CLINTON STREET CSO ABATEMENT ENVIRONMENTAL INFORMATION DOCUMENT CSO TREATMENT TECHNOLOGIES ADVANTAGES AND DISADVANTAGES
Treatment Technology
Sewer Separation
Advantages
• Separates sanitary wastewater from combined sewage for separate treatment at wastewater treatment plant. • Provides high degree of pollutant removal, including nutrients, contained in sanitary sewage. • Low operation and maintenance requirements in comparison to other CSO abatement approaches.
Disadvantages
• Requires disconnection of existing building sewers from combined sewer and connection to new sanitary sewer (highly disruptive construction in urban areas including business access impacts, pedestrian traffic impacts, extensive utility relocations, etc.). • May require building re-plumbing to separate sanitary piping from roof drain piping. • Does not eliminate contamination associated with urban stormwater runoff: - Suspended solids - Oil and grease - Antifreeze - Trash, floatables - Pathogens - Heavy metals - Nutrients - Organics - Pesticides - Fertilizers • Larger separate stormwater discharges will likely require separate treatment to comply with forthcoming Federal Standards. • High initial capital cost in comparison to RTF CSO abatement approaches. • Extended implementation period when compared to RTF implementation period; results in delayed water quality benefits. • Land area requirement (2-3 acres) results in limited siting alternatives within an urban area. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs. • Above grade facilities will have more visual impact in comparison to regional storage facility
Vortex Separators
Vortex Separators
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• Designed to operate under all, including extremely high, flow conditions. • Reduced land area requirements in comparison to the Overflow Retention Facility (ORF) and storage alternatives. • High degree of settleable solids and floatables removal. • Provides sufficient treatment for downstream disinfection. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller
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Treatment Technology
(continued)
Advantages
area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Provides slightly enhanced removal efficiency in the vortex separator compared to non-enhanced vortex separator. • Reduced land area requirements in comparison to ORF and storage alternatives. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Potential to remove some TSS and BOD. • May provide sufficient treatment for downstream disinfection. • Reduced land area requirements in comparison to ORF alternative. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • High degree of TSS, BOD, settleable solids, TKN, and TP removal. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed.
Disadvantages
Enhanced Vortex Separators
• Technology has only been demonstration tested at low operating/loading rates. • Lengthy start-up time required to stabilize the operation. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Continuous Deflective Separation (CDS)
• Limited operating experience. • Potentially high operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Ballasted Flocculation
Lengthy start-up time required to stabilize the operation. Preliminary fine screening is required. High operation and maintenance. Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs. • • • •
Coarse Screening
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• Proven floatables and solids removal for solids greater than 1-inch.
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• Poor TSS and BOD removal may require additional provisions downstream to remove the pollutants in order to
Treatment Technology
Advantages
• Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Smaller space requirements in relation to other CSO technologies (provided downstream treatment is not required).
Disadvantages
achieve target bacterial reduction limits. • Potentially high operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Fine Screening
• Proven floatables and solids removal for solids greater than 1/6-inch. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Smaller space requirements in relation to other CSO technologies (provided downstream treatment is not required). • Somewhat effective at removing floatables and solids. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Capable of removing floatables and solids greater than 1/12-inch. • Considerable TSS and BOD removal. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Smaller space requirements in relation to other CSO
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• Poor TSS and BOD removal may require additional provisions downstream to remove the pollutants in order to achieve target bacterial reduction limits. • Potentially high operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Brush Screens
Rotary Drum Screen/Sieves
• Limited operating experience. • Poor TSS and BOD removal may require additional provisions downstream to remove the pollutants in order to achieve target bacterial reduction limits. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs. • Preliminary coarse screening is required. • High operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Rotary Drum Screen/Sieves (continued)
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Treatment Technology
technologies. Microscreens
Advantages
• Capable of removing floatables and solids greater than 74 microns. • High degree of TSS, BOD, and settleable solid removal. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Capable of removing floatables and solids greater than ½-inch. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Captures smaller intensity storms for post-storm treatment at wastewater treatment plant. • High degree of settleable solids and floatables removal. • Provides sufficient treatment for downstream disinfection. • Provides capture and treatment of stormwater pollutants, as well as sanitary wastewater pollutants. • Disruption due to construction is confined to a smaller area in comparison to sewer separation. • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed. • Smaller abovegrade facilities will result in less visual impact in comparison to vortex separator facility. • Conveys a large volume of CSO to wastewater treatment plant for treatment in comparison to a vortex separator facility.
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Disadvantages
• Preliminary coarse or fine screening is required. • High operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs.
Net Bags
• Poor TSS and BOD removal may require additional provisions downstream to remove the pollutants in order to achieve target bacterial reduction limits. • High operation and maintenance. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • May not allow permanent closure of CSOs. • Land area requirement (2-3 acres) results in limited siting alternatives within an urban area. • Larger consolidation pipelines required for regional treatment facilities will require deeper and wider excavation areas in comparison to sewer separation. • Less efficient during high flow rates in comparison to vortex separator facility. • Requires additional land area requirements in comparison to vortex separator facility. • Requires larger capacity pumps to dewater the facility in the same amount of time as the vortex separator facility. • May not allow permanent closure of CSOs. • Above grade facilities will have more visual impact in comparison to regional storage facility.
Overflow Retention Facility (ORF)
ORF (continued)
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Treatment Technology
Storage Facility
Advantages
• Captures higher volume storms for post-storm treatment at Metro • High degree of settleable solids, TSS, BOD, TKN, P and floatables removal • Provides capture and treatment of storm water pollutants as well as sanitary wastewater pollutants • Disruption due to construction is confined to a smaller area in comparison to sewer separation • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed • Smaller above grade facilities will result in less visual impact in comparison to vortex separator facility and overflow retention facility (ORF) • Conveys a larger volume of CSO to Metro for treatment in comparison to a vortex separator facility and ORF • Higher degree of settleable solids, TSS, BOD, TKN, P and floatables removal in comparison to full service area vortex separator • Provides capture and treatment of storm water pollutants as well as sanitary wastewater pollutants • Provides sufficient treatment for downstream disinfection • Disruption due to construction is confined to a smaller area in comparison to sewer separation • Existing sanitary connections and storm leaders within buildings in the urban area are undisturbed • Smaller above grade facilities will result in less visual impact in comparison to full service area vortex separator facility • Conveys a larger volume of CSO to Metro for treatment in comparison to a full service area vortex separator facility • Has lower annual O&M costs in comparison to full service area vortex separator
Disadvantages
• Land area requirement (2-3 acres) results in limited siting alternatives within an urban area • Larger consolidation pipelines required for regional storage facilities will require deeper and wider excavation areas in comparison to sewer separation • Does not provide back-to-back storm protection for nondisinfected bacteria laden discharges. • Requires additional land area requirements in comparison to vortex separator facility and ORF • Requires larger capacity pumps to dewater the facility in the same amount of time as the vortex separator facility and ORF • May not allow permanent closure of CSOs • For Clinton Street CSO service area, MIS available capacity limits total allowable storage volume, requiring additional, more costly sewer separation • Requires additional land area requirements in comparison to full service area vortex separator facility • Larger consolidation pipelines required for regional storage facilities will require deeper and wider excavation areas in comparison to sewer separation • Requires larger capacity pumps to dewater the facility in the same amount of time as the full service area vortex separator facility • May not allow permanent closure of CSOs • Has higher total project cost, construction cost and net present worth cost in comparison to full service area vortex separator • Requires greater need for groundwater pumping and risk of settlement due to more extensive deep excavation in comparison to full service area vortex separator
Upstream Storage/Reduced Size Vortex Separator
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