A critical review of inverse fluidized bed reactors-start-up optimization strategies and wastewater treatment

A critical evaluation of strategies used for reducing start-up time and biological wastewater treatment using an inverse fluidized bed reactor (IFBR) was done. The start-up of an IFBR is one of the most important, time-consuming, and limiting steps in wastewater treatment using biofilm reactors. Evaluation of different strategies used by various researchers is helpful in future research works with this reactor. Different types of treated wastewater, the effect of wastewater characteristics, carriers used, and reactor hydrodynamics on the reactor performance were reviewed in detail in the first part. The second part of this review covers the use of an IFBR in the biological treatment of different wastewaters through multiple biochemical pathways and how it helped improve performance compared to other reactors. This will enable the researchers to understand the novelty of an IFBR for wastewater treatment and allow them to use it as a potential reactor.

Role of zinc oxide nanoparticles for effluent treatment using Pseudomonas putida and Pseudomonas aureofaciens

The biological treatment of textile effluent is enhanced by the use of zinc oxide (ZnO) nanoparticles for the reduction in chemical oxygen demand (COD) from its initial value of 1700 ppm. The present research investigated the effect of ZnO nanoparticles when microbial cultures of Pseudomonas putida and Pseudomonas aureofaciens were used to treat textile effluent in three-phase inverse fluidized bed bioreactor. The parameters like-size of ZnO nanoparticles, static bed height, superficial gas velocities and solid media particle size-together affected the COD reduction and all of these were investigated in this paper. ZnO nanoparticles of 280 nm reduced the maximum COD to 47 ppm (97.24%) at low gas velocity of 0.0027 m/s at 10% inoculum size and at a static bed height of 2.43 cm.

COD reduction of textile effluent in three-phase fluidized bed bioreactor using Pseudomonas aureofaciens and Escherichia coli

This paper investigated the effect of mixed cultures of Pseudomonas aureofaciens and Escherichia coli and air as gas on degradation of chemical oxygen demand (COD) in three-phase inverse fluidized beds (TPIFBs) for textile effluents with initial COD of 1200 ppm (effluent 1) and 640 ppm (effluent 2). Investigators focused on the importance of different design of gas spargers of the TPIFB for checking its effect on COD reduction performance. For this purpose, four different gas spargers were fabricated for gas flow entry into bioreactor with different  % open area: Gas sparger 1 (18% open area), sparger 2 (10.42% open area), sparger 3 (8.077% open area) and sparger 4 (1.53% open area). These percentage open area decided the amount of gas flow in a unit time in batch studies, which in turn rely mainly on superficial gas velocity. The reduction in COD was measured at two different superficial gas velocity (0.00343 and 0.004068 m/s) and at two ratio of static bed height to diameter (H/D) of 0.5 and 0.25 in an aerobic mode. Textile effluent 1 resulted in 98.07% COD reduction with sparger 3 and discharged at 23.14 ppm in 28 h. Textile effluent 2 resulted in 96.5% COD reduction with sparger 2 and discharged at 22.4 ppm in 22 h. The resulting COD values of Effluent 1 and effluent 2 were in range of discharge limit and resulted at a low gas velocity of 0.00343 m/s and low H/D ratio of 0.25. The gas holdup correlation was found to be ε _g = 0.0064 U _g^0.98 .

Studies on Performance Analysis and Computer Aided Design of Inverse Fluidized Bed Bioreactors with Nanosupport Particles

Attempts have been made to propose a modified design of inverse fluidized bed bioreactor (IFBBR) that utilizes immobilized enzyme nanosilica particles. The substrate solution is mixed uniformly with nanosilica particles, and the resultant slurry flows down the reactor keeping particles in suspension. The performance characteristics of the bioreactor of proposed design have been analysed both mathematically and experimentally. In the mathematical analysis, dispersed flow of suspension down the reactor tubes has been assumed. The mathematical results (from the developed software package) agree closely with the experimental results, the maximum deviation being 9.5%. The bioreactor provides high fractional conversion at high substrate flow rates, but demands low reactor volume. In addition, the operating cost of the reactor is substantially low. In reactors of this kind, resistance to substrate transfer into the support particles (nanoparticles) is negligible, and the global rate is essentially equal to the intrinsic rate (as the computed value of effectiveness factor is equal to unity for different types of kinetic equations and within wide range of substrate concentration). This must be attributed to the nanosize and consequent large specific surface of support particles. The present design of IFBBR is thus anticipated to be quite attractive for successful industrial adaptation.