Steady state behaviour of three phase air lift bioreactors - an integrated model and experimental verification

Abstract

Beneckea natriegens growing both in suspension and immobilised on diatomaceous earth (silica) support particles, in a 3 dm three phase air lift bioreactor (TPALB), was employed to demonstrate the relationship between substrate loading rate and immobilised biomass loading at steady state. Sterile conditions were maintained during the experiments, while the hydraulic conditions and the inlet¯owrate remained constant. The experiment ran for 12 days, whilst the inlet substrate (n-propanol) concentration was varied both upwards and downwards between 250 and 750 mg dm (2)± (6) and (8)

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

“…Tijhuis et al ,52 who worked with immobilized cells growing self‐attached on support particles in an airlift reactor, concluded that when dilution rate is far greater than µ max biomass production mainly occurs in the biofilm, and during steady state most of this biomass production is transferred from the biofilm to the liquid phase, by a detachment process, and washes out of the reactor. Similar conclusions have been reached in our laboratory, with respect to the production of suspended biomass in a TPALB, operating at dilution rates significantly higher than µ max 37. Thus, we assume that also in the present system most of the suspended biomass exiting the TPALB during steady‐state conditions, at dilution rates higher than µ max , has been synthesized in the biofilm.…”

“…Biomass quality might be uniform throughout the biofilm, or might have significant variation across the biofilm if diffusional gradients are significant. Loss of biomass from the biofilm might be due to attrition from the external surface of the biofilm, or to sloughing of whole sections of the biofilm, leaving the support surface bare in some areas 33–38. By comparing the radioactive fractions of immobilized and suspended biomass following the tracer pulses, we can learn more about how biomass grows and depletes from a steady‐state biofilm.…”

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

“…Tijhuis et al ,52 who worked with immobilized cells growing self‐attached on support particles in an airlift reactor, concluded that when dilution rate is far greater than µ max biomass production mainly occurs in the biofilm, and during steady state most of this biomass production is transferred from the biofilm to the liquid phase, by a detachment process, and washes out of the reactor. Similar conclusions have been reached in our laboratory, with respect to the production of suspended biomass in a TPALB, operating at dilution rates significantly higher than µ max 37. Thus, we assume that also in the present system most of the suspended biomass exiting the TPALB during steady‐state conditions, at dilution rates higher than µ max , has been synthesized in the biofilm.…”

“…Biomass quality might be uniform throughout the biofilm, or might have significant variation across the biofilm if diffusional gradients are significant. Loss of biomass from the biofilm might be due to attrition from the external surface of the biofilm, or to sloughing of whole sections of the biofilm, leaving the support surface bare in some areas 33–38. By comparing the radioactive fractions of immobilized and suspended biomass following the tracer pulses, we can learn more about how biomass grows and depletes from a steady‐state biofilm.…”

The combined effects of shear stress and mass transfer on the balance between biofilm and suspended cell dynamics

“…Gikas and Livingston [28] observed, in a three phase air lift bioreactor, that even if suspended biomass does not represent a significant fraction of the total biomass it can contribute significantly to the total substrate uptake. Thus, substrate consumption in the system results from a combined action of both, planktonic and biofilm cells.…”

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

“…Tijhuis et al ,52 who worked with immobilized cells growing self‐attached on support particles in an airlift reactor, concluded that when dilution rate is far greater than µ max biomass production mainly occurs in the biofilm, and during steady state most of this biomass production is transferred from the biofilm to the liquid phase, by a detachment process, and washes out of the reactor. Similar conclusions have been reached in our laboratory, with respect to the production of suspended biomass in a TPALB, operating at dilution rates significantly higher than µ max 37. Thus, we assume that also in the present system most of the suspended biomass exiting the TPALB during steady‐state conditions, at dilution rates higher than µ max , has been synthesized in the biofilm.…”

“…Biomass quality might be uniform throughout the biofilm, or might have significant variation across the biofilm if diffusional gradients are significant. Loss of biomass from the biofilm might be due to attrition from the external surface of the biofilm, or to sloughing of whole sections of the biofilm, leaving the support surface bare in some areas 33–38. By comparing the radioactive fractions of immobilized and suspended biomass following the tracer pulses, we can learn more about how biomass grows and depletes from a steady‐state biofilm.…”

The combined effects of shear stress and mass transfer on the balance between biofilm and suspended cell dynamics

“…Gikas and Livingston [28] observed, in a three phase air lift bioreactor, that even if suspended biomass does not represent a significant fraction of the total biomass it can contribute significantly to the total substrate uptake. Thus, substrate consumption in the system results from a combined action of both, planktonic and biofilm cells.…”

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

“…Tijhuis et al ,52 who worked with immobilized cells growing self‐attached on support particles in an airlift reactor, concluded that when dilution rate is far greater than µ max biomass production mainly occurs in the biofilm, and during steady state most of this biomass production is transferred from the biofilm to the liquid phase, by a detachment process, and washes out of the reactor. Similar conclusions have been reached in our laboratory, with respect to the production of suspended biomass in a TPALB, operating at dilution rates significantly higher than µ max 37. Thus, we assume that also in the present system most of the suspended biomass exiting the TPALB during steady‐state conditions, at dilution rates higher than µ max , has been synthesized in the biofilm.…”

“…Biomass quality might be uniform throughout the biofilm, or might have significant variation across the biofilm if diffusional gradients are significant. Loss of biomass from the biofilm might be due to attrition from the external surface of the biofilm, or to sloughing of whole sections of the biofilm, leaving the support surface bare in some areas 33–38. By comparing the radioactive fractions of immobilized and suspended biomass following the tracer pulses, we can learn more about how biomass grows and depletes from a steady‐state biofilm.…”

The combined effects of shear stress and mass transfer on the balance between biofilm and suspended cell dynamics

“…Gikas and Livingston [28] observed, in a three phase air lift bioreactor, that even if suspended biomass does not represent a significant fraction of the total biomass it can contribute significantly to the total substrate uptake. Thus, substrate consumption in the system results from a combined action of both, planktonic and biofilm cells.…”