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Table 1 Comparison among bioreactors

From: Biological wastewater treatment and bioreactor design: a review

BioreactorMeritsLimitations
Stirred tankSimple in construction and operation. Uses suspended growth of microbes. Suitable for aerobic and anaerobic processes.Restricted to low capacities.
Trickle bed biofilm reactorUse of attached growth of microbes. Low operating cost due to down flow mode of operation. High cell mass concentration in biofilm promotes rate of bioconversion.Mainly for aerobic BOD removal. Low capacity due to low feed flow rate maintained.
Moving bed biofilm reactor (slurry reactor)Heterogeneous version of stirred tank. High cell concentration in biofilm promotes rate of bioconversionCapacity wise inferior to column reactors. Biofilm could get disturbed due to high rate of agitation.
Fluidized bed biofilm reactorOperates at high capacities, provides high degree of bioconversion. Once fully fluidized, pressured drop across the bed remains constant and does not increase with increase in feed flow rate. Degree of bioconversion increases with increase in feed flow rate due to bed expansionEntrainment loss of particle-biofilm aggregates possible. Operating cost higher than trickle bed (packed bed).
Semifluidized bed biofilm reactorHigher degree of bioconversion (than fluidized beds) at higher capacities and low reactor volume requirement. Degree of bioconversion increases with increase in feed flow rate, even if reactor volume is kept constant.Higher operating cost than fluidized beds. Continuous, circulating mode of operation not possible.
Inverse fluidized biofilm reactorLow operating cost due to down flow mode of operation. Larger size particles could be used. Reasonably large degree of bioconversion.Lower capacity than fluidized /semi-fluidized bed. Larger reactor volume requirement
DSFF bioreactorSimple in construction and operation. No support particles required. Low operating cost due to downflow mode of operation. Multiple tubes / columns could be used to increase capacity.Presently restricted to anaerobic operation. Large reactor volume requirement at high capacities.
UASB reactorSimple in construction. No support particles used. Provides substantially high degree of bioconversion at distinctly high capacities and even with high strength feedstock.Restricted to anaerobic processes, employing complex culture of microbes. Enormously large startup time.