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Dosing free nitrous acid for sulfide control insewers: Results of field trials in Australia

Guangming Jiang a, Anthony Keating b, Shaun Corrie c, Kelly O’halloran d,Lam Nguyen e, Zhiguo Yuan a,*aAdvanced Water Management Centre, The University of Queensland, QLD, AustraliabCloevis, UniQuest Pty Limited, The University of Queensland, QLD, AustraliacCWE Corrie Water and Environment, QLD, AustraliadGold Coast City Council, QLD, AustraliaeUS Peroxide LLC, Atlanta, GA 30339, USA

a r t i c l e i n f o

Article history:

Received 14 February 2013

Received in revised form

10 April 2013

Accepted 10 May 2013

Available online 24 May 2013

Keywords:

Sewer

Free nitrous acid

Hydrogen peroxide

Biofilm

Sulfide

Odour

Abbreviations: ADWF, Average dry-weathHRT, Hydraulic retention time; SRB, Sulphat* Corresponding author. Tel.: þ61 7 3365 437E-mail addresses: g.jiang@awmc.uq.edu.a

riewater.com.au (S. Corrie), KOHALLORAN@uq.edu.au (Z. Yuan).0043-1354/$ e see front matter ª 2013 Elsevhttp://dx.doi.org/10.1016/j.watres.2013.05.024

a b s t r a c t

Intermittent dosing of free nitrous acid (FNA), with or without the simultaneous dosing of

hydrogen peroxide, is a new strategy developed recently for the control of sulfide pro-

duction in sewers. Six-month field trials have been carried out in a rising main sewer in

Australia (150 mm in diameter and 1080 m in length) to evaluate the performance of the

strategy that was previously demonstrated in laboratory studies. In each trial, FNA was

dosed at a pumping station for a period of 8 or 24 h, some with simultaneous hydrogen

peroxide dosing. The sulfide control effectiveness was monitored by measuring, on-line,

the dissolved sulfide concentration at a downstream location of the pipeline (828 m from

the pumping station) and the gaseous H2S concentration at the discharge manhole.

Effective sulfide control was achieved in all nine consecutive trials, with sulfide production

reduced by more than 80% in 10 days following each dose. Later trials achieved better

control efficiency than the first few trials possibly due to the disrupting effects of FNA on

sewer biofilms. This suggests that an initial strong dose (more chemical consumption)

followed by maintenance dosing (less chemical consumption) could be a very cost-effective

way to achieve consistent control efficiency. It was also found that heavy rainfall slowed

the recovery of sulfide production after dosing, likely due to the dilution effects and

reduced retention time. Overall, intermittent dose of FNA or FNA in combination with H2O2

was successfully demonstrated to be a cost-effective method for sulfide control in rising

main sewers.

ª 2013 Elsevier Ltd. All rights reserved.

er flow; COD, Chemical oxygen demand; FNA, Free nitrous acid; H2O2, Hydrogen peroxide;e-reducing bacteria; WWTP, Wastewater treatment plant.4; fax: þ61 7 3365 4726.u, guangming.jiang@gmail.com (G. Jiang), t.keating@eait.uq.edu.au (A. Keating), info@cor-goldcoastwater.com.au (K. O’halloran), lamnguyen@h2o2.com (L. Nguyen), Zhiguo@awmc.

ier Ltd. All rights reserved.

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 94332

1. Introduction sewer biofilms to a high-level of nitrite over an extended

Hydrogen sulfide, produced by sulphate-reducing bacteria

(SRB) in sewers under anaerobic conditions, is an important

source of sewer odours, corrosion and health hazards

(Pomeroy and Bowlus, 1946; US EPA, 1974;WERF, 2007). Sulfide

released into the atmosphere through manholes or pumping

stations may cause odour complaints from nearby residents.

Also, hydrogen sulfide is toxic to human and animals (WHO,

2003). The generation of hydrogen sulfide from sewage and

the transfer to the sewer atmosphere can cause serious con-

crete corrosion, creating major challenges to infrastructure

management through reduced service life and high costs for

sewer (US EPA, 1992).

Many chemical dosing technologies have been developed

to prevent hydrogen sulfide production/emission in sewer

systems (Ganigue et al., 2011; Zhang et al., 2008). There are

four commonly used strategies:

1) Sulfide removal by oxidation through injection of air, oxy-

gen, and nitrate (Gutierrez et al., 2008; Mohanakrishnan

et al., 2009). Addition of stronger oxidants like hydrogen

peroxide, ozone was also reported (US EPA, 1992);

2) Sulfide removal by precipitation through the addition of

iron salts (Firer et al., 2008; Zhang et al., 2009a);

3) Reduction of H2S transfer from liquid to air by pH elevation,

typically through the use of magnesium hydroxide or lime

(Gutierrez et al., 2009; Rees et al., 2003).

4) Prevention of sulfide generation by inhibiting the activities

of sulphate-reducing bacteria or inactivating them through

the use of inhibitors or biocides like caustic and molybdate

(Predicala et al., 2008; Zhang et al., 2009b).

The first three types of strategies require continuous

chemical addition in order to achieve effective sulfide control

at all times, incurring high chemical consumption and oper-

ational costs (Jiang et al., 2011a). In contrast, biocides have the

potential to disrupt the sulfide generating capacity of the

sewer biofilm for extended periods following application. As a

result, treatment with biocides may only need to be inter-

mittent with the intervals between treatments determined by

how rapidly the sulfide generating capacity recovers, i.e. the

regrowth rate of SRB in biofilms.

Currently, caustic compounds are the most common

biocidal agent used for sulfide control in sewers (Ganigue et al.,

2011). Sodium hydroxide is added to wastewater to cause a pH

shock (10e11) to suppress sulphate reduction activity in sewer

biofilms. However, the effectiveness of caustic shock was

limited in real applications with H2S being reduced by 40e50%

(O’Gorman et al., 2011; Tomar andAbdullah, 1994). In addition,

costs of caustic shock are comparable to continuous dosing of

oxidants or precipitants. Another SRB inhibitor, molybdate,

was only demonstratedwith pure cultures of SRB or for sulfide

control in oil fields or anaerobic digesters (Kjellerup et al., 2005;

Nemati et al., 2001; Tanaka and Lee, 1997). The persistence of

molybdate in dosed water and the potential negative impacts

on environment is still a significant concern.

Nitrite causes specific inhibition to dissimilatory sulphate

reduction (Greene et al., 2006) and therefore an exposure of

period of time (weeks) caused a gradual decrease of the SRB

population and hence the loss of biofilm activity (Jiang et al.,

2010; Mohanakrishnan et al., 2008). Jiang et al. (2011b)

further found that simultaneous addition of nitrite and acid

deactivated sewer biofilm activity with an exposure time of

6e24 h. It was revealed that free nitrous acid (FNA or HNO2)

formed from nitrite at acidic conditions has a strong biocidal

effect on anaerobic sewer biofilms, with the viable microbial

cells in biofilms decreased from approximately 80% prior to

FNA dosage to 5e15% after the biofilm was exposed to FNA at

0.2e0.3 mg HNO2eN/L for 6e24 h.

Hydrogen peroxide, in combinationwith FNA,was found to

enhance the microbial inactivation by 1-log (Jiang and Yuan,

2013), in comparison with FNA dosing alone. About 2-log of

microbial inactivation was achieved when biofilms were

exposed to FNA at 0.2 mgN/L or above and H2O2 at 30 mg/L or

above for 6 h or longer. FNA was identified as the primary

inactivation agent and H2O2 enhanced its efficiency. The in-

termediates of reactions between FNA and H2O2, such as

peroxynitrite and nitrogen dioxide, were suggested to be

responsible for the synergism between FNA and H2O2.

The strong biocidal effect of FNA on sewer biofilms implies

that the simultaneous dosage of nitrite and acid could achieve

rapid inactivation of SRB in sewer biofilms, making it possible

to achieve sulfide control through intermittent FNA dosing.

Through laboratory sewer reactor studies, Jiang et al. (2011a)

showed that 12-h dosing of FNA at a concentration of

0.26 mg-N/L every 5 days could reduce the average sulfide

production by >80%. The recovery time was doubled to

approximately 10 days in another laboratory sewer reactor

study by simultaneous addition of FNA and H2O2 due to the

increased inactivation efficiency (Jiang and Yuan, 2013).

Although laboratory studies showed great promise of using

FNA in sewers, the completely mixed nature in the lab-scale

sewer reactors are different from real sewers, which are

plug-flow systems. Therefore, biofilms at different locations in

a sewer main may be exposed to FNA at different concentra-

tions due to possible variations in nitrite and H2O2 concen-

trations and pH level during the transport of wastewater.

Consequently, the effectiveness of FNA dosing on sulfide

control in real sewers may be different from that previous

observed in laboratory sewer reactors. In addition, previous

laboratory studies were carried out with limited numbers of

consecutive dosing, and hence the long-term effect of FNA

dosing on sewer biofilm activities has not been assessed. It is

possible that sewer biofilms develop resistance to FNA during

repetitive dosing.

The primary aim of this study is to investigate the long-

term effectiveness of FNA dosing, with and without simul-

taneous H2O2 dosing, in controlling sulfide production in full

scale rising main sewers. Field trials were carried out at a

rising main sewer with a diameter of 150 mm and a length of

1080 m. Different chemical combinations of FNA and

hydrogen peroxide were added into the wet well at the

pumping station for different dosing durations. Both dis-

solved sulfide in the downstream pipeline and H2S gas in the

discharge manhole were continuously monitored with online

sensors, and were used as indicators of sulfide-producing

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 9 4333

activity in the pipe. The trials were carried out over a 6-month

period. Impacts of rain events were also evaluated based

upon SCADA data of sewage flow and hydraulic retention

time.

2. Materials and methods

2.1. Field trial site description

UC9 is a sewage pumping station located in the Gold

Coast, Australia (Google map latitude and longitude co-

ordinates: �27.9, 153.3). The annual mean atmospheric tem-

perature is between 17.2 and 25.1 �C, respectively. Mean

annual rainfall is 1376.5 mm (http://www.weatherzone.com.

au/). The UC9 pumping station receives domestic waste-

water from residential propertieswith an average daily flow of

206 m3/d. The rising main pipe leading from UC9 to a

discharge wet well is 1080 m long, and has a diameter of

150 mm.

The UC9 pumping station is operated with pumps turned

on and off when the water level in the wet well reaches above

18% and below 7%, respectively, of the total depth. Each

pumping event delivers about 2.2 m3 of wastewater into the

rising main pipe. The hydraulic retention time (HRT) of

wastewater in the UC9 pipe is representative of typical rising

main sewers, which varies between 3 and 7 h during a dry

weather day.

2.2. Dosing schemes

The dosing schemes of the field trials were designed based on

results of previously reported laboratory-scale experiments

(Jiang et al., 2011a, 2011b; Jiang and Yuan, 2013). Nine trials

were carried out from March to September in 2012 with

testing conditions summarized in Table 1. Chemicals were

added directly to the wet well at the UC9 pumping station

(starting point of the sewer pipe) during the specified dosing

period, followed by a recovery period which lasted between 1

and 4 weeks. During the recovery period, the sewer system

was allowed to run without chemical dosing. Subsequent

dosing (the next trial) was conducted when sulfide and H2S

Table 1 e Dosing schemes (chemicals and dosing durations) fo

Trial no. Chemical mix

Nitrite (mg-N/L) H2O2 (mg/L) pH (with

1 100 60 6

2 100 60 6

3 100 60 6

4 100 0 6

5 100 0 6

6 100 0 6

7 100 0 6

8 100 0 6

9 100 60 6

a FNA concentration is jointly determined by pH and the nitrite conce

(Ka � 10pH), where Ka is the ionization constant of the nitrous acid equilib

concentrations recovered to 20e50% of the baseline sulfide

level.

Two chemical mixes, i.e. FNA alone and FNA þ H2O2, were

tested in the trials. The FNA and H2O2 concentrations in all

trials were 0.26 mg HNO2eN/L and 60 mg/L, respectively,

selected according to results obtained in previous laboratory

studies. In addition, the duration of chemical addition is a

critical dosing parameter, as it determines the exposure time

of sewer biofilms to the biocidal chemicals, and also the

amount of chemicals required (for the given concentrations).

Previous lab studies indicated that an exposure timebetween6

and 24 h would be adequate to inactivate microbes in sewer

biofilms. Two dosing durations, which are 8 and 24 h, respec-

tively, were chosen to reflect the effective exposure time

required, and also to coincide with the 8-hour working shift in

Australia.

Chemicals were added to the UC9wet well via dosing pipes

dipping below the water surface For each trial, sodium nitrite

(40% solution) was added to the wet well immediately after a

pumping event to the residual wastewater in the well

(approximately 4 m3). The dosing amount was designed such

that a nitrite concentration of 100 mg-N/L in the wet well

would be achieved in the wastewater when the well was filled

up to the 18% level (i.e. before each pumping event). Hydro-

chloric acid (36%) was added continuously to maintain a

sewage pH of 6.0 at all times while the well was filled up with

wastewater. Continuous inflow of wastewater into the wet

well between pumping events (with intervals between 20 min

and 1 h) allowed adequate mixing of chemicals with waste-

water in the well. For some trials (trial No. 1, 2, 3, and 9),

hydrogen peroxide (stock concentration at 35%) was also

added immediately before a pumping event to reach a con-

centration of 60 mg/L in the wet well. During each trial (Table

1), three wastewater samples were taken from the wet well

over the trial period to verify the nitrite dosage. The con-

sumption of each of the chemicals during each trial was

recorded by measuring the stock levels before and after each

trial, to independently verify the dosing rates. Three waste-

water samples were also taken at the downstream sampling

location (see Fig. 1A) to reveal any variation of nitrite con-

centration in the pipe. The volume of chemicals being added

was also recorded to ensure the correct dosing levels.

r the trials.

FNAa (mg HNO2eN/L) Dosing duration (h)

HCl)

0.26 24

0.26 24

0.26 24

0.26 24

0.26 24

0.26 8

0.26 8

0.26 8

0.26 8

ntration (Weon et al., 2002). FNA was calculated as FNA ¼ NO2�eN/

rium equation. The value of Ka is determined by Ka ¼ e�2300/(273þ�C).

Fig. 1 e Map of the UC9 pumping station and the sewer

section used for the field trials (top); pumping events and

the diurnal pattern of hydraulic retention time in a typical

dry weather day (bottom).

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 94334

2.3. Monitoring and sampling

A UVeVIS spectrometer (S:CAN, Messtechnik GmbH, Austria)

capable of monitoring dissolved sulfide concentration in

Fig. 2 e Dosing and online monitoring arrangemen

sewage was installed at 828 m downstream of the pumping

station (Figs. 1 and 2). Manual cleaning of the sensor lens was

carried out every second day during the online monitoring

periods. The sensor was calibrated before the start of trials as

previously described (Sutherland-Stacey et al., 2008). pH was

also monitored at this location with a pH probe built in the

spectrometer unit. The recorded online data of HS� and pH

were used to calculate the dissolved H2S concentration, with

the total dissolved sulfide concentration (ST) obtained as the

sum of S2�, HS� and H2S concentrations.

ST ¼ ½H2S� þ�HS��þ �

S2�� ¼ �HS���1þ 10�pH

K1þ K2

10�pH

�

where, K1 ¼ ½HS��=½H2S�10�pH and.K2 ¼ ½S2��=½HS��10�pH At

25 �C, pK1 and pK2 were reported to be 7.05 and 13.8 (Ellis and

Milestone, 1967), respectively.

An online gas logger (Odalog� 10-1000 Logger L2) was

installed in the discharge wet well to monitor the gaseous H2S

concentration. The H2S sensor records the gaseous H2S con-

centration and temperature at 2 min intervals. The H2S data

were used in combinationwith the dissolved sulfide data from

the UVeVIS spectrometer as the gauge of sulphate-reducing

activity in the sewer pipe.

Both sensors were installed 6 weeks before the first dosing

trial to establish the baseline levels of dissolved sulfide and

gaseous H2S. This baseline serves as a measure of the unaf-

fected level of the sulfide producing activity of the sewer pipe,

which is used to calculate the level of suppression achieved

after each dose and the speed of recovery. Both dissolved

sulfide and H2S concentrations varied daily due to the dy-

namic pumping pattern and varying HRTs (see Results and

Discussion section), and therefore daily average concentra-

tions were employed as indicator of sulfide production on

each day.

2.4. Chemical analysis

For the analyses of dissolved sulfide, 1.5 mL wastewater was

filtered (0.22 mmmembrane) into 0.5mL preserving solution of

sulfide anti-oxidant buffer (SAOB) (Keller-Lehmann et al.,

2006). Samples were then analysed within 24 h on an ion

chromatograph (IC) with a UV and conductivity detector

(Dionex ICS-2000). For the analysis of nitrite, 1 mL of sewage

t during the trials at the UC9 pumping station.

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 9 4335

was filtered similarly, diluted 10 times and analysed using a

Lachat QuikChem 8000 (Milwaukee) flow-injection analyser

(FIA).

3. Results and discussion

3.1. Diurnal profiles of dissolved sulfide and gaseousH2S concentrations

Fig. 3A showsprofile of dissolved sulfide concentrationat 828m

downstream of UC9 wet well two days prior to the first dosing

event. The average sulfide concentration on the day was

7.4� 2.4mg-S/L, varying from0.6 to13.5mg-S/L. Sulfideprofiles

during other days in the baseline period were similar. The

average dissolved sulfide level over the entire baseline period

was 7.4 � 0.6 mg-S/L. The peaks of dissolved sulfide on the

diurnal profile corresponded to the HRT peaks shown in Fig. 2.

Especially, the longest HRT occurring around 6:00 AM each day

coincided with the highest daily dissolved sulfide concentra-

tion. As an example, Fig. 3A also shows a 24-h profile of dis-

solved sulfide measured 2 days after a dosing, which indicates

clearly lower concentrations in the range of 0e2.0 mg-S/L.

Sulfide was present at negligible concentrations for about half

of the time during the day (mainly during periods with shorter

HRT, i.e. in the afternoon). There was some sulfide production

during periods with longer HRT (>4 h), which indicates that a

small proportion of SRB survived the dosing event.

Sewage pH varied between 7.0 and 8.0, with its peak value

(approximately 8) between 6:00 AM to 12:00 PM. No discernible

change of pH was observed during the recovery period after

the dosing event.

Fig. 3 e Typical profiles of dissolved sulfide and wastewater pH

dosing (A); and H2S gas and atmospheric temperature in discha

Fig. 3B shows diurnal profiles of gaseous H2S concentra-

tions and temperature in the UC9 discharge wet well corre-

sponding to the same pre- and post-dosing time shown in

Fig. 3A. During the baseline period, the average H2S gas con-

centration and temperature were 36.5 � 6.4 ppmv and

26.3 � 1.5 �C, respectively. Temperature in the discharge wet

well 2 days after the 1st dosing was similar to the baseline

levels. H2S concentration increased sharply with each

pumping event, which discharged sulfide-containing waste-

water to the discharge well. The H2S then decreased to below

10 ppmv during the quiescent period (no discharge of waste-

water) presumably due to air dilution or leakage to the at-

mosphere. The gaseous H2S profile correlates well with

dissolved sulfide profile shown in Fig. 3A. The H2S profile

during 2 days after the first dosing, averaged at 1.5 ppmv,

shows much lower H2S concentrations supporting the dis-

solved sulfide measurement.

3.2. Comparison of the nine dosing trials

Fig. 4AeD show the daily averages of dissolved sulfide and

gaseous H2S concentrations measured at the downstream

location (828 m) and in the discharge wet well, respectively,

after each of the nine dosing trials. The baseline period before

the first dosing event is shown as negative days in Fig. 4. The

dosing day is indicated as day 0 and the following recovery

period after each trial is indicated as positive days up to 16

days (See Figure S1 for complete recovery up to 27 days). Both

dissolved sulfide and H2S concentrations are shown in com-

parison to their average values during the baseline period.

For all trials, the dosing event immediately reduced the

dissolved sulfide and gaseous H2S concentrations by over 95%.

at 828 m downstream of UC9 pump station before and after

rge wet well before and after dosing (B).

Fig. 4 e Summary of total dissolved sulfide at 828 m (A&B) and H2S in the headspace of the discharge wet well (C&D) for the

five 24-h (dashed lines, A&C) trials, and the subsequent four 8-h (solid lines, B&D) trials. Baseline levels were shown as daily

average with error bars for standard deviations.

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 94336

This could be due to the autotrophic or chemical oxidation of

sulfide by nitrite. Indeed, a slight decrease of nitrite concen-

tration (by 10e30 mgN/L) was measured in the pipe from the

wet well to the downstream sampling point, to which het-

erotrophic denitrification may also contributed.

The daily average sulfide concentration decreased to below

0.5 mg-S/L, while the gaseous H2S concentration decreased to

below 1 ppmv. The dissolved sulfide and H2S measured at

828 m and the discharge well, respectively, were mainly pro-

duced in the pipeline, because dissolved sulfide in the

pumping station wet well was negligible (<0.1 mg-S/L). The

recovery of sulfide and H2S after each dosing resembles the

pattern of microbial regrowth (Jiang et al., 2010). These results

confirmed laboratory findings that FNA and FNA þ H2O2 are

biocidal to sulfide-producing biofilms.

After 8 or 24 h of chemical dosing, sulfide production in the

sewer pipeline was allowed to recover gradually. The recovery

represents the period that SRB in biofilms regrow after being

inactivated by the biocidal chemicals, either FNA or FNA with

H2O2. It is evident from Fig. 5 that trial 1-7 have similar re-

covery time, t20, the time taken to attain 20% of the pre-dosing

concentration, is around 7e10 days for all these trials. The

subsequent trials, i.e. trial No. 8 and 9, showedmuch longer t20around 20 days. The increasing recovery time from early trials

to late trials could have been caused by the weakened state of

the biofilm after the successive trials. Biofilm detachment was

observed previously in the lab-scale sewer reactors dosedwith

FNA þ H2O2 (Jiang and Yuan, 2013).

The difference between dosing with FNA alone and

FNA þ H2O2 is most clearly illustrated by differences in re-

covery between Trials 1 and 4. For dissolved sulfide, the first

trial (FNA þ H2O2) shows 20% recovery after 7 days, while for

FNA 20% recovery occurs before the 5th day, although the

recovery decreased due to a heavy rainfall event since day 7.

A similar difference is observed in gaseous H2S levels

measured by the Odalog sensor. In general, FNA þ H2O2

showed improved performance over FNA alone, suggesting

that the time between dosing could be increased if FNA and

hydrogen peroxide are used together.

Trials 6, 7, and 8 with 8-hr dosing showed even slower re-

covery than Trials 4 and 5with 24-hr FNA dosing. For example,

Trial 4 reached 30% recovery on day 10 while Trial 6 still

maintained a recovery level around 20% on day 10. For

FNA þ H2O2, similar observations can be made that recovery

gets slower when more trials have been carried out. This

suggests that an initial strong dose (FNA þ HP) with long

exposure (24 h) followed by maintenance dosing (FNA only)

with short exposure (8 h) could be a very cost effective way to

achieve consistent control efficiency.

3.3. Effects of environmental factors

Some of the previous field trials found that the dynamic flow

in a sewer affects the efficiency of chemical dosing because

segments of wastewater with chemicals have different

retention times in the pipelines (Sercombe, 1995). Also, uti-

lizing the low flow period in the pump station could save

chemical consumption when adding sodium hydroxide to

elevate the sewage pH for a certain time period (Tomar and

Abdullah, 1994). In general, sewer conditions, like flow dy-

namics and hydraulic retention time (HRT), affect the imple-

mentation and effectiveness of a field trial. However, most of

these field trials did not investigate effects of rainfall, which

directly changes the sewer flow dynamics.

Wastewater flow at the UC9 pumping station is largely

affected by rainfall despite it being a sanitary sewer. Fig. 5A

shows the time taken for each trial to reach 20% of the base-

line level after the dosing event, also the cumulative rainfall

Fig. 5 e (A) The 20% recovery time and cumulative rainfall

during the recovery periods of trials. (B) Average daily

temperature in the UC9 discharge manhole. (C) The

correlation between 20% recovery time and average daily

temperature.

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 9 4337

during the corresponding recovery period. It is evident that

high rainfall during the recovery time slowed down the re-

covery of sulfide production. Especially, during the recovery

periods following Trials 2 and 6, heavy rainfall of 134 and

67 mm, respectively, was experienced. The 20% recovery for

these two trials clearly took longer than other trials under

similar conditions but without rainfall events.

Sulfide being generated in a sewer pipe is a product of

sulfide producing rate and sewage retention time. Rainwater

dilutes substrates in sewage, which would induce lower sul-

fide producing rate. Rainwater also causes higher flow and

thus shorter HRT because of more frequent pumping events.

Thus, heavy rain falls would result in lower sulfide concen-

trations in sewers. Another potential effect of rainfall is the

possible sloughing of sewer biofilms due to increased flow rate

and shear in the pipeline. This could also contribute to the

extended recovery period after rainfall events.

The nine trials were performed during March to

September, which covered three seasons including late

autumn, winter and early spring. As shown in Fig. 5B, the

average daily temperature during the recovery period

following each trial varied between 19 and 25 �C. The variation

of temperature may have effects on the dosing effectiveness,

by affecting the sulphate reducing rate and the growth rate of

SRB in sewer biofilms. Sulphate reducing rate is affected

strongly by the temperature, with an increase of 2e3.9 folds

for a temperature increase of 10 �C (Nielsen, 1987). Fig. 5C

shows the correlation between the time required for 20% re-

covery (t20) and the average daily temperature. There is a very

weak trend (R2 ¼ 0.0161) that t20 increase with the gradual

decrease of average temperature. This suggests that temper-

ature only had a marginal effect on the recovery of sulphate

reduction.

It is also clear from Fig. 5 that the recovery time increased

from Trial 1 to Trial 9, especially in the last two trials. This

observation does not support the hypothesis that sewer bio-

film would adapt to FNA after repetitive dosing, which would

have caused a gradual decrease of the recovery timewith later

trials. It is more likely that the sewer biofilmsmight have been

weakened (biofilm sloughing and detachment) due to repeti-

tive impacts by successive dosing events, leading to longer

recovery time after repetitive dosing.

3.4. Potential impact on downstream wastewatertreatment plants

One of the potential impacts of FNA dosing is the increase of

the total nitrogen-load in the receiving wastewater treatment

plant (WWTP). To assess this potential effect, a dilution

calculation was employed to estimate the possible impacts of

FNA dosing on the nitrite concentration in the WWTP inflow.

The average daily flow of UC9 was 206 m3/d (0.206 ML/d) and

the average dry-weather flow (ADWF) of its receiving WWTP

(Coombabah) is 70 ML/d. Even assuming there is no nitrite

removal during the whole residence time in the sewer

network, the increase of N-load to the plant in the form of

nitrite would be less than 0.3 mgN/L, which is negligible

considering the fact that the nitrogen concentration in

wastewater is typically around 50 mgN/L (Jiang et al., 2009).

Also, this level of nitrite is not expected to have any inhibitory

effects on the microorganisms in the plant (Zhou et al., 2011).

In practice, the nitrite added would most likely be completely

removed in sewers before reaching the WWTP. The above

calculation was based on the assumption that only one sec-

tion in the entire network was receiving FNA dosing. When

multiple sections require dosing, a similar calculation can be

performed to determine the maximum number of sections

that can receive dosing at the same time. As revealed in this

study, FNA dosing is intermittent, so it should be possible to

establish dosing schemes that would not lead to unacceptable

nitrite levels in wastewater arriving at the treatment plant.

The reduction of nitrite added either in the sewer network

or in the downstream WWTP will consume organic carbon.

However, the consumption of chemical oxygen demand (COD)

in the FNA dosed wastewater is assessed to be much lower

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 94338

(negligible) when compared to other commonly used chem-

icals like oxygen and nitrate for sulfide control in sewers. This

is mainly due to the low chemical consuming nature of

intermittent dosing and the complete suppression ofmethane

production (Jiang et al., 2011b; Jiang and Yuan, 2013), which

usually consumes a big portion of COD. In contrast, dosing of

nitrate or oxygen was shown not to be able to completely

suppress methane production (Jiang et al., 2013).

3.5. Economic evaluation

Economic analysis as shown in Table S1 (supplementary

information) indicated that chemical costs, based on field

trial dosages of FNA alone at 0.26mgN/L or with 60 mg/L H2O2,

with a dosing duration of 8 h, and a recovery period of 10 days,

is only 0.01 $/m3 sewage (0.63 $/kg-sulphur), and 0.01 $/m3

sewage (0.8 $/kg-sulphur) respectively. This is far below the

costs associated with the currently used chemicals, including

ferrous or ferric chloride, nitrate, oxygen, magnesium hy-

droxide, and intermittent dosing of sodium hydroxide, used

widely by water utilities. A recent industry survey in Australia

revealed that the costs for the use of these chemicals range

between 0.04 and 0.48$/m3 sewage (Ganigue et al., 2011).

However, it should be highlighted that a full economic

assessment must be done on a case by case basis considering

the specific conditions of the systems and also the chemical

supplier and delivery options.

4. Conclusions

In this study, we investigated the long-term effectiveness of

free nitrous acid dosing, with or without simultaneous addi-

tion of hydrogen peroxide, to control sulfide production in

sewers, through field trials in real rising main sewers. The

main conclusions are:

� Intermittent dosing of FNA or FNA þ H2O2 can achieve

effective control of sulfide production in risingmain sewers.

One single dose for 8e24 h can provide lasting effectiveness

up to 10 days for an average reduction of sulfide by 80%.

� No biofilm adaptation to FNA or FNA þ H2O2 has been

observed through the 6-month trials. Instead, successive

dosing may achieve better control efficiency due to repeti-

tive weakening of the biofilms.

� Rainfall can cause extended recovery time following

chemical dosing of FNA in the sewer system.

Acknowledgements

The authors acknowledge the financial support provided by

the Australian Research Council and many members of the

Australian water industry through LP0882016 the Sewer

Corrosion and Odour Research Project (www.score.org.au).

Guangming Jiang is especially grateful to the research fund by

the New Staff Start-up Grant from the University of Queens-

land. We also thank Gold Coast City Council for support and

cooperation with the field trials. UniQuest and US Peroxide

LLC are highly acknowledged for funding and in-kind support.

DCM Process Control is gratefully acknowledged for their

technical support provided to the use of the S:CAN sensor.

Appendix A. Supplementary data

Supplementary data related to this article can be found at

http://dx.doi.org/10.1016/j.watres.2013.05.024.

r e f e r e n c e s

Ellis, A.J., Milestone, N.B., 1967. The ionization constants ofhydrogen sulphide from 20 to 90�C. Geochimica etCosmochimica Acta 31 (4), 615e620.

Firer, D., Friedler, E., Lahav, O., 2008. Control of sulfide in sewersystems by dosage of iron salts: comparison betweentheoretical and experimental results, and practicalimplications. Science of the Total Environment 392 (1),145e156.

Ganigue, R., Gutierrez, O., Rootsey, R., Yuan, Z., 2011. Chemicaldosing for sulfide control in Australia: an industry survey.Water Research 45 (19), 6564e6574.

Greene, E.A., Brunelle, V., Jenneman, G.E., Voordouw, G., 2006.Synergistic inhibition of microbial sulfide production bycombinations of the metabolic inhibitor nitrite and biocides.Applied and Environmental Microbiology 72 (12), 7897e7901.

Gutierrez, O., Mohanakrishnan, J., Sharma, K.R., Meyer, R.L.,Keller, J., Yuan, Z., 2008. Evaluation of oxygen injection as ameans of controlling sulfide production in a sewer system.Water Research 42 (17), 4549e4561.

Gutierrez, O., Park, D., Sharma, K.R., Yuan, Z., 2009. Effects oflong-term pH elevation on the sulfate-reducing andmethanogenic activities of anaerobic sewer biofilms. WaterResearch 43 (9), 2549e2557.

Jiang, G., Gutierrez, O., Sharma, K.R., Keller, J., Yuan, Z., 2011a.Optimization of intermittent, simultaneous dosage of nitriteand hydrochloric acid to control sulfide and methaneproduction in sewers. Water Research 45 (18), 6163e6172.

Jiang, G., Gutierrez, O., Sharma, K.R., Yuan, Z., 2010. Effects ofnitrite concentration and exposure time on sulfide andmethane production in sewer systems. Water Research 44(14), 4241e4251.

Jiang, G., Gutierrez, O., Yuan, Z., 2011b. The strong biocidal effectof free nitrous acid on anaerobic sewer biofilms. WaterResearch 45 (12), 3735e3743.

Jiang, G., Sharma, K.R., Guisasola, A., Keller, J., Yuan, Z., 2009.Sulfur transformation in rising main sewers receiving nitratedosage. Water Research 43 (17), 4430e4440.

Jiang, G., Sharma, K.R., Yuan, Z., 2013. Effects of nitrate dosing onmethanogenic activity in a sulfide-producing sewer biofilmreactor. Water Research 0.

Jiang, G., Yuan, Z., 2013. Synergistic inactivation of anaerobicwastewater biofilm by free nitrous acid and hydrogenperoxide. Journal of Hazardous Materials 0.

Keller-Lehmann, B., Corrie, S., Ravn, R., Yuan, Z., Keller, J., 2006.Preservation and simultaneous analysis of relevant solublesulfur species in sewage samples. In: Proceedings of theSecond International IWA Conference on Sewer Operationand Maintenance, Vienna, Austria.

Kjellerup, B.V., Veeh, R.H., Sumithraratne, P., Thomsen, T.R.,Buckingham-Meyer, K., Frolund, B., Sturman, P., 2005.Monitoring of microbial souring in chemically treated,produced-water biofilm systems using molecular techniques.Journal of Industrial Microbiology & Biotechnology 32 (4),163e170.

wat e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 3 3 1e4 3 3 9 4339

Mohanakrishnan, J., Gutierrez, O., Meyer, R.L., Yuan, Z., 2008.Nitrite effectively inhibits sulfide andmethane production in alaboratory scale sewer reactor. Water Research 42 (14),3961e3971.

Mohanakrishnan, J., Gutierrez, O., Sharma, K.R., Guisasola, A.,Werner, U., Meyer, R.L., Keller, J., Yuan, Z., 2009. Impact ofnitrate addition on biofilm properties and activities in risingmain sewers. Water Research 43 (17), 4225e4237.

Nemati, M., Mazutinec, T.J., Jenneman, G.E., Voordouw, G., 2001.Control of biogenic H2S production with nitrite andmolybdate. Journal of Industrial Microbiology & Biotechnology26 (6), 350e355.

Nielsen, P.H., 1987. Biofilm dynamics and kinetics during high-rate sulfate reduction under anaerobic conditions. Appliedand Environmental Microbiology 53 (1), 27e32.

O’Gorman, J., Purssell, I., Iori, G., 2011. Caustic soda washing of asewer pressure main e cost-effective removal of biofilm thatreduced both odour and methane. Water 38 (1), 83e87.

Pomeroy, R., Bowlus, F.D., 1946. Progress report on sulfide controlresearch. Sewage Works Journal 18 (4), 597e640.

Predicala, B., Nemati, M., Stade, S., Lague, C., 2008. Control ofH2S emission from swine manure using Na-nitrite and Na-molybdate. Journal of Hazardous Materials 154 (1e3),300e309.

Rees, M.J., Sickerdick, L.M., van Merkestein, R., Dowd, A., 2003. Anevaluation of liquid magnesium hydroxide for the control ofhydrogen sulfide gas odour. In: Proceedings of OzWater 2003.In: AWA 20th Convention, Perth, Western Australia.

Sercombe, D.C.W., 1995. The control of septicity and odors insewerage systems and at sewage-treatment works operatedby Anglian-water-services-limited. Water Science andTechnology 31 (7), 283e292.

Sutherland-Stacey, L., Corrie, S., Neethling, A., Johnson, I.,Gutierrez, O., Dexter, R., Yuan, Z., Keller, J., Hamilton, G.,2008. Continuous measurement of dissolved sulfide insewer systems. Water Science and Technology 57 (3),375e381.

Tanaka, S., Lee, Y.H., 1997. Control of sulfate reduction bymolybdate in anaerobic digestion. Water Science andTechnology 36, 143e150.

Tomar, M., Abdullah, T.H.A., 1994. Evaluation of chemicals tocontrol the generation of malodorous hydrogen sulfide inwaste water. Water Research 28 (12), 2545e2552.

US EPA, 1974. Process Design Manual for Sulfide Control inSanitary Sewer Systems.

USEPA,1992.Detection,Control, andCorrectionofHydrogenSulfideCorrosion in Existing Wastewater System. Office of WastewaterEnforcement and Compliance, Washington, DC, p. 20460.

Weon, S.-Y., Lee, C.-W., Lee, S.-I., Koopman, B., 2002. Nitriteinhibition of aerobic growth of Acinetobacter sp. WaterResearch 36 (18), 4471e4476.

WERF, 2007. In: Apgar, D., Witherspoon, J., Easter, C., Bassrai, S.,Dillon, C., Torres, E., Bowker, R.P.G., Corsi, R., Davidson, S.,Wolstenholme, P., Forbes, B., Quigley, C., Ward, M., Joyce, J.,Morton, R., Weiss, J., Stuetz, R. (Eds.), Water EnvironmentResearch Fundation: Minimization of Odor and Corrosion inCollection Systems Phase 1. (London, UK).

WHO, 2003. World Health Organization: Hydrogen Sulfide:Human Health Aspects. In: Concise International ChemicalAssessment Document, 53. (Geneva).

Zhang, L., De Schryver, P., De Gusseme, B., De Muynck, W.,Boon, N., Verstraete, W., 2008. Chemical and biologicaltechnologies for hydrogen sulfide emission control in sewersystems: a review. Water Research 42 (1e2), 1e12.

Zhang, L., Keller, J., Yuan, Z., 2009a. Inhibition of sulfate-reducingand methanogenic activities of anaerobic sewer biofilms byferric iron dosing. Water Research 43 (17), 4123e4132.

Zhang, L., Mendoza, L., Marzorati, M., Verstraete, W., 2009b.Decreasing sulfide generation in sewage by dosingformaldehyde and its derivatives under anaerobic conditions.Water Science and Technology 59 (6), 1248e1254.

Zhou, Y., Oehmen, A., Lim, M., Vadivelu, V., Ng, W.J., 2011. Therole of nitrite and free nitrous acid (FNA) in wastewatertreatment plants. Water Research 45 (15), 4672e4682.