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!