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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.	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
	Micro-filtration	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
	Nano-filtration	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
	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	X	X
	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