Evaluating Potential Impacts of Food Waste Co
Evaluating Potential Impacts of Food Waste Co-Digestion in Municipal Digesters Matt Seib, PhD May 23, 2017
Acknowledgements Special Thanks To: UW Dept of Civil Engineering • Diantha Drown • Dr. Daniel Noguera UW Office of Sustainability MMSD Staff • Alan Grooms • Steve Reusser • Rhonda Riedner
Background • Need to divert food waste from landfill • Extend landfill useful life • Prevent greenhouse gas emissions • Create valuable products from traditional “waste”
• Increase energy independence • Produce methane to reduce reliance on grid electricity and natural gas
Objectives • Evaluate co-digestion of source separated organics (SSO) using Madison Metropolitan Sewerage District’s (MMSD) unique process flow scheme • Specific items of interest: • Biogas methane content • Volatile solids reduction • System stability (volatile fatty acids (VFA), ammonia/TKN) • Dewatering/thickening characteristics
MMSD Co-Digestion Process Primary Clarifier
Headworks
Bio-P Secondary
Secondary Clarifier
WAS P-release
Primary Thickening Food Waste
Methane Digester
Struvite Harvesting
Gravity Belt Thickener
Acid Digester
Biosolids
Gravity Belt Thickener
Effluent
Experimental Setup Reactor
Control R1 R2 R3
Food Waste Feed (mL) 50 83 100
Acid Sludge Feed (mL) 200 200 167 200
Volumetric Food Waste / Acid Sludge Proportion (% / %) - / 100 20/ 80 33 / 67 33 / 67
SRT (d)
OLR (g VS/Lr)
30 24 24 20
1.3 2.4 2.9 3.5
• 6 L working volume • Temp = 37 oC in all reactors
Feed Characterization Feed Type Acid sludge Food waste
TS (%)
VS (%)
Total VFA (mg/L)
4.9 ± 0.3 3.9 ± 0.3 6,300 ± 1,700 14 ± 6.5
13 ± 6.0
N/A
Food waste Collected from UW Union South once/week Created a slurry using a blender Targeted (by volume): • 25% protein (meat, dairy) • 75% fruit, vegetables, carbohydrates
Total Ammonia Nitrogen (mg/L N)
TKN (mg/L N)
760 ± 300
3,100 ± 530
N/A
6,000, ± 5,500
Co-Digestion Performance Reactor
Eff. TS (%)
Eff. VS (%)
Total VS Destruction (%)
Food Waste VS Destruction (%)
Biogas CH4 (%)
pH (SU)
Control
2.8 ± 0.5 1.8 ± 0.3
53 ± 9
N/A
63 ± 2.2
7.9 ± 0.19
R1
3.1 ± 0.9 2.0 ± 0.4
61 ± 11
75 ± 19
62 ± 3.5
8.0 ± 0.18
R2
3.1 ± 0.7 2.1 ± 0.5
63 ± 15
78 ± 14
61 ± 6.1
8.0 ± 0.15
R3
3.2 ± 0.3 2.2 ± 0.2
64 ± 13
76 ± 12
61 ± 6.4
8.0 ± 0.20
Full Scale* 3.0 ± 0.1 2.0 ± 0.1
48 ± 4
N/A
58 ± 1.4
7.4 ± 0.09
*Full-scale methane-phase treatment of acid sludge
28000
14000
24000
12000
20000
10000
16000
8000 6000
12000
4000
8000
2000
4000 0
0 0
100
Acid Digester
Control
Control Average NH3-N mg/L
R1
1,630 ± 370 2,430 ± 650
Day R1
200 R2
300 R3
Food Waste TKN
R2
R3
2,600 ± 830
2,720 ± 780
TKN, mg/L
Total VFA as Acetate, mg/L
Impact of Food Waste TKN
Dewatering Testing Lab method to approximate GBT performance • Mix polymer with digestate • Pour aliquot onto GBT filter cloth inside Buchner funnel • Place plate & 450 g weight on top of sample to simulate “squeezing” • Compare filtrate TSS to raw sample
Dewatering Characteristics 100%
NSWWTP
Percent Solids Capture
95%
Control
90%
R1
85%
R2
80%
R3
75%
NSWWTP Trend Control Trend
70%
R1 Trend
65%
R2 Trend
60%
R3 Trend
55% 0
2 4 6 8 10 12 14 16 18 20 Polymer Dose, kg active polymer/1000 kg solids
22
Conclusions • Overall VS destruction increased 10% with addition of food waste in all conditions • Addition of 20% and 33% of high protein food waste resulted in 50% higher digester ammonia concentrations • Spikes in food waste TKN resulted in rapid VFA increase requiring temporary suspension of feeding, especially in higher loaded reactors • Dewaterability and polymer demand for 20% and 33% food waste addition was similar to full scale noncodigestion results
Future Considerations • • • • • •
Identify reliable food waste/ SSO sources in area Evaluate pretreatment and equalization needs Determine resulting nutrient load to mainline treatment Understand impacts on biosolids reuse program Evaluate utilization options for additional biogas Understand additional biogas conditioning needs
Questions
Acknowledgements Special Thanks To: UW Dept of Civil Engineering • Diantha Drown • Dr. Daniel Noguera UW Office of Sustainability MMSD Staff • Alan Grooms • Steve Reusser • Rhonda Riedner
Background • Need to divert food waste from landfill • Extend landfill useful life • Prevent greenhouse gas emissions • Create valuable products from traditional “waste”
• Increase energy independence • Produce methane to reduce reliance on grid electricity and natural gas
Objectives • Evaluate co-digestion of source separated organics (SSO) using Madison Metropolitan Sewerage District’s (MMSD) unique process flow scheme • Specific items of interest: • Biogas methane content • Volatile solids reduction • System stability (volatile fatty acids (VFA), ammonia/TKN) • Dewatering/thickening characteristics
MMSD Co-Digestion Process Primary Clarifier
Headworks
Bio-P Secondary
Secondary Clarifier
WAS P-release
Primary Thickening Food Waste
Methane Digester
Struvite Harvesting
Gravity Belt Thickener
Acid Digester
Biosolids
Gravity Belt Thickener
Effluent
Experimental Setup Reactor
Control R1 R2 R3
Food Waste Feed (mL) 50 83 100
Acid Sludge Feed (mL) 200 200 167 200
Volumetric Food Waste / Acid Sludge Proportion (% / %) - / 100 20/ 80 33 / 67 33 / 67
SRT (d)
OLR (g VS/Lr)
30 24 24 20
1.3 2.4 2.9 3.5
• 6 L working volume • Temp = 37 oC in all reactors
Feed Characterization Feed Type Acid sludge Food waste
TS (%)
VS (%)
Total VFA (mg/L)
4.9 ± 0.3 3.9 ± 0.3 6,300 ± 1,700 14 ± 6.5
13 ± 6.0
N/A
Food waste Collected from UW Union South once/week Created a slurry using a blender Targeted (by volume): • 25% protein (meat, dairy) • 75% fruit, vegetables, carbohydrates
Total Ammonia Nitrogen (mg/L N)
TKN (mg/L N)
760 ± 300
3,100 ± 530
N/A
6,000, ± 5,500
Co-Digestion Performance Reactor
Eff. TS (%)
Eff. VS (%)
Total VS Destruction (%)
Food Waste VS Destruction (%)
Biogas CH4 (%)
pH (SU)
Control
2.8 ± 0.5 1.8 ± 0.3
53 ± 9
N/A
63 ± 2.2
7.9 ± 0.19
R1
3.1 ± 0.9 2.0 ± 0.4
61 ± 11
75 ± 19
62 ± 3.5
8.0 ± 0.18
R2
3.1 ± 0.7 2.1 ± 0.5
63 ± 15
78 ± 14
61 ± 6.1
8.0 ± 0.15
R3
3.2 ± 0.3 2.2 ± 0.2
64 ± 13
76 ± 12
61 ± 6.4
8.0 ± 0.20
Full Scale* 3.0 ± 0.1 2.0 ± 0.1
48 ± 4
N/A
58 ± 1.4
7.4 ± 0.09
*Full-scale methane-phase treatment of acid sludge
28000
14000
24000
12000
20000
10000
16000
8000 6000
12000
4000
8000
2000
4000 0
0 0
100
Acid Digester
Control
Control Average NH3-N mg/L
R1
1,630 ± 370 2,430 ± 650
Day R1
200 R2
300 R3
Food Waste TKN
R2
R3
2,600 ± 830
2,720 ± 780
TKN, mg/L
Total VFA as Acetate, mg/L
Impact of Food Waste TKN
Dewatering Testing Lab method to approximate GBT performance • Mix polymer with digestate • Pour aliquot onto GBT filter cloth inside Buchner funnel • Place plate & 450 g weight on top of sample to simulate “squeezing” • Compare filtrate TSS to raw sample
Dewatering Characteristics 100%
NSWWTP
Percent Solids Capture
95%
Control
90%
R1
85%
R2
80%
R3
75%
NSWWTP Trend Control Trend
70%
R1 Trend
65%
R2 Trend
60%
R3 Trend
55% 0
2 4 6 8 10 12 14 16 18 20 Polymer Dose, kg active polymer/1000 kg solids
22
Conclusions • Overall VS destruction increased 10% with addition of food waste in all conditions • Addition of 20% and 33% of high protein food waste resulted in 50% higher digester ammonia concentrations • Spikes in food waste TKN resulted in rapid VFA increase requiring temporary suspension of feeding, especially in higher loaded reactors • Dewaterability and polymer demand for 20% and 33% food waste addition was similar to full scale noncodigestion results
Future Considerations • • • • • •
Identify reliable food waste/ SSO sources in area Evaluate pretreatment and equalization needs Determine resulting nutrient load to mainline treatment Understand impacts on biosolids reuse program Evaluate utilization options for additional biogas Understand additional biogas conditioning needs
Questions
