Changes of microbial characteristics of retained sludge during low-temperature operation of an EGSB reactor for low-strength wastewater treatment

Abstract

In this study, a lab scale EGSB reactor was operated for 400 days to investigate the influence of temperature-decrease on the microbial characteristic of retained sludge. The EGSB reactor was started-up at 15 degrees C seeding with 20 degrees C-grown granular sludge. The influent COD of synthetic wastewater was set at 0.6-0.8 gCOD/L. The process-temperature was stepwise reduced from 15 degrees C to 5 degrees C during 400 days operation. Decrease of temperature of the reactor from 15 degrees C to 10 degrees C caused the decline of COD removal efficiency. However, continuous operation of the EGSB reactor led the efficient treatment of wastewater (70% of COD removal, 50% of methane recovery) at 10 degrees C. We confirmed that the both acetate-fed and hydrogen-fed methanogenic activities of retained sludge clearly increased under 15 to 20 degrees C. Changes of microbial profiles of methanogenic bacteria were analyzed by 16S rDNA-targeted DGGE analysis and cloning. It shows that genus Methanospirillum as hydrogen-utilizing methanogen proliferated due to low temperature operation of the reactor. On the other hand, genus Methanosaeta presented in abundance as acetoclastic-methanogen throughout the experiment.

Microbial community structure and dynamics in anaerobic fluidized‐bed and granular sludge‐bed reactors: influence of operational temperature and reactor configuration

“…In case of the EGSB reactor some part of the MMB population shifted towards Methanospirillum ‐like organisms deduced from A8 (T3a, 15°C) from day 298 onwards. Many studies have indeed documented that methanogenesis predominantly proceeded through the hydrogenotrophic route in low‐temperature anaerobic reactors (Syutsubo et al ., ; O'Reilly et al ., ; McKeown et al ., ). In these situations, conditions with low hydrogen availability and high biomass concentration seemed to favour hydrogenotrophic methanogens due to their higher affinity for H 2 and thus they out‐competed homoacetogens for hydrogen (Kotsyurbenko, ).…”

“…Low-temperature AD (LTAD) has emerged as an economically attractive waste treatment strategy, which confers considerable advantages over conventional mesophilic (~30°C) and thermophilic (~55°C) treatments, primarily due to the capacity to treat the wide variety of cool, dilute wastewaters, previously considered as not suitable for AD (McKeown et al, 2012). LTAD has been successfully applied at laboratory-and pilot-scale, using a variety of reactor types, for the treatment of a broad range of wastewaters (for example, Lettinga et al, 2001;Collins et al, 2003;McHugh et al, 2004;Syutsubo et al, 2008;Bergamo et al, 2009;McKeown et al, 2012). LTAD is an attractive technology because the process is stable, simple to operate and requires very low energy input.…”

Psychrophilic methanogenic community development during long-term cultivation of anaerobic granular biofilms

“…Such a shift is likely as a result of enhanced homoacetogenic activity (Schulz and Conrad, 1996). Conversely, methanogenesis has been shown to predominantly proceed through the hydrogenotrophic route in low-temperature natural (Horn et al, 2003;Kotsyurbenko et al, 2007) and engineered anaerobic bioreactors Connaughton et al, 2006;Syutsubo et al, 2008). Under low-temperature conditions, improved thermodynamics of methane formation from H 2 / CO 2 , coupled with the enhanced solubility and therefore accessibility of H 2 /CO 2 in the reactor liquor, are thought to account for this phenomenon (Lettinga et al, 2001).…”

“…Low-temperature AD (LTAD) has emerged as an economically attractive waste treatment strategy, which confers considerable advantages over conventional mesophilic (420 1C) and thermophilic (445 1C) treatments, primarily due to increased net energy yields (Lettinga et al, 2001). This technology has been successfully applied at laboratory-scale for the treatment of a broad range of wastewaters (for example, Rebac et al, 1999;Enright et al, 2005;Collins et al, 2006;Syutsubo et al, 2008;Bergamo et al, 2009). Improved bioreactor designs now enable high rates of conversion under low-temperature conditions through a combination of (i) high mixing intensities (that is, facilitates high rates of mass transference) and (ii) enhanced retention of psychroactive biomass.…”

Bioreactor Scalability: Laboratory-Scale Bioreactor Design Influences Performance, Ecology, and Community Physiology in Expanded Granular Sludge Bed Bioreactors

“…The EGSB is an anaerobic digester type utilizing retained granular biomass for high-rate treatment of high-strength, low-solids industrial wastes. EGSB bioreactors have previously been used in many laboratory-scale trials investigating adaptation of the EGSB to the treatment of a growing range of wastes (Pereira et al, 2002; Fang et al, 2011), contaminants (Collins et al, 2005; Enright et al, 2005; Scully et al, 2006; Londoño and Peñuela, 2015), and operating conditions (Syutsubo et al, 2008; O'Reilly et al, 2010) which, if applicable at full-scale, have the potential to revolutionize the way we treat wastewater. Hence, this bioreactor design represents an ideal reactor type in which to investigate the effects of scale.…”