PilotScale Studies of Cryptosporidium Inactivation Using Ozone

1
Pilot-Scale Studies of Cryptosporidium
Inactivation Using Ozone

• Thomas M. Gigliotti, P.E., Stanley J. States,
  Ph.D.,
• and
• Leonard W. Casson, Ph.D., P.E.
• Pittsburgh Water and Sewer Authority
• and
• University of Pittsburgh

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Problem Statement

• The Pittsburgh Water and Sewer Authority operates
  a 60 MGD drinking water treatment and
  distribution system
• A series of seven open finished water reservoirs
  were constructed in the 1800s and 1900s
• By 1999, all open water reservoirs in the system
  had been covered or replaced except for Highland
  Park 1.

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Problem Statement

• The Pennsylvania Department of Environmental
  Protection has mandated that all finished water
  reservoirs in Pennsylvania be covered
• Highland Park Reservoir 1 has a volume of 125
  MG and also serves as a scenic waterway within
  the City of Pittsburgh and
• Suggestions that this reservoir be covered for
  public health considerations have been met with
  strong resistance from citizens groups.

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Overall Objective

• The objective of this pilot-study was to
  investigate the use of ozone for inactivation of
  Cryptosporidium in finished water, as an
  alternative to covering a finished water
  reservoir.

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Materials and Methods

• Bench-Scale and pilot-scale ozone inactivation
  studies were performed on live Cryptosporidium
  parvum oocysts (approximately 3 x 106) in
  finished water from Highland Park Reservoir 1.
• Oocyst viability was determined using the method
  of in-vitro excystation (Robertson et al., 1993).
• Ozone residual in water was measured using an
  Orbisphere (model 26506) monitor.

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Materials and MethodsBench-Scale Studies

• Bench-scale inactivation experiments were
  performed in 500 ml and 1L Erlenmeyer flasks
• Ozone gas was bubbled through a diffuser stone
  into solution. In addition, a teflon coated
  magnetic stir bar and stirring plate were used to
  disperse the ozone gas into solution and
• Live Cryptosporidium parvum oocysts were pipetted
  directly into the flask after a stable ozone
  concentration was achieved.

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Materials and MethodsPilot-Scale Studies

• Pilot-scale studies were performed using a
  pilot-scale system consisting of two 10.75 foot
  long 4 inch diameter glass contact chambers in
  series
• Fluoride tracer studies were performed to define
  the hydraulic characteristics of the system
• Ozone was injected into the system using a Mazzei
  venturi injector (Model 384) and
• Live oocysts were injected downstream of the
  venturi.

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Pilot-Scale Treatment Schematic
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Bench-Scale Ozone Inactivation of
Cryptosporidium parvum oocysts
 
   
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Pilot-Scale Ozone Inactivation of
Cryptosporidium parvum oocysts
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Cryptosporidium parvum Inactivation Using Ozone
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Summary and Conclusions

• In bench-scale studies using finished drinking
  water, ozone inactivated up to 1.2 log-units of
  Cryptosporidium
• In pilot-scale studies using finished drinking
  water, ozone inactivated up to 0.5 log-units of
  Cryptosporidium at reduced water temperatures
• Ozone inactivation of Cryptosporidium was
  observed to decrease with decreasing water
  temperatures

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Summary and Conclusions(Continued)

• For similar CT values, ozone was observed to be
  more effective in inactivating Cryptosporidium in
  bench-scale studies than in pilot-scale studies
• Bench-scale studies from this research and
  previously reported research have shown ozone to
  be an effective disinfectant for Cryptosporidium
  however, pilot-scale results reported herein did
  not support the findings of the bench-scale
  studies

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Summary and Conclusions(Continued)

• A scale-up factor must be applied in translating
  results from bench-scale to pilot-scale. However,
  this factor appears to be greater than reported
  in the literature and
• Additional pilot-scale studies are necessary to
  confirm the results reported herein.