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…