THE BALANCECollection System Corrosion and Odor Control andits Impact on the BNR Process2012 Central States Annual ConferenceSt. Charles, IllinoisMay 16, 2012Presented By: Patrick Shea and Tracy Hodel

INTRODUCTION Wastewater Treatment System St. Cloud, MinnesotaSEWER INTERCEPTORSYSTEM (SIS)19 MILESEmergency SewerFailures- 2002- 2007- 2008

INTRODUCTION Wastewater Treatment System St. Cloud, MinnesotaSt. Cloud WWTF serves 5additional communitiesPopulation served is 110,000Expanded to 17.9 MGD in 2012Upgraded treatment process tofull biological nutrient removal

July 2002

July 2007

January 2008

Presentation Overview System HistoryBiological Nutrient Removal ProcessHydrogen Sulfide Corrosion Corrosion Control Methods Implemented in St. CloudChemical AdditionPolypigging – Forcemain Cleaning

Biological Nutrient RemovalSt. Cloud, MinnesotaPHBStored PStored PAnaerobic ZoneAerobic Zone

Nutrient RemovalSt. Cloud, MinnesotaSt. Cloud Wastewater Treatment FacilityInfluent & Effluent Phosphorus1212EFFLUENT PHOSPHORUS (mg/L)108642108642INFLUENT PHOSPHORUS (mg/L)00

Environmental ExcellenceAwardsSt. Cloud Wastewater Treatment2000 – Voluntarily Implemented a Phosphorus Management PlanFacility2003 – MN Governor’s Award for Excellence in Waste and Pollution Prevention2004 – National Most Valuable Pollution Prevention Award – PMP2007 – EPA Award of Excellence for Outstanding Operation & Maintenance

Hydrogen Sulfide CorrosionSt. Cloud, MinnesotaSO4-2 + Organic Matter + Anaerobic Bacteria =S- + H2O + CO2S- + 2H+ = H2SH2S + 2O2 = H2SO4

Corrosion Control MethodsImplementedChemical AdditionChemical Oxidation (e.g. chlorine or hydrogen peroxide)Sulfate Reduction Inhibition by providingadditional oxygen source (e.g. nitrate based chemical)Precipitation (e.g. metal salts)pH Control (e.g. lime or sodium hydroxide)

Corrosion Control MethodsImplementedChemical AdditionChemical Selected – Nitrate basedS- + 2H+ = H2SIf nitrate is present, no sulfate reduction will occuruntil all the nitrate is reducedIf no reduction occurs, no hydrogen sulfide isgenerated

Corrosion Control MethodsImplementedChemical Addition Start-up; lessons learnedThirteen (13) Feed SitesFabricated equipment andbulk delivery systemAnnual O&M Cost Savings

Corrosion Control MethodsImplementedChemical Addition121086420City of St. Joseph, MinnesotaHydrogen Sulfide (mg/L) Concentrationat St. Cloud Entry Point

Forcemain CleaningLiftstation #1 BEFORE PIGGING 9/20/11 to 9/26/11 AVERAGE H2S = 4mg/L AFTER PIGGING MAXIMUM H2S = 9/29/11 to 10/3/1195 mg/L AVERAGE H2S = 0 mg/L MAXIMUM H2S = 0 mg/L

Corrosion Control MethodsImplemented30” Forcemain - Polypigging

Corrosion Control MethodsImplemented30” Forcemain - Polypigging

Corrosion Control MethodsImplementedSewer Entry Realignment ProjectManhole that the City ofSt. Joseph discharges intothe St. Cloud WastewaterConveyance SystemInstalled in 2007Significant deteriorationin just 4 years

Corrosion Control MethodsImplementedSewer Entry Realignment Project

Corrosion Control MethodsImplementedSewer Entry Realignment Project120Sauk River CrossingHydrogen Sulfide Levels10080mg/L6040200

gallonsImpacts on the TreatmentProcessVolatile Fatty Acids2Volatile Fatty Acids's2milligrams per liter00

ConclusionsSt. Cloud, Minnesota#1 Consideration of downstream treatment processes iscritical to developing a successful corrosion and odor controlstrategy.#2 One size does not fit all:•System characteristics – Identification of potential issues•Selection of a feed chemical•Collection system maintenance and operation – cleaning,inspection, testing

Plan Moving ForwardSt. Cloud, Minnesota§Forcemain Entry Point; Reviewduring Design Phase§Corrosion Resistant Materials(Pipe, manhole, coatings, etc.)§Commitment to routineInspection, Cleaning,Televising§Commitment to ongoingmonitoring, sampling andanalysis§Maintain Sewer GIS Application

THANK YOUPatrick Shea, Public Services Hodel, Assistant Public Utilities Central States Annual ConferenceSt. Charles, IllinoisMay 16, 2012

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