Presentation on theme: "Desalination Becomes A Reality In Tampa Bay Florida"— Presentation transcript:
1Desalination Becomes A Reality In Tampa Bay Florida Interaction of Clarifiers with Other FacilitiesClarifier Design MOP FD-8Jim JensenSenior Project Manager PB Water Area ManagerParsons Brinckerhoff Quade & Douglas, Inc. San DiegoNBWA Water ConferenceApril 2, 2004Nikolay Voutchkov, PE, DEESenior Vice PresidentPoseidon Resources Corporation
2Clarifier Interactions Clarifier Performance Is Affected by:Wastewater Collection System;Screening Facilities;Grit Removal System;Plant Side-streams.Clarifier Performance Impacts:Biological Treatment;Solids Handling.
3Effect of WW Collection System on Clarifier Design Combined Sewer Systems – Subject to Wide Flow Variations;CSO Control Measures Necessitate Clarifier Design for Peak Wet-Weather Conditions;Transient Flows Impact Clarifier Effluent Quality and Sludge Density;Cooler Storm Water Deteriorates Clarifier Settling and Overall Hydraulic Performance;Prolonged Wet-Weather Events Result in Grit Washout to Primary Clarifiers;I&I Reduction Programs Result in 5 to 25 % of Influent Flow Decrease and Wastewater Strength Increase:Increase in Sludge Production and Blanket Depth;Elevated Potential for More Frequent Sludge Bulking.
4Impact of Sewer System on Clarifier Design Average and Peak Daily Flows Used to:Calculate Hydraulic and Solids Loading Rates;Select Type, Size and Configuration of Sludge Collection and Withdrawal Systems.Peak Hourly Flow Used to:Estimate Maximum Clarifier and Sludge Blanket Depths;Identify the Need for Flow Equalization;Determine Sludge Inventory Control Strategy During Transient Flow Conditions.Peak Instantaneous Flow Used to:Determine Influent Pump Capacity;Select Sludge Blanket Depth Control Strategy.
5Transient Flow Impact Mitigation – Sewer System Complete More Frequent Sewer Line Cleaning Restores System Storage Capacity;Reduce Peak Industrial Discharge Flows by On-Site Equalization;Enlarge Bottlenecking Sections of the Sewer System;Construct Sewer System Retention Tanks;Implement Comprehensive I&I Reduction Program.
6Transient Flow Impact Mitigation – Treatment Plant Equalize Influent Flows/Loads;Use Deep Clarifiers;Reduce Sludge Inventory;Increase RAS and WAS Rate;Use Sludge Contact Stabilization;Implement Step-Feed Aeration;Construct Adjustable Aeration Basin Effluent Weirs;Shut Down Aeration For a Brief Period of Time.
7Flow and Load Equalization Typically Cost-Effective if Plant Peak Hourly Factor > 2.5;Allows Decreasing Size and Depth of Primary & Secondary Clarifiers;Provides Opportunity to Run at Higher Sludge Inventories (MLSS & SRT);May Cause Odor Problems;Equalization of Primary Effluent More Desirable.
13Lower Solids Inventory = Reduced Sludge Blanket An Alternative to Deeper Clarifiers or Lower SORs;Only Suitable When SRT can Be Reduced Significantly (20 to 40 %) w/o Effluent Quality Penalty;Limited Application for BNR Systems;Main Reason Why Shallow and Deep Clarifiers May Show Similar Performance.
14RAS and WAS Rate Increase RAS Rate Increase Has Only Temporary Relief Effect and is Limited by Critical Flux;WAS Increase After Critical Flux is Reached;Gradual Increase in Essential – “Rat-holing”;Design RAS Pump Capacity % of Avg. Dry-Weather Flow or 50% of Peak Wet Weather Flow.WAS Pump Capacity – Determined by Min SRT Acceptable at Wet Weather Conditions.
15Contact Stabilization Sludge Moved Out of the Anaerobic Clarifier BlanketAnd Shifted to Aerobic Conditions.Contact Zone – 1 to 2 Hrs of HRTStabilization Zone – 4 to 6 Hrs of HRT
17Clarifiers & Pretreatment Influent Pumps (Hydraulic Surges):VFDs;Screw Pumps – Dampen Flow Variations.Screens – Type and Size Affects Sludge:Grinders – 5 to 10 % Sludge Increase.Clarifier Sludge Collection & Withdrawal Affected;Suction Sludge Withdrawal Not Suitable for Grinders;Use of Grinders May Plug Lamella Openings.
18Grit Chamber Performance Impacts Sludge Quantity and Quality Effective Grit Removal Is Essential;Grit Accumulates in Primary Sludge and Digesters;Excessive Grit in Primary Sludge May Cause Collector Mechanism Damage;De-gritting of Primary Sludge Recommended if Grit Chambers are Overloaded/Ineffective;Aerated Grit Chambers Help Address Sludge Septicity/Excessive H2S;Good Point of Chemical Addition for Mixing & Flocculation.
19Primary Clarifiers & Nutrient Removal Sedimentation Affects BOD : N : P Ratio;Chemical Phosphorus Removal:Over 90 % of Particulate Phosphorus Could Be Removed;Use of Iron Salts Also Controls Odors/H2S;Use of Aluminum Salts Minimizes Phosphate Release in Anaerobic Digesters;Increased Sludge Amount and Elevated Metal Content;Reduction in Influent Alkalinity (5.8 mg/mg Al & 2.5 mg/mg Fe);Excessive Removal Could Hinder Denitrification Due to Nutrient Deficiency.
20Use of Primary Clarifiers for Solids Pre-fermentation Volatile Fatty AcidsVolatile Fatty AcidsSludge RecirculationRegular Removal of Methane Organisms
21Secondary Clarifier Design for Enhanced Nutrient Removal Apply Conservative SOR – 300 to 600 gpd/sf;Use Deep Clarifiers – 12 to 16 ft SWD;Maintain Shallow Sludge Blankets < 1.5 ft/ Leave 0.6 ft of Blanket for Compaction;Keep Sludge Blanket Retention Time Below 3 Hrs;Design for High RAS Rates (50 to 75 %);Provide Anaerobic or Anoxic Selectors to Control Filaments;Operate at High DO Levels – 2.5 to 3 mg/L;
22Interaction With Thickeners Thickening in Deep Primary Clarifiers is OK - 3 to 6 % Solids;If Influent Prone to Septicity – Use Shallow Clarifiers & Thicken Separately;Thickening in Secondary Clarifiers Usually Causes More Harm than Good;Co-thickening in Primary Clarifiers:Suitable for Trickling Filter Sludge;Usually Detrimental for Primary Clarifiers in WAS Used.When in Dough – Thicken Separately!
23Interaction With Anaerobic Digesters Homogenous Sludge Feed is of the Essence;Thicken if Feed Sludge is Below 1 % Solids;Optimum Primary Sludge Concentration – 4 to 6 %;Minimize Activated Sludge Production;Ferric Salt Addition is Effective in Controlling H2S (Ferrous Sulfate – the Best);Avoid Addition of Chlorine and FeCl3 at the Same Point – Iron Sulfide is Difficult to Settle;Chemically Enhanced Sedimentation Increases Sludge Quantity.
24Clarifiers & Aerobic Digestion Aerobic Digestion of Primary Sludge is Several Times More Costly than WAS (More Energy);Thickening is Essential – Aeration Costs Driven by Mixing;Higher Target Thickening Goals – 4 to 6 % vs. 3 to 4 % for Primary Digesters;Achilles Heal – Foaming – Control Using Activated Sludge System Selectors.
25Summary & ConclusionsClarifiers are the “Cross-Roads” of the Treatment Plant;Clarifier Performance and Design are Strongly Influenced by:Wastewater Collection System Type and Performance;Screening and Grit Removal;Effluent Treatment Goals.Influent Septicity Most Critical for Primary Clarifier Design;Solids Inventory Most Critical for Secondary Clarifier Performance;Optimized Clarifier Operation Is Essential For Cost Effective Solids Handling.