Modeling of the attached and suspended biomass fractions in a moving bed biofilm reactor

Nitrogen can be eliminated effectively from sludge digester effluents by anaerobic ammonium oxidation (anammox), but 55-60% of the ammonium must first be oxidized to nitrite. Although a continuous flow stirred tank reactor (CSTR) with suspended biomass could be used, its hydraulic dilution rate is limited to 0.8-1 d-1 (30¡C). Higher specific nitrite production rates can be achieved by sludge retention, as shown here for a moving-bed biofilm reactor (MBBR) with Kaldnes® carriers on laboratory and pilot scales. The maximum nitrite production rate amounted to 2.7 gNO2-Nm-2d-1 (3 gO2m-3d-1, 30.5°C), thus doubling the dilution rate compared to CSTR operation with suspended biomass for a supernatant with 700 gNH4-Nm-3. Whenever the available alkalinity was fully consumed, an optimal amount of nitrite was produced. However, a significant amount of nitrate was produced after 11 months of operation, making the effluent unsuitable for anaerobic ammonium oxidation. Because the sludge retention time (SRT) is relatively long in biofilm systems, slow growth of nitrite oxidizers occurs. None of the selection criteria applied - a high ammonium loading rate, high free ammonia or low oxygen concentration - led to selective suppression of nitrite oxidation. A CSTR or SBR with suspended biomass is consequently recommended for full-scale operation.

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Microbial Community Composition and Dynamics of Moving Bed Biofilm Reactor Systems Treating Municipal Sewage

Applied and Environmental Microbiology ◽

10.1128/aem.06570-11 ◽

2011 ◽

Vol 78 (3) ◽

pp. 855-864 ◽

Cited By ~ 33

Author(s):

Kristi Biswas ◽

Susan J. Turner

Keyword(s):

Wastewater Treatment ◽

Microbial Community ◽

Microbial Communities ◽

Community Composition ◽

Biofilm Reactor ◽

Rrna Gene ◽

Moving Bed Biofilm Reactor ◽

Moving Bed ◽

Content Type ◽

Suspended Biomass

ABSTRACTMoving bed biofilm reactor (MBBR) systems are increasingly used for municipal and industrial wastewater treatment, yet in contrast to activated sludge (AS) systems, little is known about their constituent microbial communities. This study investigated the community composition of two municipal MBBR wastewater treatment plants (WWTPs) in Wellington, New Zealand. Monthly samples comprising biofilm and suspended biomass were collected over a 12-month period. Bacterial and archaeal community composition was determined using a full-cycle community approach, including analysis of 16S rRNA gene libraries, fluorescencein situhybridization (FISH) and automated ribosomal intergenic spacer analysis (ARISA). Differences in microbial community structure and abundance were observed between the two WWTPs and between biofilm and suspended biomass. Biofilms from both plants were dominated byClostridiaand sulfate-reducing members of theDeltaproteobacteria(SRBs). FISH analyses indicated morphological differences in theDeltaproteobacteriadetected at the two plants and also revealed distinctive clustering between SRBs and members of theMethanosarcinales, which were the onlyArchaeadetected and were present in low abundance (<5%). Biovolume estimates of the SRBs were higher in biofilm samples from one of the WWTPs which receives both domestic and industrial waste and is influenced by seawater infiltration. The suspended communities from both plants were diverse and dominated by aerobic members of theGammaproteobacteriaandBetaproteobacteria.This study represents the first detailed analysis of microbial communities in full-scale MBBR systems and indicates that this process selects for distinctive biofilm and planktonic communities, both of which differ from those found in conventional AS systems.

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