-largest city, and tenth largest
metropolitan area in the Nation. With an estimated population of greater than 5 million
people in 2003 (Texas State Data Center, 2004a). Historically the Houston area depended
pre-dominantly on ground water for their municipal and industrial water needs. Due to
the effects of shallow fluid (predominately groundwater) withdrawal on water-level and
subsidence in this area (Kasmarek and others, 2005), regulation of groundwater
withdrawals has initiated the conversion of the City of Houston’s main source of water
from groundwater to surface water. Subsidence, as well as a projected 60 percent increase
in population by 2040 (Texas State Data Center, 2004b), in part, have led to a
commitment by most water managers in the area to increase the use of surface water to
80 percent of the total demand by 2030.

        Lake Houston is the major surface-water-supply and provides a recreation
resource for the Houston metropolitan area. It was constructed in 1954 by the City of
Houston and has a current capacity of about 130,000 acre-feet (Texas Water
Development Board, 2004). Lake Houston exists in the San Jacinto River Basin across
northern Harris and southeastern Montgomery counties, northeast of downtown Houston.
The mean depth of the lake is about 12 feet with the maximum depth reaching about 50
feet (Liscum and East, 2000).

        Beginning in 1983, the USGS in cooperation with the COH, has collected water-
quality and stage data at Lake Houston, as well as water-quality and discharge data for its
major tributaries. These data have been summarized and interpreted (Liscum and others,
1999), and were used to develop a two-dimensional water-quality model of the reservoir
(Liscum and East, 2000). Although eutrophication has not been a significant problem in
the reservoir, these findings indicate that sufficient concentrations of nutrients (nitrogen
and phosphorus) were present in adequate quantities to cause problematic algal blooms
(Sneck-Fherer, in press, 2005).

         In order to reduce subsidence and preserve the remaining groundwater sources
while meeting increasing water demands, the COH is converting a significant portion of
its existing potable water demand from groundwater to surface water sources. As part of
this effort, the Northeast Water Purification Plant (NEWPP) was constructed in two
phases. The Phase 1 with the 40-MGD firm capacity was put in service on August 1,
2005. The Houston Area Water Corporation (HAWC), which was created by the City of
Houston, accepted the Phase 2 construction work with an additional 40-MGD treatment


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capacity in August 2006. The NEWPP is currently serving the North and West region of
Harris County (Area 3).

        The NEWPP, serving as a convention treatment plant, consists of raw water
intake, raw water pump station, flocculation and sedimentation basins, dual media filters,
UV disinfection reactors, clearwell transfer pump stations, 10-MG and 15-MG ground
storage tanks, high service pump station, and 84-inch and 42-inch transmission pipelines
to connect to the City of Houston distribution system. The water source for the NEWPP
is from Lake Houston. The daily average flowrate of the NEWPP is about 25 MGD.

        In its first year service, the NEWPP experienced a significant taste and odor event
in December 2005. This event directly led to the plant operation shutdown. To identify
and solve taste and odor issues in Lake Houston, the COH and the USGS conducted a
water quality study in the intake area and through the plant operation processes.
Although there is only limited water quality data available, it is likely that the cause of
the taste and odor appears to have been MIB (2-methylisoboneol) and geosmin produced
by blue-green algae (cyanobacteria), and possibly some sulfides produced by algae or
other decaying organic material at the bottom of the lake. Related research indicated that
the human beings could identify at a level of 10 parts per trillion (ppt) of MIB and
geosmin.

APPROACHES
        To mitigate the taste and odor issues, the City started to focus on improving raw
water quality by eliminating lake stratification and inactivating the blue-green algae
(BGA) growth in the intake area in January 2006. By comparison of various blue-green
algae treatment methods, solar-powered circulators were chosen as a cost effective mean
to inhibit the BGA growth in the NEWPP intake area.

         Each circulator consists of a set of stainless steel rotating assembly, three 80-watt
solar panels, a battery storage, three floats in triangular pattern, a direct electric motor,
and hose pipes. Each unit is designed to pump 3,000 gallons per minute (gpm) up its
intake hose, and create 7,000 GPM of induced flow, for a total of 10,000 GPM leaving
the machine. Water enters the SolarBee horizontally from a fixed depth in the lake (there
is a 1 ft opening between the intake hose and the bottom plate beneath, so water comes to
the machine laterally), and a specialized dish that distributes the flow radially outward
from the machine at the lake’s surface (see Figures 1 and 2). Since Year 2001, the solar-
powered circulators installed in 160 Lakes in the US for improving the water quality,
which also includes over 60 municipal drinking water reservoirs.

        In March 2006, the HAWC signed a rental contract with the SolarBee, Inc., which
is the manufacturer of the solar-powered circulators. A month later, twenty (20)
circulators were installed near the intake area, which is shown in Figure 3. Each unit
was located at ¼ mile apart away from the others. Their intake hose depth was 6 ft above
the bottom of the lake. With this setting, warm water is drawn into the circulator intake
hose from just above the thermocline, and is pushed out equally at the surface in all
directions from it. Since all the water being pumped and mixed is warm water of nearly


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the same density, long-distance mixing is accomplished allowing for maximum spacing
at about 30-35 acres per a unit. This horizontal and vertical epilimnetic mixing directly
disrupts the ability of the blue-green algae to form blooms and dominate the lake, thus
preventing MIB and gesomin problems.




                       Figure 1. Solar-powered Circulator Flow Patterns




                           Figure 2. Solar-powered Circulator



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  Figure 3. Approximate Locations of the Solar-powered Circulators at Lake Houston

       To evaluate the effects of solar-powered circulation on raw water quality of Lake
Houston, the USGS and the COH also initiated a study for real-time water quality
monitoring program. Three real-time monitoring stations with vertical profiling
capabilities were installed in August 2006.

        Figure 4 presents the locations of these three monitoring stations. Site A is
located above the zone of influence, and Site B is near the NEWPP intake area, which is
directly in the zone of influence of the solar-powered circulators. The location of Site C
is down-gradient, below the zone of influence of the circulators.

        Each monitoring station consists of a floating platform anchored in place on the
lake, which includes a gage house, solar panels, 12-volt batteries and an omni-directional
antennae (see Figure 5). Each gage house contains a multi-parameter instrument the
collects data from 4 different water depths (1, 6, 12, and 16 ft) using a pump and switch
method once per hour (see Figure 6). Every fifteen minutes a switch for a specific depth
opens, a pump turns on and passes water through a flo-thru chamber attached to the
multi-parameter instrument for 2.5 minutes and readings are recorded near the end of the
pump cycle. Parameters being monitored at each depth include: water temperature (flo-
thru and in-situ), specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll.
Once an hour the latitude and longitude are recorded, as well as pyranometer readings,
which measures the solar radiation hitting the lake surface at the platform. The data from
each depth are transmitted hourly through the NOAA GOES network, transferred into the
USGS NWIS database, and are displayed on the USGS webpage. The USGS personnel
in a weekly basis visit these monitoring stations, and all analyzers in the gage are
recalibrated twice per month.


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       The real-time water quality parameters data are available to be downloaded from
the USGS webpage (listed in Table 1) in two formats, either graphs or table of data.
Especially, the water quality data graph directly provides viewers the change trends of
some specific water quality parameters. Figures 7-12 show various water quality
parameters trends at water depth 12 ft at the NEWPP intake area on the date of Feb. 22 to
Mar. 1, 2007.

      Table 1 summarizes water quality parameters being monitored in these three real-
time monitoring stations and their web links.

                     Table 1. USGS Real-time Monitoring Stations
Monitoring       Real Time Water Quality                            USGS Web Links
 Stations              Parameters
   Site A      Temperature, Specific Conductance,   http://waterdata.usgs.gov/tx/nwis/uv/?site_no=295724095
               pH, Chlorophyll, dissolved oxygen,   092301&PARAmeter_cd=00010,00095,00300,00400,000
               and turbidity                        03,00055,00076,63680
   Site B      Temperature, Specific Conductance,   http://waterdata.usgs.gov/tx/nwis/uv/?site_no=295554095
               pH, Chlorophyll, dissolved oxygen,   093401&PARAmeter_cd=00010,00095,00300,00400,000
               and turbidity                        03,00055,00076,63680
   Site C      Temperature, Specific Conductance,   http://waterdata.usgs.gov/tx/nwis/uv/?site_no=295510095
               pH, Chlorophyll, dissolved oxygen,   084801&PARAmeter_cd=00010,00095,00300,00400,000
               and turbidity                        03,00055,00076,63680




     Figure 4. Approximate Locations of the USGS Real-time Monitoring Stations




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                    Figure 5. Site A Real-time Monitoring Station




                                Figure 6. Site A Gage House

       In addition, there are two another existing USGS stream flow gages, which are
located at Spring Creek and New Caney, the northeast and northwest quadrants of the
Lake Houston, respectively. Similarly, these gages also provide a daily water-quality
network by USGS installing, operating, and maintaining five-parameter real-time
monitoring equipment, which includes discharge flowrate, gage height, temperature,


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specific conductance, dissolved oxygen, pH, and turbidity. These sites will also be
reviewed weekly and the probes will be inspected and re-calibrated about every two
weeks. High data rate GOES radios will provide hourly updated data to the USGS
database via the internet. The following table presents the water quality parameters being
monitored in these two monitoring stations and their web links.

      Table 2. USGS Real-time Monitoring Stations at Upstream of Lake Houston
Monitoring       Real Time Water Quality                                USGS Web Links
 Stations              Parameters
Spring Creek   Discharge flowrate, Gage height,         http://waterdata.usgs.gov/nwis/uv?site_no=08068500
               Specific Conductance, pH,
               temperature, dissolved oxygen, and
               turbidity
 New Caney     Discharge flowrate, Gage height,         http://waterdata.usgs.gov/nwis/uv?site_no=08070200
               Specific Conductance, pH,
               temperature, dissolved oxygen, and
               turbidity




         Figure 7. Temperature at 12-ft Water Depth at the NEWPP Intake Area




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Figure 8. Specific Conductance at Water Depth 12 ft at the NEWPP Intake




        Figure 9. pH at Water Depth 12 ft at the NEWPP Intake




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Figure 10. Dissolved Oxygen at Water Depth 12 ft at the NEWPP Intake




   Figure 11. Chlorophyll at Water Depth 12 ft at the NEWPP Intake




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             Figure 12. Turbidity at Water Depth 12 ft at the NEWPP Intake

SUMMARY
        The COH started to use the solar-powered circulators for preventing the blue-
green algae growth in the NEWPP intake area in April 2006. Based on the water quality
data at four different water depths in the first couple of months, the raw water in the
intake area was mixed well, and did not indicate distinguishing lake stratification. No
data indicated there exist blue-green algae bloom in the intake area since April 2006. The
monthly grab sample results for MIB and geosmin in the raw water were consistently
below 5 ppt since then. It is also noticed that the NEWPP powder activated carbon
(PAC) dosage was reduced from 15 to 10 mg/L by deploying these twenty circulators.
The annual PAC cost savings was $150,000 per year at a daily average flow of 25 MGD.

        Since these USGS real-time monitoring stations were in service, they play a role
as the early-warning system for the treatment plant operation. For example, the
precipitation at Lake Houston achieved 16-inch within a week of the October 2006.
During that event, the real-time water quality date from these monitoring stations
indicated that the specific conductance in the raw water was dropped from 150 to 60
usimens/cm while the turbidity there was increased from 40 to 200 NTU suddenly. Upon
receiving this information from the webpage, coagulant and lime slurry dosages were
adjusted immediately for maintaining good coagulation processes so that the good quality
finished water is remained continuously into the distribution system in that event.

        The real-time raw water quality data collected from these monitoring stations is
still very limited since August 2006. In terms of the solar-powered circulator


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performance, it is too early to draw any firm conclusions on it. The comprehensive
evaluation will be performed after collecting 1 or 2 years raw water quality data from
these stations.

        In the future, the USGS will work with the COH to develop and calibrate a
predictive model for taste and odor events at Lake Houston by using the real-time water
quality data. It will be of help for the plant operation staff to have enough time to deal
with the taste and odor events and other issues by treatment process adjustments.

ACKNOWLEDGEMENTS
       We would like to thank Mr. Timothy Orden with the United States Geological
Survey for his hard work on the USGS real-time monitoring stations at Lake Houston. In
addition, we would also like to thank for a great technical support from the SolarBee, Inc.

REFERENCES
1.   Kasmarek, M.C., Reese, B.D., and Houston, N.A., 2005, Evaluation of groundwater
     flow and land-surface subsidence caused by hypothetical withdrawals in the northern
     part of the Gulf Coast aquifer system, Texas. U.S. Geological Survey Scientific
     Investigations Report 2005-5024.
2.   Liscum, Fred, Goss, R.L., and Rast, Walter, 1999, Characteristics of Water-Quality
     Data for Lake Houston, Selected Tributary Inflows to Lake Houston, and the Trinity
     River Near Houston (a Potential Source of Interbasin Transfer), August 1983-
     September 1990: U.S. Geological Survey Water- Resources Investigations Report
     99-4129, 56 p.
3.   Liscum, Fred, and East, J.W., 2000, Estimated effects on water quality of Lake
     Houston from interbasin transfer of water from the Trinity River, Texas: U.S.
     Geological Survey Water-Resources Investigations Report 00-4082, 50 p.
4.   Sneck-Fahrer, Debra, Oden, Jeannette, East, Jeffery W., and Milburn, Matthew, in
     press, Water-Quality Assessment of Lake Houston near Houston, Texas, 2000-2004:
     U.S. Geological Survey Scientific Investigations Report 06-XXXX.
5.   Texas State Data Center, 2004a, 2003 Total population estimates for Texas statistical
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     and       Projections    Program.     Accessed      January     15,     2005       at
     http://txsdc.utsa.edu/tpepp/2003_txpopest_msa.php
6.   Texas State Data Center, 2004b, 2004 Methodology for Texas population
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     Projections        Program.      Accessed       January      15,      2005         at
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7.   Texas Water Development Board, 2004. Surface water, lake volumetric surveys.
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     surfacewater_toc.asp




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