ALGAL PRODUCTION STUDIES AT THE PEACH BOTTOM NUCLEAR POWER

algal production studies at the peach bottom nuclear power facility: a status report first draft 8/7/2011 patrick ka

ALGAL PRODUCTION STUDIES AT THE PEACH BOTTOM NUCLEAR POWER FACILITY:
A STATUS REPORT
First Draft 8/7/2011
Patrick Kangas
Environmental Science and Technology Department
University of Maryland
College Park, Maryland
NARRATIVE
The algae production project at the Exelon Corporation’s Peach Bottom
Nuclear Power Facility began in the spring of 2010, building on an
earlier experience at Exelon’s Muddy Run Hydroelectric Power Facility.
The Peach Bottom facility is located in southeastern Pennsylvania
adjacent to the Susquehanna River. Water from the river is used to
help cool the nuclear reactor and the heated water is discharged back
into the river through a long canal. The overall purpose of the
project is to test an algae production system at the nuclear power
facility using the heated discharge water as a resource. This kind of
algal system has been shown to be effective as a water quality
management option that removes nutrients and adds oxygen to polluted
waters (Adey 2010, Adey et al. 2011, Anonymous 2011). It is hoped that
the heated discharge waters will extend the growing season of algae in
temperate climates and lead to increased algal growth and performance.
In particular, use of heated discharge water from Peach Bottom may
provide a major stimulus to cleaning up the Chesapeake Bay through
controlled algal growth, since the majority of nutrients that pollute
the Bay enter through the Susquehanna River. Thus, the Peach Bottom
Nuclear Power Facility is at a strategic location to positively impact
restoration of the entire Chesapeake Bay Estuary.
The algal production system used at Peach Bottom is an experimental
raceway that is one foot wide and 300 feet long. The length of the
system is important to study longitudinal patterns of algal growth and
nutrient removal. The raceway at Peach Bottom is an aluminum trough
with a plastic liner, elevated off the ground with a 2% slope from top
to bottom. Water is pumped from the heated water discharge canal to
the top of the raceway where it flows by gravity to the bottom. Output
water at the bottom of the raceway is released into a wetland that
drains back into the heated water discharge canal. The system is an
Algal Turf Scrubber ™ or ATS in which water is pulsed from a surge box
at the top of the system to generate turbulence in the water flow and
algae are grown attached to a plastic mesh screen placed in the bottom
of the trough.
This particular raceway had been used to study algae production at the
Exelon Corporation’s Muddy Run Hydroelectric Facility, located across
the river from Peach Bottom, from June 2008 to November 2009 with
support from the Lewis Foundation through the Smithsonian Institution
(Kangas et al. 2010). A license agreement to operate the algae system
at Peach Bottom between the Exelon Corporation and the University of
Maryland was extended from an earlier agreement for Muddy Run. This
agreement was signed in March 2010. After funding ran out from the
Smithsonian Institution, the system was disassembled and moved to
Peach Bottom from Muddy Run and it was reconstructed under the
supervision of Tim Goertemiller of Living Ecosystem LLC of Easton,
Maryland. Mark Ross has been the main contact for the project at Peach
Bottom with assistance from Chris Crabtree and Kevin Bristol.
The project functionally began when water flow to the system began in
July 2010, without external funding support. The system operated
routinely until early September when power outages began to occur due
to construction activities at the power plant. These outages caused
the pump to turn off, which dried out the algae in the system and
reduced productivity. The algae production system operated irregularly
through the early fall due to the power outages. Eventually by the end
of October 2010 power was completely turned off and, therefore, the
algae production system was turned off. A newspaper article about the
early operation, arranged by David Tillman, Communications Manager at
Peach Bottom, was published on the front page of the Baltimore Sun on
September 20, 2010 (see Appendix 1).
Through the efforts of Mr. Ross, a solar-powered pump system was
purchased for the project with funding from several departments at
Peach Bottom. The solar power system was designed and constructed by
Smucker’s Energy of Kinzer, Pennsylvania. Using this system water flow
was reinstated in the algal production system in May of 2011. The
system operated for about five weeks until the pumps failed,
presumably due to clogging. A new pump is scheduled to be installed in
early August 2011 to restart operations, with supervision from Mr.
Goertemiller.
GOALS OF THE PROJECT
The main goal of the project has been to test the performance of the
algal production system using heated discharge waters from the nuclear
power plant. In particular, the hope is that the growing season of the
algae can be extended through the winter months, when cold
temperatures normally cause the system to be closed down. A special
feature of the project is the ability to compare algal production
between a site without heated waters (Muddy Run from 2008-2009) with a
site with heated waters (Peach Bottom in 2011-2012). Appendix 2 is the
original proposal for the project.
An additional goal emerged once the project began in 2010. Mr. Ross
recognized the potential utility of the algal production system for
cooling the heated discharge waters. Because algae are grown with a
shallow sheetflow of water (about 1 inch or 3 cm deep), heat in the
thermal discharges readily exchanges with the atmosphere. This heat
exchange causes water temperature to decrease from the top to the
bottom of the raceway. Mr. Ross coined the term “green cooling tower”
for the algae production system because of this potential. Therefore,
study of temperature changes has become an important goal of the
project.
CONCEPTUAL BASIS OF THE ALGAL PRODUCTION SYSTEM
The algal production system functions as a water quality management
tool because algae remove nutrients from and add oxygen to the
polluted water passing through the system as they grow. Nutrients are
removed from the system when algae are harvested. Thus, harvesting
takes place frequently in order to optimize the water quality
improvement function of the algal production system.
In the larger context, the algal biomass harvested from the system has
value as a byproduct (eg., as a feedstock for biofuel production), but
in terms of water quality management the biomass just has to be
removed from the system to achieve nutrient reductions The objective
of this ecotechnology is then to maximize the growth rate of algae.
METHODS
Algae were harvested from the system usually every 1-2 weeks. Before a
harvest, the pump is turned off and water is allowed to drain by
gravity for 30 minutes to an hour. Then algae is physically scrapped
off the screen and placed in buckets for processing. Samples of the
algal biomass from the top, middle and bottom of the raceway are dried
and weighed and productivity is calculated as the increase in biomass
between harvest dates.
Before and after harvesting, several water quality measurements are
made to help assess the performance of the system, using a YSI
hand-held meter. Water temperature, dissolved oxygen concentration and
the degree of oxygen saturation are measured at the top and the bottom
of the system in order to assess the effects of algal growth. Change
in dissolved oxygen concentration and percent oxygen saturation help
assess photosynthesis and respiration rates of the algal community on
the screens, while change in temperature helps measure the cooling
effect (eg., “green cooling tower” effect).
Finally, samples of the algal community were taken for identification
of the dominant taxa with light microscopy. This information is
qualitative and is described in Appendix 3 in note form.
RESULTS
Algal Production
Productivity data for 2010 at Peach Bottom are shown in Table 1 from
late summer. Growth rate of algae increased over several weeks, then
averaged nearly 15 grams dry weight/m2/day. This value was higher than
for corresponding dates a year earlier at Muddy Run, presumably
because the higher temperature water at Peach Bottom caused an
increase in algal metabolism.
Productivity data for 2011 are shown in Table 2 for early summer.
Productivity was variable but averaged about 13 g dry wt./m2/day.
Water flow rates basically declined over the study period and
eventually, after the end of June, the pumps stopped functioning.
Dissolved oxygen data reflects the photosynthetic production of the
algae by the increases between the top and the bottom of the raceway
(Tables 3-5), since algae are adding oxygen to the water as they
metabolize. On average photosynthesis by algae increased dissolved
oxygen concentration by about 4 mg/l and increased percent saturation
by about 55% from the top to the bottom of the raceway for these point
measures.
Water Temperature Decreases
Temperature data, taken after harvest, for 2010 are shown in Table 6.
During the study period the average decrease in temperature from top
to bottom of the raceway was – 1.8 degrees C. This same data from 2011
are shown in Table 7. During this study period the average decrease in
temperature from top to bottom of the raceway was – 0.4 degrees C.
Interestingly, higher decreases were found for measurements taken
before harvest in 2011 (see Tables 3-5). On these three dates in June
2011 the average decrease in temperature from top to bottom of the
raceway was – 2.4 degrees C, six times greater than measurements taken
after harvest (Table 7). This comparison suggests a direct role in
temperature decreases from the algal biomass.
Algal Species Composition
Although studies described in this report only adequately cover the
summer season (late summer in 2010 and early summer in 2011), an
interesting seasonal succession of algal species seems to occur at
Peach Bottom. In 2010 when water temperatures were highest (high 30s
and low 40s in degrees C) diversity was severely truncated in the
algal community, presumably due to an upper temperature threshold. At
this time to a dramatic extent only two species of blue green algae of
the family Oscillatoriaceae were found and one of these may be a
species new to Science (H. D. Laughinghouse, personal communication).
Under these high temperature conditions the algal community in the
raceway was similar to that found in a thermal spring ecosystem (Brock
1978). Before and after the highest temperatures occur, filamentous
green algae and pennate diatoms increase in relative abundance to join
the blue green species as dominants in the community. During these
periods of cooler water temperatures, the species composition more
closely resembles the composition that was found across the river at
Muddy Run during 2008-2009 (Kangas et al. 2010).
Of interest, aquatic fly larvae of the family Chironomidae reached
outbreak population densities during the fall of 2010 and during early
summer of 2011 (as they did at Muddy Run in 2009). In these outbreaks
the fly larvae cause “eatouts” or bare patches of screen due to their
grazing on algae. Apparently the fly larvae can not persist at the
highest water temperatures during the late summer, but their
population can increase and impact algal productivity at other times
of the year. Additionally, pulmonate snails of the family Physidae
reached high population densities in early summer of 2011 but their
grazing did not cause “eatouts” on the screen.
FUTURE PLANS
Immediate goals of the present project are to:
1.
Operate the system through the winter months of 2011-2012 in order
to measure algal production in heated waters during the cold
season,
2.
Develop enough data on temperature changes from the top to the
bottom of the raceway to quantify the “green cooling tower”
effect, and
3.
Carry out appropriate taxonomic research to establish the identity
of the thermophilic blue green alga that dominated the system in
late summer.
We also hope to begin investigations with an in-water algal production
system (called the Aquatic Biomass Production System) to test the
potential of another design for controlled algal growth with heated
discharge waters.
LITERATURE CITED
Adey, W. H. 2010. Algal Turf Scrubber (ATS) Algae to Energy Project.
Report to the Lewis Foundation, Cleveland, OH.
Adey, W. H., P. C. Kangas and W. Mulbry. 2011. Algal turf scrubbing:
cleaning surface waters with solar energy while producing a biofuel.
BioScience 61:434-441.
Anonymous. 2011. Chesapeake Algae Project: A Report on Research.
Report to the STATOIL Corporation, Norway.
Brock, T. D. 1978. Thermophilic Microorganisms and Life at High
Temperatures. Springer-Verlag, New York, NY.
Kangas, P., W. Mulbry, P. Klavon and H. D. Laughinghouse. 2010. Final
Report on the Susquehanna River Algal Turf Scrubber Project. Appendix
B, pp. 61-82. in: Adey, W. H. Algal Turf Scrubber (ATS) Algae to
Energy Project. Report to the Lewis Foundation, Cleveland, OH.
™ The Algal Turf Scrubber is a trademark registered to the Hydromentia
Company of Ocala, Florida
Table 1. Comparison of late summer 2010 productivity values for the
aluminum ATS at Exelon sites on the lower Susquehanna River. Data are
in units of grams dry weight/m2/day.
Date Muddy Run in 2008 Peach Bottom in 2010
Last week of July 17.5 5.5
Week 1 of August 10.1 8.3
Week 2 of August 8.7 14.9
Week 3 of August 10.5 11.3
Week 4 of August 11.0 17.8
Table 2. Productivity and water flow rate at the experimental ATS
raceway during early summer 2011. The system was operational on
4/29/11.
Date productivity, g dry wt./m2/day water flow rate, gallons/minute
5/6/11 ---- 12
5/27/11 7.1 ----
6/3/11 21.6 13
6/15/11 9.7 9
6/22/11 9.1 9
6/29/11 15.9 8
Table 3. Water quality comparison of inflow and outflow of the
experimental ATS raceway before harvest – 6/29/11.
Parameter top of ATS bottom of ATS
Temperature,
degrees C 34.5 31.2
Dissolved oxygen concentration,
mg/l 6.9 11.5
Percent of oxygen saturation,
% 86 156
Table 4. Water quality comparison of inflow and outflow of the
experimental ATS raceway before harvest – 6/22/11.
Parameter top of ATS bottom of ATS
Temperature,
degrees C 33.5 32.9
Dissolved oxygen concentration,
mg/l 6.1 9.8
Percent of oxygen saturation,
% 86 136
Table 5. Water quality comparison of inflow and outflow of the
experimental ATS raceway before harvest – 6/15/11.
Parameter top of ATS bottom of ATS
Temperature,
degrees C 32.7 29.4
Dissolved oxygen concentration,
mg/l 6.4 10.4
Percent saturation of oxygen,
% 89 137
Table 6. Temperature comparisons of the experimental ATS raceway after
harvest in 2010. Data were gathered around mid-day and are in degrees
C.
Parameter Canal top of ATS bottom of ATS River
7/30/10 40.2 40.0 37.6 30.0
8/6/10 40.0 39.8 38.1 29.7
8/12/10 41.1 41.1 40.4 31.0
8/20/10 39.8 39.5 38.4 28.9
8/24/10 37.9 37.5 34.0 26.4
9/9/10 36.2 35.9 31.0 25.7
9/28/10 33.2 33.5 33.1 23.1
10/8/10 22.5 22.3 22.6 15.5
10/20/10 24.4 ----- ----- 14.1
Table 7. Temperature comparisons of the experimental ATS raceway after
harvest in 2011. Data were gathered around mid-day and are in degrees
C.
Parameter Canal top of ATS bottom of ATS River
5/6/11 25.2 25.0 25.0 14.8
5/27/11 30.4 30.4 30.7 20.9
6/3/11 32.5 32.2 29.9 23.3
6/15/11 34.3 34.0 33.9 25.6
6/22/11 35.5 35.4 36.6 26.2
6/29/11 36.1 35.5 34.0 26.9
APPENDIX 3. Notes on algal species composition.
Microscopy Notes: 2010
7/30/10
Blue green mat that floats – monoculture of very fine
Oscillatoriaceae; no diatoms!
Dark blue green “filaments” – actually colonies of the very fine
Oscillatoria plus afew larger filaments of Phormidium?
Blue green mat that sinks – lots of detritus and large filaments
(Phormidium?) are common – the mat matrix seems like a dense
mucilaginous crust
8/12/10
Mat has several kins of protozoans and worms!
Phormidium is either uncommon or common depending on the patch but the
“filamentous” blue green algae is dominant
Mat is comprised of thick bundles of very thin Oscillatoria that trail
downstream in the current – is this colony-type induced by the high
flow rate?
Lots of detritus in the encrusting mat
10/21/10
An explosion of pennate diatoms; Melosira common; green filaments
(Mougeotia?) are rare
Lots of detritus – probably because the water was turned off
Phormidium is abundant
Microscopy Notes: 2011
5/11/11
Encrusting mat dominated by Oscillatoria with a very diverse set of
pennate diatoms; Phormidium uncommon
Microspora dominates the attached filamentous green algae with lots of
pennate diatoms
6/3/11
Green filaments at top of ATS – dominated by Microspora plus
Phormidium fragments, pennate diatoms are very common but less so than
the previous week? Is rising temperature affecting them? Also a thin
green unidentified filament is uncommon
Encrusting mat – Oscillatoria dominates with Pleurococcus-like di-cell
alga, pennate diatoms are very common
6/15/11
Top filaments – Microspora common but fine green unidentified filament
is dominant – probably Ulothrix, Phormidium fragments rare, pennate
diatoms rare
Middle mat – dominated by Phormidium, Oscillatoria rare, pennate
diatoms common, Spirogyra rare, green unidentified filaments rare –
also other blue green filaments?
Bottom eatout zone – Microspora and Ulothrix dominate, Spirogyra
common, pennate diatoms common
6/22/11
Encrusting mat – dominated by very fine Oscillatoria, Phormidium
uncommon
Main turf – Phormidium rare, Oscillatoria common, Microspora common,
Spirogyra common, pennate diatoms uncommon
Patches of green filaments – dominated by Spirogyra, Ulothrix
uncommon, Microspora rare
6/29/11
Patches of green filaments – Microspora dominates, Spirogyra common,
Oedogonium rare, pinnate diatoms rare, very fine filaments are
uncommon – is this the thermophilic blue green?
Encrusting blue green mat – Oscillatoria dominates, Phormidium rare,
Spirogrya and Microspora uncommon – no pennate diatoms