title: Assessment of pH shock as a method for controlling sulfide and methane formation in pressure main sewer systems.
abstract: Caustic dosing to raise pH above 10.0 for short periods (hours) is often used by water utilities for controlling sulfide formation in sewers. However the effectiveness of this strategy is rarely reported and the impact of pH level and exposure time on the effectiveness is largely unknown. The effectiveness of this strategy under various pH levels (10.5-12.5) and exposure time (0.5-6.0 h) in controlling sulfide and methane production was 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 was reduced by 70-90% upon the completion of the pH shock, while the methane production rate decreased by 95-100%. It took approximately one week for the sulfate-reducing activity to recover to normal levels. In comparison, the methanogenic activities recovered to only about 10% in 4 weeks. The slow recovery is explained by the substantially loss of cell viability upon pH shocks, which recovered slowly after the shocks. Laboratory studies further revealed that a pH level of 10.5 for 1-2 h represent cost-effective conditions for the pH shock treatment. However, field trials showed a higher pH (11.5) and larger dosing times are needed due to the pH decreases along the sewer line and at the two ends of the caustic-receiving wastewater slugs due to dilution. To have effective sulfide and methane control, it is important to ensure effective conditions (pH > 10.5 and duration >1-2 h) for the entire sewer line.
authors.affiliation: 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. Electronic address: oriol@awmc.uq.edu.au.
authors.forename: Oriol
authors.initials: O
authors.lastname: Gutierrez
authors.forename: Gatut
authors.initials: G
authors.lastname: Sudarjanto
authors.forename: Guo
authors.initials: G
authors.lastname: Ren
authors.forename: Ramon
authors.initials: R
authors.lastname: Ganigué
authors.forename: Guangming
authors.initials: G
authors.lastname: Jiang
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Yuan
mesh_terms: D000693:Anaerobiosis; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000096:biosynthesis*; D011312:Pressure; D012722:Sewage; D013440:Sulfides / Q000378:metabolism*
chemical_list: D012722:Sewage; D013440:Sulfides; D008697:Methane
keywords: Caustic; Methane; Methanogens; Sewer; Sulfate; Sulfate-reducing bacteria; Sulfide; Wastewater; pH shock