Post-Storage Treatment Process Considerations
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Post-Storage Treatment Process Description and Considerations Treatment Alternatives Target Pollutants Capital Cost O&M Level Energy Needs Advantages over Alternatives Disadvantages over Alternatives
Dissolved Solids Removal Filtration generally is used to remove residual solids that will not settle spontaneously from harvested water through sedimentation or which may become re-suspended in storage. Filters come in a variety of different types and sizes. The type of filter depends on the class of pollutants targeted for removal. Coarse & fine filters
  • Suspended solids
Med Med Med
  • Lower overall O&M costs than other filtration
  • Does not remove micro-organisms
  • Suspended solids
  • Micro-organisms
Med Med Med
  • Smaller footprint required
  • May reduce disinfection requirements
  • Captures microorganisms
  • Higher capital costs
  • Higher O&M costs including membrane replacement, energy, performance monitoring, and residuals disposal
  • Dissolved salts
  • Bacteria/ viruses
  • Proteins
Med Med High
  • Requires less energy than reverse-osmosis and ion-exchange filters
  • Requires large amount of pretreatment to remove metals that cause scaling and particulates that cause biofouling
  • Produces a larger waste stream than reverse-osmosis
  • Dissolved salts
  • Dissolved solids
  • Ions
  • Bacteria/ viruses
High High High
  • Highest removal efficiency
  • Produces the smallest waste stream
  • Commercially available
  • Requires more energy than nanofiltratoin
Ion-exchange filter
  • Charged ions
  • Dissolved salts
High High High
  • Requires the least amount of pretreatment
  • Produces the largest waste stream
  • Requires more energy than nanofiltration
  • Make-up water is required to continuously wash membranes
Disinfection Disinfection processes kill, remove, or deactivate pathogenic microorganisms in harvested water. Chlorination – injects chlorine into stormwater
  • bacteria
  • viruses
  • other pathogenic organisms
Low Low Low
  • Most common disinfection technology
  • Least cost
  • Requires calibration of dosage control devices
  • Does not kill cysts
Ultra-violet light (UV) radiation – stormwater is passed over an ultraviolet lamp
  • bacteria
  • viruses
  • other pathogenic organisms
Med High High
  • No byproducts
  • Minimal energy requirements compared to chlorination/ozonation
  • Requires cartridge filters ahead of the UV light, with routine cleaning of filters – UV is ineffective on unfiltered stormwater
  • UV lamps must be replaced periodically
Ozonation – diffused ozone released through a fine bubble diffuser at the bottom of the storage tank (possible with stormwater but rarely used) Med Med Med
  • Also removes dissolved organics
  • More effective disinfectant than chlorination
  • Treatment of off-gases required
  • High energy requirements
  • Corrosion protection required
  • Requires monitoring of influent to adjust doses
  • Requires routine check for leaks
Other treatments (e.g., pH adjustment) Treatment for pH adjustment may be needed if the end use of harvested water requires a neutral pH or if harvested water will come in contact with metal pipes or surfaces. Rainwater tends to be slightly acidic and harvested stormwater may retain this characteristic. Acidity can cause metal pipes to corrode leading to contamination of harvested water. Chemical additive
  • acidic or alkali substances
Low Low Low
  • N/A
  • N/A