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A wastewater treatment facility’s experience with a fresh water sponge infestation and methods used in control and eradication John Bowman, Regional Business Manager, CH2M HILL
A wastewater treatment facility’s
experience with a fresh water
sponge infestation and methods
used in control and eradication
John Bowman, Regional Business Manager,
CH2M HILL
Dried Sponge
Background
Prescott Valley, Arizona, Wastewater Treatment Plant, owned
by town and operated and maintained by CH2M HILL
Fungus-like growth first discovered in summer 2008
Sample sent to Dr. Michael Richard for analysis
Identified as species of fresh water sponges
Background
First thought to be beneficial to wastewater treatment process,
as may feed on nutrients left after tertiary filtration
Methods of removal were discussed in case sponges became a
problem
Eventually, sponges became a problem
Sponge structure magnified
Infestation
Effluent numbers varying without explanation
– Staff investigation discovered extreme number of sponges in effluent
discharge line
– Line jetted to restore flow and readings
Heavy sponge accumulations removed manually
– Disk filters
– Ultraviolet racks
– Effluent storage pond
Disk filters removed for cleaning
Disk filter membrane support frame
Challenges
Sponges interfered with filtration, UV disinfection, and effluent
flow measurements
Informational search provided minimal results
No information found on control methods
Other CH2M HILL facilities were questioned, but none had
experience with sponge infestation
UV disinfection system
UV channel
Effluent storage pond
Effluent storage pond
Challenges
One technologist with CH2M HILL had some experience
Suggested dosing system with chlorine
– No consensus on concentration, how and where to feed, or exposure length
Pilot study determined necessary
Challenges
PVWWTP uses tertiary Aqua Aerobics disk filters
– Fabric not compatible with chlorine
– Replacement fabric was $26,000
Could take filter offline and use retired sand filters
– Sand filters had been offline for more than a year
– Extensive work required to return them to operational state
Challenges
UV disinfection system not compatible with chlorine residuals
greater than 3 mg/L
– If chlorine used, UV system would need to be taken offline
– Lamp assemblies would need to be removed from channels
– Chlorine then required as disinfectant for final effluent
– ADEQ would need to approve change
– Discharge permit does not allows discharging chlorine residual
– Dechlorination of effluent would be required
Dye testing revealed 7.5 minute detention time
Challenges
Gary McConnell, Town of Prescott Valley, conducted further
research
– Found articles online by Dr. Tim Wood
– Had experience with dealing with similar organisms called bryozoans in
Asia, specifically Thailand
– Dr. Wood was consulted and recommended treatment plan
Potassium permanganate (KMnO4) at 50 ppm would be used to
fight sponge infestation
Pilot test objectives
Primary – Test recommended dose of KMnO4 in small scale
control environment
Secondary – Observe and record any unintended consequences
of treatment
Pilot test
Bio-boxes were built and sponge colonies established in them
Pumping system ensured flow of filtered plant effluent
Solution of 50 mg/l KMnO4 was prepared
Chemical feed rate was 2.8mL/min per
Sponges in bio-boxes
Pilot test
One bio-box was dosed with 50 mg/l solution for one hour
Other bio-box was control
24 hours later, one sponge removed from both boxes
– Sponges were examined and broken open
– Putrid odor, indicating dead or dying sponge, was present in dosed sponge
Normal effluent flow was continued for additional month to test
for sponge reestablishment in test box
Bio-boxes during pilot test
Bio-boxes during pilot test
48 hour test results
Treated sponges
– Appear darker in color and more granular
– Stronger odor when removed and split open
Smaller sponges responded more to treatment than larger
sponges
Sponges 48 hours later
Sponges 48 hours later
Sponges 48 hours later
8 days after treatment
Blood worm observed in test tank
– Control tank remained lifeless
Treated sponges remained dark in color
– Control sponges stayed bright white
Treated sponges also had strong, musty odor when broken
open
– Odor absent in control sponges
Sponge comparison 8 days after treatment
Treated sponge 8 days after treatment
Full-scale treatment
System cleaned prior to full treatment
– Sponges removed from disk filters, UV racks, and effluent storage pond
KMnO4 color comparison standards were made at 50, 40, 30
10, 0.5 and 0.3 mg/L levels
Treatment solution mixed
– 17.4 pounds of KMnO4 to 35.7 gallons of water
Disk filter cleaning
Sponges removed from UV system
Disk filter effluent launder
KMnO4 standards
Mixing KMnO4 solution
Full-scale treatment
Effluent storage pond
– No discharge of KMnO4 allowed, so held in effluent storage pond
– Pond holds 123,000 gallon or 26,000 gallons per foot
– Pond level lowered 2.7 ft to hold 71,000 gallons of treated effluent, based
on 0.5 mgd (347 gpm) for 2 hours
– Pumped pond down to 1 foot, using recharge and utility water pumps
Started with clarifier number one, treating for 30 minutes at 0.3
gpm.
Dosed clarifiers two and three
Clarifier number one
Disk filter launder during treatment
Full-scale treatment
When color reached UV channel, discharging stopped and flow
diverted to holding pond
Pond level reached 1.5 ft, utility pumps started
Belt filter presses run in wash down mode
Non-potable hose bibs opened to distribute solution throughout
plant water system
After all traces of KMnO4 were gone from holding pond, normal
flow was re-established
Effluent holding pond
Discussion
KMnO4 treatments successfully reduced sponge population
and their negative impacts
Additional treatments have been required
Sponges appear to becoming immune to the solution
Infestation continues to be monitored
Work to keep sponge population in check is performed regularly
Staff continues to research freshwater sponges and study other
methods to better manage or totally eradicate the infestation
Conclusion
Bryozoans are rare problem at wastewater treatment plants
which hampered understanding and treatment
Teamwork and extensive research contributed to discovering
the sponges nature and figuring out how to control them
Questions?
Thank you!
