Half-saturation Coefficient Research Articles

Optimal impulsive control in RNA interference mediated by exogenous dsRNA with physiological delays

Therapeutic agents acting on RNA, including RNA modification, RNA editing and RNA interference (RNAi), play a vital role in gene function study, signaling pathway, drug discovery, disease treatment, vaccine development and so on. Therein, RNAi as an emerging gene therapy has been widely applied in many cancer studies by silencing oncogenes or specific mRNA in malignant tumor cells. Mechanism and efficiency of RNAi are the key issues of RNAi technology. RNA silencing involves dynamic modeling, analyses and optimal control of RNAi gene system. Physiological delay and Hill response describing off-target are considerable elements involving RNAi efficiency. In this paper, we first formulate a four-dimensional RNAi model with time delays and Hill functions, and then investigate the complex dynamic behaviors including the number, existence and stability of internal equilibria and Hopf bifurcations of single delay and two delays. Furthermore, based on the specific mRNA degradation adopted in impulsive patterns, we build an optimal problem by adding exogenous dsRNA at alterable time points in variable dosages in a treatment session. By the method of gradient formula, we can find the optimal impulsive time and proportion of dsRNA. Finally, simulation indicates that (1) physiological lags not only raise the oscillations of mRNA but also cut down the levels of cost; (2) smaller delays and larger rates of siRNA–mRNA complex formation and dsRNA synthesis imply the rapid composition of RISC and fast synthesis of dsRNA leading to more desirable therapeutic schedule, which affords evidence for gene regulation and RNAi; (3) a larger half-saturation coefficient characterizes a unique and stable higher targeted mRNA, whereas a smaller half-saturation coefficient generates bistability in which the higher and lower targeted mRNAs simultaneously emerge; and (4) the bistability will provide a good guidance to control, suppress and degrade targeted mRNA.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

Kinetic studies and dynamic modeling of sophorolipids production by Candida catenulata using different carbon sources

Abstract The kinetic study on sophorolipids (SLs) production by Candida catenulata from glucose, raw sunflower soapstock was investigated at different initial concentrations ranging from 0 to 100 g L−1. The Monod model with a maximum specific growth rate (μ max) of 0.0167 h−1 and half-saturation coefficient (K S ) of 6.91 g L−1 best described the cell growth kinetics of C. catenulata on glucose. The best-fitted constants of the Monod model for raw sunflower soapstock were μ max = 0.0157 h−1 and K S = 16.01 g L−1. Determination of Luedeking-Piret constants indicated SLs mainly produced as an associated growth product in the systems. Dynamic features of the fermentation were modeled using the obtained constants and results showed the prediction power of the developed model in describing the behavior of the process. Also, a modified kinetic model was developed for the dynamic modeling of the dual carbon sources system.

A model-based approach for evaluating the effects of sludge rheology on methane production during high solid anaerobic digestion: Focusing on mass transfer resistance

Mass transfer process is vital for biochemical reactions, which is related to sludge rheology. But this inherent interaction has not yet been established for sewage sludge anaerobic digestion (AD). This work investigated the role of sludge rheology in bio-kinetics of AD. AD of sodium acetate and microcrystalline cellulose under different total solids (TS of 6.29%, 7.63%, 9.02%, 11.06%) of digested sludge was set up to identify the role of sludge rheology. Results showed that rheological properties, e.g., viscosity and viscoelasticity, increased with the increase of TS content. These resulted in negative effect on methane production of sodium acetate with lag phase increased from 0.93 d to 1.57 d, but almost no effect was observed for microcrystalline cellulose. An extended ADM1 model was developed, which revealed that enhanced sludge rheological properties increased mass diffusion resistance and reduced uptake rate of acetate. This effect can be described explicitly by mass transfer coefficient (kla_Sac). However, from the original ADM1, this effect was indistinctly lumped in apparent half-saturation coefficient (ksac). Based on the role of sludge rheology in mass transfer and bio-kinetics, it is suggested that modeling the methane production based on TS contents and sludge rheology is possible, which should be considered in giving an insight into the micro-scale phenomena (e.g. mass transport, bio-kinetics) in high solid AD.

Organic mass and nitrogen removal kinetic modeling in sequencing batch reactor

In this paper, the novelty consists of determining kinetic parameters for sequencing batch reactor (SBR) operated for the experimental design Nº1 (ED-1) under single (oxic) and combined biological sequences in two phases (anaerobic-oxic) treating a Chemical Oxygen Demand (COD) influent around 5,466 mg/L. ED-2 comprised three phases (anoxic I-oxic-anoxic II) with the influent containing COD (1,119-1,598 mg L−1), NH4 +-N (63-94.5 mg L−1 and Total Kjeldahl Nitrogen (126 - 175 mg L−1). Kinetic parameters corresponded to the substrate maximum utilization rate r(m,S) and the half-saturation coefficient (K s) The r (m,COD) and K s was increased as the biological phases were increased from single oxic phase (−60 mg L−1 h−1; 2704 mg L−1), anaerobic-oxic phases (−100 mg L−1 h−1; 1,069.8 mg L−1) to the anoxic I –oxic-anoxic II phases (−250 mg L−1 h−1). The kinetic coefficients were significant in the first anoxic and the oxic phases of SBR, for conventional and simultaneous nitrification-denitrification.

Upgrading ADM1 by Addition of Lag Phase Sub-model to Simulate Acidic Inhibition of Methanogenic Reactor

This study is aimed at improving calculation quality for IWA Anaerobic Digestion Model No.1 (ADM1) to simulate acidic failure of the methane fermentation systems and its performance recovery. The methanogen collected from digestate at a municipal wastewater treatment plant was cultivated in a lab-scale continuous reactor receiving acetate as a sole organic source. By varying the influent concentration during 400 days of operation, 6 datasets of acidification events were obtained to simulate the concentrations of acetate, VSS, pH, and the methane production rate. The ADM1 equipped with either pH sub-model or undissociated acetate sub-model could reproduce the deterioration of reactor performance in the acidic failure but totally failed to simulate the recovery in the subsequent lowered volumetric loading rate. The statistical analysis revealed both ADM1 models had relatively low correlation coefficient (Nash-Sutcliffe model efficiency coefficient (NSE)) of 0.31–0.38 although these were considerably improved from that without parameter calibration (NSE = −0.04). To cope with the mismatch, a lag phase sub-model was developed. The sub-model is composed of the remaining relative activity of the microorganism at which the inhibition peaked, and the half-saturation coefficient to express the specific length of lag phase. By adding the sub-model into the calibrated ADM1, NSE was significantly improved to 0.49–0.53.

Significance of enriched culture on the assessment of the acute inhibitory impact of sulfamethoxazole on nitrifying biomass

AbstractBACKGROUNDAutotrophic microorganisms are quite vulnerable to environmental conditions and to inhibitory actions that would upset nitrification mechanisms. A reliable numerical assessment of the adverse impact is needed for proper remedial action. This study focused on the kinetic response of the nitrifying fraction within the activated sludge biomass under acute exposure to sulfamethoxazole (SMX), utilizing and emphasizing the role of enriched culture. A mixed culture sustained with an enrichment technique was used to generate oxygen uptake rate profiles, where ammonia was the sole substrate with different SMX concentrations.RESULTSModel calibration studies yielded specific growth rates of 1.40/day for the ammonia oxidizing fraction and 0.65/day for the nitrite oxidizing fraction acting as the rate limiting step for the overall nitrification process. SMX did not appreciably affect the specific growth rates, but it induced a significant increase in half saturation coefficients. Moreover, increased endogenous decay rates were estimated.CONCLUSIONModel calibration values indicated that SMX induced competitive inhibition on microbial growth and enhanced endogenous respiration due to an increasing demand for the maintenance energy to activate antibiotic resistance. This underlines the merit of further studies on conditions to sustain resistant microorganisms capable of tolerating and even degrading antibiotics in biological systems. © 2022 Society of Chemical Industry (SCI).

Kinetic modelling of yeast growth and pollutant removal in secondary effluent

In recent years, there has been significant interest in yeast-based wastewater treatment due to its high pollutant removal rate and ability to perform in non-sterile environments. In this work, a kinetic model was developed to predict yeast growth and substrate consumption during wastewater treatment. To determine the biological constants for use in the kinetic models, a unique approach is presented. Candida utilis was cultivated in synthetic wastewater, using eight different ratios of carbon, nitrogen and phosphorus to determine its growth rate, and the removal rates of carbon, nitrogen, and phosphorus. The concentrations of C, N and P were chosen within the range of secondary effluent wastewater. In all experiments, carbon was found to be the limiting substrate, and 100 % TOC removal was achieved in all cases. Candida utilis reduced the COD concentration by up to 99 % in <24 h. In the model, both yeast growth and substrate consumption were satisfactorily described by Monod kinetics. The apparent half-saturation coefficients for carbon, nitrogen, and phosphorus, determined via the optimization of the model, were found to the function of initial substrate concentration. The maximum specific growth rate found was 0.59 h−1. This model was used on different initial concentrations of substrates, and predicted data with an R2 above 80 %. Both model and experimental results suggest that Candida utilis can be used in the tertiary treatment of wastewater. The simple approach described here can be applied to find biological coefficients for other microorganisms.

Biokinetic Study of Microbial Decontamination of Oilfield Produced Water

This work was aimed at identifying microbials and determining the biokinetic parameters for bio-decontamination of oilfield produced water. An extant physical treatment unit for produced water was re-engineered and retrofit with a discontinuous aerobic bioreactor (Bio-Unit) system. The Bio-Unit was operated in a fill-and-draw sequence and the rates of total organic carbon (TOC) removal and biomass growth were monitored. The isolated microbial strains were identified as Bacillus, Pseudomonas and Chryseobacterium spp. The biokinetic parameters of the bio-detoxification process were determined by fitting experimental data into the Monod Equation. The maximum specific substrate utilization rate (k_m), maximum specific growth rate (μ(m,h )), substrate half saturation coefficient (K(STOC )), yield (Y), and endogenous decay rate (b_h), were found to be 0.20 day-1, 0.31 day-1, 2.7 mg TOC/l, 1.6 mg MLSS/mg TOC, and 0.23 day-1, respectively. These values are within the range published in literatures for oilfield produced water, thus will suffice for designing, modeling and control of biological treatment systems, since biokinetic parameters for real oilfield produced water treatment using discontinuous biological configuration is scanty.

Biodegradation modeling of phenol using Curtobacterium flaccumfaciens as plant-growth-promoting bacteria

Phenol is a major worry pollutant resulting from industrialized manufacturing and chemical reactions. The growth kinetics and biodegradation of phenol were initially investigated using C. flaccumfaciens, a recently identified plant growth stimulating bacterium. Based on the Haldane inhibition model, Haldane's growth kinetics inhibition coefficient (Ki), half-saturation coefficient (Ks), and the maximum specific growth rate (max) for phenol-dependent growth kinetics were estimated to be 329 (mg/L), 9.14 (mg/L), and 1.05 (h−1), respectively. With a sum of squared error (SSR) of 1.36 × 10−3, the Haldane equation is well adapted to empirical data. The improved Gombertz model also accurately predicts phenol biodegradation trends. The rate of phenol biodegradation and the lag time both increased as the initial phenol concentrations were increased. C. flaccumfaciens growth and phenol biodegradation were best achieved at a pH of 7.0 at a temperature of 28 °C incubation. A phenol biodegradation mechanism by C. flaccumfaciens has been proposed. In conclusion, this study revealed the ability of C. flaccumfaciens to promote plant growth and biodegrade phenol simultaneously. This could aid in rhizoremediation and crop yield preservation in phenol-stressed conditions.

Light attenuation in enriched purple phototrophic bacteria cultures: Implications for modelling and reactor design

Light attenuation in enriched purple phototrophic bacteria (PPB) cultures has not been studied, and its understanding is critical for proper process modelling and reactor design, especially for scaled systems. This work evaluated the effect of different biomass concentrations, reactor configurations, wastewater matrices, and growth conditions, on the attenuation extent of near infra-red (NIR) and ultraviolet-visible (UV–VIS) light spectra. The results show that increased biomass concentrations lead to higher light attenuation, and that PPB absorb both VIS and NIR wavelengths, with both fractions of the spectrum being equally absorbed at biomass concentrations above 1,000 g COD·m−3. A flat plate configuration showed less attenuation compared with cylindrical reactors illuminated from the top, representative for open ponds. Neither a complex wastewater matrix nor the presence of polyhydroxyalkanoates (under nutrient limited conditions) affected light attenuation significantly. The pigment concentration (both bacteriochlorophyll and carotenoids) however, had a strong effect, with significant attenuation in the presence of pigments. Attenuation predictions using the Lambert-Beer law (excluding scattering) and the Schuster model (including scattering) indicated that light scattering had a minimal effect. A proposed mathematical model, based on the Lambert-Beer law and a Monod function for light requirements, allowed effective prediction of the kinetics of photoheterotrophic growth. This resulted in a half saturation coefficient of 4.6 W·m−2. Finally, the results showed that in dense outdoor PPB cultures (≥1,000 g COD·m−3), effective light penetration is only 5 cm, which biases design away from horizontal lagoons, and towards non-incident multi-panel systems such as flat plate reactors.

Kinetic modelling of high concentration 4-Nitrophenol biodegradation by an isolated bacterial consortium and post-treatment ecotoxicity analysis

The present study documents the kinetics of aerobic batch growth and biodegradation of 4-Nitrophenol (4-NP) by an isolated bacterial consortium capable of utilizing 700 mg l−1 of 4-NP as the sole source of carbon and energy, the highest reported concentration to be biodegraded till date. The results of the batch biodegradation studies suggested that the consortium exhibited substrate inhibition kinetics and the Haldane model fitted the experimental data well. The estimated biokinetic parameters applied to biomass growth were maximum specific growth rate, μmax = 0.1532 h−1, half saturation coefficient, Ks = 4.717 mg l−1, and inhibition coefficient, Ki = 77.34 mg l−1. The specific degradation rate, q, was fitted to the model, and the kinetic parameters obtained were: qmax = 0.1700 g g−1 h−1, K's = 5.871 mg l−1, and K'i = 171.9 mg l−1. The yield coefficient (YX/S) varied in the range of 0.93–0.23 g g−1 for 12–700 mg l−1 4-NP concentration. The maintenance coefficient (m) and true yield (YG) were calculated to be 0.04491 h−1 and 0.9496 g g−1, respectively, based on the Pirt's equation. Furthermore, cytotoxicity and phytotoxicity assessment involving the animal cell line HEK293 and different seed variants, respectively, confirmed the detoxification of the biodegraded product, emphasizing the biocatalytic efficiency of the consortium in the bioremediation of 4-NP contaminated wastewater and suitability of its environmental discharge.

Plant Growth-Promoting Rhizobium Nepotum Phenol Utilization: Characterization and Kinetics

Phenol is a severe pollutant that harms the environment and, potentially, human health. This study aimed to investigate the biodegradability of phenol by the plant growth-promoting bacterium R. nepotum. That included studying the growth kinetics and the effects of growth conditions such as incubation temperature, pH, and the use of different substrate concentrations. As the primary substrate, six different starting concentrations of phenol were utilized. The ability of these cells to biodegrade phenol was greatly influenced by the culture conditions. After 36 and 96 hours of incubation at pH 7 and a temperature of 28 C, this organism grew the fastest and had the highest phenol biodegradation. The biodegradation rate is much higher at 700 mg/L, the highest of the six concentrations tried. In less than 96 hours of incubation, more than 90% of the phenol (700 mg/L) had been eliminated. The Haldane model has been the most accurate for determining the relationship between the initial concentration of phenol and growth rate. In contrast, the refined Gompertz model provided the most accurate depiction of phenol biodegradation over time. As predicted by the Haldane equation, the highest specific growth rate, half-saturation coefficient, and Haldane's growth kinetics inhibition coefficient are 0.7161 h1, 15.8 parts per million (ppm), and 292 parts per million (ppm), respectively. The equation of Haldane successfully fitted the experimental data by reducing the SSR (sum of squared errors) to 3.8x10 3. According to the results of the analysis by GC-MS for the bacterial culture sample, the hydroxylase enzyme was the first to convert the phenol molecule into catechol. The catechol was subsequently broken down into 2-hydroxymucconic semialdehyde by the 2,3-dioxygenase enzyme, which occurred through the meta-pathway. It is the first study showing that R. nepotum, a plant growth promoter, has high efficiency of phenol. In phenol-stressed conditions, this could help with rhizoremediation and crop yield preservation.

Thermodynamic approach to simulate current densities of energy-harvesting microbial electrochemical systems fed with human urine

Different theoretical models have been addressed to simulate electricity generation of microbial electrochemical systems (MESs) fed with a variety of organics. In the case of urine-fed MESs (u-MESs), the lack of input parameters to feed current bio-physical models has somehow restrained their theoretical approach. This study introduces a model, based on microbial energetics, to simulate current generation of u-MESs without the need of resorting to parameters typically used as simulation entries in bio-physical approaches (e.g., maximum substrate-utilization rates (qmax), Monod half-saturation coefficients (KS)). The strategy consisted in linking the catabolic energy density available in the urine medium to the specific electro-active microbial growth-rate, the latter calculated from metabolic thermodynamics (Gibbs free-energy changes for the catabolic/anabolic reactions, and Gibbs energy dissipation). Calculated growth rates were used to compute specific substrate-utilization rates, the effective flux of electrons into the anode biofilm and the resulting current densities as a function of urine concentration.

Biodegradation of bisphenol A using psychrotolerant bacterial strain Pseudomonas palleroniana GBPI_508.

A psychrotolerant bacterial strain of Pseudomonas sp. (P. palleroniana GBPI_508), isolated from the Indian Himalayan region, is studied for analyzing its potential for degrading bisphenol A (BPA). Response surface methodology using Box-Behnken design was used to statistically optimize the environmental factors during BPA degradation and the maximum degradation (97%) was obtained at optimum conditions of mineral salt media pH 9, experimental temperature 25°C, an inoculum volume of 10% (v/v), and agitation speed 130rpm at the BPA concentration 270mgL-1. The Monod model was used for understanding bacterial degradation kinetics, and 37.5mg-1 half saturation coefficient (KS) and 0.989 regression coefficient (R2) were obtained. Besides, the utmost specific growth rate µmax was witnessed as 0.080h-1 with the GBPI_508 during BPA degradation. Metabolic intermediates detected in this study by GC-MS were identified as valeric acid, propionic acid, diglycolic acid, and phenol. The psychrotolerant bacterial strain of Pseudomonas sp. (P. palleroniana GBPI_508), isolated from the Indian Himalayan region has shown good potential for remediation of BPA at variable conditions.

Phenol biodegradation by plant growth promoting bacterium, S. odorifera: kinetic modeling and process optimization.

One of the main organic pollutants that could result from industrial products and chemical transformations is phenol. In the current study, the kinetics of Serratia odorifera, which was isolated from arable soil, was studied by growing it on broth minimal medium spiked with phenol as only carbon source and energy. The newly isolated plant growth-promoting bacterium (PGPB), S. odorifera, was used for the first time for phenol biodegradation. The growth kinetics parameters (phenol-dependent) including maximum specific growth rate (μmax), half-saturation coefficient (Ks), and the Haldane's growth kinetics inhibition coefficient (Ki), were tested via Haldane inhibition model and resulted on the 0.469 (h -1), 26.6 (mgL-1), and 292 (mgL-1), respectively. The sum of squared error (SSR) of 4.89 × 10-3 was fitted to the experimental data by Haldane equation. The results of phenol biodegradation were fitted into the modified Gombertz model. The increase of phenol concentrations led to increases in both the rate of phenol biodegradation and lagging time. The optimal phenol biodegradation and bacterial growth obtained by S. odorifera, were at 28°C incubation temperature and a pH of 7.0. The pathway of phenol biodegradation by S. odorifera was proposed in the current study to provide a new insight into synchronization of phenol biodegradation and plant growth-promoting bacteria. This may play an important role in remediation of phenol-contaminated soil besides promoting the plant growth, thus lessening the plant stress.

The effect of sludge retention time (SRT) on the Nitrifier typical kinetics at ambient temperature under the low ammonia density.

Sludge retention time (SRT) regulation is one of the essential management techniques for refined control of the main-sidestream treatment process under the low ammonia density. It is indispensable to understand the effect of SRTs changes on the Nitrifier kinetics to obtain the functional separation of the Nitrifier and the refined control of the nitrification process. In this study, Nitrifier was cultured with conditions of 35 ± 0.5 °C, pH 7.5 ± 0.2, DO 5.0 ± 0.5 mg-O/L, and SRTs were controlled for 40 d, 20 d, 10 d, and 5 d. The net growth rate (μm), decay rate (b), specific growth rate (μ), the yield of the Nitrifier (YA), temperature parameter (TA), and inhibition coefficient (KI) have been measured and extended with the SRT decreases. Instead, the half-saturation coefficient (KS) decreased. In addition, the limited value of pH inhibition occurs (pHUL), and the pH of keeping 5% maximum reaction rate (pHLL) was in a relatively stable state. The trade of kinetics may be induced by the change of species structure of Nitrifier. The Nitrosomonas proportion was increased, and the Nitrospira was contrary with the SRT decreasing. It is a match for the functional separation of Nitrifier when SRTs was 20 d at ambient temperature under the low ammonia density. The kinetics of ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO) in Nitrifier under different SRT conditions should be measured respectively to the refined control of the partial nitrification process in future study.

Comprehensive evaluation of starter culture impact on the bioreactor performance and microbial kinetics

The present study investigated the disregarded impact of microbial community composition, diversity and abundance of the starter biomass on lab-scale bioreactor performance, steady-state long time operation, biodegradation outcome and microbial kinetics. Standard lab-scale experiments are usually initiated with inoculum taken from wastewater treatment plants (WWTPs) without considering microbial community composition. Two identical sequencing batch bioreactors (SBR-1, SBR-2) were operated with inocula obtained from two domestic WWTPs to assess the role of inoculum composition on reactor performance and treatment efficacy. Filamentous microorganisms were dominated in SBR-1 (SVI: 265 mL/g), whereas their supremacy was diminished in SBR-2 (SVI: 160 mL/g). Next generation sequencing analyses verified high abundance of Candidatus Microthrix (14%) and Kouleothrix spp. (3%) in SBR-1. Although Chloroflexi C10-SB1A metagenome accounted for 16% of WWTP-2 community, SBR-2 was operated at steady-state for longer period without deterioration. Statistical indicators based on molecular studies showed that WWTP-2 has higher diversity than WWTP-1. Higher biodiversity in WWTP-2 community supported the stable process performance. Modelling studies denoted an increase in half saturation coefficients (Ks) in filamentous microorganisms dominated reactor. The results of this study provide insight on how the filamentous organisms typically found in WWTPs become a fundamental constituent during the bioreactor operation.

Temperature affects the oxidation kinetics of co-cultured Nitrobacter winogradskyi and Nitrobacter hamburgensis in nitrite-oxidizing bioreactor

Nitrobacter is an important chemolithoautotrophic nitrite-oxidizing bacteria and has exhibited potential for the oxidation of nitrite to nitrate in natural and engineered ecosystems. Microbial kinetics of Nitrobacter have been widely reported and are used to model the nitrite oxidation process and optimize the design parameters of the biological processes for wastewater treatment. However, limited information is available about the nitrite oxidation kinetics of the two coexisting Nitrobacter stains, namely the Nitrobacter winogradskyi and the Nitrobacter hamburgensis. The current work mainly focuses on the influence of temperature on the kinetic characteristics of the coexistence of N. winogradskyi and hamburgensis, which were enriched in a lab-scale sequencing batch reactor (SBR) through 419 operating cycles. The results for the kinetic properties of nitrite oxidation of the enrichments within the temperature range of 15–35 °C showed that the maximum specific rate (rmax), half-saturation coefficients (KS), growth-rate constants (μmax), and temperature coefficient (θ) lied within the ranges of 22.91–93.58 mM/g/d, 0.13–2.47 mM, 0.026–0.105 1/d, and 1.038–1.137, respectively. The maximum activity and nitrite affinities of tested microorganisms were sensitive to temperature. Furthermore, the relationships between temperature and normalized kinetic parameters (rmax, μmax, and θ) were developed as: 0.069T − 0.076 (15–30 °C), 0.0057T − 0.062 (15–30 °C), and 5.7T40.9+T+T210.5 (15–35 °C), respectively. Moreover, the capabilities of N. winogradskyi and N. hamburgensis to oxidize nitrite were lost at the temperature of 35 °C and were non-recoverable at temperature of 25 °C. Overall, the findings of the present work can provide available data for future study about the mathematic models of nitrification kinetics and ecological niche differentiation of Nitrobacter species.

Biological treatment of volatile organic compounds (VOCs)-containing wastewaters from wet scrubbers in semiconductor industry

This study investigated biological treatment for two kinds of volatile organic compounds (VOCs)-containing wastewaters collected from wet scrubbers in a semiconductor industry. Batch test results indicated that one wastewater containing highly volatile organic compounds was not suitable for aerated treatment conditions while the other containing much lower volatile organic compounds was suitable for aerobic treatment. Accordingly, two moving bed bioreactors, by adding commercial biocarrier BioNET, were operated under aerobic and anoxic conditions for treating low volatility wastewater (LVW) and high volatility wastewater (HVW), respectively. During 280 days of operation, the aerobic LVW bioreactor attained the highest chemical oxygen demand (COD) removal rate of 98.9 mg-COD/L/h with 81% of COD removal efficiency at hydraulic retention time (HRT) of 1 day. The anoxic HVW bioreactor performed above 80% of COD removal efficiency with the highest COD removal rate of 16.5 mg-COD/L/h at HRT of 2 days after 380 days of operation. The specific COD removal rates at different initial substrate-to-biomass (S0/X0) ratios, using either suspended sludge or microorganisms attached onto BioNET from both bioreactors, followed the Monod-type kinetics, while the half-saturation coefficients were generally higher for the microorganisms onto BioNET due presumably to relatively poor mass transfer efficiency. Based on the results of microbial community analysis using the next generation sequencing technique, the dominant communities of suspended sludge and BioNET, including nitrifiers, denitrifiers, and degraders for polycyclic aromatic hydrocarbons, were similar in the corresponded bioreactors, but microbial community shifts were observed with increased organic loadings.