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Methane formation in sewer systems
Malin Isgren I *, Patrick Mårtensson I , Jes la Cour Jansen I , David J. I. Gustavsson II , Oriol Gutierrez III
I
Water and Environmental Engineering, Department of Chemical Engineering, Lund University, Box 124,
SE-221 00 Lund, Sweden
(E-mail:kt08mi2@student.lth.se, kt08pm4@student.lth.se, jes.la_cour_jansen@vateknik.lth.se)
II
VA SYD, Box 191, SE-201 21 Malmö, Sweden (E-mail: david.gustavsson@vasyd.se)
III
Catalan Institute for Water Research, ICRA. Scientific and Technological park of the UdG. Emili Grahit, 101
17003 Girona, Spain (E-mail: ogutierrez@icra.cat)
* Speaker We would like to present this paper as an oral presentation in English.
INTRODUCTION
Hydrogen sulphide in sewer systems is a well-known problem. However, formation of the potent
greenhouse gas methane has not received as much attention. A few studies have been executed on
rising mains (i.e. Guisasola et al., 2009) since these are theoretically the ones with the highest
potential for methane formation. Gravity mains are the most common kinds of pipes but are still
poorly investigated. Investigations of these are necessary if methane formation in sewer systems
shall be fairly evaluated. Factors that affect methane formation are among other things the presence
of organic carbon together with anaerobic conditions. The amount of methane formed per volume
wastewater depends on the ratio between the inner surface wall area covered with biofilm and the
volume of the pipe. This theory has been proved, not only in studies on rising mains but correlate
also well with formation of hydrogen sulphide. The main aim of this work was to develop a
sampling method for determination of dissolved methane in wastewater samples and to detect any
methane content in gravity mains with the highest potential for methane production in Malmö,
Sweden.
METHOD
Field samples were collected at the inlet, downstream a pressurized system at Sjölunda Wastewater
Treatment Plant (WWTP) and in scattered selected manholes in the sewer system of Malmö,
Sweden. The sampling technique enables sampling and at the same time avoids getting air into the
sampling bottles. This was accomplished by keeping the collection vials under water, while putting
the cap on (Alberto et al., 2000). Wastewater sampling at the WWTP was executed by lowering a
sampling bottle close to the incoming pipe, the device is shown in Figure 1. The rubber stopper was
released when the bottle reached the selected level.
Figure 1. Device for wastewater collection at WWTP.
Sampling in manholes was executed by climbing down and filling sampling bottles. From the
sampling occasions all laboratory analysis were performed within 24 hours. The sampling analyses
were done by filling half of a vacuum tube with wastewater and then allow equilibrium. The
methane content was determined with a gas chromatograph and the amount of methane was