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Reducing Gas Emissions from ManureStorages by Anaerobic Digestion and Aeration
Technologies
Ruihong Zhang1, Frank Mitloehner1, Yanguo Ma1,Jeff McGarvey2
1University of California, Davis2USDA-ARS Western Regional Research Center
Sponsor: California Regional Water Control Board
Gases from Manure StorageGas emission involves two processes - Generation by biochemical and chemical reactions - Mass transfer at the surface
Gases-Volatile organic compounds (VOCs)-Methane (CH4), Hydrogen sulfide (H2S), ammonia (NH3) and carbon dioxide (CO2)
Factors Controlling Emission Rate
Gas concentrations in the manure, related togeneration in the manureSurface area of storageEnvironmental conditions (temperature andwind speed at the surface)
Methods for Reducing Emissions inManure Storages
Covering storagesTreating manure prior to storage to reduce thegases generated in the storage
Solid-liquid separationBiological treatment
- Anaerobic Digestion- Aeration
Anaerobic Digestion and Aeration
Both processes use bacteria to break down andconvert organic matter under controlled conditions(retention time, temperature, organic loading rate,pH)
Both processes provide these environmental andpublic health benefits
Reduce biochemical oxygen demand (BOD)Destroy pathogensReduce odors (gases)
Research ObjectivesQuantify the effects of manure treatment byanaerobic digestion and aeration onemission reduction of gases (VOCs, CH4,H2S, NH3) from manure storagesDetermine the costs and benefits ofdifferent biological treatment technologies
Manure Treatment System I
Dairy
Liquid Storage
Water RecyclingIrrigation
AnaerobicDigestion
Biogas EnergyS/L Separation
Solids
Manure Treatment System II
Dairy
Liquid Storage
Water RecyclingIrrigation
Aeration
S/L Separation
Solids
Anaerobic Digester
Effluent Storage
Raw manure Storage
Effluent Storage
Effluent Storage
Air
Feed Tank
Biogas
Exhaust
Gas Collection
Bag
AnaerobicControl
AerobicEffluentStorage
AerobicControl
Aerobic Reactor
Anaerobic EffluentStorage
Raw dairy manure characteristicsTotal solids (TS) = 30 g/L (3%)Volatile solids (VS) = 21 g/L (2.1%)Biochemical Oxygen Demand (BOD5) = 14 g/LTotal Nitrogen (TN) = 3.8 g/LAmmoniacal Nitrogen (NH3-N) = 1.6 g/LpH = 8.0
Operation Parameters of Anaerobicand Aerobic Reactors
Anaerobic Digester (4 L Volume)OLR = 1 gVS/L/dayHRT = 20 daysTemperature = 35°C
Aerobic Reactor (2 L Volume)OLR = 2 gVS/L/dayHRT = 5 daysTemperature = 25°C (room)
Performance of Anaerobic andAerobic Reactors
Anaerobic Reactor Aerobic Reactor
Biogas Production (L/L/Day) 0.31 N/A
TS Reduction (%) 22.2 15.8
VS Reduction (%) 41.8 28.5
Two experimental trials35-day experiment in summer, 2004
VOC, VFA, CH4, and H2S measurementManure storage temperature = 20-29°C
180-day experiment in winter and spring, 2005VOC, CH4, VFA, H2S, NH3, CO2 measurement
Microbial communities (anaerobic and aerobic bacteria)Manure storage temperature = 10-19°C
Measurement of Effluent Storage
Gas phaseVolumeVOCs (GC/MS, EPA TO-15)CH4, CO2, (GC/TCD)H2S (GC/SCD)NH3 (acid trap and IC)
Liquid phaseVolumeVolatile fatty acids(GC/FID)NH3-NTS, VS, SS, BOD5, COD,
Data Analysis and Reporting MethodMass of a Gas in each storage= Mass in gas phase + Mass in liquid phase
Mass production of a gas in each storage per unitof total solids in manure fed into the storage over35 or 42 days
VOCs – ug/gTS manureVFAs – mg/gTS manureCH4 – mg/gTS manureH2S – g/gTS manure
Findings from a 35-day lab study inSummer, 2004
Anaerobic digestion achieved over 95%VOC, 90% VFA, and 83% CH4 reductionsin storage.Aerobic treatment achieved over 95% VOC,79% VFA, and 39% CH4 reductions instorage.
Major VOCs (EPA-TO15) found inManure Storages
BenzeneTolueneAcetoneMethalene ChlorideCarbon Disulfide2-ButanoneCyclonehexane
VFAs found in Manure StoragesAceticPropionicIsobutyric and butyricIso-valeric and n-valericIso-caprioc and n-capriocHeptanoic
Findings from 42-day Lab Study inWinter, 2004-2005.
Anaerobic digestion achieved 64% VFA,25% CH4, 40% H2S reductions in storage.Aerobic treatment achieved 84% VFA, 95%CH4 and 31% H2S reductions in storage.
VFA Production in Different Storages(Winter, 2005)
84.22
30.13
83.81
13.82
0102030405060708090
AnaerobicControl
AnaerobicEffluentStorage
AerobicControl
AerobicEffluentStorage
VFA
(mg/
gTS
as a
cetic
aci
d)
Methane Production in Different Storages(Winter, 2005)
0.0445
0.0335
0.0497
0.0026
0.000
0.010
0.020
0.030
0.040
0.050
0.060
AnaerobicControl
AnaerobicEffluentStorage
AerobicControl
AerobicEffluentStorage
CH
4 (m
g/gT
S)
Hydrogen Sulfide Production inDifferent Storages
0.0150
0.0089
0.0164
0.0114
0.00000.00200.00400.00600.00800.01000.01200.01400.01600.0180
AnaerobicControl
AnaerobicEffluentStorage
AerobicControl
AerobicEffluentStorage
H2S
(g/g
TS)
17.0
10.5
15.8
12.5
0.02.04.06.08.0
10.012.014.016.018.0
AnaerobicControl
AnaerobicEffluentStorage
AerobicControl
AerobicEffluentStorage
VS C
once
ntra
tion
(g/L
)
VS Concentration in Different Manure Storages
ConclusionsAnaerobic digestion and aeration haveshown significant effects on the reductionof VOCs, VFAs, CH4, H2S in manurestorage.Their gas reduction quantity for manurestorages are influenced by the temperaturevariation in the storages, therefore thesetechnologies should be evaluated fordifferent seasons.
Continuing ResearchDetermine the effects of anaerobic andaerobic treatment on gas production over alonger period (180 days) of storage time.Determine the effects of aeration in manurestorages on gas production in the storage.Determine the costs and benefits ofdifferent biological treatment processes.