Anaerobic MBR: Challenges and Opportunities · AnMBR Remains Challenging for Municipal...
Transcript of Anaerobic MBR: Challenges and Opportunities · AnMBR Remains Challenging for Municipal...
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March 18-19, 2015
Anaerobic MBR:
Challenges & Opportunities
Art Umble, PhD, PE, BCEE
Americas Wastewater Practice Leader
Symposium:
Hydrogen, Hydrocarbons, and
Bioproduct Precursors from Wastewaters National Renewable Energy Laboratory
Washington, DC
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Outline
■ Challenge for Municipal Wastewater
■ Membrane Fouling
■ Energy Potential
■ System Economics
■ Research Needs
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Challenges: Municipal Wastewater
Treatment Using AnMBR
• Low temperatures in municipal
wastewaters
• Low strength municipal
wastewaters
• Bioreactors must be heated
• Long SRTs are required
• Post-treatment is required for
direct discharge
• High SO4 reduces methane
production
• Methane solubility at low
temperatures limits recovery
• GHG emissions 3
Biogas
Influent Retenate
Permeate
Membrane
Module
Bioreactor
WAS Biogas
Influent
Permeate
Bioreactor
WAS
PVDF
PES
Metallics
Inorganics
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Challenges: Municipal Wastewater
Treatment Using AnMBR
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• Limited Development Realized Since Early 2000s
– Anaerobic processes are complex
– Methanogens highly sensitive to wastewater toxicity
– Difficulty in managing variable conditions
– Membrane fouling
– Relatively low flux
• Necessity of Operating at Ambient Temperatures
– Low organic strength low methane production
– Low methane production limited heating potential
– Long SRTs increases membrane fouling
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Challenges with Membrane Fouling
• Internal fouling generally
irreversible
• External fouling generally
reversible
• Internal deposits generally
more inorganic
• Long SRT operation
promotes internal pore
blocking
• Fouling higher costs &
membrane replacement
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Pore
Blocking
Internal External
Membrane
Surface
Porous
Layer
Suspended biomass, colloidal solids, SMP, EPS,
Attached cells, inorganics (e.g., struvite)
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Fouling Control Methods
• Biogas sparging
• Backflushing
• Periodic membrane
relaxation
• PAC/GAC addition
• Combinations
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Operational/Performance Considerations
• OLR: >10 kg COD/m3/d
• HRT: ~ 8-12 hours
• Sustainable flux rate:
< 15 LMH
• Temperature
• Methane solubility
• >85% COD removal
• >99% TSS removal
• TN and TP removals
negligible
• Effluent COD/N & COD/P
unfavorable for downstream
BNR
7
0
20
40
60
80
100
0 5 10 15 20 25 30 35 40 45 50
tCO
D R
em
ov
al, %
time, hrs
COD Removal
Adapted from: Smith, et al. Bioresource Technology 122 (2012)
Tradeoff:
Increased biological
activity across biofilm;
but increased fouling
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AnMBR Performance – COD Removal
8 Source: U4R08 WERF; Raskin, et al. (2012)
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Methane Production Potential
• Colder reactor temperatures result in lower methane production
9
0
10
20
30
40
50
60
70
80
Day 1 Day 15 Day 30 Day 45 Day 60 Day 75
mL
CH
4/g
VS
S -
d
Specific Methanogenic Activity
Suspended @ 25oC
Suspended @ 15oC
Attached @ 25oC
Attached @ 15oC
Adapted from: Ho and Sung, Bioresource Technology 101 (2010)
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Methane Production Potential
10 Source: U4R08 WERF; Raskin, et al. (2012)
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Methane Production Potential
11 Source: Gimenez, et al. Bioresource Technology; 118 (2012)
CH
4 R
eco
very
Eff
icie
ncy,
%
Biogas production rate/L per m3 of treated wastewater
Theoretical Recovery @ 33oC
Theoretical Recovery @ 20oC
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Methane Solubility Creates a Challenge
• CH4 ~ 1.5x more soluble at
15oC than at 35oC
• Dissolved CH4 leaving
process in permeate is
significant fraction to total
CH4 generated
• Permeate concentration
tends to be oversaturated
• Impact on GHGs
• Post-treatment stripping
• Degassing membrane
• Downflow Hanging Sponge
reactor
12 Adapted from Uemura and Harada, (2010)
Influent
Effluent
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Implications for Energy Recovery
• Production is function of:
– Temperature
– Loading rate
– Operating condition
– Influent pre-treatment
– Influent pre-heating
• 110-320 mL CH4/g COD
removed
• Net energy recovery
achievable at 9.5 g
COD/L or higher 13
WARM
WATER
OUT
COLD
WATER
IN
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Methane Production
14 Source: Wei, et. al; Bioresource Technology 166 (2014)
Me
tha
ne
vo
lum
e f
rac
tio
n (
%)
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Economic Overview
15
11.3
72.3%
2.2 5.7
5.9 1.2 1.4
Capital Cost Elements
Tank
Membranes
Liquid Pumps
Gas Blowers
Screens
PLCs
Other
46.7%
13.7
7.2
32.5
Operational Cost Elements
Scouring Energy
Pumping Energy
sludge Disposal
Chemical Consumption
0
20
40
60
80
1000 5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
10
0% o
f M
em
bra
ne C
ost
Design Flux (LMH)
Flux Influence on Cost
Adapted from: Lin, et. al; Desalination 280 (2011)
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Research Needs for AnMBRs
• Membrane fouling,
particularly with low-
strength wastewaters
• Consumption and
optimization of energy
• Relationship between
HRT, SRT, performance
and fouling
• Methane solubility at low
temperatures.
• Operation at low and
high temperatures
• Effects of microbial
seeding
• Nutrient removal
systems
• Comprehensive effects
of OLR on methane
production
• Pre-treatment effects
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Summary
■ AnMBR Remains Challenging for Municipal
[email protected] Denver, CO USA
■Membrane Fouling Solutions are Elusive
■ Significant Impediment is Nutrient Removal
■Methane Solubility a Challenge for Recovery
■Membranes Remain Primary Capital Cost
■ Scouring Energy Primary Operational Cost
■Research Opportunities Remain High