A wastewater treatment facility s experience with a fresh water sponge infestation and methods used in control and eradication

Transcription

1 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

2 Dried Sponge

3 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

4 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

5 Sponge structure magnified

6 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

7 Disk filters removed for cleaning

8 Disk filter membrane support frame

9 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

10 UV disinfection system

11 UV channel

12 Effluent storage pond

13 Effluent storage pond

14 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

15 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

16 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

17 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

18 Pilot test objectives Primary Test recommended dose of KMnO4 in small scale control environment Secondary Observe and record any unintended consequences of treatment

19 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

20 Sponges in bio-boxes

21 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

22 Bio-boxes during pilot test

23 Bio-boxes during pilot test

24 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

25 Sponges 48 hours later

26 Sponges 48 hours later

27 Sponges 48 hours later

28 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

29 Sponge comparison 8 days after treatment

30 Treated sponge 8 days after treatment

31 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

32 Disk filter cleaning

33 Sponges removed from UV system

34 Disk filter effluent launder

35 KMnO4 standards

36 Mixing KMnO4 solution

37 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

38 Clarifier number one

39 Disk filter launder during treatment

40 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

41 Effluent holding pond

42 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

43 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

44 Questions? Thank you!