Ju-Sheng Huang

Effect of biofilm thickness distribution on substrate-inhibited kinetics

Abstract The effect of biofilm thickness distribution (BTD) on substrate-inhibited kinetics in anaerobic filters was evaluated. The modeling results show that the kinetic behavior of normal BTD is different from that of uniform biofilm thickness when the substrate utilization rate of some biofilms is limited by diffusion or reaction. However, when all biofilms are either diffusion-limited or reaction-limited, kinetic behaviors of normal BTD and uniform biofilm thickness are identical. In addition, the BTD can reduce the apparent maximum substrate utilization rate and narrow the multiple steady-state region of substrate-inhibited kinetics. In this study, phenol was used as an inhibitory substrate. A general agreement was found between the numerical simulation results using the normal BTD and experimental results for anaerobic filters. On the contrary, numerical simulation using uniform biofilm thickness failed to predict the outcome of the experiments. This indicates that an anaerobic filter is composed of a biofilm with varying thickness and thus, the BTD of a filter is of great importance, especially for treating wastewater containing inhibitory substrates.

Deep-biofilm kinetics of substrate utilization in anaerobic filters

Acetate fermentation in anaerobic filters was performed to study the deep-biofilm kinetics of substrate utilization. Small Peclet number ranging from 0.01 to 1.5 found in the tracer test indicates that the flow regime in anaerobic filters is close to complete-mix. An axial dispersion model coupled with deep-biofilm kinetics is simulated along the biofilter height. A good agreement between the calculated and experimental results indicates that the proposed deep-biofilm model can be used to estimate the removal efficiency of the readily degradable substrate in anaerobic filters if the ratio of voidage to specific surface area is greater than several millimeters. Also, a higher influent substrate concentration gives a higher substrate removal efficiency if the surface loading is kept the same.

Comparative bioparticle and hydrodynamic characteristics of conventional and tapered anaerobic fluidized‐bed bioreactors

By maintaining the same operational conditions of one conventional fluidized-bed bioreactor (CFB) and two tapered fluidized-bed bioreactors (TFBs), the performance of the TFBs with taper angles of 5 ° and 2.5 ° were found to be superior to that of the CFB with a taper angle of 0 °. Experimental results together with statistical analyses showed that the bioparticle and hydrodynamic characteristics of the TFBs were significantly different from those of the CFB. Also, bioparticle stratification occurred in the three bioreactors. The biofilm thickness (δ) and the specific biomass (β) of the three bioreactors varied in the following decreasing order 5 ° > 2.5 ° > 0 ° under the same volumetric loading. Meanwhile, the specific energy dissipation rate (ω) and the bioparticle washout rates (W = 0.214 ± 0.219; 0.537 ± 0.493 g BAC dm−3day−1) of the two TFBs were considerably lower than that of the CFB (W = 1.086 ± 0.916 g BAC dm−3 day−1). A lower ω value results in increases in δ and β, and a lower dry density of the biofilm (ρd). Accordingly, the performance enhancement with TFBs should be related to their lower ω and W, thicker δ and larger β values. © 2000 Society of Chemical Industry

Bioparticle characteristics of tapered anaerobic fluidized-bed bioreactors

When the volumetric loading is greater than 50 kg-COD/m3-d, the performance of the tapered anaerobic fluidized-bed bioreactors is more efficient than that of the conventional anaerobic fluidized-bed bioreactor; however, the increasing percentages of the COD removal efficiency are not very significant when the taper angle is greater than 5°. The arithmetic means of the biofilm thickness, specific surface area and specific biomass of the former (increased with the increasing taper angle) are all larger than those of the latter; and the distribution of bioparticles in the former is more uniform than that in the latter. There is a fairly good agreement between the experimental and simulated removal efficiencies of the substrate, and thus, the proposed kinetic model can be used for the predicting purpose. The sensitivity analysis result together with the calculated values of Thiele modulus and the effectiveness factor reveal that the acetate methanogenesis in the anaerobic fluidized-bed bioreactors is reaction-controlled, and the biofilm is fully penetrated by the substrate.

Effect of addition of Rhodobacter sp. to activated-sludge reactors treating piggery wastewater.

Under aerobic conditions, the decay rates of purple nonsulfur bacteria (Rhodobacter sp.) in the light and dark follow first-order kinetics with rate constants of 0.22 and 0.32 day(-1), respectively. The performance of the conventional activated-sludge reactor (CASR) treating anaerobically pretreated piggery wastewater (656-1.110 mg chemical oxygen demand, COD/L) can be enhanced by the addition of Rhodobacter sp. By performing regressive and statistical analyses using the proposed model and experimental data, the kinetic constants k and Y(T), and the fraction of refractory organic materials (f) of the Rhodobacter sp.-supplemented activated-sludge reactor (RASR) are 40% larger, 21% less, and 34% less than those of the CASR, respectively. From parametric sensitivity analyses, the substrate removal efficiencies of the CASR and RASR are most sensitive to the parameters k and the food to microorganisms ratio (F/M) but least sensitive to the parameter f; the specific oxygen utilization rates of the CASR and RASR are most sensitive to the parameters a and k but least sensitive to the parameter b.

Consecutive reaction kinetics involving distributed fraction of methanogens in fluidized-bed bioreactors.

A kinetic model involving the distributed fractions of acidogens and methanogens is proposed. To determine the fluxes and biochemical reaction rates of the substrate sucrose and its intermediates, volatile fatty acids (VFAs) in bulk liquid and within the biofilm, a kinetic model was developed by combining the solid-phase model with the liquid-phase model. The predicted substrate removal efficiencies of the conventional and tapered fluidized-bed bioreactors (CFB, TFBs) are in good agreement with the experimental results. The biofilm thickness in TFBs are thicker than that in CFB, resulting in performance enhancement with TFBs. The simulated results obtained from the kinetic model show that methanogenesis is the rate-limiting step of degradation of the simple organic compound (sucrose), and the chemical oxygen demand (COD) concentration in the effluent is mainly contributed by the intermediates VFAs. The distributed fractions of acidogens and methanogens determined experimentally are 0.4 and 0.6, respectively.

Species control of microalgae in an aquaculture pond

Abstract To effectively control and maintain microalgal species in an aquaculture pond is necessary because microalgae play an important role in stabilizing pond water quality via either ammonia uptake or oxygen production. In this study, microalgae taken from a tilapia rearing pond were cultured, under various temperatures and ammonia-N concentrations, by using both continuous-flow and batch reactors. The succession of dominant microalgal species was examined. The dominant microalgae species in batch reactors are Chlorella vulgaris, Scenedesmus ellipsoideus, S. dimorphus and Westella botryoides under the conditions of dilution rate, 0.25 day −1 ; temperature, ranging from 17 to 32°C; ammonia-N concentration, less than 15 mg/l and light intensity, 4000 lux. The dominant species found in batch reactors are more stable than those found in continuous-flow reactors. Low concentrations of both ammonia-N and microalgae are desirable for obtaining a better control of dissolved oxygen level in an aquaculture pond.

Performance evaluation of single-sludge reactor system treating high-strength nitrogen wastewater.

In the single-sludge reactor system treating high-strength nitrogen wastewater (similar to anaerobically pretreated piggery wastewater), the NH4(+)-N removal efficiencies (98-82%) are higher than total nitrogen removal efficiencies (71-43%). The mixed liquor recycle ratio only imposes a slight effect on total nitrogen removal efficiency. The alkalinity change data could be used for monitoring and control of the reactor system. To evaluate the performance of the single-sludge reactor system, a simplified nitrification-denitrification model (with nitrification capacity, denitrification capacity, and denitrification potential concepts) and a graphically analytical technique are proposed. It turns out that ammonia nitrification and total nitrogen removal efficiencies are strongly dependent on the process load and reactor configuration, and an optimal operating condition requires a proper match between nitrification and denitrification.

Kinetics of denitritification and denitratification in anoxic filters

Denitritification and denitratification in anoxic filters were performed to generate experimental data. Also, a kinetic model of denitratification that accounts for intrinsic biokinetics and hydrodynamic behavior of the biofilter is proposed. In denitritification, the simulated results are in good agreement with the experimental data; and a higher nitrite influent concentration gives a higher nitrite reduction efficiency if the denitrifying loading is kept the same. In denitratification, the intermediate nitrite tends to accumulate, and a higher denitrifying loading results in a higher nitrite effluent concentration. By inserting biological and physical parameter values into the kinetic model, the variations in distributed fractions of nitrate-reductase (f) and nitrite-reductase (1-f) with different denitrifying loadings can be estimated by fitting in experimental data. The estimated f increased with an increase in denitrifying loading, implying that a higher denitrifying loading results in a higher nitrite effluent concentration. From parametric sensitivity analyses, the parameter f is more sensitive than other biological and physical parameters. Accordingly, the proposed kinetic model of denitratification can be used to predict the treatment performance of anoxic filters appropriately. Copyright 1998 John Wiley & Sons, Inc.