Influence of 2,4-dinitrophenol on the characteristics of activated sludge in batch reactors

The response of activated sludge characteristics to the presence of 2,4-dinitrophenol (dNP) in batch cultures was investigated in this study. The sludge yield slightly decreased with an increase in dNP concentration. At 10 mg l(-1), or lower, dNP significantly reduced sludge yield and relative specific growth rates (mu/mu0), but didn't substantially affect its relative specific chemical oxygen demand removal rate (q/q0). Presence of dNP at 1-20 mg l(-1) increased the specific oxygen uptake rate of activated sludge, and slightly changed its hydrophobicity. An analysis on inhibition indicated that the reduction in sludge yield in the presence of dNP was mainly attributed to the significant decreased sludge growth, rather than the reduced substrate degradation.     

Anaerobic digestion of cheese whey using up-flow anaerobic sludge blanket reactor

Anaerobic treatment of cheese whey using a 17·5-litre up-flow anaerobic sludge blanket reactor was investigated in the laboratory. The reactor was studied over a range of influent concentration from 4·5 to 38·1 g chemical oxygen demand per litre at a constant hydraulic retention time of 5 days. The reactor start-up and the sludge acclimatization were discussed. The reactor performance in terms of methane production, volatile fatty acids conversion, sludge net growth and chemical oxygen demand reduction were also presented in this paper. Over 97% chemical oxygen demand reduction was achieved in this experiment. At the influent concentration of 38·1 g chemical oxygen demand per litre, an instability of the reactor was observed. The results indicated that the up-flow anaerobic sludge blanket reactor process could treat cheese whey effectively.     

Biological kinetic behaviors and operational performances in aerated and oxygenated systems

Biological kinetic behaviors of the oxygenated and aerated activated sludge process were studied and compared in both once-through and constant sludge recycle systems. The models derived by Herbert, Elsworth, and Telling [J. Gen. Microbiol., 14 , 601 (1956)] and Ramanathan and Gaudy [Biotechnol. Bioeng., 11 , 207 (1969)] were used for the studies of once-through and constant sludge recycle systems, respectively. Soft drink waste water was used for the growth limiting substrate. Temperature was controlled within 30 ± 2°C. The influent substrate concentration was maintained at 1,000 mg/liter. The experiments were conducted at various dilution rates (from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{9} $\end{document} to 1/1.0 hr^?1), and recycle solids concentration values (from 5,000 to 10,000 mg/liter), with hydraulic recycle ratio, α, at 0.3. Biological kinetic constants were evaluated and compared. It was found that these constants were different for the aerated and oxygenated systems within a certain range of dilution rates studied. The critical dilution rates for diluting out effluent chemical oxygen demand (COD) occurred at 0.1 and 0.2 hr^?1in the once-through operation, and 0.2 and 0.4 hr^?1in the sludge recycle operation for aerated and oxygenated systems, respectively. Observed sludge yield values and specific growth rate were varied with the type of aeration and with and without constant sludge recycle concentration applied. Sludge carbohydrates and proteins content in the oxygenation system (cell recycle) were 10.1–21.6% and 35.6–52.2%. Sludge volume index in the air and oxygenation systems varied from 41.4 to 354 and 31.9 to 58.5, respectively.     

Electricity generation from bio-treatment of sewage sludge with microbial fuel cell

A two-chambered microbial fuel cell (MFC) with potassium ferricyanide as its electron acceptor was utilized to degrade excess sewage sludge and to generate electricity. Stable electrical power was produced continuously during operation for 250 h. Total chemical oxygen demand (TCOD) of sludge was reduced by 46.4% when an initial TCOD was 10,850 mg/l. The MFC power output did not significantly depend on process parameters such as substrate concentration, cathode catholyte concentration, and anodic pH. However, the MFC produced power was in close correlation with the soluble chemical oxygen demand (SCOD) of sludge. Furthermore, ultrasonic pretreatment of sludge accelerated organic matter dissolution and, hence, TCOD removal rate in the MFC was increased, but power output was insignificantly enhanced. This study demonstrates that this MFC can generate electricity from sewage sludge over a wide range of process parameters.     

Bio-oxidation of a refractory gold bearing high arsenic sulphide concentrate: A pilot study

Abstract: A modular mobile bioleach pilot plant has been designed and constructed by Coastech Research Inc. The pilot plant was designed to be transported on two flatbed trucks to any location in North America for on-site piloting.The first bioleach demonstration pilot study was completed on a refractory gold bearing high arsenic (7.5% As) sulphide (28.9cf S) flotation concentrate. A production capacity of up to 562 kg per day at a feed solids concentration of approximately 14Of (w/w) solids and overall retention time of 115 h was achieved under steady operating conditions. Sulphide oxidation exceeded 75% while almost complete arsenic solubilization was observed for the final bioleached product. Oxygen and carbon dioxide uptake rates were obtained from off gas analyses. Oxygen uptake rates as high as 0.99 kg h^-1 m³ were observed. A critical dissolved oxygen concentration, to maintain chemical oxidation, within the range of 0.7-1.1 ppm was observed. Carbon dioxide uptake ratcs were decreased at dissolved oxygen concentrations below approximately 0.7-0.5 ppm. Gold extraction was enhanced from approximately 5% for the pretreated flotation concentrate, to in excess of 90% for the final bioleached product. A worker environment monitoring program was undertaken during the pilot plant operation. All samples taken for air-borne and urinary monitoring were below their respective time weighted average exposure limits.     

Effect of dissolved oxygen concentration on sludge settleability

This laboratory study presents a detailed evaluation of the effects of dissolved oxygen concentration and accumulation of storage polymers on sludge settleability in activated sludge systems with an aerobic selector. The oxygen and substrate availability regime were simulated in laboratory sequencing batch reactor systems. The experiments showed that low dissolved oxygen concentration (1.1 mg O₂ l^–1) had a strong negative effect on sludge settleability, leading to the proliferation of filamentous bacteria (Thiothrix spp., Type 021N and Type 1851). This negative effect was stronger at high chemical oxygen demand loading rate. This indicates that a compartmentalised (plug flow) aerobic contact tank, designed at short hydraulic residence time to guarantee a strong substrate gradient, with low dissolved oxygen concentration, might be worse for sludge settleability than an "overdesigned" completely mixed contact tank. Contrary to the general hypothesis, the maximum specific acetate uptake rate, poly--hydroxybutyrate production rate, and resistance to short starvation periods are similar in both poor- and well-settling sludge. The results of this study support our previous hypothesis on the importance of substrate gradients for the development of filamentous structures in biological flocs, from soluble organic substrate gradients to dissolved oxygen gradients in sludge flocs.     

High-rate anaerobic treatment of wastewater at low temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8 degrees C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids-1 day-1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40 degrees C.     

Respiratory relationships of a symbiotic algal-bacterial culture for wastewater nutrient removal

A continuous symbiotic algal-bacterial system was developed consisting essentially of a mixed Chlorella-activated sludge culture which would efficiently remove nutrients from wastewater under aerobic conditions without supplementary aeration. Oxygen decline data were fitted to a mathematical model used to predict respiratory rates, photosynthetic oxygenation, and steady-state oxygen concentrations. Stable relative biological populations and a dissolved oxygen concentration of about 2 mg/1 were maintained during steady-state operation with daily harvesting of excess biomass. Respiratory and physiological relationships indicated that the carbon dioxide-oxygen balance is a primary control that governs the steady-state operation of a symbiotic algal-bacterial culture. The close association of the algae and bacteria resulted in an algal-bacterial floc with settled rapidly yielding a clear supernatant.     

Osmotic, biomass, and oxygen effects on the growth rate of Fusarium oxysporum using a dissolved-oxygen-controlled turbidostat

The system described is a modified Hospodka's turbidostat. This device helps to measure the maximum growth rate of fungi in steady-state aerobic conditions with defined and independent concentration of dissolved oxygen, biomass, and substrate even unlimited. The principle consists of a turbidostat controlled by the dissolved oxygen concentration. The inlet medium pump operates when the dissolved oxygen concentration falls below the set point value. This method allows us to study independently effects of different physical and chemical variables on the maximum specific growth rate of microorganisms. A fungus, Fusarium oxysporum 47 isolated from soil, does not show a depressive effect on growth when dissolved oxygen concentration decreases to 5% and osmotic potential to -25 bars. Increasing biomass concentration in the range 0.1-1.0 g/L appears to depress markedly the maximum growth rate.     

The pH mediated effects of initial glucose concentration on the transitory occurrence of extracellular metabolites, gas exchange and growth yields of aerobic batch cultures of Klebsiella pneumoniae

The changes in growth kinetics in aerobic batch cultures of Klebsiella pneumoniae were followed by measurements of extracellular metabolites, rates of gas exchange, dissolved oxygen tension, pH, and carbon balance at all stages of growth. When the initial growth-limiting glucose concentration in media without pH control was increased from 1.0 g carbon L(-1) to 2.2 g carbon L(-1), the number of different, mainly acidic, extracellular metabolites of glucose at the end of exponential growth increased, while the proportion of acetate decreased. During the postexponential growth phase, the extracellular metabolites were oxidized, resulting in an increasing complexity of changes in pH, gas exchange, and dissolved oxygen tension with increasing initial substrate concentration. All these parameters showed concomitant stepwise changes. This pattern was independent of the dissolved oxygen tension in the range 30-200 muM. When pH was kept constant, the number, slope, and relative magnitude of the steps in gas exchange and dissolved oxygen tension were pH-dependent, being most complex at low pH. Detailed carbon balances showed that 20% of the initial glucose was converted into extracellular metabolites at the end of exponential growth at neutral pH. In the postexponential phase, pyruvate (2%) was reoxidized first followed by acetate (13%). The observed molar growth yield coefficient (Y(ATP)) was 8.4 if the transitory occurrence of pyruvate and acetate was accounted for, and 6.4 if it was neglected. The corrected observed molar growth yield coefficient (Y'(ATP)) was 9.4 and compared well with the true molar growth yield coefficient (Y(Max) (ATP)), which was found to be 11.0. Specific in situ respiration rates of the exponential growth phase of cultures grown at different controlled pH values compared well with in situ values for energy-limited chemostat grown cells at the same growth rates, suggesting that growth in the batch culture was energy-limited throughout the exponential growth phase. This view was supported by low levels of intracellular glycogen and exopolysaccharides of all cultures, by the value of Y'(ATP) of 9.4, and by a constant specific production rate of the extracellular metabolites throughout exponential growth. It was concluded that even under strictly aerobic conditions, control of pH is as important as control of dissolved oxygen tension during growth of enterobacteriaceae in batch cultures.     

Continuous culture of Thiorhodaceae

Summary In sulfide limited continuous culture of a marine isolate of Chromatium vinosum, sulfide was undetectable in steady states below dilution rates of 0.06h^-1, that is 1/2 of the maximum specific growth rate. In the same range, sulfur is assumed to attain the role of the growth rate limiting substrate. Furthermore, it could be shown that the rate of sulfur oxidation is a function of the surface area of the sulfur globules rather than of the sulfur concentration. In completely filled chemostats, steady states were obtainable only at dilution rates not exceeding 0.09 h^-1. In the presence of a nitrogen flushed gas phase, steady states were obtained at dilution rates approaching the maximum specific growth rate (0.12h^-1). This phenomenon is ascribed to the particular sulfide tolerance of our strain of Chromatium vinosum. The saturation constant and the inhibition constant (lowest, respectively highest total sulfide concentration at which the specific growth rate is equal to one-half of the maximum specific growth rate in the absence of inhibition) were 0.007 mM and 0.85 mM, respectively.The ecological significance of the data is discussed.Contribution No. 2406 from the Woods Hole Oceanographic Institution.     

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.     

Effect of hydraulic retention time on membrane fouling and biomass characteristics in submerged membrane bioreactors

In this paper, three identical membrane bioreactors (MBRs) were operated in parallel in order to specify the influence mechanism of hydraulic retention time (HRT) on MBR. The results showed that the removal efficiency of chemical oxygen demand (COD) was stable though it decreased slightly as HRT decreased, but biomass activity and dissolved oxygen (DO) concentration in sludge suspension decreased as HRT decreased. The filamentous bacteria grew easily with decreasing HRT. The extracellular polymeric substances (EPS) concentration and sludge viscosity increased significantly as filamentous bacteria excessively grew. The over growth of filamentous bacteria, the increase of EPS and the decrease of shear stress led to the formation of large and irregular flocs. Furthermore, the mixed liquid suspended solids (MLSS) concentration and sludge viscosity increased significantly as HRT decreased. The results also indicated that sludge viscosity was the predominant factor that affecting hydrodynamic conditions of MBR systems.     

The effect of dissolved oxygen and aeration rate on antibiotic production of Streptomyces fradiae

Different dissolved oxygen concentrations and aeration rates were imposed on a stable mutant of Streptomyces fradiae during the antibiotic-producing phase. At high aeration rate (1 vvm), the tylosin yield in the fermentor broth with dissolved oxygen (DO) concentrations controlled close to 100% saturation (6-8 ppm) increased 10% as against uncontrolled. The rates of cellular growth, oil consumption, and tylosin production were severely reduced when DO concentration fell below 25% saturation, but all resumed to their initial rates when DO was raised to saturation level again. The DO concentration in combination with air flow rate affected the pattern of the antibiotics produced. At high DO levels, an additional macrolide antibiotic, macrocin, was synthesized to more than one-third the amount of tylosin at high aeration rate (1 vvm). On the other hand, tylosin production rate remained constant and no significant amount of macrocin was produced at low aeration rate (0.2 vvm).     

High-Rate Anaerobic Treatment of Wastewater at Low Temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8°C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids⁻¹ day⁻¹, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40°C.     

Use of continuous-culture techniques for determining the growth kinetics of a celluloytic Thermoactinomyces sp.

In order to better understand the kinetics of cellulose degradation by Thermoactinomyces sp., continuous-culture experiments were performed utilizing the various intermediates of cellulose degradation as the feed substrates. Steady-state data from the glucose runs suggest that this organism has a growth yield of 0.42 g cell/g glucose, and a specific maintenance of 0.24 g glucose/g cell/hr. The Monod equation did not seen to model the growth well, since a plot of 1/D vs. 1/S gave a maximum specific growth rate that was even lower than one of the steady-state dilution rates. A dynamic washout experiment suggested a maximum specific specific growth rate of 0.36 hr^?1 and indicated that glucose is only slightly growth inhibitory as the inhibition constant, K_i, is 19 g glucose/liter. An equation for substrate concentration for washout conditions was derived. This equation predicted the transient glucose concentration relatively well. A fill-and-draw technique was investigated for determination of the growth parameters. It was not successful because of difficulties in contamination and accurately monitoring the dissolved oxygen in the small highly agitated vessel. However, the technique could be useful in studying the growth characteristics of sludge in a waste treatment system where contamination is not a worry. One could cover the medium surface and use a nonsterilizable dissolved oxygen probe of high sensitivity membrane to overcome these difficulties.     

Effect of dissolved oxygen control on growth and antibiotic production in Streptomyces clavuligerus fermentations.

A proportional-integral control system was used to control dissolved oxygen in a fermentor at constant shear and mass transfer conditions. Growth and antibiotic production in Streptomyces clavuligerus were studied at different dissolved oxygen levels during the fermentation. Three protocols were employed: no-oxygen control to provide a base case, oxygen controlled to a preset saturation level throughout the fermentation, and oxygen controlled at a high level only during the growth phase. The last protocol was aimed at optimizing the consumption of oxygen. Lower specific growth rates and cephamycin C yields were obtained when dissolved oxygen was controlled at 50% throughout the fermentation, compared to the base case. A 2.4-fold increase in the final cephamycin yield was observed when dissolved oxygen was controlled at saturation levels during the growth phase, compared to the experiments without dissolved oxygen control. This enhancement in yield was independent of the dissolved oxygen (DO) level after exponential growth, in the range of 50-100% saturation. The most effective control strategy, therefore, was to control DO only during active growth when the biosynthetic enzymes were probably synthesized.     

Modeling and simulation of oxygen-limited partial nitritation in a membrane-assisted bioreactor (MBR)

Combination of a partial nitritation process and an anaerobic ammonium oxidation process for the treatment of sludge reject water has some general cost-efficient advantages compared to nitrification-denitrification. The integrated process features two-stage autotrophic conversion of ammonium via nitrite to dinitrogen gas with lower demand for oxygen and no external carbon requirement. A nitrifying membrane-assisted bioreactor (MBR) for the treatment of sludge reject water was operated under continuous aeration at low dissolved oxygen (DO) concentrations with the purpose of generating nitrite accumulation. Microfiltration was applied to allow a high sludge retention time (SRT), resulting in a stable partial nitritation process. During start-up of the MBR, oxygen-limited conditions were induced by increasing the ammonium loading rate and decreasing the oxygen transfer. At a loading rate of 0.9 kg N m(-3) d(-1) and an oxygen concentration below 0.1 mg DO L(-1), conversion to nitrite was close to 50% of the incoming ammonium, thereby yielding an optimal effluent within the stoichiometric requirements for subsequent anaerobic ammonium oxidation. A mathematical model for ammonium oxidation to nitrite and nitrite oxidation to nitrate was developed to describe the oxygen-limited partial nitritation process within the MBR. The model was calibrated with in situ determinations of kinetic parameters for microbial growth, reflecting the intrinsic characteristics of the ammonium oxidizing growth system at limited oxygen availability and high sludge age. The oxygen transfer coefficient (K(L)a) and the ammonium-loading rate were shown to be the appropriate operational variables to describe the experimental data accurately. The validated model was used for further steady state simulation under different operational conditions of hydraulic retention time (HRT), K(L)a, temperature and SRT, with the intention to support optimized process design. Simulation results indicated that stable nitrite production from sludge reject water was feasible with this process even at a relatively low temperature of 20 degrees C with HRT down to 0.25 days.     

Dependence of nitrogenase switch-off upon oxygen stress on the nitrogenase activity in Azotobacter vinelandii.

Azotobacter vinelandii was grown diazotrophically in chemostat cultures limited by sucrose, citrate, or acetate. Specific activities of cellular oxygen consumption (qO2) and nitrogenase (acetylene reduction) were measured in situ at different dilution rates (D, representing the specific growth rate mu at steady state). Sucrose-limited cultures exhibited linear relationships between qO2 and D, each of which, however, depended on the dissolved oxygen concentration in the range of 12 to 192 microM O2. From these plots, qO2 required for maintenance processes (mO2) were extrapolated. mO2 values did not increase linearly with increasing dissolved oxygen concentrations. With citrate- or acetate-limited cultures qO2 also depended on D. At 108 microM O2, however, qO2 and mO2 of the latter cultures were significantly lower than those of sucrose-limited cultures. Specific rates of acetylene reduction increased linearly with D, irrespective of the type of limitation and of the dissolved oxygen concentration (J. Kuhla and J. Oelze, Arch. Microbiol. 149:509-514, 1988). The reversible switch-off of nitrogenase activity under oxygen stress also depended on D and was independent of qO2, mO2, or the limiting substrate. Increased switch-off effects resulting from increased stress heights could be compensated for by increasing D. Since D represents not only the supply of the carbon source but also the supply of electrons and energy, the results suggest that the flux of electrons to the nitrogenase complex, rather than qO2, stabilizes nitrogenase activity against oxygen inactivation in aerobically growing A. vinelandii.     

Biodegradation of tech-hexachlorocyclohexane in a upflow anaerobic sludge blanket (UASB) reactor

Biodegradability of technical grade hexachlorocyclohexane (tech-HCH) was studied in an upflow anaerobic sludge blanket reactor (UASB) under continuous mode of operation in concentration range of 100-200 mg/l and constant HRT of 48 h. At steady state operation more than 85% removal of tech-HCH (upto 175 mg/l concentration) and complete disappearance of beta-HCH was observed. Kinetic constants in terms of maximum specific tech-HCH utilization rate (k) and half saturation velocity constant (K(L)) were found to be 11.88 mg/g/day and 8.11 mg/g/day, respectively. The tech-HCH degrading seed preparation, UASB reactor startup and degradation in continuous mode of operation of the reactor is presented in this paper.