Wen K. Shieh

Biological fate of organic priority pollutants in the aquatic environment

Abstract This is a review of the literature on the fate of the organic priority pollutants in the aquatic environment including biological wastewater treatment systems. Included is a brief discussion of the biological processes—mineralization, cometabolism, bioaccumulation and polymerization—and conditions under which biodegradation occurs. Observed biodegradation data from laboratory studies and biological treatment systems are summarized.

Fluidization and reactor biomass characteristics of the denitrification fluidized bed biofilm reactor

Abstract The fluidization and reactor biomass characteristics of the denitrification fluidized bed biofilm reactor (FBBR) were investigated. Experimental evidence obtained indicates that Richardson-Zaki correlation, which was developed for rigid solid particles, provides an excellent description of the fluidization mechanics of a denitrification FBBR. However, correlations for calculation of drag coefficient and expansion index should be modified to account for the FBBR characteristics that the degree of bed expansion increases with increased bioparticle size (i.e. increased biofilm thickness). The fluidization and reactor biomass correlations developed in this investigation are capable of providing a direct and accurate prediction of biomass concentration and bed expansion in FBBRs designed for wastewater treatment applications. Engineering applications of these correlations are discussed.

Batch Phenol degradation by Candida tropicalis and its fusant

Phenol degradation by Candida tropicalis and its fusant, which is produced using protoplast fusion as a selective technique, is evaluated under batch and high concentration conditions. The respirometric data show that oxygen uptake activities of both yeast strains peak at pH 7.0 and 32 degrees C, but the fusant is more active than the control strain. Although the data show that both yeast strains are capable of sustaining discernible degradation in the presence of phenol inhibition, however, the C. tropicalis fusant is capable of attaining better phenol degradation than the control strain and it is less susceptible to phenol inhibition. Under the conditions tested, C. tropicalis is completely inhibited at phenol concentrations >/=3,300 mg/L, whereas for the C. tropicalis fusant complete inhibition is absent until phenol concentrations are >/=4, 000 mg/L. The observed cell yields of both yeast strains are virtually identical and remain fairly constant at approximately 0.5 mg MLVSS/mg C6H5OH (MLVSS: mixed liquor volatile suspended solids). Copyright 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 391-395, 1998.

Anaerobic treatment of kraft pulp-mill waste activated-sludge: Gas production and solids reduction

Anaerobic digestion of kraft pulp-mill waste activated-sludge was studied in a pilot-scale unit. The anaerobic digester was operated for 21 months over a wide range of volatile solids (VS) loading rates (1·5–5·2 kg VS/m3 day; Hydraulic Retention Time, HRT, 24-8 days) to establish the optimum operational conditions for solids reduction and biogas production. The process started up in 6 weeks using a mixture of municipal-digester sludge and sediment slurry, which was acclimated to kraft pulp-mill effluent, as seed material. Digestion of sludge containing about 38% lignin showed the median VS removal of 40% with the median biogas production of 220 litres/kg VS added or 570 litres/kg VS removed. The respective 90 percentiles were 60% for VS reduction and 350 litres/kg VS added or 780 litres/kg VS removed for biogas production. Optimal process performance was obtained at the VS loading of 2·2 kg VS/m3 day. Alkali addition (13 g NaOH/kg VS) to feed sludge, and sludge recycle (with ratio of 0·25) were required for stable operation at VS loadings exceeding 1·5 kg VS/m3 day. The anaerobic process remained stable even at the VS loading of 5·2 kg/m3 day.

Biomass loss from an anaerobic fluidized bed reactor

The phenomena of biomass loss during reactor startup and steady-state operation of an anaerobic fluidized bed (AFB) reactor using porous media particles and fed with acetic acid are studied. The amount of biomass lost during reactor startup is found to be correlated to both substrate utilization and biogas production. However, the level of biomass lost does not impede reactor startup and a rapid buildup of attached biomass in the reactor is attainable. Under the fluidization conditions commonly found in steady-state AFB reactors, mechanical attrition caused by interparticle collision is unlikely to alter the balance established between bacterial growth and maintenance metabolism.

Evaluation of intrinsic and inhibition kinetics in biological fluidized bed reactors

Abstract An experimental approach is developed in which batch experiments are directly performed in steady-state biological fluidized bed (BFB) reactors for the evaluation of biofilm intrinsic and inhibition kinetics. Experimental evidence verifies that intrinsic data can be obtained from the batch experiments performed over short periods of time without alteration of immobilized cell physiology in reactors. Furthermore, the phenomena of substrate inhibition can also be examined using the proposed approach. BFB reactors are capable of regaining their steady-state performance within 24 h after the termination of batch experiments without showing any distress symptoms.

Effects of microcarrier pore characteristics on methanogenic fluidized bed performance

Abstract The cell retention capacities of three porous microcarriers with diversified pore characteristics and Ottawa silica sand were studied in methanogenic fluidized bed reactors with acetic acid as the sole substrate. Batch kinetic experiments on substrate utilization at different initial bulk-liquid substrate concentrations were also performed. The experimental data reveal that, under similar startup conditions, porous microcarriers are capable of reducing the startup times by more than 50% as compared to sand. Furthermore, under pseudo-steady-state conditions at an organic loading of 6 g total organic carbon (TOC)/1-day, porous microcarriers are capable of retaining three times more immobilized cells as compared to sand. More than 90% of total reactor cell mass is immobilized on porous microcarriers as opposed to 80% on sand. As a result, porous microcarriers are conducive for better proliferation of slow-growing methanogenic bacterial consortia. The experimental data clearly indicate that surface area, total pore volume and mean pore diameter should be used concomitantly to obtain better insight into the cell retention capacity of a given porous microcarrier. Batch kinetic data on substrate utilization reveal that mass transfer limitations are absent in methanogenic fluidized bed reactors at bulk-liquid TOC concentrations > 10 mg/l. The observed maximum substrate utilization rates, which are independent of initial bulk-liquid TOC concentrations ranging from 200 to 1000 mg/l, are low for porous microcarriers as compared to sand (0.5 vs 2.25 day − ). These data confirm the results of the microscopic examinations performed which indicate that porous microcarriers attract Methanothrix type bacterial consortia whereas Ottawa silica sand attracts a mixture of Methanothrix and Methanosarcina .

The intrinsic kinetics of nitrification in a continuous flow suspended growth reactor

Abstract The intrinsic rate of nitrification was observed in a continuous flow reactor by eliminating external and internal diffusional resistances. The former were minimized by means of intense agitation, and the latter by mechanical rupture of the activated sludge floc using high impeller rotational speeds. The experimental results obtained from the continuous flow experiments confirmed the applicability of Michaelis-Menten kinetics to the activated sludge nitrification process. A possible dependency of k on contact time was found, larger values of k being observed under shorter contact times. The Michaelis constant K, was found practically unaffected by the contact times used in this study.

Analysis of an upflow bioreactor system for nitrogen removal via autotrophic nitrification and denitrification

The upflow bioreactor system without biomass-liquid separation unit was evaluated for its efficacy in sustaining autotrophic nitrification and denitrification (AND). The bioreactor system was capable of sustaining AND by means of carefully controlled oxygenation to achieve the maximum NH(4)(+)-N removal rate of 0.054 g N gVSS(-1) day(-1) (38% removal efficiency) at the oxygen influx and nitrogen loading rate of 3.68 mg O(2) h(-1) L-bioreactor(-1) and 182 mg N day(-1) L-bioreactor(-1), respectively. Additional nitrogen removal was achieved in a two-stage bioreactor configuration due to endogenous denitrification under long mean cell residence time. Quiescent conditions maintained in the bioreactor provided stable hydrodynamic environments for the chemoautotrophic biomass matrix, which revealed porous, loosely-structured, and mat-like architecture. More than 95% of the total biomass holdup (1.3-1.5 g VSS) was retained, thereby producing low biomass washout rate ( approximately 40 mg VSS day(-1)) with VSS < 11 mg VSSL(-1) in the effluent.

OPTIMAL CONTROL OF WASTEWATER TREATMENT PLANTS VIA INTEGRATED NEURAL NETWORK AND GENETIC ALGORITHMS

Abstract The successful operation of wastewater treatment plants involves many uncertain factors. Not only the physical and chemical properties of wastewater streams but also the complexity of biological mechanism would significantly influence the performance of treatment process. Due to the rising concerns of environmental and economic impacts, improved control algorithms, using artificial intelligence technologies, have gradually received wide attention in the scientific community. This paper develops a genetic algorithm-based neural network for the assistance of intelligent controller design. An industrial wastewater treatment plant in Taiwan verified the applicability of such a methodology. The hybrid intelligent control technology applied in this paper is suitable to many other types of wastewater treatment plants by a slightly modified concept.