Water Residuals Management Presented by Michael F. Graves, PE CP&Y Co-Authors Larry L. Hare, PE Oklahoma City J. Dustin Segraves Oklahoma City October 2014
Discussion Topics Project Background Thickening and Dewatering Hefner WTP Evaluation Develop Your Goals Know Your Residuals Review Your Process Consider Operating Options
Hefner WTP Residuals Study
Hefner WTP Residuals Study Hefner WTP located in Oklahoma City Currently rated for 100 MGD Future expansion to 200 MGD Lime Softening Process
Hefner Residual Handling Layout Five Clarifiers Pump Station Two backwash ponds Five Sludge Lagoons
Gravity Thickening Gravity Thickeners; Smaller Circular Concrete Tanks Mechanical Rake Mechanism Overflow Weirs Thickened Sludge Trench
Gravity Belt Thickeners Gravity Belt Thickeners; Polymer added before process Conditioned sludge moves on belt Water drains through the belt Thickened sludge discharged at end
Mechanical Dewatering Belt Filter Presses Polymer added to condition sludge Sludge moves across a series of belts Rollers increase pressure Water drains through belt Sludge is discharged at end of belt
Mechanical Dewatering Centrifuge Polymer Added to condition sludge Sludge is added to high speed scroll Bowl and Scroll offer high differential Speed Water flows through openings in bowl Sludge is discharged at the end
Project Design Goals 100% mechanical dewatering during all treatment conditions up to 200 MGD High level of redundancy Recovery Pump Station: 15-20% recycle at 150 MGD Sludge Pump Station: Dry pit to reduce maintenance
Mass Balance Lime Usage
Mass Balance Hardness Removal
Mass Balance Solids Production Raw/recovery water solids: 24,236 lb/d (5.6%) Ferric precipitates: 7,074 lb/d (1.6%) Lime precipitates: 400,628 lb/d (92.8%) Predominated
Review Process Changes Based on Historical Chemical Usage Parameter Unit Capacity 75 mgd 100 mgd 150 mgd 200 mgd Solids Handling Capacity lb/d dry (Historical Lime Dose) solids 215,000 287,000 430,000 575,000 Wet Solids Volume (1% Solids Content) Solids Handling mgd 2.5 3.5 5 7 Impact of Polymer Parameter Unit Capacity 75 mgd 100 mgd 150 mgd 200 mgd Solids Handling Capacity lb/d dry (Optimized Lime Dose) solids 140,000 190,000 280,000 370,000 Wet Solids Volume (4% Solids Content) Solids Handling mgd 0.4 0.6 0.8 1.1
Consider Constructibility Solids Handling Facility Site Force Main Solids Pump Station
Proposed Process Clarifiers Flow / Solids Meters Solids Pump Station Mechanical Dewatering Balancing Tanks Thickeners Solids Storage Hauling and Disposal
Consider How You Want to Load the Trucks Direct Loading Advantages Stacking Pad Advantages Minimize stacking of product. Reduces storage of the product on-site. Eliminates handling the product multiple times. Allows for Operational Flexibility. More storage available. Single story building. Less dependent on truck hauling schedules. Small Footprint
Belt Filter Press 24/7 with Stacking Pad
Centrifuge 24/7 with Direct Loading
Scenarios 1. Base Scenario 2. High Lime - Historical Lime Dosages 190 mg/l of Lime Mechanical Dewatering to 200 MGD 3. Low Lime Considers Polymer Usage 110 mg/l of Lime Mechanical Dewatering to 200 MGD 4. Hybrid Partial Use of Lagoons to Save Capital 110 mg/l of Lime Partial Mechanical Dewatering to 80 MGD. Over 80 MGD, solids flow to lagoons.
Base Scenario Costs Base Scenario Item Operation with Polymer Operation without Polymer (Lime Dosage = 110 mg/l) (Lime Dosage = 190 mg/l) Capital Cost $14,570,000 $14,570,000 30-year Dewatering, Hauling, and $118,090,000 $136,480,000 Disposal Total 30-Year Cumulative Value $132,660,000 $151,050,000 30-Year Net Present Value $72,900,000 $82,200,000
Mechanical Dewatering Scenarios Item Scenario 1 - High Lime Scenario 2 Low Lime Capital Cost $27,670,000 $23,390,000 Maintenance Costs $5,020,000 $4,280,000 Operations Cost $52,820,000 $49,320,000 Hauling, and Disposal $30,330,000 $26,250,000 Total 30-Year Cumulative Value $115,840,000 $103,240,000 30-Year Net Present Value $70,000,000 $61,800,000 Item Hybrid Partial Mechanical Dewatering Capital Cost $12,030,000 Maintenance Costs $5,320,000 Operations Cost $47,900,000 Hauling, and Disposal $36,700,000 Total 30-Year Cumulative Value $101,950,000 30-Year Net Present Value $56,400,000
Take Aways Consider the entire plant treatment process in evaluating residuals Design Goals - The cheapest solution may not be the best for a utility
Questions & Answers