Maximum Specific Utilization Rate Research Articles

Kinetics and Performance of Biological Activated Carbon Reactor for Advanced Treatment of Textile Dye Wastewater

The kinetics and performance of a biological activated carbon (BAC) reactor were evaluated to validate the proposed kinetic model. The Freundlich adsorption capacity (Ka) and adsorption intensity constants (n) obtained from the batch experiments were 1.023 ± 0.134 (mg/g) (L/mg)1/n and 2.036 ± 0.785, respectively. The effective diffusivity (Ds) of the substrate within the activated carbon was determined by comparing the adsorption model value with the experimental data to find the best fit value (4.3 × 10–4 cm2/d). The batch tests revealed that the yield coefficient (Y) was 0.18 mg VSS/mg COD. Monod and Haldane kinetics were applied to fit the experimental data and determine the biokinetic constants, such as the maximum specific utilization rate (k), half-saturation constant (KS), inhibition constant (Ki), and biomass death rate coefficient (kd). The results revealed that the Haldane kinetics fit the experimental data better than the Monod kinetics. The values of k, KS, Ki, and kd were 3.52 mg COD/mg VSS-d, 71.7 mg COD/L, 81.63 mg COD/L, and 4.9 × 10−3 1/d, respectively. The BAC reactor had a high COD removal efficiency of 94.45% at a steady state. The average influent color was found to be 62 ± 22 ADMI color units, and the color removal efficiency was 73–100% (average 92.3 ± 10.2%). The removal efficiency for ammonium was 73.9 ± 24.4%, while the residual concentration of ammonium in the effluent was 1.91 ± 2.04 mg/L. The effluent quality from the BAC reactor could meet the discharge standard and satisfy the reuse requirements of textile dye wastewater.

Kinetics of Cometabolic Transformation of 4-chlorophenol and Phenol Degradation by Pseudomonas putida Cells in Batch and Biofilm Reactors

The biodegradation kinetics of 4-chlorophenol (4-CP) and phenol and microbial growth of Pseudomonas putida (P. putida) cells were estimated in batch and biofilm reactors. The kinetic parameters of cells on phenol were determined using the Haldane formula. The maximum specific growth rate of P. putida on phenol, the half-saturation constant of phenol and the self-inhibition constant of phenol were 0.512 h−1, 78.38 mg/L and 228.5 mg/L, respectively. The yield growth of cells on phenol (YP) was 0.618 mg phenol/mg cell. The batch experimental results for the specific transformation rate of 4-CP by resting P. putida cells were fitted with Haldane kinetics to evaluate the maximum specific utilization rate of 4-CP, half-saturation constant of 4-CP, and self-inhibition constant of 4-CP, which were 0.246 h−1, 1.048 mg/L and 53.40 mg/L, respectively. The negative specific growth rates of cells on 4-CP obtained were fitted using a kinetic equation to investigate the true transformation capacity and first-order endogenous decay coefficient, which were 4.34 mg 4-CP/mg cell and 5.99 × 10−3 h−1, respectively. The competitive inhibition coefficients of phenol to 4-CP transformation and 4-CP to phenol degradation were 6.75 and 9.27 mg/L, respectively; therefore, phenol had a higher competitive inhibition of 4-CP transformation than the converse. The predicted model examining cometabolic transformation of 4-CP and phenol degradation showed good agreement with the experimental observations. The removal efficiencies for phenol and 4-CP were 94.56–98.45% and 96.09–98.85%, respectively, for steady-state performance.

Kinetics of nutrients remediation from sugar industry effluent-treated substrate using Agaricus bisporus: mushroom yield and biochemical potentials.

This study investigated the yield and biochemical potential of Agaricus bisporus mushroom cultivated on agricultural waste substrate supplemented with treated sugar industry effluent (SIE). Laboratory-scale experiments were performed for the cultivation of A. bisporus on a mixture of wheat straw and sugar cane bagasse moistened with different doses of borewell water (BWW) and treated SIE (0-100%). Besides this, the simultaneous effects of the SIE amendment on total Kjeldahl's nitrogen (TKN) and total phosphorus (TP) contents of substrate and kinetics of their utilization by A. bisporus were studied. Results showed a relatively higher utilization of TKN (38.10 ± 1.60%) and TP (47.4 ± 6.44%) in a 25:75 ratio of BWW and SIE, respectively. The kinetics studies of TKN and TP utilization using Lineweaver-Burk models described the maximum specific utilization rates (V max) of 0.165 and 0.125mg·kg-1·d-1 and saturation points (K m ) of 72.401 and 33.283mg·kg-1, respectively, which are in good agreement as indicated by R 2 values (> 0.90). In addition, the maximum significant (P < 0.01) yield (159.31 ± 8.85g·Kg-1), biological efficiency (106.21 ± 3.84%), total phenols (3.03 ± 0.07mg·g-1), ascorbic acid (0.44 ± 0.03mg·g-1), and β-carotene (3.36 ± 0.05μg·g-1) of A. bisporus were observed using the same treatment. Therefore, this paper reported sustainable utilization of TKN and TP nutrients from SIE for A. bisporus mushroom cultivation.

Acetic acid inhibition on methanogens in a two-phase anaerobic process

The inhibitory effect of acetic acid on methanogens in a two-phase anaerobic process was evaluated. The results in this study showed that some methanogens still existed in the acidogenic phase although their dominance in the total microbial community was only 1% compared to 9.6% in the methanogenic phase. The inhibition threshold of acetic acid on acidogenic phase methanogens was, however, higher than that on methanogenic phase methanogens. At pH 6.00, acetic acid inhibition on methanogenic phase methanogens was observed when acetic acid concentration was higher than 1619.47mg HAc/L although there was no obvious inhibition on acidogenic phase methanogens in the range of 1646.47–2781.19mg HAc/L. There was also no acetic acid inhibition on acidogenic phase methanogens at pH 5.50, 6.00 and 6.50 in the range of 565.29–2781.19mg HAc/L. However, for methanogenic phase methanogens, the inhibition was obvious and a second order substrate inhibition model, qs=qmS/[Ks+S+(S2/Ki)], could be adapted to describe the inhibition kinetics and mechanism of undissociated acetic acid on methanogenic phase methanogens. The results showed substrate saturation constant Ks, substrate inhibition constant Ki, and maximum specific utilization rate of acetic acid qm, were 1.66mg unHAc/L, 145.17mg unHAc/L, and 3.53mgHAc/LgMLVSSh, respectively.

Microbial kinetic model for the degradation of poorly soluble organic materials

A novel mechanistic model is presented that describes the aerobic biodegradation kinetics of soybean biodiesel and petroleum diesel in batch experiments. The model was built on the assumptions that biodegradation takes place in the aqueous phase according to Monod kinetics, and that the substrate dissolution kinetics at the oil/water interface is intrinsically fast compared to biodegradation kinetics. Further, due to the very low aqueous solubility of these compounds, the change in the substrate aqueous-phase concentration over time was assumed to approaches zero, and that substrate aqueous concentration remains close to the saturation level while the non-aqueous phase liquid (NAPL) is still significant. No former knowledge of the saturation substrate concentration (Ssat) and the Monod half-saturation constant (Ks) was required, as the term Ssat/(Ks + Ssat) in the Monod equation remained constant during this phase. The n-alkanes C10–C24 of petroleum diesel were all utilized at a relatively constant actual specific utilization rate of 0.01–0.02 mg-alkane/mg-biomass-hr, while the fatty acid methyl esters (FAMEs) of biodiesel were utilized at actual specific rates significantly higher with increasing carbon chain length and lower with increasing number of double bonds. The results were found to be in agreement with kinetic, genetic, and metabolic evidence reported in the literature pertaining to microbial decay rates, uptake mechanisms, and the metabolic pathway by which these compounds are assimilated into microorganisms. The presented model can be applied, without major modifications, to estimate meaningful kinetic parameters from batch experiments, as well as near source zone field application. We suggest the estimated actual microbial specific utilization rate (kC) of such materials to be a better measure of the degradation rate when compared to the maximum specific utilization rate (k), which might be orders of magnitude higher than kC and might never be observed in reality.

Nitrous Oxide (N&lt;SUB&gt;2&lt;/SUB&gt;O) Reduction by Denitrifying Bacteria: Relating Kinetics and Gene Expression

Nitrous Oxide (N2O) Reduction by Denitrifying Bacteria: Relating Kinetics and Gene ExpressionNitrous oxide is a potent greenhouse gas that can be formed in wastewater treatment, and there is increasing interest in its fate in treatment processes. In this research, kinetic parameters and denitrification-gene expression levels were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Batch tests were carried out with acetate as an electron donor and nitrate (NO3−), nitrite (NO2 −), or nitrous oxide (N2O) as electron acceptors. Tests also addressed concurrent growth on NO3− + N2O and NO2 − + N2O. The maximum specific growth rate μ for N2O was lower than that for NO3− or NO2 −. However, the maximum specific utilization rate q for N2O was 4.4 gN gCOD−1 d−1, compared to only 0.89 gN gCOD−1 d−1 for NO2 − reduction to...Author(s)J.P. PavissichB.L. Read-DailyK. SandbergF. SabbaR. NerenbergSourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Sep, 2012ISSN1938-6478DOI10.2175/193864712811708211Volume / Issue2012 / 12Content sourceWEFTECCopyright2012Word count300

Sensitivity Analysis of Phenol Degradation with Sulfate Reduction Under Anaerobic Conditions

This study derives a mathematical description of the kinetics of phenol degradation with sulfate reduction by an anaerobic mixed-culture biofilm on an inert medium. The model incorporates the mechanisms of diffusive mass transport and Monod kinetics. It is solved using both the orthogonal collocation method and Gear’s method. Sensitivity studies were performed to investigate the dependence of process dynamics on the model parameters pertaining to biokinetic parameters, liquid film mass transport, and the biofilm and reactor operational parameters. Sensitivity analysis quantifies the magnitude of the effect of each variable on the simulated results using the least-square method. The transient-state process dynamics are sensitive to the biokinetic parameters including yield coefficient of phenol-utilizing bacteria, Monod maximum specific utilization rate of phenol, and the decay coefficient of phenol-utilizing bacteria. The process efficiency is also sensitive to biofilm parameters such as biofilm density of phenol-utilizing bacteria and initial biofilm thickness , and to such operational parameters as the influent phenol concentration and the hydraulic retention time of the system. The process dynamics are relatively insensitive to mass transport parameters, including the film transfer coefficient of phenol and the diffusion coefficient of phenol. Sensitivity analysis of the process dynamics to model parameters helps determine how to alter process conditions to enhance removal efficiency.

Co-digestion of sewage sludge with glycerol to boost biogas production

The feasibility of adding crude glycerol from the biodiesel industry to the anaerobic digesters treating sewage sludge in wastewater treatment plants was studied in both batch and continuous experiments at 35 °C. Glycerol addition can boost biogas yields, if it does not exceed a limiting 1% (v/v) concentration in the feed. Any further increase of glycerol causes a high imbalance in the anaerobic digestion process. The reactor treating the sewage sludge produced 1106 ± 36 ml CH 4/d before the addition of glycerol and 2353 ± 94 ml CH 4/d after the addition of glycerol (1% v/v in the feed). The extra glycerol-COD added to the feed did not have a negative effect on reactor performance, but seemed to increase the active biomass (volatile solids) concentration in the system. Batch kinetic experiments showed that the maximum specific utilization rate ( μ max) and the saturation constant ( K S ) of glycerol were 0.149 ± 0.015 h −1 and 0.276 ± 0.095 g/l, respectively. Comparing the estimated values with the kinetics constants for propionate reported in the literature, it can be concluded that glycerol uptake is not the rate-limiting step during the process.

Kinetics of Chemoheterotrophic Microbially Mediated Reduction of Ferric EDTA and the Nitrosyl Adduct of Ferrous EDTA for the Treatment and Regeneration of Spent Nitric Oxide Scrubber Liquor

Biomass from a prototype reactor was used to investigate the kinetics of chemoheterotrophic reduction of solutions of ferric ethylenediaminetetraacetic acid (EDTA) and solutions containing the nitrosyl adduct of ferrous EDTA using ethanol as the primary electron donor and carbon source. A series of batch experiments were conducted using biomass extracted from the scrubber solution treatment and regeneration stage of a prototype iron EDTA-based unit process for the absorption of nitric oxide with subsequent biological treatment. Using a linear-sweep voltammetric method for analysis of the ferric EDTA concentration, iron-reducing bacteria were found to behave according to the Monod kinetic model, at initial concentrations up to 2.16 g chemical oxygen demand (COD) as ethanol per liter, with a half-velocity constant of 0.532 g COD as ethanol/L and a maximum specific utilization rate of 0.127 mol/L of ferric ethylenediamine-tetraacetic acid [Fe(III)EDTA]*(g volatile suspended solids [VSS]/L)d(-1). Based on batch analyses, biomass yield and endogenous decay values of iron-reducing bacteria were estimated to be 0.055 g VSS/g COD and 0.017 L/d, respectively. An average of 1.64 times the theoretical (stoichiometric) demand of ethanol was used to complete reduction reactions. Kinetics of the reduction of the nitrosyl adduct of ferrous EDTA are summarized by the following kinetic constants: half-velocity constant (Ks) of 0.39 g COD/L, maximum specific utilization rate (k) of 0.2 mol/L [NO x Fe(II)EDTA(2-)](g VSS/L)d(-1), and inhibition constant (K(I)) of 0.33 g COD/L, as applied to the modified Monod kinetic expression described herein. Based on batch analyses, the biomass yield of nitrosyl-adduct-reducing bacteria was estimated to be 0.259 g VSS/g COD, endogenous decay was experimentally determined to be 0.0569 L/d, and an average of 1.26 times the stoichiometric demand of ethanol was used to complete reduction reactions.

Optimization of Nitrogen Removal and Startup of Psyttalia Sewage Treatment Works

Bench scale experiments were conducted in order to finalize the design of the secondary treatment stage of Psyttalia Sewage Treatment Works that serves the Greater Athens area with a population equivalent of 3.5 million. Carbon and nitrogen removal efficiencies and activated sludge settling characteristics were determined through continuous flow experiments and determination of the maximum specific utilization rates of ammonia (AUR) and nitrate (NUR). According to the results of the pilot experiments the need arose for a significant increase in the initial design's anoxic volume to ensure a 70% average annual nitrogen removal. AUR experiments showed an insignificant inhibition to the nitrification process in the order of 0-30%, representative of typical domestic sewage. The findings of the pilot study were in good agreement with full scale data obtained during the start up of Psyttalia biological treatment plant. According to full scale data and AUR tests a very satisfactory nitrogen removal efficiency was obtained during start up. Finally both lab scale and full scale data indicated that the activated sludge plant operating on Psyttalia primary effluent that has a high oil and grease content, is prompt to experience foaming problems due to the excessive growth of filamentous microorganisms M. parvicella and Gordona amarae – like microorganisms.

Toluene removal in membrane bioreactors under recirculating and non-recirculating liquid conditions

A single-, dual- and multiple-tube dense phase silicone rubber membrane bioreactor were investigated for control of toluene-contaminated air under circulating and non-recirculating liquid conditions. A mathematical model was developed to describe the system. The reactors were seeded with a mixed bacterial consortium isolated from activated sludge and capable of aromatic biodegradation. After operating with recirculating liquid nutrient solution, the reactors were operated with no recirculation of the liquid, for 50 days or more in each instance. Average toluene removal measured in the single-tube reactor was 93 ppm with recirculating liquid and 102 ppm without recirculation of the liquid. Average removal measured in the dual-tube reactor was 396 ppm with recirculating liquid and 319 ppm without recirculation of the liquid. Operation under stagnant liquid conditions had no significant detrimental impact on bioreactor performance. Biokinetic parameters were measured for both the suspension and biofilm with values of the maximum specific utilization rate values (k) ranging from 0.01 to 0.42 h−1 and half saturation constant values (K S) ranging from 1.5 to 14.3 mg L−1. Results suggest that membrane bioreactors might be operated under non-recirculating liquid conditions without performance detriment, reducing or eliminating the energy requirements and costs associated with pump operation.

Comparison of Influence of Free Ammonia and Dissolved Oxygen on Nitrite Accumulation Between Suspended and Attached Cells

The shortcut biological nitrogen removal (SBNR) hybrid (suspended cells combined with attached cells) process is an innovative technology that nitrosofies ammonium to nitrite and then denitrifies nitrite to nitrogen gas. Theoretically, this results in a 25% savings of the oxygen needed for nitrification and a 40% of savings in carbon source needed for denitrification. In this study, the influences of free ammonia (FA) and dissolved oxygen (DO) concentrations on nitrite accumulation were investigated to find the optimal operational factors for stable nitrite accumulation over a long period. The maximum specific utilization rates for ammonium (qa) and nitrite (qn) were determined for suspended and attached cells taken from a bench-scale SBNR reactor and a pilot-scale livestock wastewater treatment plant reactor. For the ammonium and nitrite oxidations in both reactors, the attached cells were more resistant to the FA concentration, but were more significantly influenced by the DO concentration than the suspended cells. In addition, the effect of the DO concentration was more significant than that of the FA concentration for both types of cells from both reactors. In this SBNR hybrid system, a simultaneous manipulation of DO concentration (<1.5 mg l-1) and FA concentration (10-20 mg l-1) was required for maintaining high levels of nitrite accumulation.

1-Butanol Removal from a Contaminated Airstream under Continuous and Diurnal Loading Conditions

A polysulfone microporous membrane module was investigated for control of 1-butanol-contaminated gas streams. A diurnal loading condition, using two different butanol concentrations, was used to simulate startup and stop conditions associated with shift work. The membrane module was also used to remove 1-butanol from air under continuous loading conditions in a bioreactor. The reactors were seeded with a mixed bacterial consortium capable of butanol biodegradation. Biokinetic parameters for butanol utilization were determined for the culture to be a maximum specific utilization rate (k) equal to 4.3 d−1 and a half saturation constant (Ks) equal to 8.9 mg L−1. A biofilter running only with diurnal loading conditions giving a “40-hr workweek” had an average 1-butanol removal rate of 29% (111 ppm, 74 gm−3 hr−1) from a 350-ppm influent at the end of an 8-hr operational day. End-of-day removal varied between 4 and 67% during the operational period. With continuous steady-state operation followed by placement on a diurnal loading schedule and influent butanol concentrations increased to 700 ppm, butanol removal averaged 38% (269 ppm, 145 gm−3 hr−1). Under continuous loading, steady-state conditions, 1-butanol removal from the airstream was greater than 99% (200 ppm, 73 gm−3 hr−1). These results suggest that the bioreactor can be operated on a diurnal schedule or 40-hr week operational schedule without any decline in performance.

Influence of anaerobic culture acclimation on the degradation kinetics of various substrates.

The adaptation of an anaerobic culture (anaerobic sludge) to a specific substrate brings significant changes to its microbial population. These changes can be described by the sludge's ability to treat various substrates such as carbohydrates or proteins or "intermediate" products of anaerobic metabolism such as L-lactic, propionic, and acetic acids. The activity of the sludge with respect to a specific substrate is a critical parameter, because the anaerobic degradability of wastewaters depends strongly on it. This work examines and quantifies the differentiation of two anaerobic sludges of the same origin, following an adaptation period of about 18 months to lactose and gelatin, respectively. The acclimation has a significant effect on the maximum specific utilization rates of various compounds and on their apparent consumption kinetics. It is noticeable, however, that even if the anaerobic cultures were not exposed to a specific substrate for a prolonged period of time (more than a year), they still kept the ability of hydrolyzing or degrading it. In addition, the acclimation has an unquestionable effect on the stoichiometry of the production of volatile fatty acids and L-lactate. Finally, from codigestion experiments it is shown that codigestion of lactose and gelatin appears to have no effect on their hydrolysis kinetics in any of the lactose or gelatin acclimated cultures; specifically, the hydrolysis kinetics remained the same as calculated when lactose or gelatin were the only fed substrates. Similarly, the kinetics of L-lactate and D-glucose biodegradation seemed to be unchanged. On the other hand, codigestion has a significant effect on the production of L-lactic, propionic, and acetic acids, which can be attributed to the increased hydrogen production accompanying gelatin biodegradation.

Pelagic microbial activity in an arctic polynya: Testing for temperature and substrate interactions using a kinetic approach

To test the hypothesized inhibition of high‐latitude marine bacteria living at lower temperatures when organic matter is scarce, the effects of temperature and organic substrate concentration on pelagic microbial heterotrophy were investigated in the perennially cold surface waters of a summertime arctic polynya. Utilization (incorporation plus respiration) of radiolabeled amino acids was measured as a function of increasing added substrate concentration at in situ (subzero) temperature and under short‐term warming. Results analyzed using analysis of variance (ANOVA) showed that increased substrate concentration had a significant effect on utilization rates at all stations, suggesting that communities were always living well below saturating levels of substrate. About half of the communities sampled revealed a significant temperature response using ANOVA; interactions between temperature and substrate concentration were detected only rarely. Kinetic parameters, used to link microbial activity and substrate utilization with temperature sensitivity, exhibited mixed responses to short‐term warming. Maximum specific utilization rates showed the greater temperature sensitivity, with Q10 values ranging from 0.25 to 13. Specific affinities responded to temperature significantly at only about half of the stations in the polynya. Psychrophilic behaviors (e.g., highest specific affinities and oligotrophic capacities at lower incubation temperatures) were observed at stations most likely to be influenced by direct Arctic Ocean outflow. Complete agreement with the hypothesis of enhanced substrate requirement by bacteria living at subzero temperature was not found. An improved understanding of the diversity of cold‐tolerant and cold‐loving microorganisms is needed before generalizing or predicting the role of temperature in the cycling of organic matter at high latitudes.

Kinetics of an anaerobic fluidized bed reactor using biolite carrier

Start-up and steady state operation of anaerobic fluidized bed reactors (AFBRs) with biolite as the inert carrier material was studied. Start-up and concomitant biofilm development of AFBRs was performed using two common start-up techniques, the maximum efficiency profile (MEP) technique and the maximum load profile (MLP) technique. The MEP start-up technique increases the volumetric organic loading rates to the reactor gradually and is tied to the removal efficiency of the process. The MLP start-up technique maintains a moderately high but constant volumetric organic loading rate irrespective of reactor performance. Using sucrose-based wastewater as feed, both start-up techniques led to equally fast biofilm development and start-up times of approximately 5 weeks. However, the MEP technique resulted in more stable controlled reactor operation during the start-up period. The quick start-up confirms the high compatibility of biolite for bio-adhesion and the development of a healthy active biofilm.High concentrations of biofilm biomass achieved in AFBRs (69 g volatile biofilm solids (VBS)/L of expanded bed volume at an organic loading rate of 25 g COD/(Lùd)) allowed the successful treatment of wastewaters at high organic loading rates and organic removal efficiencies. During steady state experiments, organic removal efficiencies over 80% were obtained for organic loading rates as high as 20 g COD/(L∙d). It was found that the dependence of removal efficiency on hydraulic retention time is influenced by substrate concentration. Total biofilm yield was determined to be 0.08 g VBS/g COD removed, demonstrating the low net synthesis of solids in the AFBR. AFBRs had an average solids retention time of 150 days, corresponding to a washout factor of 0.01. Extrinsic kinetics of the AFBRs was determined to be zero order with a maximum specific utilization rate of 0.48 g COD/(g VBS∙d).AFBRs used to treat municipal landfill leachate with a BOD5:COD ratio of 0.86 achieved steady state COD removal efficiencies that ranged from 70% to 87%, depending on the reactor organic loading rate and the concentration of the leachate being treated. During leachate treatment, biofilm biomass gradually became "mineralized" as a result of precipitation of metal sulfides and carbonates. This eventually resulted in a decrease in biofilm microbial activity and the need for higher pumping rates to maintain the same degree of bed expansion. Key words: anaerobic, biological fluidized bed reactor, biolite, landfill leachate, sucrose, modeling, start-up, steady state kinetics.

Characterization of Functional Microorganism Groups and Substrate in Activated Sludge and Wastewater by AUR, NUR and OUR

Activated sludge functional microorganism groups: nitrifiers, denitrifiers and heterotrophs, were characterized through determinations of maximum specific utilization rates of ammonia (AUR) nitrate (NUR) and oxygen (OUR). Characterizations of the functional groups were done on activated sludges from a pilot plant and from full-scale plants. Influent wastewater covered a wide spectrum, including raw wastewater, primary wastewater and chemically pretreated wastewater. AUR determinations showed significant variation with influent COD:N ratio, and good agreement was found with expected rates from mathematical simulations. For increased contents of particles in influent wastewaters a decreased maximum OUR was found, while maximum NUR was slightly increased or not affected. Based on NUR and OUR the fraction of denitrifiers to heterotrophs was estimated in the range of 41-73% in nitrogen removal sludges. The results indicated that influent biomass is of significance for the obtained fraction of denitrifiers to heterotrophs. For a separate nitrification stage activated sludge without denitrification a fraction of denitrifiers of 15-20% was found. The results of endogenous NUR and OUR determinations indicated that hydrolysis of activated sludge COD takes place with the same rate under anoxic and aerobic process conditions.

In situ determination of kinetic parameters for biofilms: Isolation and characterization of oligotrophic biofilms

This article develops and utilizes an in situ technique to estimate the Monod half-maximum rate concentration, K(s) and the maximum specific utilization rate constant, k, for biofilms. The technique employs a curve-matching method with kinetic results from several short-term experiments with completely mixed biofilm reactors. Use of the in situ method eliminates the two drawbacks of using conventional suspended-growth measurements to characterize biofilm: possible alteration of cell physiology and a major investment to run the suspended-growth tests. Results with five cultures of biofilm-forming oligotrophs demonstrated the in situ technique and supported the hypothesis that K(s) values were lower for the biofilm oligotrophs than for typical copiotrophs.