Pathogen Flow Tool (PFT)

Predicts the reduction and flow of pathogens (viruses, bacteria, protozoa and helminths) through onsite sanitation and centralized treatment systems to support the selection of technologies and interventions

About the Tool

  • Predicts pathogen reduction by group (i.e., bacteria, viruses, protozoa and helminths) for a given combination of treatment technologies based on design, environmental, and operational factors
  • Allows users to run scenarios to compare baseline conditions with onsite sanitation interventions or centralized treatment system upgrades
  • Consists of an on-site sanitation and centralized sanitation system component
  • There are three ways to use the tool:
    1. on-site only,
    2. centralized only,
    3. on-site and centralized treatment together (i.e., the entire sanitation service chain)

How to Use the Tool

  1. Define a geographic boundary by drawing a polygon to select the desired area or by using the search bar at the top. The population size is auto-populated based on underlying georeferenced population databases. The prevalence rate for a particular pathogen of interest can be specified by the user, otherwise it is assumed to be 15%.
  2. Upload your own data or select from available data. The tool provides a template to input your own data (or assumptions) about onsite sanitation services, or you can select from data compiled through the UNICEF/WHO Joint Monitoring Program. Note: This step is used for analyzing onsite sanitation systems (option A) or the entire sanitation service chain (option C). Users only concerned with centralized treatment (option B) can skip this step.
  3. Choose or sketch a centralized treatment system. Users can a) select from a drop-down menu of typical wastewater or fecal sludge treatment plants or b) use a customized “drag and drop” online tool to “sketch” out the configuration of the centralized treatment system, specifying whether the treatment plant accepts sewage, fecal sludge, or both, then specifying which unit processes are included in the treatment plant, how they are designed and operated, how they are connected and configured (e.g., in series or in parallel), how residuals (sludge) are managed or treated, and how the final treated effluent and biosolids are discharged or reused. Note: This step is used for analyzing centralized treatment systems (option B) or the entire sanitation service chain (option C). Users only concerned with onsite sanitation (option A) can skip this step.

  1. Run the model and view the results and visualizations. On this page, you can view or download model outputs that show the following results:

    • For onsite sanitation component is used (option A), the following results can be downloaded:
      • jmpLadder.csv: A plot or table showing a “JMP-like” sanitation ladder (% open defecation, % unimproved, basic, or safely managed sanitation) for each region or subregion specified in the data set
      • onsiteReduction.csv: A plot or table showing the percent of pathogens reduced, broken down by geographic region or by sanitation technology
      • onsiteLoading.csv: A plot or table showing the number of people using different onsite sanitation technologies compared with the estimated emissions coming from each technology
    • If the centralized treatment component is used (option B), the following results can be downloaded:
      • centralReduction.csv: A plot or table showing the predicted log reduction values for the different centralized treatment plant sketches the user would like to compare
      • centralLoading.csv: A plot or table showing the predicted pathogen loads coming into the treatment plant in fecal sludge vs. sewage, and the predicted pathogen loads exiting the treatment plant in liquid effluent and sludge biosolids, for each of the different centralized treatment plant sketches the user would like to compare
    • If both onsite and centralized components of the tool are used (option C), the user can download all of the results shown above, plus the following additional result:
      • overallLoading.csv: A plot or table showing the breakdown of pathogens emitted to the surface, to the subsurface (groundwater), in treated liquid effluent from a treatment plant, or in the sludge biosolids from a treatment plant.

Highights of the Pathogen Flow Tool

Onsite Sanitation Component
  • It estimates the pathogen decay (die-off) rate in a pit with respect to time and the use of different additives or disinfectants (lime, ash, urea, lime + urea, etc.)
  • It estimates the loadings and the percent reduction of pathogens achieved onsite (broken down by technology type or broken down geographically by region or subregion)
  • It shows a breakdown of which technologies are most responsible for pathogen emissions to the surface or to the subsurface, and compares the relative total emissions to the percent of people using these technologies
Centralized Treatment Component
  • It allows users to create customized sketches of their treatment plant(s) or proposed upgrades to their treatment plant(s), showing the unit processes how they are arranged (in series or parallel).
  • It predicts the overall reduction of pathogens achieved in onsite and centralized portions of the sanitation service chain.
  • It predicts the number of pathogens emitted annually in the sludge (biosolids) compared with the number of pathogens emitted annually in the liquid effluent of a treatment plant.
  • For some of the treatment technologies, the user can also specify design, operational, or environmental factors that influence pathogen reduction efficiency, such as hydraulic retention time and depth (for ponds) or holding time (for sludge drying beds).
  • Pathogen reduction models for viruses, bacteria, protozoa and helminths are available for the following technologies in the tool:
  • Waste stabilization ponds (anaerobic, facultative, or maturation). Predicted pathogen reduction varies based on ambient temperature, pond depth, and retention time.Facultative ponds (can vary temperature, depth, and retention time)
  • Sludge drying beds (covered). Predicted pathogen reduction varies based on the initial moisture content and the total holding time.
  • Trickling filters
  • Settling or sedimentation basins

Current Limitations

  • The model currently cannot predict the reduction of pathogens from pit toilets to the groundwater (i.e. removal by the soil); the model assumes a 2-log (99%) reduction, although users can specify a different assumed removal value for the purposes of running scenarios.
  • The model currently does not have disinfection added as a process for centralized treatment plants.

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