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R. M. Glória 1, C. L. Souza1, C. A. L. Chernicharo1, M. E. A. do Carmo1, P. V. O. Silva1
Department of Sanitary and Environmental Engineering
Federal University of Minas Gerais - Brazil
Effectiveness of a Desorption Chamber for the Removal of Dissolved Gases
from Anaerobic Effluents
Considered a established technology in some warm
climate countries
Mostly used treatment technology in Brazil: more than
600 full-scale reactors in operation
Many advantages: low sludge production, low O&M
costs, small foot print, good efficiency, possibility of
resource recovery
UASB technology for domestic wastewater treatment
Brief Background
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Treatment installed capacity (m3.s-1)
Sample universe: 1439 STPs (9 states + Federal District)
STPs 10,000 – 100,000 inhab.STPs < 10,000 inhab. STPs > 100,000 inhab.
Brief Background:
Acceptance of the Anaerobic Technology in Brazil
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UASB technology: some limitations still exist
Loss of dissolved methane
o emission of GHG
o loss of energy potential
Emission of dissolved hydrogen sulfide
o can cause bad odour and corrosion
Brief Background
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Losses of dissolved methane
Brief Background
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Methane losses in UASB reactors
Influent
• Mass transfer from the open liquid
surface to the atmosphere
• Release to the atmosphere through the
hydraulic structures that produce
turbulence
• Dissolution in the liquid phase and
washing out with the final effluent
• Recovery inside the gas-collectors is only
partial as the effluent stream is often
supersaturated with dissolved CH4
Brief Background: Previous studies
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Due to its high solubility in water, H2S tends to remain in
solution when the liquid effluent exits the reactor
However, turbulence produced by the free fall of the effluent
(outlet structures of the reactor) can cause severe emissions
of odorous compounds (Pagliuso et al.,2002)
Measured values inside splitting boxes can reach values as
high as 500 ppm
Hydrogen Sulfide losses in UASB reactors
Brief Background: Previous studies
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None of them have yet proved to be fully viable or
effective.
Brief Background – Previous studies
Micro-aeration using biogas (Hartley and Lant, 2006)
Micro-aeration using air (Bartacek et al., 2013)
Degasifying membranes (Cookney et al., 2010;
Bandara et al., 2011, 2012)
Air injection in the upper part of the settler
compartment (Gloria et al., 2015)
Vacuum chamber
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Objective
To evaluate the effectiveness of the desorption
technique for the removal of methane and
hydrogen sulfide dissolved in the effluent of a
pilot-scale UASB reactor.
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Waste gas from settlers
Degasified effluent
Biogas
Effl
uent
sat
urat
ed w
ith C
H4
Was
te g
as fr
om p
relim
inar
y
trea
tmen
t an
d pu
mpi
ng s
tatio
n
Fan
Fan
Possible alternative for combined management of methane and hydrogen sulfide in small size plants
Combined biological oxidation
of sulfide and methane
Degasification unit
Biogas flare
The idea behind the proposal
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Experiments carried out in a 360-L pilot-scale UASB reactor and a Desorption Chamber (DC)
The reactor was fed on real wastewater taken from a chamber upstream the primary clarifiers of a full-scale treatment plant, after being submitted to preliminary treatment
UASB reactor: average HRT of 7 hours
The DC was installed downstream the UASB reactor
Material and Methods
Schematic configuration of experimental apparatus.
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Material and Methods
Positioning and view of the Desorption Chamber
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Material and Methods
Characteristics and operating conditions of the Desorption Chamber
Operational
Phases
Exhaustion
rate
(L.min-1)
Exhaustion
time
(min)
Number of air
renovations*
(renews.h-1)
Free drop
height inside
DC (m)
Chamber
volume
(L)
RQ**
(times)
1 1.2 3.3 18 0.5 4 1,1
2 1.6 2.5 24 0.5 4 1,5
3 1.6 5 12 1.0 8 1,5
4 3.2 2.5 24 1.0 8 3,1
Diameter: 20 cm
Drop heights tested: 0.5 and 1.0 m
Hydraulic loading rate: 0.132 m3.m-2.min-1
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RQ: air to wastewater flow ratio
1
3 4
Sulfide in the liquid samples: protocol adapted by Plas et al.
(1992),
Dissolved methane: Alberto et. al. (2000) and Hartley and Lant
(2006).
Waste gas (oxygen, nitrogen, CO2 and H2S): portable analyser
LANDTEC type GEMTM 5000.
Methane in the waste gas: gas chromatography
Material and Methods
Gas analyses
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12
3
phase 1 phase 2 phase 3 phase 4
Experimental phases
0
10
20
30
40
50
60
70
80
90
100
Meth
ane r
em
oval (%
)
Median
25%-75%
Min-Max
phase 1 phase 2 phase 3 phase 4
Experimental phases
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Wast
e g
as
- C
H4 (
%)
Median
25%-75%
Min-Max
Removal Efficiencies Concentration in the waste gas
Results
Dissolved Methane
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phase 1 phase 2 phase 3 phase 4
Experimental phases
0
10
20
30
40
50
60
70
80
90
100
Sulfid
e r
em
oval (%
)
Median
25%-75%
Min-Max
phase 1 phase 2 phase 3 phase 4
Experimental phases
0
100
200
300
400
500
600
700
800
900
1000
Wa
ste
ga
s -
H2S
(p
pm
)
Median
25%-75%
Min-Max
Results
Removal Efficiencies Concentration in the waste gas
Hydrogen Sulfide
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Conclusions
The use of the Desorption Chamber (DC) allowed good removal
efficiencies of the dissolved gases contained in the effluent of the
UASB reactor.
For the best operating condition (free fall of 1.0 m, air to
wastewater flow ratio of 3.1, and 24 renews per hour), the
dissolved methane removal efficiency was close to 60%.
As related to the removal of dissolved hydrogen sulfide,
efficiencies as high as 80% were achieved for the same operating
conditions.
Overall, these results prove that simple devices such as the DC
tested in this research can effectively contribute for the control of
methane and hydrogen sulfide emissions in anaerobic-based
sewage treatment plants.
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Thank you for your kind attention
