Irving J. Dunn

Behavior of Biofilters for Waste Air Biotreatment. 1. Dynamic Model Development

An novel diffusion reaction model for the determination of both the steady-state and transient-state behavior of biofilters for waste air biotreatment is developed and discussed. The model considers the reactor to comprise finite sections, for each of which transient mass balances are established and solved by digital simulation. The elimination of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) vapors from air as single and mixed pollutants serves as an example to illustrate and discuss both the models response and its parametric sensitivity. Experimental evaluation of the model is presented in part 2 of this paper.

Behavior of Biofilters for Waste Air Biotreatment. 2. Experimental Evaluation of a Dynamic Model

Experimental evaluation of a diffusion reaction model (part 1) for the determination of both steady- and transient-state behavior of biofilters for waste air biotreatment is presented. The model, applied to the aerobic biodegradation of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) vapors from air as single and as mixed pollutants, proved appropriate for describing most of the experiments undertaken and served as a basis for comprehensive understanding of biofilter operation.

Comparative Scale-Up and Cost Estimation of a Biological Trickling Filter and a Three-Phase Airlift Bioreactor for the Removal of Methylene Chloride from Polluted Air

Abstract Laboratory scale biological trickling filters and three-phase airlift bioreactors have been studied for the elimination of methylene chloride (or dichloromethane) vapors from waste air, and the results used herein for the design of small industrial-scale reactors. The conditions chosen for scale-up were an air flow rate of 100 m3 h-1, a methylene chloride inlet concentration of 2 g m-3, and a target removal of 99.5%. The scale-up procedure, design, and cost analysis are discussed. The full-scale biotrickling filter appears to be the most cost-effective reactor, with global costs of about

Adaptive on-line optimal control of bioreactors: application to anaerobic degradation

62 per 1,000 m3 treated. Treatment in the airlift reactor was estimated to be twice as expensive and catalytic oxidation 5 times as expensive. Biological waste air treatment offers economical alternatives to conventional techniques for waste air treatment.

Phenol degradation in a three-phase biofilm fluidized sand bed reactor

Abstract The control of bioreactors is particularly important due to ever-changing reactor and feed conditions. In adaptive optimal control reactor, conditions are adjusted to obtain the best performance, as determined by a performance index (PI), which is often a function of more than one output variable. An empirical, linear input-output model is used whose parameters are updated at each sampling time using on-line measurements. In this example, for anaerobic wastewater treatment, two relations are used of the form, y 1 ( t ) = b 1 , 1 u ( t −1 - d 1 ) + c 1 ; y 2 ( t ) = b 2 , 1 u ( t − 1 − d 2 ) + c 2 . These are linear models relating feed flow rate, u, to methane production rate, y 1 , and organic acids concentration y 2 . The performance index (PI) was taken as a compromise between high methane rate and low organic acids as PI = methane production rate - Constant X (Total organic acids conc.). This was expressed in terms of the model parameters and maximized by the method of steepest ascent. In this way the feed rate could be continually adjusted for changing conditions, as caused by feed disturbances or biological adaptation. This dynamic optimization method has considerable advantage for slow systems, in that a steady state is not needed. One and two stage, anaerobic biofilm fluidized sandbed reactors were used to continuously degrade whey to biogas and residual organic acids. A PC computer was used to handle the on-line GC data and to serve as controller for the feed flow rate. Preliminary work involved testing conventional feedback control, for which pH setpoint control performed best. A complex simulation model based on mechanistic, dynamic mass balance-kinetic relations was established to describe the experimental response of the reactors. The simulation model was used to design the controller and to determine useful values for the control parameters; it proved extremely useful as it made lengthy experiments unnecessary. The PI function was shown by simulations to have a suitably sharp optimum. Automatic control experiments for one and two stage reactors were made in which responses were obtained for step changes in the performance index constant and for square wave increases in the feed concentration. The optimizer performed well, changing the feed rate to maintain the loading approximately constant with changed feed concentration. For a single stage system a new optimum was found after 5 h for a change in the PI constant and after 2 h for a step change in the feed concentration.

Protection of biofilms against toxic shocks by the adsorption and desorption capacity of carriers in anaerobic fluidized bed reactors

A previous three phase fluidized sand bed reactor design was improved by adding a draft tube to improve fluidization and submerged effluent tubes for sand separation. The changes had little influence on the oxygen transfer coefficients(KL a), but greatly reduced the aeration rate required for sand suspension. The resulting 12.5 dm3 reactor was operated with 1 h liquid residence time, 10.2dm3/min aeration rate, and 1.7–2.3 kg sand (0.25–0.35 mm diameter) for the degradation of phenol as sole carbon source. The KLa of 0.015 s−1 gave more than adequate oxygen transfer to support rates of 180g phenol/h · m3 and 216 g oxygen/h · m3. The biomass-sand ratios of 20–35 mg volatiles/g gave estimated biomass concentrations of 3–6 g volatiles/dm3. Offline kinetic measurements showed weak inhibition kinetics with constants ofKs=0.2 mg phenol/dm3, Ko2=0.5 mg oxygen/dm3 and KinI= 122.5 mg phenol/dm3. Very small biofilm diffusion effects were observed. Dynamic experiments demonstrated rapid response of dissolved oxygen to phenol changes below the inhibition level. Experimentally simulated continuous stagewise operation required three stages, each with 1 h residence time, for complete degradation of 300 mg phenol/dm3 · h.

Biological cyanide degradation in aerobic fluidized bed reactors: treatment of almond seed wastewater

The aim of this study was to select a support medium for an anaerobic biofilm fluidized bed reactor (AFBR) for waste water treatment. Six materials, shale, pumice, porous glass, quartz sand, activated carbon and anthracite were used as carriers for the biofilm. The reactors were operated in parallel for several months with vapour condensate from a sulfite cellulose process as feed. The criteria used for the evaluation were: a) Reproducibility of the reactor performance, b) performance of the different carriers under various loading rates, c) stability against toxic shock loadings using 2,4,6-trichlorophenol (TCP) as toxicant, d) recovery capacity after intoxication and starvation, e) adsorption/desorption behavior of the carriers.A comparison between four runs showed good reproducibility of the steady state removal rates. The performance of the reactors and the stability of the degradation rates were tested for a range of loading conditions. Unbuffered, buffered and pH controlled conditions were compared. The pumice carrier was best with respect to the degradation rate achieved per carrier mass. The response of the reactors to massive TCP step loadings was tested. Loadings less than 1.5 kg TCP/m3d resulted in initially normal gas production rates for all the systems, except the activated carbon, whose gas production was partially inhibited from the start. After increasing the load to 1.5 kg TCP/m3d the gas production rates of all the other reactors fell abruptly to zero. Restarting after 2 months, all reactors showed methanogenic activity without requiring new inoculum.Adsorption and desorption experiments with TCP showed that only the anthracite and activated carbon adsorbed appreciable amounts. The activated carbon had the greatest adsorption capacity but did not release the TCP by desorption, as did the anthracite.A bicomponent (pumice and anthracite) carrier mixture was compared in biological experiments with pumice and anthracite carrier alone, with and without TCP loading. The pumice and the carrier-mix performed equally well under non-toxic-loading conditions. With TCP toxic loading, the performance of the anthracite was superior. The anthracite carrier could be regenerated, owing mainly to its capacity for desorption.

Determining specific biomass activity in anaerobic wastewater treatment processes

The continuous aerobic transformation of synthetic cyanide waste-water, amygdalin solutions and almond seed extract containing cyanide was investigated in several fluidized bed reactors. Various inocula consisting of activated sludge or soil slurry were used. Successful inoculation was achieved with simple soil slurry. No significant influence was found between the performance of the systems inoculated with a cyanide contaminated soil and a garden soil. The performance and stability of the reactors with respect to degradation rate were tested for a range of cyanide loading conditions, with feed containing only cyanide, and with different additional carbon sources, as well as various C∶N ratios at a hydraulic retention time of 24 h. No growth with cyanide as the sole source of carbon and nitrogen was observed. The system with lactate as the organic C-source was capable of operating at cyanide concentrations of 160 ppm cyanide with a conversion rate of 0.125 kg cyanide/m3 d. Ammonia was the end product and the effluent concentration was 0.5 ppm CN−. The systems with ethanol as the organic C-source could degrade only 0.05 kg cyanide/m3 d, whose feed concentration was 60 ppm cyanide. Amygdalin, an organic cyanide-containing compound present in stone fruit seeds, was fed as a model substrate. Degradation rates up to 1.2 kg COD/m3 d could be measured with no free or organically bound cyanide in the effluent. These rates were limited by oxygen transfer, owing to the large amount of degradable COD. The further investigations with almond seed extracts, confirmed the applicability of the aerobic process to treat food-processing waste streams having low concentrations of cyanide with high COD content.

Gas measurement methods for laboratory-scale anaerobic reactors.

An experimental method for the measurement of specific gas production rate was developed and tested with biomass samples taken from anaerobic fluidized bed reactors, operating with a variety of carriers with molasses, condensate from cellulose production and brewery wastewater as feeds. The method is based on reactor sampling and offline gas volume measurement during a known time interval. Important factors are biomass and liquid sampling under oxygen-free conditions, using the liquid from the reactor as substrate, providing sufficient mixing and maintaining the physical integrity of the biomass. The method was developed in such a way that small samples (20 ml) were taken under anaerobic conditions (poising agent) for short-term (2–3 min.) gas rate measurements in a small fluidized bed (25 ml) batch reactor with U-tube. Biomass content was measured by an instrumental nitrogen method (Dumas), followed by weight determination of the carrier. The gas rates measured with the test system, and their dependence on substrate concentration, were in good agreement with those directly measured from the continuous fluidized bed reactor. Additions of molasses and acetate to the sample proved that the influence of concentration on the biomass activity can be obtained only by operating the continuous reactor at the concentration levels of interest. Comparison between the reactors showed large differences in the specific activity and the total reactor activity. It was found when comparing two reactors, that the values of the specific and the total activities permitted the calculation of the relative biomass quantities. In this way the influence of the carrier-type could be evaluated.

Non-Invasive On-Line Investigations of Industry Style Bioreactors

Various methods exist to measure gas production from anaerobic reactors but not all can easily be used to obtain the rate directly, and some are limited by small flow rates. A review of gas measurement methods is given. Two simple online gas monitoring systems, are described. The reactor design with respect to liquid overflow and gas take-off is shown to be important.