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?