Investigation of nitrogen converters in membrane bioreactor

Abstract

In this study, the activity and diversity of nitrogen converters, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), ammonia-oxidizing archaea (AOA) and Anammox bacteria in a pilot-scale membrane bioreactor (MBR) were investigated and monitored using amoA and 16S rDNA-based molecular tools. The pilot-scale MBR (100 m(3)/day) was located inside the full-scale Pasakoy Advanced Wastewater Treatment Plant (WWTP), and operated for approximately 5 months without sludge purge. During 148 days of operation, volatile suspended solids (VSS) concentration increased from 2,454 mg/L to 10,855 mg/L and the average organic carbon and ammonia nitrogen removal rates were 92% and 99%, respectively. Real-time PCR results indicated that the fraction of AOB increased from 2.94% to 4.05% when VSS concentration reached to 3,750 mg/L throughout 148 days of operation. At higher VSS concentrations, the fraction of AOB declined gradually to 1.15% while the fraction of Nitrospira population was varied between 8.23 and 13.01%. However, significant change or any positive and negative correlations between VSS concentration and Nitrospira population were not observed in this period. The phylogenetic analysis revealed that MBR harbored diverse AOB community which was related to the Nitrosomonas and Nitrosospira lineage. Candidatus Nitrospira defluvii was the only detected NOB in this study.

Ecophysiology of nitrifying communities in membrane bioreactors

“…as the most abundant with a population about 10 times higher than AOB as the system proceeded towards the high MLSS. Ozdemir et al (2011) also observed that the MBR was diverse in AOB richness, with different members of the Nitrosomonas and Nitrosospira lineage, whereas Candidatus Nitrospira defluvii was the only NOB detected throughout the study. Similarly, a study conducted by Zhang et al (2009a), on AOB community on MBR, treating municipal wastewater, reported a shift in AOB dominance from initial Nitrosomonas spp.…”

“…In two different MBRs investigated (one was adapted with biofilm support medium), Liang et al (2010) noted that high nitrification rates correlated with the high species richness of nitrifying bacteria. Various authors have reported 96-99 and 92-98 % ammonia-nitrogen and COD removals, respectively, in MBRs investigated Yu et al 2010;Ozdemir et al 2011). Although a higher nitrogen removal is being reported in MBR by various authors in comparison with conventional activated sludge systems, MBRs seem not to have an edge in terms of specific nitrification rates.…”

“…The growth rate of autotrophic bacteria (nitrifiers) is five times slower than that of heterotrophic bacteria in WWTPs (Ozdemir et al 2011). Thus, the nitrifiers form only 3-10 % of the total bacteria in activated sludge (Gerardi 2002), which makes the isolation of nitrifiers difficult.…”

“…Although a higher nitrogen removal is being reported in MBR by various authors in comparison with conventional activated sludge systems, MBRs seem not to have an edge in terms of specific nitrification rates. 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).…”

“…However, a higher AOB and NOB fraction (7.19 %) of the total bacteria was reported in MBRs compared to the CAS (Zhang et al 2011b). A study conducted by Ozdemir et al (2011), on nitrification in MBRs (operating at an MLSS of 4.62 g/L), observed NOB (Nitrospira sp.) as the most abundant with a population about 10 times higher than AOB as the system proceeded towards the high MLSS.…”