Acetate and ammonium diffusivity in membrane-aerated biofilms: improving model predictions using experimental results

Shanahan, John W.; Cole, Alina C.; Semmens, Michael J.; LaPara, Timothy M.

doi:10.2166/wst.2005.0190

Cited by 11 publications

(7 citation statements)

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“…2a, b). This heterogeneity would substantially affect model predictions for mass transfer of nutrients within the biofilm and for the rates of bacterial metabolism within the MABs [20].…”

Section: Discussionmentioning

confidence: 99%

The effects of organic carbon, ammoniacal-nitrogen, and oxygen partial pressure on the stratification of membrane-aerated biofilms

LaPara

Cole

Shanahan

et al. 2005

J IND MICROBIOL BIOTECHNOL

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The purpose of this study was to examine the effects of different nutrient (carbon, nitrogen, oxygen) concentrations on the microbial activity and community structure in membrane-aerated biofilms (MABs). MABs were grown under well-defined conditions of fluid flow, substrate concentration, and membrane oxygen partial pressure. Biofilms were then removed and thin-sliced using a cryostat/microtome parallel to the membrane. Individual slices were analyzed for changes with depth in biomass density, respiratory activity, and the population densities of ammonia-oxidizing and denitrifying bacteria populations. Oxygen-sensing microelectrodes were used to determine the depth of oxygen penetration into each biofilm. Our results demonstrated that ammonia-oxidizing bacteria grow near the membrane, while denitrifying bacteria grow a substantial distance from the membrane. However, nitrifying and denitrifying bacteria did not grow simultaneously when organic concentrations became too high or ammonia concentrations became too low. In conclusion, membrane-aerated biofilms exhibit substantial stratification with respect to community structure and activity. A fundamental understanding of the factors that control this stratification will help optimize the performance of full-scale membrane-aerated biofilm reactors for wastewater treatment.

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“…2a, b). This heterogeneity would substantially affect model predictions for mass transfer of nutrients within the biofilm and for the rates of bacterial metabolism within the MABs [20].…”

Section: Discussionmentioning

confidence: 99%

The effects of organic carbon, ammoniacal-nitrogen, and oxygen partial pressure on the stratification of membrane-aerated biofilms

LaPara

Cole

Shanahan

et al. 2005

J IND MICROBIOL BIOTECHNOL

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“…The biofilm density was assumed to be constant through the biofilm. Biofilm density has been shown to vary with depth in an MAB containing both nitrifiers and heterotrophs (Shanahan et al, 2005); however, density in a mainly nitrifying MAB was shown to be relatively consistent through the use of FISH (Downing and Nerenberg, 2008), and therefore the density was assumed to be constant.…”

Section: Modelingmentioning

confidence: 99%

Effect of oxygen gradients on the activity and microbial community structure of a nitrifying, membrane‐aerated biofilm

Downing

Nerenberg

2008

Biotech & Bioengineering

117

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Shortcut nitrogen removal, that is, removal via formation and reduction of nitrite rather than nitrate, has been observed in membrane-aerated biofilms (MABs), but the extent, the controlling factors, and the kinetics of nitrite formation in MABs are poorly understood. We used a special MAB reactor to systematically study the effects of the dissolved oxygen (DO) concentration at the membrane surface, which is the biofilm base, on nitrification rates, extent of shortcut nitrification, and microbial community structure. The focus was on anoxic bulk liquids, which is typical in MAB used for total nitrogen (TN) removal, although aerobic bulk liquids were also studied. Nitrifying MABs were grown on a hollow-fiber membrane exposed to 3 mg N/L ammonium. The MAB intra-membrane air pressure was varied to achieve different DO concentrations at the biofilm base, and the bulk liquid was anoxic or with 2 g m(-3) DO. With 2.2 and 3.5 g m(-3) DO at the biofilm base, and with an anoxic bulk-liquid, the ammonium fluxes were 0.75 and 1.0 g N m(-2) day(-1), respectively, and nitrite was the main oxidized nitrogen product. However, with membrane DO of 5.5 g m(-3), and either zero or 2 g m(-3) DO in the bulk, the ammonium flux was around 1.3 g N m(-2) day(-1), and nitrate flux increased significantly. For all experiments, the cell density of ammonium oxidizing bacteria (AOB) was relatively uniform throughout the biofilm, but the density of nitrite oxidizing bacteria (NOB) decreased with decreasing biofilm DO. Among NOB, Nitrobacter spp. were dominant in biofilm regions with 2 g m(-3) DO or greater, while Nitrospira spp. were dominant in regions with less than 2 g m(-3) DO. A biofilm model, including AOB, Nitrobacter spp., and Nitrospira spp., was developed and calibrated with the experimental results. The model predicted the greatest extent of nitrite formation (95%) and the lowest ammonium oxidation flux (0.91 g N m(-2) day(-1)) when the membrane DO was 2 g m(-3) and the bulk liquid was anoxic. Conversely, the model predicted the lowest extent of nitrite formation (40%) and the highest ammonium oxidation flux (1.5 g N m(-2) day(-1)) when the membrane-DO and bulk-DO were 8 g m(-3) and 2 g m(-3), respectively. The estimated kinetic parameters for Nitrospira spp., revealed a high affinity for nitrite and oxygen. This explains the dominance of Nitrospira spp. over Nitrobacter spp. in regions with low nitrite and oxygen concentrations. Our results suggest that shortcut nitrification can effectively be controlled by manipulating the DO at the membrane surface. A tradeoff is made between increased nitrite accumulation at lower DO, and higher nitrification rates at higher DO.

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“…The highest ammonia removal at stable state did not occur at the highest mixing level for both reactors. This phenomenon can be explained by the fact that the higher shear force reduces the thickness of biofilms while facilitating the formation of denser biofilm which has a lower effective diffusivity of substrates (Shanahan et al 2005). Strong mixing was identified as the cause for the low ammonia removal in S2 in MABR1.…”

Section: Effects Of Mixingmentioning

confidence: 97%

Nitrification Comparison between Synthetic Wastewater and Secondary Effluent Using Membrane-Aerated Biofilm Reactor (MABR) Process

Long¹,

Lishman²,

Zhou³

et al. 2011

proc water environ fed

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Two pilot-scale membrane aerated biofilm reactors (MABR) were operated for over 530 days to compare the nitrification in both synthetic wastewater and secondary effluent, and to examine the impacts of hydrodynamic shear caused by adjusting effluent recirculation on ammonia removal. The results showed that secondary effluent had enhanced the nitrifying biofilm formation and/or detention. The ammonia removal efficiencies up to 0.262±0.024 and 0.252±0.023 kgN/m 3 /d were achieved for synthetic wastewater and secondary effluent, respectively. An optimum fluid mixing existed so that the balance between biofilm detachment and substrate mass transfer can be maintained for maximum oxidation capacity. Furthermore, the optimum mixing conditions were found to be dependent of influent composition. Further evaluation shows that low mixing intensity is a good strategy for the initiation of nitrifying biofilm in MABR, especially for the treatment of wastewater of no organic carbon.

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Acetate and ammonium diffusivity in membrane-aerated biofilms: improving model predictions using experimental results

Cited by 11 publications

References 0 publications

The effects of organic carbon, ammoniacal-nitrogen, and oxygen partial pressure on the stratification of membrane-aerated biofilms

The effects of organic carbon, ammoniacal-nitrogen, and oxygen partial pressure on the stratification of membrane-aerated biofilms

Effect of oxygen gradients on the activity and microbial community structure of a nitrifying, membrane‐aerated biofilm

Nitrification Comparison between Synthetic Wastewater and Secondary Effluent Using Membrane-Aerated Biofilm Reactor (MABR) Process

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