Advancing Anaerobic Digestion of Wastewater Solids and Food Waste for Energy and Resource Recovery:

Science and Solutions - A Framework for the Practice of Co-Digestion

Matt Seib

Madison Metropolitan Sewerage DistrictKevin Jankowski

Milwaukee Metropolitan Sewerage District

Introduction & Background

Co-Digestion Framework

Side-Effects & Strategies

Waste Receiving

Wrap-up & Discussion

Presentation Overview

Introduction & Background

Purpose:

Aggregate knowledge from operators, consultants, and academia

Determine areas of consensus

Identify knowledge gaps to improve viability of future co-digestion projects

NSF/WERF (WRF) Workshop

NSF/WERF (WRF) Workshop

Group of 40 speakers and participants discussed:

existing co-digestion programs

practices to improve the success of co-digestion programs

recommendations and research needs for the industry

WERF (WRF) Report ENER20W17

Final Report

Co-digestion Framework

1. Mission

2. Feedstocks

3. Operations

4. Products

Framework Pyramid – Four Pillars

What feedstock is available, why is it available, and how much of it is available?

Of the feedstock available, does it meet four essential criteria (non-toxic, energy value, low inerts, digestible)?

Are there thresholds that would determine any feedstock as unacceptable?

What rate structures, testing, and work flow are appropriate based on the feedstock (personnel, leadership, communication/ arrangements with solid waste sector, etc.)?

Questions for Feedstock Generators

Sample co-digestion feedstock to determine suitability

Looking for beneficial & negative characteristics

Quality Criteria

Biochemical methanogenic potential (BMP)

Anaerobic Toxicity Assay (ATA)

What is your baseline capacity and equipment suitability for solids processing, gas processing, and gas use?

What are the potential staffing implications? Who does the sampling?

What is the effect on permit compliance? Do we need additional sidestream treatment?

Do we need feedstock receiving infrastructure?

How will we use the energy generated?

Questions for WRRF Staff (Operators)

Examples of Pilot Results

0

250,000

500,000

750,000

1,000,000

1,250,000

1,500,000

1,750,000

2,000,000

2,250,000

2,500,000

2,750,000

7/19/2018 8/18/2018 9/17/2018 10/17/2018

Dig

est

er

Gas

, cu

ft/d

ay

DG_Calc DG_meas DG_PS DG_WAS DG_HSW DG_NoHSW

Permit Compliance?(effluent & biosolids)

Permit Compliance?(air permit)

Side-Effects & Strategies

Additional substrate may have impact in a number of areas including:

Odor control

Digester foaming and gas quality

Sidestream impacts

Sludge dewaterability

Residuals production

Co-Digestion “Side-effects”

General Feedstock Balance

VS

FS

pCOD

sCOD

AD

CH4pCOD

sCOD

VS

FS

pCOD

VSpCOD

sCOD

sCOD

Digester Gas

Biomass

UndegradedFeedstock

Co-digestion Feedstock

Example Residual CalculationVariable Description Value Units Notes

Substrate Sample Analysis

Substrate Name Example

Q Volume 7,123 gallons truck load

COD Chemical Oxygen Demand 27,000 mg/L lab results

TS Total solids 21,000 mg/L lab results

%VSS Volatile solids fraction 75% % lab results

Process Calculations

C1 COD to VSS ratio 1.71 lbs COD/lb VSS assumed, can be determined by lab

TS Total solids 1,248 lbs calculated

VS Volatile solids 936 lbs calculated

FS Fixed solids 312 lbs calculated

COD Total COD load 1,604 lbs calculated

sCOD soluble COD load 0 lbs calculated

pCOD particulate COD load 1,604 lbs calculated

%REM1 Volatile solids destruction rate 53.00% VSrem/VS 2015 Average, WIMS Var 5027

%REM2 Anaerobic soluble removal rate 100.00% sCODrem/COD 1/21/14 meeting

%REM3 Anaerobic composite removal rate 53.00% CODrem/COD calculated

%REM4 Aerobic removal rate 75.00% CODrem/COD assumed, 25% in dewatered biosolids

Y1 Anaerobic biomass yield 0.10 lbs VS/lb COD assumed, from Dr.Z

Y2 Aerobic biomass yield 0.50 lbs VS/lb COD assumed, from Dr.Z

Xv1 Anaerobic biomass produced 85 lbs Assumes no endogenous decay

Xv2 Aerobic biomass produced 283 lbs Assumes no endogenous decay

Xv Net biomass produced 368 lbs calculated

ndVSS non-degraded VSS 440 lbs calculated

Tse

Additional solids to be treated1,119 lbs calculated

0.56 Tons calculated

Unit Values0.157 lbs/gallon calculated

0.0001 tons/gallon calculated

Waste Receiving

Receiving station

Unloading system

Tanks/equalization

Wash down facilities

Construction materials

Odor control

Pumps

Heat exchange

Explosion resiliency

Permit requirements

Redundancy

Staffing

Facility Design Concerns

Vehicle traffic

Organic loading rates

Vector attraction reduction

Recuperative thickening

Mixing

Digester cleaning

Reject management

Process Concerns

Waste Receiving

Waste Receiving

Waste Receiving

Wrap-up & Discussion

Discussion…