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

Control System – No Treatment

Dairy

Liquid Storage

Water RecyclingIrrigation

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

Biological Reactor

Effluent Tank

Gas CollectionBag

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.