The coexistence of sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) in anaerobic biofilms developed in sewer inner pipe surfaces favors the accumulation of sulfide (H2S) and methane (CH4) as metabolic end products, causing severe impacts on sewerage systems. In this study, we investigated the time course of H2S and CH4 production and emission rates during different stages of biofilm development in relation to changes in the composition of microbial biofilm communities. The study was carried out in a laboratory sewer pilot plant that mimics a full-scale anaerobic rising sewer using a combination of process data and molecular techniques (e.g., quantitative PCR [qPCR], denaturing gradient gel electrophoresis [DGGE], and 16S rRNA gene pyrotag sequencing). After 2 weeks of biofilm growth, H2S emission was notably high (290.7 ± 72.3 mg S-H2S liter-1 day-1), whereas emissions of CH4 remained low (17.9 ± 15.9 mg COD-CH4 liter-1 day-1). This contrasting trend coincided with a stable SRB community and an archaeal community composed solely of methanogens derived from the human gut (i.e., Methanobrevibacter and Methanosphaera). In turn, CH4 emissions increased after 1 year of biofilm growth (327.6 ± 16.6 mg COD-CH4 liter-1 day-1), coinciding with the replacement of methanogenic colonizers by species more adapted to sewer conditions (i.e., Methanosaeta spp.). Our study provides data that confirm the capacity of our laboratory experimental system to mimic the functioning of full-scale sewers both microbiologically and operationally in terms of sulfide and methane production, gaining insight into the complex dynamics of key microbial groups during biofilm development

Authors thank the four anonymous reviewers for the useful comments and suggestions made during the review process. This study was partially funded by the Spanish Government Ministerio de Economía y Competitividad through projects GEISTTAR (CTM2011-27163) and ARCOS (CGL2012-33033) and by the European Commission through projects FP7-PEOPLE-2011-CIG303946, 2010-RG277050 and the ITN-Project SANITAS (the REA agreement 289193). Maite Pijuan is a recipient of a Ramon y Cajal research fellowship (RYC-2009-04959) and Olga Auguet benefits from a FI research fellowship (2014FI_B1 00032) from the Catalan Government. ICRA is a recipient of a Consolidated Research Group grant (2014 SGR 291) from the Catalan Gove