w a t e r r e s e a r c h 4 8 ( 2 0 1 4 ) 5 6 9 e5 7 8
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/watres
Assessment of pH shock as a method for controlling sulfide and methane formation in pressure main sewer systems Oriol Gutierrez a,b,1, Gatut Sudarjanto a,1, Guo Ren a, Ramon Ganigue´ a, Guangming Jiang a, Zhiguo Yuan a,* a b
Advanced Water Management Centre, The University of Queensland St. Lucia, Brisbane, Australia Catalan Institute for Water Research, ICRA, Scientific and Technological Park of The University of Girona, Spain
article info
abstract
Article history:
Caustic dosing to raise pH above 10.0 for short periods (hours) is often used by water
Received 5 July 2013
utilities for controlling sulfide formation in sewers. However the effectiveness of this
Received in revised form
strategy is rarely reported and the impact of pH level and exposure time on the effec-
4 October 2013
tiveness is largely unknown. The effectiveness of this strategy under various pH levels (10.5
Accepted 5 October 2013
e12.5) and exposure time (0.5e6.0 h) in controlling sulfide and methane production was
Available online 23 October 2013
evaluated in laboratory scale anaerobic sewer reactors and then in a real sewer system. Laboratory studies showed that the sulfide production rate of the laboratory sewer biofilm
Keywords:
was reduced by 70e90% upon the completion of the pH shock, while the methane pro-
Caustic
duction rate decreased by 95e100%. It took approximately one week for the sulfate-
pH shock
reducing activity to recover to normal levels. In comparison, the methanogenic activities
Methane
recovered to only about 10% in 4 weeks. The slow recovery is explained by the substantially
Methanogens
loss of cell viability upon pH shocks, which recovered slowly after the shocks. Laboratory
Sewer
studies further revealed that a pH level of 10.5 for 1e2 h represent cost-effective conditions
Sulfate
for the pH shock treatment. However, field trials showed a higher pH (11.5) and larger
Sulfate-reducing bacteria
dosing times are needed due to the pH decreases along the sewer line and at the two ends
Sulfide
of the caustic-receiving wastewater slugs due to dilution. To have effective sulfide and
Wastewater
methane control, it is important to ensure effective conditions (pH > 10.5 and duration >1 e2 h) for the entire sewer line. ª 2013 Elsevier Ltd. All rights reserved.
1.
Introduction
The formation of sulfide and subsequent release of hydrogen sulfide (H2S) to the gas phase is a major problem in sewer
systems, causing serious problem for wastewater authorities (Pomeroy, 1959; USEPA, 1974; Boon, 1995; Hvitved-Jacobsen, 2002). Sulfate-reducing bacteria (SRB) in the biofilms on sewer walls reduce sulfate to sulfide (Thistlethwayte, 1972;
* Corresponding author. E-mail addresses: [email protected], [email protected] (O. Gutierrez), [email protected] (G. Sudarjanto), g.ren@ awmc.uq.edu.au (G. Ren), [email protected] (R. Ganigue´), [email protected] (G. Jiang), [email protected] (Z. Yuan). 1 Joint first authors. 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.10.021
570
w a t e r r e s e a r c h 4 8 ( 2 0 1 4 ) 5 6 9 e5 7 8
USEPA, 1974; Hvitved-Jacobsen, 2002). H2S emission to sewer air causes biogenic sulfuric acid-induced corrosion of concrete sewer lines in gravity sewers, obnoxious odour and also health problems to sewer workers (Thistlethwayte, 1972; USEPA, 1974; Hvitved-Jacobsen, 2002). The anaerobic condition in sewers may also lead to the formation of methane (CH4), which is a potent greenhouse gas (GHG) and is explosive at low concentrations (Spencer et al., 2006; Guisasola et al., 2008; Foley et al., 2009). A significant fraction of the methane produced in sewer systems will be released to the atmosphere in gravity sections of sewers or at a wastewater treatment plant (Guisasola et al., 2008). Methane formation also consumes valuable COD (Chemical Oxygen Demand) required for biological nutrient removal at the downstream wastewater treatment plants. Various operational methods have been developed to control sewer corrosion and odour problems. These include: mechanical cleaning to remove sewer biofilms, design optimization of sewer hydraulics to reduce sulfide formation, ventilation followed by sewer gas treatment and chemical and/or biomaterial addition (USEPA, 1974; Scrivener et al., 1999; Monteny et al., 2000; Yamanaka et al., 2002; Nielsen et al., 2006; Zhang et al., 2008). Amongst these mitigation strategies, the addition of chemicals to the liquid phase is the most commonly used (Ganigue et al., 2011) which include the following approaches: Prevention of anaerobic conditions by adding oxidants such as air, oxygen and nitrate (Ochi et al., 1998; HvitvedJacobsen, 2002; Zhang et al., 2008; Gutierrez et al., 2008; Mohanakrishnan et al., 2009). Precipitation of sulfide formed with metal salts, such as iron, zinc, lead, copper. (Jameel, 1989; Padival et al., 1995; Firer et al., 2008; Zhang et al., 2008, 2012) Reduction of H2S transfer from liquid to air by means of pH elevation which reduces the molecular hydrogen sulfide fraction of dissolved sulfide (Yongsiri et al., 2003; Gutierrez et al., 2009) Most of the aforementioned methods need continuous chemical addition which will cause high chemical consumption and operational costs (Ganigue et al., 2011). Even though most of the mentioned approaches inhibit anaerobic biofilm
activities to some extent, they do not have a long-term persisted inhibitory effect (Padival et al., 1995; Okabe et al., 2007; Gutierrez et al., 2009; Mohanakrishnan et al., 2009). Therefore, strategies aimed to achieve longer term inhibitory/biocidal effect of sewer biofilms are of particular interest to the water industry, as intermittent rather than continuous dosing is typically adequate when such chemicals are used. Chlorine, hypochlorite, ozone, hydrogen peroxide, free nitrous acid, potassium permanganate and alkali are some of these chemicals (Millero et al., 1989; Tomar and Abdullah, 1994; Zhang et al., 2008; Jiang et al., 2010, 2011a,b). The addition of alkali to sewage, commonly named as pH shock, consists of a drastic increase of sewage pH to above 11.0e11.5 for a short period of time (hours). An industry survey in Australia (Ganigue et al., 2011) revealed that this strategy is frequently used for sulfide control in small sewer pipes (
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/watres
Assessment of pH shock as a method for controlling sulfide and methane formation in pressure main sewer systems Oriol Gutierrez a,b,1, Gatut Sudarjanto a,1, Guo Ren a, Ramon Ganigue´ a, Guangming Jiang a, Zhiguo Yuan a,* a b
Advanced Water Management Centre, The University of Queensland St. Lucia, Brisbane, Australia Catalan Institute for Water Research, ICRA, Scientific and Technological Park of The University of Girona, Spain
article info
abstract
Article history:
Caustic dosing to raise pH above 10.0 for short periods (hours) is often used by water
Received 5 July 2013
utilities for controlling sulfide formation in sewers. However the effectiveness of this
Received in revised form
strategy is rarely reported and the impact of pH level and exposure time on the effec-
4 October 2013
tiveness is largely unknown. The effectiveness of this strategy under various pH levels (10.5
Accepted 5 October 2013
e12.5) and exposure time (0.5e6.0 h) in controlling sulfide and methane production was
Available online 23 October 2013
evaluated in laboratory scale anaerobic sewer reactors and then in a real sewer system. Laboratory studies showed that the sulfide production rate of the laboratory sewer biofilm
Keywords:
was reduced by 70e90% upon the completion of the pH shock, while the methane pro-
Caustic
duction rate decreased by 95e100%. It took approximately one week for the sulfate-
pH shock
reducing activity to recover to normal levels. In comparison, the methanogenic activities
Methane
recovered to only about 10% in 4 weeks. The slow recovery is explained by the substantially
Methanogens
loss of cell viability upon pH shocks, which recovered slowly after the shocks. Laboratory
Sewer
studies further revealed that a pH level of 10.5 for 1e2 h represent cost-effective conditions
Sulfate
for the pH shock treatment. However, field trials showed a higher pH (11.5) and larger
Sulfate-reducing bacteria
dosing times are needed due to the pH decreases along the sewer line and at the two ends
Sulfide
of the caustic-receiving wastewater slugs due to dilution. To have effective sulfide and
Wastewater
methane control, it is important to ensure effective conditions (pH > 10.5 and duration >1 e2 h) for the entire sewer line. ª 2013 Elsevier Ltd. All rights reserved.
1.
Introduction
The formation of sulfide and subsequent release of hydrogen sulfide (H2S) to the gas phase is a major problem in sewer
systems, causing serious problem for wastewater authorities (Pomeroy, 1959; USEPA, 1974; Boon, 1995; Hvitved-Jacobsen, 2002). Sulfate-reducing bacteria (SRB) in the biofilms on sewer walls reduce sulfate to sulfide (Thistlethwayte, 1972;
* Corresponding author. E-mail addresses: [email protected], [email protected] (O. Gutierrez), [email protected] (G. Sudarjanto), g.ren@ awmc.uq.edu.au (G. Ren), [email protected] (R. Ganigue´), [email protected] (G. Jiang), [email protected] (Z. Yuan). 1 Joint first authors. 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.10.021
570
w a t e r r e s e a r c h 4 8 ( 2 0 1 4 ) 5 6 9 e5 7 8
USEPA, 1974; Hvitved-Jacobsen, 2002). H2S emission to sewer air causes biogenic sulfuric acid-induced corrosion of concrete sewer lines in gravity sewers, obnoxious odour and also health problems to sewer workers (Thistlethwayte, 1972; USEPA, 1974; Hvitved-Jacobsen, 2002). The anaerobic condition in sewers may also lead to the formation of methane (CH4), which is a potent greenhouse gas (GHG) and is explosive at low concentrations (Spencer et al., 2006; Guisasola et al., 2008; Foley et al., 2009). A significant fraction of the methane produced in sewer systems will be released to the atmosphere in gravity sections of sewers or at a wastewater treatment plant (Guisasola et al., 2008). Methane formation also consumes valuable COD (Chemical Oxygen Demand) required for biological nutrient removal at the downstream wastewater treatment plants. Various operational methods have been developed to control sewer corrosion and odour problems. These include: mechanical cleaning to remove sewer biofilms, design optimization of sewer hydraulics to reduce sulfide formation, ventilation followed by sewer gas treatment and chemical and/or biomaterial addition (USEPA, 1974; Scrivener et al., 1999; Monteny et al., 2000; Yamanaka et al., 2002; Nielsen et al., 2006; Zhang et al., 2008). Amongst these mitigation strategies, the addition of chemicals to the liquid phase is the most commonly used (Ganigue et al., 2011) which include the following approaches: Prevention of anaerobic conditions by adding oxidants such as air, oxygen and nitrate (Ochi et al., 1998; HvitvedJacobsen, 2002; Zhang et al., 2008; Gutierrez et al., 2008; Mohanakrishnan et al., 2009). Precipitation of sulfide formed with metal salts, such as iron, zinc, lead, copper. (Jameel, 1989; Padival et al., 1995; Firer et al., 2008; Zhang et al., 2008, 2012) Reduction of H2S transfer from liquid to air by means of pH elevation which reduces the molecular hydrogen sulfide fraction of dissolved sulfide (Yongsiri et al., 2003; Gutierrez et al., 2009) Most of the aforementioned methods need continuous chemical addition which will cause high chemical consumption and operational costs (Ganigue et al., 2011). Even though most of the mentioned approaches inhibit anaerobic biofilm
activities to some extent, they do not have a long-term persisted inhibitory effect (Padival et al., 1995; Okabe et al., 2007; Gutierrez et al., 2009; Mohanakrishnan et al., 2009). Therefore, strategies aimed to achieve longer term inhibitory/biocidal effect of sewer biofilms are of particular interest to the water industry, as intermittent rather than continuous dosing is typically adequate when such chemicals are used. Chlorine, hypochlorite, ozone, hydrogen peroxide, free nitrous acid, potassium permanganate and alkali are some of these chemicals (Millero et al., 1989; Tomar and Abdullah, 1994; Zhang et al., 2008; Jiang et al., 2010, 2011a,b). The addition of alkali to sewage, commonly named as pH shock, consists of a drastic increase of sewage pH to above 11.0e11.5 for a short period of time (hours). An industry survey in Australia (Ganigue et al., 2011) revealed that this strategy is frequently used for sulfide control in small sewer pipes (
