Sludge Happens. Louise Heffernan Metropolitan Council Environmental Services Empire Wastewater Treatment Plant Anaerobic Digester Pilot Project.

Sludge Happens

Louise HeffernanMetropolitan Council

Environmental Services

Empire Wastewater Treatment Plant Anaerobic Digester Pilot Project

• Empire wastewater facility• Dewaterability issues• Designed to produce cake solids content~16-18%• Recent years ~ 11-12%• Storage pad usage, hauling and land application• Impacts operational costs

Introduction

• Empire current operations11% cake – $310,000/year land application cost

• Target operations18% cake – $200,000/year land application cost

Why does this matter?

Empire WWTP, Empire Township

BiosolidsPad

• Evaluate treatment options • Improve dewaterability• Establish stable pilots• Monitor performance • Gather data• Analyze system results• Examine methods to achieve target cake• Implement at the Empire WWTP

Purpose

• Bacteria only make up 10-20% of the organic matter mass in a floc

• Most of the remainder is biopolymer (protein and polysaccharides)

Biofloc Makeup

Higgins, 2012

• Chemical conditioning prior to BFP• Alter biomass matrix• Good floc formation and settling• DCB negatively charged biopolymers• Lower soluble P

Chemical Addition Treatments

• Current practice at EmpireWAS is thickened, accounts for 50% digester feedNot stored at any point

• S.T.WAS treatmentUnaerated storage of WAS prior to thickeningAllows time for P, K, Mg release Removal prior to digestion

• Research suggests dewatering ability linked to cation concentration

Stored/Thickened WAS Treatment

Pilot Test Variables• Pilot # 1 : Stored/Thickened WAS (S.T.W.A.S.)

Unaerated storage > 4 days

•Pilot # 2 : Chemical addition (FeCl3)•Pilot # 3 : Control•Pilot # 4 : Chemical addition (MgCl2)

Pilot Digesters 2013

Results/Analysis

0.0

2.0

4.0

6.0

8.0

10.0

12.0

S.T.WAS Pilot Dewatering ResultsTypical Cake Solids Before Treatment S.T.WAS (2.08 SRT)S.T.WAS (2.95 SRT)

Best

Cak

e So

lids

(%TS

)

Cake Solids:11.1%

Polymer Dose:15.3 lb /dt

Cake Solids:11.7%

Polymer Dose:16.6 lb /dt

Days of Operation:52

Cake Solids:10.8%

Polymer Dose:20.5 lb /dt

Days of Operation:74

Results/Analysis

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Ferric Chloride Pilot Dewatering ResultsTypical Cake Solids Before Treatment Ferric Chloride (1.58 SRT)Ferric Chloride (2.48 SRT)

Best

Cak

e So

lids

(%TS

)

Cake Solids:11.1%

Polymer Dose:15.3 lb /dt

Cake Solids:13.7%

Polymer Dose:11.0 lb /dt

Days of Operation:40

Cake Solids:14.3%

Polymer Dose:12.4lb /dt

Days of Operation:63

Results/Analysis

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Magnesium Chloride Pilot Dewatering ResultsTypical Cake Solids Before Treatment Magenesium Chloride (1.60 SRT) Magnesium Chloride (2.29 SRT)

Best

Cak

e So

lids

(%TS

)

Cake Solids:11.1%

Polymer Dose:15.3 lb /dt

Cake Solids:12.5%

Polymer Dose:19.3 lb /dt

Days of Operation:42

Cake Solids:12.2%

Polymer Dose:12.2lb /dt

Days of Operation:60

• Empire has low cake solids (11-12%)• Potential methods to improve dewaterability

investigated• System will continue to run past 3 SRTS• Results from 2013 pilot digesters:

Stability was achievedAll treatments showed decrease in soluble P and KAll treatments showed increase in cake solidsDewatering performance below target values

Summary and Conclusions

• Must investigate more alternatives to achieve 18%• Future option: STWAS & chemical

addition• Thermal pretreatment technologies• Other chemicals

Mg(OH)2

Recommendations

My Experience

• Networking opportunities• Communicate with wide range of professionals• Great educational experience• Met Council tours• Lead into independent study

Questions?