Wet Weather Planning for Wastewater Treatment Plants June 23, 217
Peak Flow Management: Collection vs. Treatment Collection System Peak Flow Management Single 24 hour design storm I/I reduction SSO elimination by increasing system capacity WWTP Peak Flow Management All flows go to the WWTP Increased peak flows to the WWTP Single storm event is not indicative of wet weather event Wet weather periods of longer duration
Collection System Hydrograph Peak Flow Multiplier x Q avg 4. 3.5 3. 2.5 2. 1.5 1. 5 YR, 24 Hour Peak Flow Hydrograph SSOs Flows Metered Peak at WWTP 4 8 12 16 2 24 Time (Hrs)
Pre I/I and SSO Reduction Program Base Flow Infiltration Inflow Overflow Manhole Inflow Infiltration Overflow Manhole Sanitary Sewer Overflows (SSOs) Inflow Infiltration Overflow Manhole Inflow Infiltration Wastewater Treatment Plant Base Flow Plant Influent Flow System Outflows Infiltration / Inflow 2.5 x Q avg 1.5 x Q avg Flow Profile, Pre SSO Reduction
I/I Reduction & SSO Elimination Peak Flow Multiplier x Q avg 4. 3.5 3. 2.5 2. 1.5 1. 5 YR, 24 Hour Peak Flow System Hydrograph Projected Peak Flows to WWTP 15% I/I Reduction 4 8 12 16 2 24 Time (Hrs)
Post I/I and SSO Reduction Program Base Flow Infiltration Manhole Inflow Inflow Surcharge Inflow Infiltration Manhole I/I Reduction and SSO Elimination Manhole Wastewater Treatment Plant Base Flow Infiltration / Inflow 3.25 x Q avg Plant Influent Flow System Outflows Eliminated Flow Profile Post SSO Reduction
Reality of I/I and SSO Reduction at the WWTP Post I/I and SSO Reduction Increased Peak Flow Base Flow Plant Influent Flows Base Flow Infiltration / Inflow 2.5 x Q avg Infiltration / Inflow 3.25 x Q avg Collection System Outflows Pre I/I and SSO Reduction
Wet Weather Event Duration Peak wet weather flows to WWTPs are not representative of a single 5-yr. 24 hr. Storm event Typical wet weather events last 7 to 1 days Events may not or may not contain a 5-yr. 24 storm event Daily rainfall totals are key to designing a representative Wet Weather Event
Building Representative WWE Flow 7Q Coupling SS Modeling Results w/ Measured Flows Rainfall Hydrographs 6Q 5Q Flow (MGD) 4Q 3Q 2Q 1Q WWE Recorded Influent Flow (Q) Modeled Hydrographs for WWE Daily Rainfall 24 48 72 96 12 144 168 192 216 24 48 Time (Hrs)
Representative WWE Design Flows 7Q 6Q Recorded Flow Data Coupled w/ SS Modeling Results Design WWE (Q) Recorded Influent Flow (Q) Historical Diurnal Flow Pattern (Q) 2 hr. Peaks Flow (MGD) 5Q 4Q 3Q 2Q Average Sustained Peak Flow 1Q 24 48 72 96 12 144 168 192 216 Time (Hrs)
Historic Peak Rainfall Intensity
Peak TSS Loadings Pollutographs
Developing Peak Solids (TSS) Loading Requires data sets; Peak TSS concentration for increasing antecedent dry weather conditions. Peak TSS loadings during measured peak influent flows.
Resulting Pollutograph 5 YR, 24 Hour Peak Flow System Hydrograph Peak Flow Multiplier x Q avg 4. 3.5 3. 2.5 2. 1.5 1. 3 hour Flow to WWTP TSS Concentration 7. 6. 5. 4. 3. 2. 1. Peak TSS Multiplier x TSS avg 4 8 12 16 2 24 Time (Hrs)
Design WWE Solids Loading Profile: First Flush Pollutograph 1,38 mg/l 7Q 15 hour 1,4 Design WWE (Q) 6Q Historical Diurnal Flow Pattern (Q) TSS Concentration (mg/l) 1,2 5Q 1, Flow (Q) 4Q 3Q 2Q 2.2 Q 8 6 4 TSS ( mg/l) 1Q 2 24 48 72 96 12 144 168 192 216 Time (Hrs)
Optimizing Peak Wet Management at the WWTP Peak Flow Process Addition COMPLEXITY $$$ Peak Flow Storage Addition Maximize Sustained Treatment Capacity Primary Objective is to Protect the Biological Process
Sustained Treatment Capacity & Remaining Excess Flow 7Q 6Q 5Q Design WWE (Q) Historical Diurnal Flow Pattern (Q) Total Mass Loading (mg/l) Sustained Treatment Capacity 1,4 1,2 1, Flow (Q) 4Q 3Q 3.8 Q Excess Flow 8 6 TSS ( mg/l) 2Q 4 1Q Sustained Treatment 2 24 48 72 96 12 144 168 192 216 Time (Hrs)
Step Feed Addition Maximizes Sustained Peak Flow Treatment Step Feed Arrangement Step Feed Vortex Grit Primary Clarifier Secondary Clarifier Effluent Filters Aeration Basin Cost effective, no permitting required, and slightly increases complexity. RAS Disinfection
RAS Storage Addition Maximizes Sustained Peak Flow Treatment Offline MLSS Storage Arrangement Vortex Grit Primary Clarifier Aeration Basin Secondary Clarifier Effluent Filters MLSS Storage Basin RAS Disinfection Less cost effective and more complex, but no permitting required, and provides better protection of RAS.
Addition of Offline Storage Increases Peak Flow Capacity Raw Offline Influent Storage Vortex Grit Primary Clarifier Aeration Basin Secondary Clarifier Effluent Filters EQ Basins Cost effective, easily permitted, but increases complexity, and isn t as aesthetically acceptable. Disinfection
Addition of Partially Treated Peak Flow Storage Increases Capacity High Rate Clarification Storage Vortex Grit Primary Clarifier Aeration Basin Secondary Clarifier Effluent Filters High Rate Clarification EQ Basins Disinfection Less cost effective, increased complexity, but easily permitted, and more aesthetically acceptable
Addition of Parallel Phys./Chem. Process Increases Treatment Capacity Enhanced High Rate Clarification Vortex Grit Primary Clarifier Aeration Basin Secondary Clarifier Effluent Filters High Rate Clarification Disinfection Cost effective, but difficult to permit, and complex to operate intermittently.
Addition of Parallel Peak Flow Biological Process Increases Treatment Capacity High Rate Biological Treatment Arrangement Vortex Grit Primary Clarifier Aeration Basin Secondary Clarifier Effluent Filters High Rate Biological Process Disinfection Less cost effective and more complex to operate intermittently, but easily permitted.
Analyze Conventional/High Rate Treatment vs. Storage 7Q 6Q 5Q Design WWE (Q) Peak Flow Treatment Capacity (Q) Total Mass Loading (mg/l) Sustained Treatment Capacity (Q) 1,4 1,2 1, Flow (Q) 4Q 3Q Storage Volume 8 6 TSS ( mg/l) 2Q Peak Flow Treatment 4 1Q Sustained Conventional Treatment 2 24 48 72 96 12 144 168 192 216 Time (Hrs)
Optimization & Cost Savings Treatment and storage options must be balanced based on total associated costs Site Constraints Aesthetics
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