research article bioconversion of high...

Research ArticleBioconversion of High Concentrations of Hydrogen Sulfide toElemental Sulfur in Airlift Bioreactor

Mohamed Abdel-Monaem Zytoon12 Abdulraheem Ahmad AlZahrani3

Madbuli Hamed Noweir4 and Fadia Ahmed El-Marakby2

1 Department of Industrial Engineering King Abdulaziz University PO Box 80204 Jeddah 21589 Saudi Arabia2Department of Occupational Health and Air Pollution High Institute of Public Health Alexandria University165 El Horreya Avenue Alexandria Egypt

3 Department of Chemical and Material Engineering King Abdulaziz University PO Box 80204 Jeddah 21589 Saudi Arabia4Center of Excellence for Environmental Studies King Abdulaziz University PO Box 80204 Jeddah 21589 Saudi Arabia

Correspondence should be addressed to Mohamed Abdel-Monaem Zytoon mzytoonkauedusa

Received 7 May 2014 Revised 4 July 2014 Accepted 4 July 2014 Published 22 July 2014

Academic Editor Anli Geng

Copyright copy 2014 Mohamed Abdel-Monaem Zytoon et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Several bioreactor systems are used for biological treatment of hydrogen sulfide Among these airlift bioreactors are promising forthe bioconversion of hydrogen sulfide into elemental sulfur The performance of airlift bioreactors is not adequately understoodparticularly when directly fed with hydrogen sulfide gas The objective of this paper is to investigate the performance of an airliftbioreactor fed with high concentrations of H

2S with special emphasis on the effect of pH in combination with other factors such

as H2S loading rate oxygen availability and sulfide accumulation H

2S inlet concentrations between 1008 ppm and 31215 ppm

were applied and elimination capacities up to 113 gH2Smminus3 hminus1 were achieved in the airlift bioreactor under investigation at a pH

range 65ndash85 Acidic pH values reduced the elimination capacity Elemental sulfur recovery up to 95 was achieved under oxygenlimited conditions (DO lt 02mgL) and at higher pH values The sulfur oxidizing bacteria in the bioreactor tolerated accumulateddissolved sulfide concentrations gt500mgL at pH values 80ndash85 and near 100 removal efficiency was achieved Overall theresident microorganisms in the studied airlift bioreactor favored pH values in the alkaline range The bioreactor performance interms of elimination capacity and sulfur recovery was better at pH range 8ndash85

1 Introduction

Hydrogen sulfide is emitted from many industrial activitiesThe toxicity malodor and corrosiveness of H

2S necessitate

its removal from waste gas streams The classical physico-chemical processes for H

2S control have many drawbacks

such as large energy requirements high capital and operatingcosts and production of secondarywastes [1ndash7] On the otherhand biological processes for the removal of H

2S are more

attractive because they are believed to be inexpensive andcause no environmental pollution [5]

Biofilters packed with compost and other natural media[8ndash12] and those with synthetic beds [2 3 5 6 13ndash19] havebeen studied However these types of biofilters are limited to

air streams with low concentrations of H2S In addition they

producewaste streams containing sulfatesulfuric acid whichneed further treatment

Several trials have been conducted to convert H2S biolog-

ically into elemental sulfur (So) that can be easily separatedfrom the waste stream and further treated for marketing Insome of these heterotrophic sulfide oxidizing bacteria (SOB)were used [20] However the cost of continuous organiccarbon supply is one drawback of such process Also iron-based biological processes have been studied [21ndash24] Theprocess consisted of two reactors which increased the capitaland operating costs of the process

Biotrickling filters with synthetic packing materials werestudied for bioconversion of H

2S to So using autotrophic

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 675673 10 pageshttpdxdoiorg1011552014675673

2 The Scientific World Journal

FM2

VBL1

VNG1

H2SCYL

FM1

TJ1 VNG3

COMP

PRG1

PRG2

VNG2SMP1

VNG4

TJ2

TWCBVBL2

T2 PP2

ALB

R SS

OUT

PDT1

PDT2

REC

CSS

T1 PP1

VBL3

VBL4

C3 SMP2

T3PP

VBL6

VBL5 P1

VBL7SMP3

VBL8SMP4

VNG4

Figure 1 Schematic of the bioreactor system ALBR air-lift bioreactor COMP air compressor CSS cell and sulfur suspension FM flowmeter H

2SCYLH

2S cylinder OUT outlet air to hood P circulation pump PDT pHDOTemp sensors PP peristaltic pump PRG pressure

reducer and pressure gauge REC recycled cell suspension SMP gasliquid sampling SS sulfur settler T tanks (1 nutrient 2 HCl and 3sulfur sludge) TJ tee joint TWCB thermostated water circulation bath VNG gas needle valve and VBL liquid ball valve

SOB [1 25ndash27] However the problem with these types ofreactors is that the produced sulfur particles block poresof the packing material and increase back pressure in thebioreactor Therefore they may not be suitable for treatmentof gas streams with high H

2S concentrations or loads where

large amount of elemental sulfur is expected to be producedsuch as in case of air streams with high H

2S concentrations

(up to several hundred or few thousands ppm) and energy-rich gases such as biogas from anaerobic digesters or landfillswhich may contain H

2S concentrations up to several thou-

sand ppmSuspended-growth bioreactors have no packing materi-

als When seeded with autotrophic SOB they can overcomethe aforementioned drawbacks Study of the applicationof these bioreactors for biological oxidation of sulfide toelemental sulfur has been reported [28ndash32] In these studiesthe inlet streams were sulfide-containing solutions ratherthan H

2S gas

The objective of the current study was to study biologicaltreatment of high concentrations of H

2S in an airlift biore-

actor where direct injection of H2S gas into the bioreactor

is applied with special emphasis on the effect of pH incombination with other factors such as sulfide loading rateoxygen availability and sulfide accumulation

2 Materials and Methods

21 Experimental Set-Up The experimental set-up shownin Figure 1 consisted of three main sections the H

2S-air

preparation section the airlift bioreactor and the sulfursettler The airlift bioreactor consisted of two concentric

140 cm long acrylic tubes the draft tube and the downcomertube The inside diameters of the two tubes were 6 cm and15 cm respectively The working volume was 2475 liters Thephase separator was 30 cm long with 30 cm inside diameterand filled up to 50 of its heightThe bioreactor was jacketedwith a 20 cm inside diameter acrylic tube for temperaturecontrol inside the bioreactor Several ports for inlet and outletgas streams nutrient supply pH adjustment solutions cellsuspension circulation between the bioreactor and the settlerand pHDOtemperature sensors existed

The sulfur settler was constructed from an acrylic tubewith 40 cm height and 40 cm inside diameter fitted to aconical bottom with 20 cm height The bioreactor solutionwas continuously withdrawn to the settler for separationof the formed sulfur and the supernatant from the settlerwas recycled to the bioreactor The settled sulfur slurry waswithdrawn from the bottom of the settler cone for furthertreatment

Air was driven to the bioreactor by a compressor Beforeentering the bioreactor bottom air was mixed with a streamof H2S coming from a cylinder at a controlled flow rate to

bring about a calculated H2S concentration Gas flow meters

(Cole-Parmer EW-3227-0828) were used to control air andH2S flow rates and consequently H

2S concentrations

22 Microbial Culture and Operation of the Bioreactor Thebioreactor was inoculated with 05 kg of activated sludgefrom Bani Malik Sewage Treatment Plant A mixed cultureof SOB was enriched using a thiosulfate nutrient solution forincreasing biomass yieldThe composition of themedium (ingL) inside the bioreactorwas as follows [4] Na

2HPO4sdot7H2O

The Scientific World Journal 3

227 KH2PO4 18 MgCl

2sdot7H2O 01 (NH

4)2SO4 198

MnCl2sdotH2O 0023 CaCl

2 003 FeCl

3sdot6H2O 0033 Na

2CO3

10 and Na2S2O3sdot5H2O 1569 Air was continuously supplied

at a flow rate of 10 Lminwithout circulation of the bioreactorsolution for 3 days after which circulation of the resultingsuspension was initiated between the airlift bioreactor andthe settler with continuous addition of the thiosulfatemineralsolution (5mLmin) and withdrawal of the settled solidsAdditional thiosulfate was added to the bioreactor on dailybasis to insure sufficient supply for the developed SOBWhenthiosulfate consumption rate by the developed SOB reached amaximum value loading of H

2S gas to the bioreactor started

and the nutrient medium without thiosulfate was suppliedDuring a period of 176 days of operation the airlift

bioreactor was fed with H2S as the sole sulfide source in pre-

determined concentrations (from 1008 ppm to 31215 ppm)in a continuous air stream of 10 litermin The inlet con-centration of H

2S was increased gradually to increase the

sulfide loading rate (from 42 up to 1324 gH2Smminus3 hminus1) The

increase of H2S inlet concentration was on the expense of

oxygen concentration resulting in a decrease in dissolvedoxygen During a period of almost stable load and dissolvedoxygen the value of pH was changed The pH value wascontrolled by adding HCl or Na

2CO3The temperature of the

bioreactor was controlled at 30∘C most of the time

23 Abiotic Experiment The abiotic experiments were con-ducted by adding sterilized activated sludge to the nutri-ent solution in the bioreactor and H

2S-air mixture (about

1000 ppm) was introduced to the bioreactor for three daysDuring the first few hours of the first day the removalefficiencywas high and then sharply decreased to amaximumof 3 during the remaining period Analysis of the bioreactorsolution revealed accumulation of the sulfide in the bioreac-tor solution without formation of elemental sulfur Only veryslight increase in sulfate (13) and thiosulfate (082) overtheir original concentrations was observed

24 Chemical Analysis Sulfur species (sulfate thiosulfatesulfide and elemental sulfur) were measured in the outletliquid solution on a daily basis Barium sulfate turbidimetricmethod [33] was used to measure sulfate concentration usinga calibrated sulfate photometer (HANNA HI93751) Sulfidethiosulfate and polysulfide concentrations were measuredby argentimetric potentiometric titration [34] using an auto-matic titrator (848 Titrino Plus Metrohm) Silver nitratewas used as the titrant The titrator was equipped witha calibrated silversilver sulfide ion selective electrode forsulfide determination and a calibrated iodide electrode withAgAgCl reference electrode for thiosulfate determination

Measurement of pH dissolved oxygen (DO) and tem-perature inside the bioreactor and the settler was carriedout using Orion 4-Star meter (Thermo Scientific) equippedwith a calibrated ROSS Ultra pH electrode and a calibratedpolarographic dissolved oxygen probe Measurement of pHand temperature outside the bioreactor was carried out witha calibrated Handylab 1 pH meter (Schott) and a FisherScientific digital thermometer respectively

0

20

40

60

80

100

020406080

100120140160

0 20 40 60 80 100 120 140 160 180

Rem

oval

effici

ency

()

Days of operation

Loading rateElimination capacityRemoval efficiency

H2S

load

ing

rate

and

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

Figure 2 Daily performance of the airlift bioreactor over the studyperiod

H2S inlet and outlet gas concentrations were monitored

by a H2S gas detector (BW GasAlertMax XT) with a mea-

suring range of 0ndash200 ppm Dilution of the gas in a dual-valve Tedlar PVF bag (Cole-Parmer EW-01409-93) withsubsequent measurement was conducted when necessary

3 Results and Discussion

31 Bioreactor Performance at Various H2S Loading Rates andpH The H

2S loading rate (LR) elimination capacity (EC)

and removal efficiency (RE) of the bioreactor were calculatedusing the following equations

LR =119862119892119894times 119876119892

119881119877

EC =[(119862119892119894minus 119862119892119900) times 119876119892minus 119862119897119900times 119876119897119900]

119881119877

RE =[(119862119892119894minus 119862119892119900) times 100]

119862119892119894

(1)

where 119862119892119894

and 119862119892119900

are the inlet and outlet gaseous sulfideconcentrations (gm3) 119862

119897119900is the liquid discharge sulfide

concentration (gm3) 119876119892is the volumetric gas flow rate

(m3h)119876119897119900is the volumetric bioreactor liquid discharge flow

rate (m3h) and 119881119877is the working volume of the bioreactor

(m3)Figure 2 shows H

2S loading rates and elimination capac-

ities as well as the removal efficiency during a 176-day periodof continuous operation Hydrogen sulfide loading rate wasincreased gradually up to 1324 gH

2Smminus3 hminus1 at day 141

and then decreased down to about 116 gH2Smminus3 hminus1 during

the remaining period Elimination capacities up to about113 gH

2Smminus3 hminus1 were attained during the study period In

terms of H2S gas removal efficiency higher than 99 could

be achieved at loading rates up to 108 gH2Smminus3 hminus1

The effect of pH on the elimination capacity of the biore-actor at steady-state condition is illustrated in Figure 3 In all


0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140H2S loading rate (g H2S mminus3 hminus1)

H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(a)

0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(b)

Actual elimination capacity100 elimination

0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(c)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(d)

Figure 3 Effect of pH on the maximum elimination capacity of the airlift bioreactor (a) pH = 65ndash69 (b) pH = 70ndash74 (c) pH = 75ndash79 and(d) pH = 80ndash85

cases the elimination capacity of the bioreactor increased asthe loading rate increased up to a maximum value beyondwhich a decrease in elimination capacity was observed Themaximum elimination capacities achieved at the studied pHranges were about 84 108 113 and 113 gH

2Smminus3 hminus1 at pH

ranges 65ndash69 70ndash74 75ndash79 and 80ndash85 respectivelyThesemaximum elimination capacities were achieved at loadingrates in the range 120ndash130 gH

2Smminus3 hminus1

Fernandez et al [26] found similar trend with pH How-ever their biotrickling filter was sensitive to H

2S overloads at

pH higher than 75 which was not the case with the current

SOBThe close results at various pH ranges particularly at pHgt7 suggest that the SOB used in the bioreactor was capableof sustaining a wide pH range This might be explained bythe fact that the used SOB originated from a mixed culturerather than being a pure cultureThemixed culture containedseveral species of SOB allowing for adaptation to variousenvironmental conditions

The relatively lowperformance of the SOB at the lower pHrange (below 70) might be attributed to biological capacityandor mass-transfer limitation H

2S is an acidic gas that

dissolves in alkaline solutions with a rate higher than that


0

20

40

60

80

100

0 05 1 15 2

Sul

fur r

ecov

ery

()

Dissolved oxygen (mgL)

y = minus2339x + 9224

R2 = 081

(a)

Sul

fur r

ecov

ery

()

0

20

40

60

80

100

0 10 20 30 40O2H2S molar ratio

y = minus192x + 10275

R2 = 099

(b)

Figure 4 Effect of oxygen availability as (a) DO and (b) O2H2S molar ratio on sulfur recovery

in acidic ones Therefore pH values in the alkaline rangeallow more H

2S to dissolve and consequently be available

for the existing SOB On the other hand low pH valuesmight affect the SOB performance due to existence of higherconcentrations of free or unionized sulfide in the solution aswill be discussed later in Section 34

The maximum elimination capacity achieved in thecurrent airlift bioreactor was higher than other bioreactorconfigurations [2 3 5 6] and comparable to others [25 27](Table 1) However it was lower than other airlift bioreactorswhere sulfide solution rather than H

2S gas was used as a feed

[29 35] One reason for that may be the absence of mass-transfer problems in the liquid sulfide-fed airlift reactorscompared to the gas-fed onesThis implies that application ofH2S gas-fed airlift bioreactors might require reactor volumes

larger than those in the sulfide-fed ones However gas-fedbioreactors eliminate the use of additional absorption columnto convert H

2S gas to sulfide solution and thus save the

associated capital and operating costs Also the eliminationcapacity of the current bioreactor was lower than that of abiotrickling filterwith polyurethane foam (PUF) packing [26]because of the highermass-transfer rate provided by the largespecific surface area of PUF However the disadvantage ofthis type of packing is pore clogging by the formed sulfurparticles which might raise maintenance problems

32 The Effect of Oxygen Availability on Bioconversion EndProduct The effect of oxygen availability as DO in the biore-actor solution is presented in Figure 4(a) which shows thatelemental sulfur is the dominant end product at low DO Forinstance higher than 90 sulfur recovery (ie conversion ofH2S into elemental sulfur) could be achieved at DO lower

than 03mgL As theDO concentrationwas increased sulfateformation increased on the expense of sulfur recovery Sulfurrecovery was lower than 40 at DO concentrations higher

than 2mgL Similar results were found by Lohwacharin andAnnachhatre [29]

Buisman et al [28] reported that biological oxidation ofsulfide to sulfate proceeds in two stages as follows

HSminus[O]+SOB997888rarr membrane bound [So] larrrarr So (2)

membrane bound [So][3O]997888rarr SO

3

minus2 [O]997888rarr SO

4

minus2 (3)

In the first stage which proceeds faster than the second stagesulfide looses two electrons andmembrane-bound polymericsulfur compounds are being formed (2) In the second stepthis sulfur is oxidized to sulfite and then to sulfate (3) Thehigher oxidized forms are formed only if the amount ofavailable oxygen is sufficient If oxygen extent is controlledfor achieving the first stage only elemental sulfur will be theend product of the process

Sulfate is not preferred as end product because of itsadverse effect on sewerage system and may constitute asecondary pollutant On the other hand elemental sulfur (So)is a noncorrosive solid that is easy to handle and transport Inaddition it has a commercial value exceeding that of sulfuricacid (or sulfate) [36]Therefore direction of bioconversion ofH2S towards elemental sulfur formation is preferredIt was reported in many published work that bioconver-

sion of the inlet sulfide can be limited to elemental sulfurby maintaining DO concentration at lt01mgL [37ndash39]The performance of aerobic SOB as related to the availableDO might be common to all bioreactor systems Howeverbioreactors might differ from each other in the operationalconditions to attain such low DO concentrations It might beeasy to control oxygen limited condition in an airlift bioreac-tor fed with liquid sulfide solutions by controlling the air doseto the bioreactor medium On the other hand in an airliftbioreactor fed with H

2S-air mixture the DO concentration


Table 1 Comparison between the maximum elimination capacity of the current airlift bioreactor and other studies

Type of bioreactor Sulfide feed form Maximum EC ReferenceBiofilter packed with sodium alginate beads H2S gas 8 gH2Sm

minus3 hminus1 [3]Fixed film bioscrubber H2S gas 194 gH2Sm

minus3 hminus1 [5]Biofilter packed with organic materials H2S gas 79 gH2Sm

minus3 hminus1 [6]Biotrickling filter packed with polyurethane foam H2S gas 55 g Smminus3 hminus1 [2]Biofilter packed with GAC H2S gas 125 gH2Sm

minus3 hminus1 [25]Biotrickling filter packed with polyurethane foam H2S gas 170 g Smminus3 hminus1 [26]Industrial scale biotrickling filter packed with polypropylene Pall rings H2S gas 110 gH2Sm

minus3 hminus1 [27]

Airlift bioreactor Sulfide solution 43 kg SkgVSSsdotd(asymp160 g Smminus3 hminus1) [29]

Airlift bioreactor Sulfide solution 67molm3sdoth

(2144 g Smminus3 hminus1) [35]

Airlift bioreactor H2S gas 113 gH2Smminus3 hminus1 This study

depends onmany factors of which O2H2Smolar ratio in the

feed gas stream and mass-transfer are important Thereforeit was important to study the relationship between O

2H2S

molar ratio and the bioreactor performance in terms of sulfur recovery and DO which is specific for each airliftbioreactor

The effect of O2H2S molar ratio on sulfur recovery

is shown in Figure 4(b) Sulfur recovery increased at lowerO2H2Smolar ratios Higher than 90 conversion to elemen-

tal sulfur was achieved at O2H2S molar ratios lower than 10

On the other hand sulfate was the dominant end product atO2H2S molar ratios gt 20

Compared to other bioreactors the O2H2S molar ratio

that achieved maximum sulfur recovery in this study wasfound to be higher In two of the other bioreactors [1 28]packingmaterial (eg polyurethane foam and polypropylenegrid) was used to enhance mass-transfer of both H

2S and

oxygen However these types of packingmaterials may sufferfrom clogging by sulfur particles In another bioreactor [30]sulfide solution and airweremixed in a separate stirred vesselwhich might add to the operating cost of the bioreactor

This comparison indicates that oxygen availability inthe cell suspension is a function of mass-transfer Figure 5shows the relationship between the inlet O

2H2S molar

ratio and dissolved oxygen which is a characteristic of thecurrent airlift bioreactor An improvement in mass-transferis expected to increase the slope of the linear equation

The maximum conversion of H2S into elemental sulfur

achieved in the airlift bioreactor with the current configura-tion was 95 which is comparable to that achieved in somestudies [1 40]while beingmuchhigher than in others [29 41]

During the last three months of the bioreactor operationthe average percentage of H

2S converted into thiosulfate

was 067 plusmn 011 mainly due to auto-oxidation of sulfide[30 41] andor reaction of sulfur with OHminus ion in alkalinesolution [34 42 43] The highest conversion to thiosulfatewas obtained at higher O

2H2S molar ratios Additionally an

average of 21 of the inlet sulfide was detected as sulfide inthe outlet solution which is very close to that reported byFortuny et al [1]

00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824

Figure 5 Correlation between O2H2S molar ratio and DO

33 The Effect of pH on Bioconversion End Product Theeffect of pH on sulfur recovery was observed under oxygen-limited conditions (Figure 6(a)) and under excess oxygen(Figure 6(b)) At oxygen-limited conditions there was a slightincrease of sulfur recovery as the pHwas increased On theother hand a decreased sulfur recovery was observed athigher pH when oxygen was in excess

It was found in previous studies that sulfur reacts withOHminus ion in alkaline solution according to the followingequation [34]

(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)

In the presence of excess sulfur (ie 119909 gt 0) whichis the case at oxygen-limited conditions polysulfide forms[42] In this study polysulfide was included in elementalsulfur concentration since So concentration was calculated bymass balance taking into account the inlet sulfide and theoutlet sulfide sulfate and thiosulfate This might explain theincreasing trend of sulfur recovery with pH at oxygen-limited


40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)

Figure 6 Effect of pH on bioconversion end product (a) O2H2S molar ratio lt10 and (b) O

2H2S molar ratio 10ndash20

conditions (Figure 6(a)) On the other hand at excessiveoxygen conditions the produced elemental sulfur in thebioreactor was less According to (4) less sulfur might resultin sulfide formation on the expense of elemental sulfur Thismight explain the decrease of sulfur recovery at high pH andexcess oxygen (Figure 6(b))

34 Effect of Accumulated Sulfide Concentration on Bio-conversion Efficiency The performance of the bioreactor interms of H

2S removal efficiency at four pH ranges and

various accumulated sulfide concentrations is illustrated inFigure 7 The removal efficiency sharply dropped below 90when the total accumulated sulfide concentration exceededabout 100 and 150mgL at pH ranges 65ndash69 and 70ndash74respectively The bioreactor performance severely droppedat higher accumulated sulfide concentrations On the otherhand much higher concentrations of accumulated sulfidewere tolerated at higher pH ranges For instance the removalefficiency was slightly affected under accumulated sulfideconcentrations higher than 320mgL at pH range 75ndash79however remaining higher than 97 At pH range of 80ndash85the removal efficiency was not affected even at accumulatedsulfide concentrations up to about 500mgL Higher concen-trations were not studied

The combined effect of both accumulated sulfide and pHmight be explained by three factors (a) mass-transfer (b)biological activity and (c) the presence of unionized sulfideH2S is an acidic gas that is expected to be absorbed in the

bioreactor solution more easily at high pH values Unlessthe resident SOB is capable of consuming the absorbed H

2S

gas dissolved sulfide will accumulate up to levels that areharmful to the resident microorganisms Sulfide is toxic athigher concentrations formany bacteriaThe inhibitory effectof sulfides presumed to be caused by unionized H

2S because

only neutral molecules can permeate well through the cellmembrane [44]

The fraction of unionized H2S of the total sulfide is very

much dependent on pH Hydrogen sulfide is a diprotic acidthat dissociate in two steps

H2Slarrrarr H+ +HSminus

1198701=

[H+] [HSminus][H2S]= 10minus7Mol Lminus1 at 20∘C

(5)

HSminus larrrarr H+ + Sminus2

1198702=

[H+] [Sminus2][HSminus]

= 08 times 10minus17Mol Lminus1 at 20∘C

(6)

Since the dissociation constant1198702is always so low (other val-

ues are reported) the equilibriumwith Sminus2 can be neglected atintermediate pH values [45] Therefore at neutral to slightlyalkaline conditions only the equilibrium between H

2S and

HSminus is consideredK1is the dissociation constant Its value changes with

temperature (119879 ∘K) according to [33]

1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)

The unionized H2S fraction of the total dissolved sulfide

(119891) can be calculated using 1198701and pH values according to

the following equation [46]

119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100

0 100 200 300 400 500Total accumulated sulfide concentration (mgL)

H2S

rem

oval

effici

ency

()

pH 65minus69pH 70ndash74

pH 75ndash79pH 80ndash85

Figure 7 Effect of accumulated sulfide on bioconversion efficiencyat various pH ranges

The accumulated sulfide concentrations 100mgL (at pHrange 65ndash69 average 67) and 150mgL (at pH range 70ndash74 average 72) beyond which inhibition of the SOB started(Figure 7) correspond to unionized H

2S fractions of 063 and

035 respectively These are equivalent to unionized sulfideconcentrations of 63 and 525mgL respectively The 50inhibitive unionized sulfide concentration was not studiedbut is expected to be higher than these two concentra-tions Considering the least unionized sulfide concentration(525mgL) the equivalent total sulfide that can be toleratedby the SOB at pH ranges 75ndash79 (average 77) and 80ndash85 (average 82) is expected to be 375 and 1050mgLrespectively

Using Henryrsquos law at 30∘C (partition coefficient is about20) the gas phase concentration of H

2S that can be tolerated

without inhibition of the resident SOB can be calculated asabout 38000 57000 142000 and 396000 ppm at pH valuesof 67 72 77 and 82 respectively assuming optimummass-transfer rate and the presence of sufficient microorganisms toconsume the absorbed H

2S

4 Conclusion

A maximum H2S elimination capacity of 113 gH

2Smminus3 hminus1

was achieved in the airlift bioreactor under investigation atloading rates up to 130 gH

2Smminus3 hminus1 a result indicating the

feasibility of using such bioreactor in biotreatment of highconcentrations of H

2S in air streams directly injected into the

bioreactorpH is an important parameter that should be adjusted for

better performance of the bioreactorThe effect of pH in asso-ciation with other factors on the bioreactor performance wasstudied It was found that the current airlift bioreactor (withthe resident SOB) was capable of achieving almost the sameH2S elimination capacity at a wide range of pH particularly

7ndash85 At lower pH values the elimination capacity was lowerThe bioreactor achieved maximum elemental sulfur

recovery (about 95) under oxygen limited conditions(DO below 02mgL) At low DO levels higher pH valuesincreased elemental sulfur recovery

The resident SOB in the bioreactor tolerated accumu-lated sulfide concentrations higher than 500mgL at higherpH values (80ndash85) and near 100 removal efficiency wasachieved However lower pH reduced the maximum toler-ated accumulated sulfide in cell suspension

The overall conclusion is therefore that the resident SOBin the studied airlift bioreactor favored pH values in theslightly alkaline range The bioreactor performance in termsof elimination capacity and sulfur recovery was better at thealkaline pH range 8ndash85 The ability of the airlift bioreactorused in this study to handle the high inlet concentrations ofH2S is a proof that it can be a promising option for treatment

of gas streams such as biogas from anaerobic digesters orlandfills which may contain H

2S concentrations up to several

thousand ppm However more studies are recommended toapply gas streams with composition similar to that emittedfrom such processes

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was funded by the Ministry of Higher Education(MOHE) Saudi Arabia under Grant no (1A3) The authorswould like to thank MOHE and King Abdulaziz UniversityDeanship of Scientific Research for technical and financialsupport

References

[1] M Fortuny J A Baeza X Gamisans et al ldquoBiological sweeten-ing of energy gases mimics in biotrickling filtersrdquoChemospherevol 71 no 1 pp 10ndash17 2008

[2] M Ramırez J M Gomez G Aroca and D Cantero ldquoRemovalof hydrogen sulfide by immobilized Thiobacillus thioparus in abiotrickling filter packed with polyurethane foamrdquo BioresourceTechnology vol 100 no 21 pp 4989ndash4995 2009

[3] J H Kim E R Rene and H S Park ldquoBiological oxidation ofhydrogen sulfide under steady and transient state conditions inan immobilized cell biofilterrdquo Bioresource Technology vol 99no 3 pp 583ndash588 2008

[4] P Oyarzun F Arancibia C Canales and G E Aroca ldquoBiofil-tration of high concentration of hydrogen sulphide usingThiobacillus thioparusrdquo Process Biochemistry vol 39 no 2 pp165ndash170 2003

[5] S Potivichayanon P Pokethitiyook and M KruatrachueldquoHydrogen sulfide removal by a novel fixed-film bioscrubbersystemrdquo Process Biochemistry vol 41 no 3 pp 708ndash715 2006

[6] J L R P Filho L T Sader M H R Z Damianovic EForesti and E L Silva ldquoPerformance evaluation of packingmaterials in the removal of hydrogen sulphide in gas-phasebiofilters polyurethane foam sugarcane bagasse and coconutfibrerdquoChemical Engineering Journal vol 158 no 3 pp 441ndash4502010

[7] D Park D S Lee J Y Joung and J M Park ldquoComparisonof different bioreactor systems for indirect H

2S removal using


iron-oxidizing bacteriardquo Process Biochemistry vol 40 no 3-4pp 1461ndash1467 2005

[8] Y C Chung C Huang and C-P Tseng ldquoMicrobial oxidationof hydrogen sulfide with biofilterrdquo Journal of EnvironmentalScience and Health vol 31 no 6 pp 1263ndash1278 1996

[9] Y Yang and E R Allen ldquoBiofiltration control of hydrogensulfide 1 Design and operational parametersrdquo Journal of the Airamp Waste Management Association vol 44 no 7 pp 863ndash8681994

[10] A H Wani A K Lau and R M R Barnion ldquoBiofiltra-tion control of pulping odors- hydrogen sulfide performancemacrokinetics and coexistence effects of organo-sulfur speciesrdquoJournal of Chemical Technology and Biotechnology vol 74 pp9ndash16 1999

[11] Y Yang and E R Allen ldquoBiofiltration control of hydrogensulfide 2 Kinetics biofilter performance and maintenancerdquoJournal of the Air and Waste Management Association vol 44no 11 pp 1315ndash1321 1994

[12] K Kim W Chung and Y Oh ldquoDynamic behavior of compostbiofilters during periods of starvation and fluctuating hydrogensulfide loadingsrdquo Journal of Environmental Science and Healthvol 39 no 1 pp 299ndash307 2004

[13] Y C Chung and C Huang ldquoRemoval of hydrogen sulphide byimmobilizedThiobacillus sp strain CH11 in a biofilterrdquo Journalof Chemical Technology and Biotechnology vol 69 no 1 pp 58ndash62 1997

[14] D Gabriel and M A Deshusses ldquoPerformance of a full-scalebiotrickling filter treating H

2S at a gas contact time of 16 to

22 secondsrdquo Environmental Progress vol 22 no 2 pp 111ndash1182003

[15] S Kim and M A Deshusses ldquoDevelopment and experimentalvalidation of a conceptual model for biotrickling filtration ofH2Srdquo Environmental Progress vol 22 no 2 pp 119ndash128 2003

[16] D H Park J M Cha H W Ryu et al ldquoHydrogen sulfideremoval utilizing immobilized Thiobacillus sp IW with Ca-alginate beadrdquo Biochemical Engineering Journal vol 11 no 2-3pp 167ndash173 2002

[17] K Shinabe S Oketani T Ochi S Kanchanatawee and MMatsumura ldquoCharacteristics of hydrogen sulfide removal ina carrier-packed biological deodorization systemrdquo BiochemicalEngineering Journal vol 5 no 3 pp 209ndash217 2000

[18] H Duan R Yan L C C Koe and X Wang ldquoCombined effectof adsorption and biodegradation of biological activated carbonon H2S biotrickling filtrationrdquo Chemosphere vol 66 no 9 pp

1684ndash1691 2007[19] H Duan L C C Koe R Yan and X Chen ldquoBiological

treatment of H2S using pellet activated carbon as a carrier of

microorganisms in a biofilterrdquo Water Research vol 40 no 14pp 2629ndash2636 2006

[20] K Cho M Hirai and M Shoda ldquoDegradation of hydrogensulfide by Xanthomonas sp strain DY44 isolated from peatrdquoApplied and EnvironmentalMicrobiology vol 58 no 4 pp 1183ndash1189 1992

[21] H S J Yoshizawa and S Kametani ldquoBacteria help desulfurizegasrdquo Hydrocarbon Processing vol 67 pp 76Dndash76F 1988

[22] S Ebrahimi F J F Morales R Kleerebezem J J Heijnen andM C M van Loosdrecht ldquoHigh-rate acidophilic ferrous ironoxidation in a biofilm airlift reactor and the role of the carriermaterialrdquo Biotechnology and Bioengineering vol 90 no 4 pp462ndash472 2005

[23] H Son and J Lee ldquoH2S removal with an immobilized cell hybrid

reactorrdquo Process Biochemistry vol 40 no 6 pp 2197ndash22032005

[24] C Pagella and D M De Faveri ldquoH2S gas treatment by iron

bioprocessrdquo Chemical Engineering Science vol 55 no 12 pp2185ndash2194 2000

[25] C Rattanapan P Boonsawang and D Kantachote ldquoRemovalof H2S in down-flow GAC biofiltration using sulfide oxidizing

bacteria from concentrated latex wastewaterrdquo Bioresource Tech-nology vol 100 no 1 pp 125ndash130 2009

[26] M Fernandez M Ramırez J M Gomez and D Cantero ldquoBio-gas biodesulfurization in an anoxic biotrickling filter packedwith open-pore polyurethane foamrdquo Journal of HazardousMaterials vol 264 pp 529ndash535 2014

[27] G Rodriguez A D Dorado M Fortuny D Gabriel and XGamisans ldquoBiotrickling filters for biogas sweetening oxygentransfer improvement for a reliable operationrdquo Process Safetyand Environmental Protection vol 92 no 3 pp 261ndash268 2014

[28] C J N Buisman B G Geraats P IJspeert and G LettingaldquoOptimization of sulphur production in a biotechnologicalsulphide-removing reactorrdquo Biotechnology and Bioengineeringvol 35 no 1 pp 50ndash56 1990

[29] J Lohwacharin and A P Annachhatre ldquoBiological sulfideoxidation in an airlift bioreactorrdquo Bioresource Technology vol101 no 7 pp 2114ndash2120 2010

[30] A J H Janssen S CMa P Lens andG Lettinga ldquoPerformanceof a sulfide-oxidizing expanded-bed reactor supplied withdissolved oxygenrdquoBiotechnology and Bioengineering vol 53 pp32ndash40 1997

[31] A J H Janssen G Lettinga and A de Keizer ldquoRemoval ofhydrogen sulphide from wastewater and waste gases by biolog-ical conversion to elemental sulphur colloidal and interfacialaspects of biologically produced sulphur particlesrdquoColloids andSurfaces A Physicochemical andEngineeringAspects vol 151 no1-2 pp 389ndash397 1999

[32] B Krishnakumar S Majumdar V B Manilal and A HaridasldquoTreatment of sulphide containing wastewater with sulphurrecovery in a novel reverse fluidized loop reactor (RFLR)rdquoWater Research vol 39 no 4 pp 639ndash647 2005

[33] American Public Health Association (APHA) Standard Meth-ods for the Examination of Water amp Wastewater APHA Wash-ington DC USA 21st edition 2005

[34] H Satake T Hisano and S Ikeda ldquoThe rapid determinationof sulfide thiosulfate and polysulfide in the lixiviation waterof blast-furnace slag by means of argentometric potentiometrictitrationrdquo Bulletin of the Chemical Society of Japan vol 54 pp1968ndash1971 1981

[35] G M M Moghanloo E Fatehifar S Saedy Z Aghaeifa andH Abbasnezhad ldquoBiological oxidation of hydrogen sulfidein mineral media using a biofilm airlift suspension reactorrdquoBioresource Technology vol 101 no 21 pp 8330ndash8335 2010

[36] P F Henshaw and W Zhu ldquoBiological conversion of hydrogensulphide to elemental sulphur in a fixed-film continuous flowphoto-reactorrdquo Water Research vol 35 no 15 pp 3605ndash36102001

[37] C Vannini G Munz G Mori C Lubello F Verni andG Petroni ldquoSulphide oxidation to elemental sulphur in amembrane bioreactor performance and characterization of theselected microbial sulphur-oxidizing communityrdquo Systematicand Applied Microbiology vol 31 no 6ndash8 pp 461ndash473 2008

[38] A J H Janssen S Meijer J Botsema and G LettingaldquoApplication of the redox potential for controlling a sulfide


oxidating bioreactorrdquo Biotechnology and Bioengineering vol 60pp 147ndash155 1998

[39] A D Levine B J Raymer and J Jahn ldquoEvaluation of biologicalhydrogen sulfide oxidation coupled with two-stage upflowfiltration for groundwater treatmentrdquo Journal of EnvironmentalScience and Health A vol 39 no 5 pp 1263ndash1279 2004

[40] P F Henshaw J K Bewtra and N Biswas ldquoHydrogen sulphideconversion to elemental sulphur in a suspended-growth con-tinuous stirred tank reactor using Chlorobium limicolardquo WaterResearch vol 32 no 6 pp 1769ndash1778 1998

[41] A J H Janssen R Sleyster C van der Kaa A Jochemsen JBontsema and G Lettinga ldquoBiological sulphide oxidation in afed-batch reactorrdquo Biotechnology and Bioengineering vol 47 no3 pp 327ndash333 1995

[42] R H Arnston F W Dickson and G Tunell ldquoSystems S-Na2O-

H2O and S-H

2O application to the mode of origin of natural

alkaline polysulfide and thiosulfate solutionsrdquoAmerican Journalof Science vol 8 pp 574ndash582 1960

[43] S A Khan ldquoUV-ATR spectroscopy study of the speciation inaqueous polysulfide electrolyte solutionsrdquo International Journalof Electrochemical Science vol 7 no 1 pp 561ndash568 2012

[44] L W H Pol P N L Lens A J M Stams and G LettingaldquoAnaerobic treatment of sulphate-rich wastewatersrdquo Biodegra-dation vol 9 no 3-4 pp 213ndash224 1998

[45] W E Kleinjan A de Keizer and A J H Janssen ldquoEquilibriumof the reaction between dissolved sodium sulfide and biolog-ically produced sulfurrdquo Colloids and Surfaces B Biointerfacesvol 43 no 3-4 pp 228ndash237 2005

[46] Z Isa S Grusenmeyer andW Vestraete ldquoSulfate reduction rel-ative to methane production in high-rate anaerobic digestiontechnical aspectsrdquoApplied and EnvironmentalMicrobiology vol51 no 3 pp 572ndash579 1986

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


FM2

VBL1

VNG1

H2SCYL

FM1

TJ1 VNG3

COMP

PRG1

PRG2

VNG2SMP1

VNG4

TJ2

TWCBVBL2

T2 PP2

ALB

R SS

OUT

PDT1

PDT2

REC

CSS

T1 PP1

VBL3

VBL4

C3 SMP2

T3PP

VBL6

VBL5 P1

VBL7SMP3

VBL8SMP4

VNG4

Figure 1 Schematic of the bioreactor system ALBR air-lift bioreactor COMP air compressor CSS cell and sulfur suspension FM flowmeter H

2SCYLH

2S cylinder OUT outlet air to hood P circulation pump PDT pHDOTemp sensors PP peristaltic pump PRG pressure

reducer and pressure gauge REC recycled cell suspension SMP gasliquid sampling SS sulfur settler T tanks (1 nutrient 2 HCl and 3sulfur sludge) TJ tee joint TWCB thermostated water circulation bath VNG gas needle valve and VBL liquid ball valve

SOB [1 25ndash27] However the problem with these types ofreactors is that the produced sulfur particles block poresof the packing material and increase back pressure in thebioreactor Therefore they may not be suitable for treatmentof gas streams with high H

2S concentrations or loads where

large amount of elemental sulfur is expected to be producedsuch as in case of air streams with high H

2S concentrations

(up to several hundred or few thousands ppm) and energy-rich gases such as biogas from anaerobic digesters or landfillswhich may contain H

2S concentrations up to several thou-

sand ppmSuspended-growth bioreactors have no packing materi-

als When seeded with autotrophic SOB they can overcomethe aforementioned drawbacks Study of the applicationof these bioreactors for biological oxidation of sulfide toelemental sulfur has been reported [28ndash32] In these studiesthe inlet streams were sulfide-containing solutions ratherthan H

2S gas

The objective of the current study was to study biologicaltreatment of high concentrations of H

2S in an airlift biore-

actor where direct injection of H2S gas into the bioreactor

is applied with special emphasis on the effect of pH incombination with other factors such as sulfide loading rateoxygen availability and sulfide accumulation

2 Materials and Methods

21 Experimental Set-Up The experimental set-up shownin Figure 1 consisted of three main sections the H

2S-air

preparation section the airlift bioreactor and the sulfursettler The airlift bioreactor consisted of two concentric

140 cm long acrylic tubes the draft tube and the downcomertube The inside diameters of the two tubes were 6 cm and15 cm respectively The working volume was 2475 liters Thephase separator was 30 cm long with 30 cm inside diameterand filled up to 50 of its heightThe bioreactor was jacketedwith a 20 cm inside diameter acrylic tube for temperaturecontrol inside the bioreactor Several ports for inlet and outletgas streams nutrient supply pH adjustment solutions cellsuspension circulation between the bioreactor and the settlerand pHDOtemperature sensors existed

The sulfur settler was constructed from an acrylic tubewith 40 cm height and 40 cm inside diameter fitted to aconical bottom with 20 cm height The bioreactor solutionwas continuously withdrawn to the settler for separationof the formed sulfur and the supernatant from the settlerwas recycled to the bioreactor The settled sulfur slurry waswithdrawn from the bottom of the settler cone for furthertreatment

Air was driven to the bioreactor by a compressor Beforeentering the bioreactor bottom air was mixed with a streamof H2S coming from a cylinder at a controlled flow rate to

bring about a calculated H2S concentration Gas flow meters

(Cole-Parmer EW-3227-0828) were used to control air andH2S flow rates and consequently H

2S concentrations

22 Microbial Culture and Operation of the Bioreactor Thebioreactor was inoculated with 05 kg of activated sludgefrom Bani Malik Sewage Treatment Plant A mixed cultureof SOB was enriched using a thiosulfate nutrient solution forincreasing biomass yieldThe composition of themedium (ingL) inside the bioreactorwas as follows [4] Na

2HPO4sdot7H2O


227 KH2PO4 18 MgCl

2sdot7H2O 01 (NH

4)2SO4 198


2 003 FeCl

3sdot6H2O 0033 Na

2CO3


















0

20

40

60

80

100

020406080

100120140160

0 20 40 60 80 100 120 140 160 180

Rem

oval

effici

ency

()

Days of operation


H2S

load

ing

rate

and

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)









LR =119862119892119894times 119876119892

119881119877


119881119877

RE =[(119862119892119894minus 119862119892119900) times 100]

119862119892119894

(1)

where 119862119892119894

and 119862119892119900

















0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(a)

0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(b)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(c)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(d)





2Smminus3 hminus1


2S overloads at







0

20

40

60

80

100

0 05 1 15 2

Sul

fur r

ecov

ery

()


y = minus2339x + 9224

R2 = 081

(a)

Sul

fur r

ecov

ery

()

0

20

40

60

80

100


y = minus192x + 10275

R2 = 099

(b)

















3


4

minus2 (3)












minus3 hminus1 [27]







2H2S








2S and



2H2S molar









00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824




(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)



40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


227 KH2PO4 18 MgCl

2sdot7H2O 01 (NH

4)2SO4 198


2 003 FeCl

3sdot6H2O 0033 Na

2CO3


















0

20

40

60

80

100

020406080

100120140160

0 20 40 60 80 100 120 140 160 180

Rem

oval

effici

ency

()

Days of operation


H2S

load

ing

rate

and

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)









LR =119862119892119894times 119876119892

119881119877


119881119877

RE =[(119862119892119894minus 119862119892119900) times 100]

119862119892119894

(1)

where 119862119892119894

and 119862119892119900

















0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(a)

0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(b)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(c)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(d)





2Smminus3 hminus1


2S overloads at







0

20

40

60

80

100

0 05 1 15 2

Sul

fur r

ecov

ery

()


y = minus2339x + 9224

R2 = 081

(a)

Sul

fur r

ecov

ery

()

0

20

40

60

80

100


y = minus192x + 10275

R2 = 099

(b)

















3


4

minus2 (3)












minus3 hminus1 [27]







2H2S








2S and



2H2S molar









00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824




(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)



40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(a)

0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(b)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(c)


0

20

40

60

80

100

120

140


H2S

elim

inat

ion

capa

city

(g H

2S m

minus3

hminus1)

(d)





2Smminus3 hminus1


2S overloads at







0

20

40

60

80

100

0 05 1 15 2

Sul

fur r

ecov

ery

()


y = minus2339x + 9224

R2 = 081

(a)

Sul

fur r

ecov

ery

()

0

20

40

60

80

100


y = minus192x + 10275

R2 = 099

(b)

















3


4

minus2 (3)












minus3 hminus1 [27]







2H2S








2S and



2H2S molar









00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824




(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)



40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

20

40

60

80

100

0 05 1 15 2

Sul

fur r

ecov

ery

()


y = minus2339x + 9224

R2 = 081

(a)

Sul

fur r

ecov

ery

()

0

20

40

60

80

100


y = minus192x + 10275

R2 = 099

(b)

















3


4

minus2 (3)












minus3 hminus1 [27]







2H2S








2S and



2H2S molar









00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824




(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)



40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








minus3 hminus1 [27]







2H2S








2S and



2H2S molar









00

05

10

15

20

25

0 5 10 15 20 25 30 35

DO

(mg

L)

O2H2S molar ratio

y = 0054x

R2 = 0824




(4 + 2119909) S + 6OHminus 997888rarr 2S119909+1

2minus+ S2O3

2minus+ 3H2O (4)



40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


40

50

60

70

80

90

100

65 70 75 80 85 90

Sul

fur r

ecov

ery

()

pH

y = 2 17x + 7382

R2 = 014

(a)

40

50

60

70

80

90

100

65 70 75 80 85

Sul

fur r

ecov

ery

()

pH

y = minus321x + 10366

R2 = 011

(b)









2S


2S because





1198701=


(5)


1198702=



(6)



2S and



1199011198701= 3255 +

151944

119879

minus 15672 log10119879 + 002722119879

1199011198701= minuslog

101198701

(7)




119891 = (1 +

1198701

10minuspH )minus1

(8)


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


60

70

80

90

100


H2S

rem

oval

effici

ency

()










2S

4 Conclusion


2Smminus3 hminus1
















Acknowledgments


References








2S removal using















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of















































H2O and S-H
















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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