Effectiveness of a Desorption Chamber for the Removal of Dissolved - - PowerPoint PPT Presentation

• 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
• emission of GHG
• loss of energy potential
• Emission of dissolved hydrogen sulfide
• 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

• f 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

Effluent saturated with CH4 Waste gas from preliminary treatment and pumping station

Fan Fan

Possible alternative for combined management of methane and hydrogen sulfide in small size plants

Combined biological oxidation

• f 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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1 2 3

phase 1 phase 2 phase 3 phase 4

Experimental phases

10 20 30 40 50 60 70 80 90 100

Methane removal (%)

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

Waste gas - CH4 (%)

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

10 20 30 40 50 60 70 80 90 100

Sulfide removal (%)

Median 25%-75% Min-Max

phase 1 phase 2 phase 3 phase 4

Experimental phases

100 200 300 400 500 600 700 800 900 1000

Waste gas - H2S (ppm)

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