Evaluation of the Inverse Fluidized Bed Biological Reactor for Treating High-Strength Industrial Wastewaters

The aim of this work was to investigate the aerobic degradation of high-strength industrial (refinery) wastewaters in the inverse fluidized bed biological reactor, in which polypropylene particles of density 910 kg/m3 were fluidized by an upward flow of gas through a bed. Measurements of chemical oxygen demand (COD) versus residence time t were performed for various ratios of settled bed volume to reactor volume (Vb/VR) and air velocities u. The largest COD reduction, namely, from 54,840 to 2,190 mg/l, i.e. a 96% COD decrease, was achieved when the reactor was operated at the ratio (Vb/VR) = 0.55, air velocity u = 0.046 m/s and t = 65 h. Thus, these values of (Vb/VR), u and t can be considered as the optimal operating parameters for a reactor when used in treatment of high-strength refinery wastewaters. In the treatment operation conducted in a reactor optimally controlled at (Vb/VR) = 0.55, u = 0.046 m/s and t = 65 h, the conversions obtained for all phenolic constituents of the wastewater were larger than 95%. The conversions of about 90% were attained for other hydrocarbons.

Optimal Aerations in the Inverse Fluidized Bed Biofilm Reactor When Used in Treatment of Industrial Wastewaters of Various Strength

The aim of this work was the determination of the optimal aerations, and more specifically the corresponding optimal air velocities uopt, at which the largest COD removals were achieved in treatment of industrial wastewaters of various strength conducted in the inverse fluidized bed biofilm reactor. The largest COD removals were achieved at the following air velocities uopt and retention times ts, and (Vb/VR) = 0.55: i) for CODo = 72,780 mg/l at uopt = 0.052 m/s and ts = 80 h;ii) for CODo = 62,070 mg/l at uopt = 0.042 m/s and ts = 65 h;iii) for CODo = 49,130 mg/l at uopt = 0.033 m/s and ts= 55 h;iv) for CODo = 41,170 mg/l at uopt = 0.028 m/s and ts = 45 h;v) for CODo = 35,460 mg/l at uopt = 0.025 m/s and ts = 27.5 h;and vi) for CODo = 26,470 mg/l at uopt= 0.014 m/s and ts = 22.5 h. In the treatment operation conducted in a reactor optimally controlled at the above values of uopt, ts and (Vb/VR), the following decreases in COD were obtained: i) from 72,780 to 5410 mg/l;ii) from 62,070 to 3730 mg/l;iii) from 49,130 to 2820 mg/l;iv) from 41,170 to 1820 mg/l;v) from 35,460 to 1600 mg/l;and vi) from 26,470 to 1180 mg/l, that is, approximately a 93%, 94%, 95%, 96%, 95% and 96% COD reduction was attained, respectively.

Effects of loading rate and hydraulic residence time on anoxic sulfide biooxidation

The optimal operation conditions in an anoxic sulfide oxidizing (ASO) bioreactor were investigated. The maximal removal rates for sulfide and nitrate were found to be 4.18 kg/(m3·d) and 1.73 kg/(m3·d), respectively. The volumetrical volumetric loading rates (LRs) observed through decreasing hydraulic retention time (HRT) at fixed substrate concentration are higher than those by increasing substrate concentration at fixed HRT. The sulfide oxidation in ASO reactor was partially producing both sulfate and sulfur; but the amount of sulfate produced was approximately one third that of sulfur. The process was able to tolerate high sulfide concentration, as the sulfide removal percentage always remained near 99% when influent concentration was up to 580 mg/L. It tolerated relatively lower nitrate concentration because the removal percentage dropped to 85% when influent con- centration was increased above 110 mg/L. The process can tolerate shorter HRT but careful operation is needed. Nitrate conversion was more sensitive to HRT than sulfide conversion since the process performance deteriorated abruptly when HRT was decreased from 3.12 h to 2.88 h. In order to avoid nitrite accumulation in the reactor, the influent sulfide and nitrate concentrations should be kept at 280 mg/L and 67.5 mg/L respectively. Present biotechnology is useful for removing sulfides from sewers and crude oil.

Sulfide oxidation in fluidized bed bioreactor using nylon support material

A continuous fluidized bed bioreactor （FBBR） with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2-3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of （30 ± 2）°C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached （42 ± 3） μm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%-92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.