Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules

Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were 0.21 g chemical oxygen demand (COD) g⁻¹ N, 0.09 h⁻¹, and 9.1 mg N L⁻¹, respectively, whereas the corresponding values for NOB were 0.05 g COD g⁻¹ N, 0.11 h⁻¹, and 4.85 mg N L⁻¹, respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules.     

A study on using fireclay as a biomass carrier in an activated sludge system

By adding a biomass carrier to an activated sludge system, the biomass concentration will increase, and subsequently the organic removal efficiency will be enhanced. In this study, the possibility of using excess sludge from ceramic and tile manufacturing plants as a biomass carrier was investigated. The aim of this study was to determine the effect of using fireclay as a biomass carrier on biomass concentration, organic removal and nitrification efficiency in an activated sludge system. Experiments were conducted by using a bench scale activated sludge system operating in batch and continuous modes. Artificial simulated wastewater was made by using recirculated water in a ceramic manufactutring plant. In the continuous mode, hydraulic detention time in the aeration reactor was 8 and 22 h. In the batch mode, aeration time was 8 and 16 h. Fireclay doses were 500, 1,400 and 2,250 mg l⁻¹, and were added to the reactors in each experiment separately. The reactor with added fireclay was called a Hybrid Biological Reactor (HBR). A reactor without added fireclay was used as a control. Efficiency parameters such as COD, MLVSS and nitrate were measured in the control and HBR reactors according to standard methods. The average concentration of biomass in the HBR reactor was greater than in the control reactor. The total biomass concentration in the HBR reactor (2.25 g l⁻¹ fireclay) in the continuous mode was 3,000 mg l⁻¹ and in the batch mode was 2,400 mg l⁻¹. The attached biomass concentration in the HBR reactor (2.25 g l⁻¹ fireclay) in the continuous mode was 1,500 mg l⁻¹ and in the batch mode was 980 mg l⁻¹. Efficiency for COD removal in the HBR and control reactor was 95 and 55%, respectively. In the HBR reactor, nitrification was enhanced, and the concentration of nitrate was increased by 80%. By increasing the fireclay dose, total and attached biomass was increased. By adding fireclay as a biomass carrier, the efficiency of an activated sludge system to treat wastewater from ceramic manufacturing plants was increased.     

Nitrate removal in a packed bed reactor using volatile fatty acids from anaerobic acidogenesis of food wastes

A packed bed reactor (PBR) was fed with nitrate containing synthetic wastewater or effluent from a sequencing batch reactor used for nitrification. The C source introduced into the PBR consisted of volatile fatty acids (VFAs) produced from anaerobic acidogenesis of food wastes. When nitrate loading rates ranged from 0.50 to 1.01 kg N/m³·d, the PBR exhibited 100∼98.8% NO₃ ⁻-N removal efficiencies and nitrite concentrations in the effluent ranged from 0 to 0.6 NO₂ ⁻-N mg/L. When the PBR was further investigated to determine nitrate removal activity along the bed height using a nitrate loading rate less than 1.01 kg N/m³·d, 100% nitrate removal efficiency was observed. Approximately 83.2% nitrate removal efficiency was observed in the lower 50% of the packed-bed height. When reactor performance at a C/N ratio of 4 and a C/N ratio of 5 was compared, the PBR showed better removal efficiency (96.5%) of nitrate and less nitrite concentration in the effluent at the C/N ratio of 5. VFAs were found to be a good alternative to methanol as a carbon source for denitrification of a municipal wastewater containing 40 mg-N/L.     

Effects of Cr(VI) on the performance and kinetics of the activated sludge process

The substrates removal performance, removal kinetics and the electron transport system (ETS) of sludge were investigated by sequencing batch reactors (SBR) and batch assays, respectively. Compared to the control system, significant decreases were observed in substrate removal efficiency with the Cr(VI)-feeding concentration up to 5 mg L⁻¹ in SBR system. And the recovery for NH₄⁺-N removal were more difficult than that of COD after the termination of Cr(VI)-feeding. Significant inhibitory effects of Cr(VI) on the ETS activity and substrate removal kinetics were observed in the batch assays. The inhibitory effects of Cr(VI) would be overestimated on COD removal and underestimated on NH₄⁺-N removal by the short-term batch assay as compared to the long-term operations. Additionally, significant correlations between the ETS activity and the inhibitory rates of Cr(VI) on substrate removal indicated the ETS activity can provide effective predictions on the potential performance of substrate removal in activated sludge.     

Adsorption and decolorization kinetics of methyl orange by anaerobic sludge

Adsorption and decolorization kinetics of methyl orange (MO) by anaerobic sludge in anaerobic sequencing batch reactors were investigated. The anaerobic sludge was found to have a saturated adsorption capacity of 36 ± 1 mg g MLSS⁻¹ to MO. UV/visible spectrophotometer and high-performance liquid chromatography analytical results indicated that the MO adsorption and decolorization occurred simultaneously in this system. This process at various substrate concentrations could be well simulated using a modified two-stage model with apparent pseudo first-order kinetics. Furthermore, a noncompetitive inhibition kinetic model was also developed to describe the MO decolorization process at high NaCl concentrations, and an inhibition constant of 3.67 g NaCl l⁻¹ was estimated. This study offers an insight into the adsorption and decolorization processes of azo dyes by anaerobic sludge and provides a better understanding of the anaerobic dye decolorization mechanisms.     

Anaerobic treatment of low-strength wastewater with a high fraction of particulate matter in an unconventional two-phase ASBRs system

The results of a two-phase anaerobic system using anaerobic sequencing batch reactors (ASBRs), treating low-strength wastewater (COD ∼ 500 mg/L) with a high fraction of particulate organic matter (70%, COD basis), are presented. Two reactors in series were used; the first one was hydrolytic–acidogenic, while the second one was methanogenic. This configuration was proposed to promote high efficiency solids removal. During the experiment, 69% and 50% efficiencies of total COD removal were obtained for OLRs of 0.63 and 1.22 kgCOD/(m³ d), respectively. Values of the solubilized organic fraction (SOF) achieved in the hydrolytic–acidogenic reactor were within the range of 0.3–0.6 gCOD_solubilized/gpCOD_removed, and the average acidified organic fraction (AOF) was 0.6 gCOD_VFA-produced/gsCOD_fed. The methanogenic reactor had a VFA removal fraction (VFARF) between 0.4 and 0.6 gCOD_VFA-removed/gCOD_VFA-fed for the OLR of 0.63 and 1.22. The two-phase ASBR system is suitable, and can be implemented, for the anaerobic treatment of this kind of wastewater.     

Properties of phenol-removal aerobic granules during normal operation and shock loading

The physical structure and activity of aerobic granules, and the succession of bacterial community within aerobic granules under constant operational conditions and shock loading were investigated in one sequencing batch reactor over ten months. While the maturation phase of the granulation process began on day 30, the structure of microbial community changed markedly until after three months of reactor operation under constant conditions with a loading rate of 1.5 g phenol L⁻¹ day⁻¹. A shock loading of 6.0 g phenol L⁻¹ day⁻¹ from days 182–192 led to divergence of bacterial community, an inhibition of the biomass activity, and a decrease in phenol removal rate in the reactor. However, phenol was still completely removed under this disturbance. After the shock loading, the mean sizes of aerobic granules increased, and the activity of the microbial population within the granules decreased, although there appeared highly resilient for the dominant bacterial community of aerobic granules which mainly included β-Proteobacteria. Correlation analysis suggested that biomass concentration and biomass loading were significantly related to the community composition of aerobic granules during the whole operational period. The development of a relatively stable bacterial community in aerobic granules implied that those distinct dominant microbes in aerobic granules were favorably selected and proliferated under the operational conditions.     

Model-based process analysis of partial nitrification efficiency under dynamic nitrogen loading

In this study, the ammonia removal efficiency for high ammonia-containing wastewaters was evaluated via partial nitrification. A nitrifier biocommunity was first enriched in a fill-and-draw batch reactor with a specific ammonium oxidation rate of 0.1 mg NH₄ ⁻-N/mg VSS.h. Partial nitrification was established in a chemostat at a hydraulic retention time (HRT) of 1.15 days, which was equal to the sludge retention time (SRT). The results showed that the critical HRT (SRT) was 1.0 day for the system. A maximum specific ammonium oxidation rate was achieved as 0.280 mg NH₄ ⁻-N/mg VSS.h, which is 2.8-fold higher than that obtained in the fill-and-draw reactor, indicating that more adaptive and highly active ammonium oxidizers were enriched in the chemostat. Dynamic modeling of partial nitrification showed that the maximum growth rate for ammonium oxidizers was found to be 1.22 day⁻¹. Modeling studies also validated the recovery period as 10 days.     

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.     

Kinetic studies on autohydrogenotrophic growth of <Emphasis Type="Italic">Ralstonia eutropha</Emphasis> with nitrate as terminal electron acceptor

Autohydrogenotrophic batch growth of Ralstonia eutropha H16 was studied in a stirred-tank reactor with nitrate and nitrite as terminal electron acceptors and the sole limiting substrates. Assuming product inhibition by nitrite, saturation kinetics with the two limiting substrates and a simple switching function, which allows growth on nitrite only at low nitrate concentrations, resulted in a kinetic growth model with nine model parameters. The data of two batch experiments were used to identify the kinetic model. The kinetic model was validated with two additional batch experiments. The model predictions are in very good agreement with the experimental data. The maximum nitrite concentration was estimated to be 30.7 mM (total inhibition of growth). After complete reduction of nitrate, the growth rate decreases almost to zero before it increases again because of the following nitrite respiration. The maximum autohydrogenotrophic growth rate of Ralstonia eutropha with nitrate as a final electron acceptor (0.509 d⁻¹) was found to be reduced by 90–95% compared to the so far reported autohydrogenotrophic growth rates with oxygen.     

Continuous bio-catalytic conversion of sugar mixture to acetone–butanol–ethanol by immobilized <Emphasis Type="Italic">Clostridium acetobutylicum</Emphasis> DSM 792

Continuous production of acetone, n-butanol, and ethanol (ABE) was carried out using immobilized cells of Clostridium acetobutylicum DSM 792 using glucose and sugar mixture as a substrate. Among various lignocellulosic materials screened as a support matrix, coconut fibers and wood pulp fibers were found to be promising in batch experiments. With a motive of promoting wood-based bio-refinery concept, wood pulp was used as a cell holding material. Glucose and sugar mixture (glucose, mannose, galactose, arabinose, and xylose) comparable to lignocellulose hydrolysate was used as a substrate for continuous production of ABE. We report the best solvent productivity among wild-type strains using column reactor. The maximum total solvent concentration of 14.32 g L⁻¹ was obtained at a dilution rate of 0.22 h⁻¹ with glucose as a substrate compared to 12.64 g L⁻¹ at 0.5 h⁻¹ dilution rate with sugar mixture. The maximum solvent productivity (13.66 g L⁻¹ h⁻¹) was obtained at a dilution rate of 1.9 h⁻¹ with glucose as a substrate whereas solvent productivity (12.14 g L⁻¹ h⁻¹) was obtained at a dilution rate of 1.5 h⁻¹ with sugar mixture. The immobilized column reactor with wood pulp can become an efficient technology to be integrated with existing pulp mills to convert them into wood-based bio-refineries.     

Continuous preparation of (S)-3-hydroxy-3-phenylpropionate by asymmetric reduction of 3-oxo-3-phenylpropionic acid ethyl ester with <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> CGMCC No.2266 in a membrane reactor

In this study, (S)-3-hydroxy-3-phenylpropionate was prepared continuously by coupling microbial transformation and membrane separation. The effect of several factors on membrane flux, reactor capacity, and reaction conversion were investigated. A kinetic model of the continuous reduction process was also developed. The appropriate molecular weight cut-off of the ultrafiltration membrane was 30 kDa. The reactor capacity reached a maximum of 0.136/h at a biomass concentration and membrane flux of 86 g/L (dry weight/reaction volume) and 20 mL/h, respectively. The (S)-3-hydroxy-3-phenylpropionate yield was 3.68 mmol/L/day after continuous reduction over seven days. The enantiometric excess of (S)-3-hydroxy-3-phenylpropionate reached above 99.5%. The kinetic constants of continuous reduction were as follows: r _m = 3.00 × 10⁻³ mol/L/h, k _cat = 3.49 × 10⁻⁴ mol/L/h, k ₁ = 3.09 × 10⁻² mol/L, and k ₂ = 5.00 × 10⁻⁷ mol/L. The kinetic model was in good agreement with the experimental data obtained during continuous reduction. Compared with batch reduction, continuous reduction can significantly improve the catalytic efficiency of microbial cells and increase the reactor capacity.     

Biodegradation kinetics of methyl iso-butyl ketone by acclimated mixed culture

Methyl iso-butyl ketone (MIBK) is a widely used volatile organic compound (VOC) which is highly toxic in nature and has significant adverse effects on human beings. The present study deals with the removal of MIBK using biodegradation by an acclimated mixed culture developed from activated sludge. The biodegradation of MIBK is studied for an initial MIBK concentration ranging from 200–700 mg l⁻¹ in a batch mode of operation. The maximum specific growth rate achieved is 0.128 h⁻¹ at 600 mg l⁻¹of initial MIBK concentration. The kinetic parameters are estimated using five growth kinetic models for biodegradation of organic compounds available in the literature. The experimental data found to fit well with the Luong model (R ² = 0.904) as compared to Haldane model (R ² = 0.702) and Edward model (R ² = 0.786). The coefficient of determination (R ²) obtained for the other two models, Monod and Powell models are 0.497 and 0.533, respectively. The biodegradation rate found to follow the three-half-order kinetics and the resulting kinetic parameters are reported.     

Kinetics of a fluidized-bed reactor for ground-water denitrification

A fluidized-bed reactor, with sand as the carrier and ethanol as the carbon and electron source, was investigated for the biological denitrification of ground water. The paper concentrates on the reactor's kinetics, with special emphasis on nitrite as the intermediate product. Intrinsic zero-order kinetic parameters for both nitrate and nitrite were determined by batch and continuous experiments. Values for the maximum specific nitrate and nitrite removal rates of 11 g and 6 g NO _inf3 ^sup– (g volatile suspended solids)^–1 day^–1, respectively, were obtained. These values were used to interpret nitrate and nitrate concentration profiles in an experimental fluidized-bed reactor operating at different conditions of hydraulic loading and retention time.     

Enrichment and granulation of Anammox biomass started up with methanogenic granular sludge

A sequencing batch reactor (SBR) seeded with methanogenic granular sludge was started up to enrich Anammox (Anaerobic Ammonium Oxidation) bacteria and to investigate the feasibility of granulation of Anammox biomass. Research results showed that hydraulic retention time (HRT) was an important factor to enrich Anammox bacteria. When the HRT was controlled at 30 days during the initial cultivation, the SBR reactor presented Anammox activity at t = 58 days. Simultaneously, the methanogenic granular sludge changed gradually from dust black to brown colour and its diameter became smaller. At t = 90 days, the Anammox activity was further improved. NH₄⁺-N and NO₂⁻N were removed simultaneously with higher speed and the maximum removal rates reached 14.6 g NH₄⁺-N /(m³ _reactor·day) and 6.67 g NO₂⁻-N /(m³ _reactor·day), respectively. Between t = 110 days and t = 161 days, the nitrogen load was increased to a HRT of 5 days (70 mg/l NH₄⁺ and 70 mg/l NO₂), the removal rates of ammonium and nitrite were 60.6% and 62.5% respectively. The sludge changed to red and formed Anammox granulation with high nitrogen removal activity.     

Biological nitrification–denitrification with alternating oxic and anoxic operations using aerobic granules

Efficient nitrification and denitrification of wastewater containing 1,700 mgl⁻¹ of ammonium-nitrogen was achieved using aerobic granular sludge cultivated at medium-to-high organic loading rates. The cultivated granules were tested in a sequencing batch reactor (SBR) fed with 6.4 or 10.2 kg NH₄⁺-N m⁻³ day⁻¹, a loading significantly higher than that reported in literature. With alternating 2 h oxic and 2 h anoxic operation (OA) modes, removal rate was 45.5 mg NH₄⁺-N g⁻¹ volatile suspended solids⁻¹ h⁻¹ at 6.4 kg NH₄⁺-N m⁻³ day⁻¹ loading and 41.3 ± 2.0 at 10.2 kg NH₄⁺-N m⁻³ day⁻¹ loading. Following the 60 days SBR test, granules were intact. The fluorescence in situ hybridization and confocal laser scanning microscopy results indicate that the SBR-OA granules have a distribution with nitrifers outside and heterotrophs outside that can effectively expose functional strains to surrounding substrates at high concentrations with minimal mass transfer limit. This microbial alignment combined with the smooth granule surface achieved nitrification–denitrification of wastewaters containing high-strength ammonium using aerobic granules. Conversely, the SBR continuous aeration mode yielded a distribution with nitrifers outside and heterotrophs inside with an unsatisfactory denitrification rate and floating granules as gas likely accumulated deep in the granules.     

Modeling of <Emphasis Type="Italic">Fusarium redolens</Emphasis> Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production

Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20–50 g l⁻¹ glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l⁻¹) than in the batch culture (194 mg l⁻¹). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures.     

Amaranth decoloration by Trametes versicolor in a rotating biological contacting reactor

Sequential batch and continuous operation of a rotating biological contacting (RBC) reactor and the effects of dissolved oxygen on the decoloration of amaranth by Trametes versicolor were evaluated. Amaranth belongs to the group of azo dyes which are potential carcinogens and/or mutagens that can be transformed into toxic aryl amines under anaerobic conditions. Cultivation of T. versicolor in a stirred tank reactor was found to be unsuitable for amaranth decoloration due to significant biomass fouling and increase in medium viscosity. Assuming that decoloration follows first-order kinetics, amaranth was decolorized more rapidly when T. versicolor was immobilized on jute twine in a RBC reactor operated either in a sequential batch (k=0.25 h^–1) or in a continuous (0.051 h⁻¹) mode compared to a stirred tank reactor (0.015 h⁻¹). Oxygen was found to be essential for decoloration with the highest decoloration rates occurring at oxygen saturation. Although longer retention times resulted in more decoloration when the RBC was operated in the continuous mode (about 33% amaranth decoloration), sequential batch operation gave better results (>95%) under similar nutrient conditions. Our data indicate that the fastest decoloration should occur in the RBC using nitrogen-free Kirk’s medium with 1 g/l glucose in sequential batch operation at rotational speeds and/or aeration rates which maintain oxygen saturation in the liquid phase.     

Bioconversion of isopropanol by a solvent tolerant Sphingobacterium mizutae strain

The bioconversion of high concentration isopropanol (2-propanol, IPA) was investigated by a solvent tolerant strain of bacteria, which was identified as Sphingobacterium mizutae ST2 by partial 16S rDNA gene sequencing. This strain of bacteria exhibited the ability to utilise high concentration isopropanol as the sole carbon source, with mineralization occurring via an acetone intermediate into central metabolism. The biodegradative performance of this strain for IPA was examined over a 2–38 g l⁻¹ concentration range, using specific growth rate (μ) and conversion rate analysis. Maximum specific growth rates (μ_max) of 0.0045 h⁻¹ were routinely obtainable on IPA. In addition, the highest specific IPA degradation rate was obtained at a concentration of 7.5 g l⁻¹ with a corresponding value of 0.045 g IPA g cells⁻¹ h⁻¹. While the highest acetone yield reached its maximum value of 0.940 g acetone g IPA⁻¹ at 7.5 g IPA l⁻¹. This is the first report on bioconversion of isopropanol at such high concentration by this solvent tolerant strain of S. mizutae and may allow its application in novel biocatalytic processes for effective biological conversion in two-phase solvent systems.     

Selection and dominance mechanisms of denitrifying phosphate-accumulating organisms in biological phosphate removal process

A sequencing batch reactor under different electron acceptor conditions was operated serially to investigate the selection and dominance mechanisms of denitrifying phosphate-accumulating organisms (DNPAOs) in a biological nutrient removal process. The presence of a small amount of NO^– ₃ at the start of the anaerobic phase stimulated the selection of DNPAOs in an anaerobic/aerobic system, and switching O₂ to NO^– ₃ as an electron acceptor enhanced the activity of anoxic phosphate uptake.