Structure and dynamics of nitrifier populations in a full-scale submerged membrane bioreactor during start-up

Abstract

Changes of microbial characteristics in a full-scale submerged membrane bioreactor system (capacity, 60,000 m(3) day(-1)) treating sewage were monitored over the start-up period (96 days). Fluorescence in situ hybridization analysis showed that the percentages of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (nitrobacter-related population) in total bacteria counted with DAPI staining increased significantly from 1.9% and 0.9% to 4.5% and 2.8%, corresponding to an increase of the specific ammonium oxidizing rate (from 0.06 to 0.12 kg N kg(-1) mixed liquor suspended solids (MLSS) per day) and the specific nitrate forming rate (from 0.05 to 0.10 kg N kg(-1) MLSS day(-1)). Both the denaturing gradient gel electrophoresis of polymerase chain reaction and clone library results showed that the AOB was dominated by the genus Nitrosomonas, the diversity of which increased markedly with operational time. Most of the day 2 clones were closely related with the uncultured Nitrosomonas sp. clone Ninesprings-49S amoA gene (AY356450.1) originated from activated sludge, while the day 96 clone library showed a more diverse distribution characterized by the appearance of the oligotrophic nitrifiers like the Nitrosomonas oligotropha- and Nitrosomonas ureae-like bacteria, perhaps due to the interception by membrane and the low food-to-microorganisms ratio environment. The above results show that the membrane bioreactor system was characterized by the increased diversity and percentage of nitrifiers, which made it possible to achieve a stable and high efficient nitrification. Ammonia-oxidizing archaea with the changing population structures were also detected, but their roles for ammonia oxidation in the system need further studies.

Ecophysiology of nitrifying communities in membrane bioreactors

“…Witzig et al (2002) observed that due to the low food-to-microorganisms conditions in MBRs with resultant low rRNA molecules for the organisms, less than half of the population were detectable by FISH whereas 80 % in CAS. However, few researchers have reported a direct correlation between nitrifier population and specific ammonium and nitrite oxidation rate using FISH probes (Yu et al 2011). Yu et al (2011) in a study using FISH observed a direct correlation between the nitrifier population and the specific ammonium and nitrite utilization rate.…”

“…Specific ammonia oxidization rate and nitrite oxidization rates were also reported to vary with no particular pattern in MBRs Yu et al 2010;Ozdemir et al 2011). Nevertheless, the major advantage of MBR over CAS is the ability to retain a more diverse nitrifying community including slow-growing species, which makes it relatively more resilient in the face of operational and environmental fluctuations (Zhang et al 2009a;Yu et al 2011).…”

“…Thus, the species specificity was a limiting factor for this technique when applying to complex environmental samples. Fluorescent in situ hybridization, a widely used molecular method, involves the binding of fluorescent oligonucleotide probes (probes available for nitrifiers are listed in Tables 3, 4, 5) to ribosomal ribonucleic acid (Nielsen 2009;Junier et al 2010;Xia et al 2010b;Yu et al 2011). This method can be employed for both identification and quantification of specific bacterial groups directly from the environment even up to the species level (Li et al 2006) (Tables 3, 4, 5).…”

“…Under these conditions, nitrifiers, which are naturally slow growers, are intercepted by the membrane and prevented from being washed out of the reactor. This allows them to have sufficient concentration of slow-growing microorganisms such as the nitrifiers and helps them to achieve a strong tolerance of shock loads with stable and highly efficient nitrification (Yu et al 2011). Membrane retention greatly influences the bioprocesses and the microbial community structure development within the MBR (Wan et al 2011).…”

“…The submerged MBR systems use membrane interception to separate activated sludge from treated water, thereby controlling and increasing the solid retention time independently from the hydraulic retention time within the bioreactor (Lesjean et al 2011;Lin et al 2011;Sarp et al 2011;Yu et al 2011;Zaw et al 2011). Under these conditions, nitrifiers, which are naturally slow growers, are intercepted by the membrane and prevented from being washed out of the reactor.…”