Effects of stratification in a fluidized bed bioreactor during treatment of metalworking wastewater

Abstract

During wastewater treatment, biofilm‐coated sand particles stratified in a fluidized bed bioreactor (FBB); particles coated by thicker biofilm segregated toward the top of the bed. Stratification was so well developed that at least two co‐existing regions of significantly different mean biofilm thickness were visually distinct within the operating FBB. The observed stratification is attributed to differences in forces of drag, buoyancy, shear, and collisional impact, as well as differences of collision rate within the different regions. Particles with thick biofilm (thickness >100 μm) near the top of the bed consumed substrate at significantly lower rates per unit biomass than particles with thin biofilm (10–20 μm) near the bottom of the bed, thereby suggesting that substrate mass‐transfer resistance through biofilm may limit biodegradation rates in the upper portion of the FBB. Large agglomerates of biomass floc and sand, which formed at the top of the fluidized bed, and sand particles with thick biofilm were susceptible to washout from the FBB, causing operational and treatment instability. Radial injection of supplemental liquid feed near the top of the bed increased shear and mixing, thereby preventing formation and washout of agglomerates and thickly coated sand particles. Supplemental liquid injection caused the mean specific biomass loading on the sand to increase and also increased the total biomass inventory in the FBB. Rates of biodegradation in the FBB appeared to be limited by penetration of substrates into the biofilm and absorption of oxygen from air into the wastewater. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 129–140, 1999.

Modelling anaerobic biofilm reactors—A review

“…Many authors (Ro and Neethling, 1994;Safferman and Bishop, 1996;Schreyer and Coughlin, 1999;Trinet et al, 1991) observed that the bed becomes stratified due to the presence of granules with different biofilm thicknesses. In such a context, the application of the Richardson and Zaki correlation remains dubious.…”

“…Biofilm has been observed to be relatively smoother and more homogeneous under conditions of high shear (i.e., high liquid velocity) than under low shear conditions (Lau, 1995;Zhang and Bishop, 1994). The study by Schreyer and Coughlin (1999) showed that the introduction of a thinner to increase the shear resulted in a non-stratified bed.…”

Anaerobic Fluidized Bed Membrane Bioreactors for the Treatment of Domestic Wastewater

“…Although this problem could be serious, research has suggested an easy solution. Applying a high shear stress (high liquid velocity) can make the biofilm thinner and more homogeneous (Zhang and Bishop 1994;Schreyer and Coughlin 1999). Further, Andrews and Tien (1979) indicated that by using a uniform size of support media, the potential for this problem was reduced.…”

Distribution characteristics of local phase holdups in gold concentrates gas-liquid-solid circulating fluidized bed

“…Because CFB has high processing capacity, low pressure drop and good phase dispersion effect, the structure simple and continuous operation easily, it has been widely used in bio-chemical industry, environment, especially metal smelting [1][2][3] . So Experimental study of dynamic characteristics in CFB is very necessary; it is the premise and basis for subsequent amplification experiments and semi-industrial experiments.…”