The use of electrical resistance tomography for the characterization of gas holdup inside a bubble column bioreactor containing activated sludge

Analysis of gas phase characteristics and mixing performance in an activated sludge bioreactor using electrical resistance tomography

“…Also, in our previous study increase in MLSS in the range 0.712-2.152 g/L resulted in higher gas holdups. This was attributed to the dominance of movement hindering forces over the coalescence inducing forces in this range of operation [26]. The same mechanism can explain the corresponding decrease in the rise velocity of bubbles with increase in MLSS concentration in this range.…”

“…The influence of different factors on these characteristics should also be investigated properly. In our previous research work, variations of global and local gas holdups with aeration intensity and MLSS concentration were studied in an activated sludge bubble column bioreactor, and the results showed an interesting trend of gas holdup versus MLSS which was never reported before in the literature [26]. Such an observation led us to investigate the influence of MLSS concentration and aeration rate on other gas phase characteristics such as bubble rise velocity and bubble size.…”

“…4 illustrates the ERT tomograms after injecting 100 mL of 4% NaCl solution to the top of the bubble column containing air/water mixture and operated at u g of 0.081 cm/s. At initial steady state condition (t = 0), the conductivity distributions at all six sensor planes were uniform and similar to each other; the slight differences between them are attributable to the axial variations of the gas holdup inside the bubble column [26]. Since NaCl solution was injected to the top of the column, it was dispersed from the top to the bottom (Plane 1-6).…”

“…In our previous study [26], the apparent viscosity of activated sludge was correlated to the superficial gas velocity and MLSS concentration. The results of that correlation show that for superficial gas velocities in the range 0.081-1.303 cm/s, all sludge samples possess higher apparent viscosities compared to water.…”

“…Seven different MLSS concentrations were employed for the hydrodynamic studies and MLSS analysis was performed based on standard methods [40]. According to the significant role of rheology in hydrodynamics, the rheological experiments were previously carried out on the sludge samples at 22 ± 0.5°C, and the power law model was reported as the most suitable description for MLSS concentrations in the range 0.712-15.86 g/L [26]. As MLSS concentration increased, the consistency index (K) and flow behavior index (n) varied in the ranges 0.005-0.054 Pa s n and 0.689-0.414, respectively.…”