Substrate Concentration Research Articles

Extraction, Purification and Characterization of Poly Phenol Oxidase from Potato and Apple and Inhibition of Enzymatic Browning

The purpose of this study was to determine the optimum conditions for the extraction of polyphenol oxidase (PPO) from potato and apple. PPO is found in a variety of fruits and vegetables and is the enzyme that causes browning reactions when handling damaged cells. At 405 nm, the enzyme activity was determined using spectrophotometry. PPO was researched to stop potato and apple from browning, which reduces their marketability. The outcomes showed that using an extraction buffer containing phosphate buffer (0.05 M, pH 6.6) was the optimum condition for the extraction of polyphenol oxidase from potato and apple. In addition, the results showed that as the temperature increased, the (PPO) activity increased, and the activity reached its peak at a temperature of 35 ͦC. The optimum pH value of (PPO) activity was 6.5 and we observed during the research that (PPO) decreased in strong acid condition and alkaline environments. Moreover, the results showed that the highest activity of polyphenol oxidase enzyme extracted from apple and potato was by using (O-dihydroxybenzene) as a substrate. As the concentration of the substrate increased, the (PPO) activity increased, reaching the optimum substrate concentration of 0.8%, and then its activity decreased. Also, we found that when using ascorbic acid, citric acid, and Na2SO3 as inhibitors, the activity of the polyphenol oxidase enzyme decreased with an increase in the concentration of ascorbic acid, citric acid, and Na2SO3. Sodium thiosulfate, 0.01 M ascorbic acid and 0.5% polyethylene glycol were extracted with an extraction ratio of 1:4 (w/v) for three minutes by using a blender. The purpose of study was to determine the optimum conditions for polyphenol oxidase extraction from potato and apple.

Substrate Competition of Diazotrophic Nitrous Oxide Assimilation Over Dinitrogen Fixation

AbstractNitrous oxide (N2O) is a potent greenhouse gas and is depleting the stratospheric ozone layer. Diazotrophic N2O assimilation to biomass represents a novel biological N2O consumption pathway in addition to canonical denitrification. Thermodynamically, N2O assimilation is more favorable than dinitrogen (N2) fixation in natural environments, especially under higher N2O concentration and cooler conditions. Via isotopic tracing experiments, N2O assimilation was detected on cultured diazotrophs Crocosphaera and Trichodesmium with specific rates from 1.27 ± 0.16 × 10−4 to 2.00 ± 0.25 × 10−4 hr−1 under elevated [N2O]/[N2] conditions (0.0005–0.01) within 24‐hr incubation. The rates of N2O assimilation during the light and dark periods were statistically insignificant compared with N2 fixation activity. In a eutrophic estuary, N2O assimilation was not detected in the absence of diazotrophic activity. A competitive substrate kinetic model with experimentally calibrated parameters successfully quantified rate ratios of N2O assimilation and N2 fixation in varying substrate concentrations. The low [N2O]/[N2] ratio in natural conditions leads to N2O assimilation rate being <0.1% of N2 fixation rate, rendering negligible impact of N2O assimilation. The model was also used to predict the time required for experimental detection of N2O assimilation in isotopic tracing experiments under varying [N2O]/[N2] ratios. This study enhances the mechanistic understanding of N2O assimilation by diazotrophs, broadening the microbial nitrogen cycle by a potential N2O sink and nitrogen source for production.

Lipase Enzyme Kinetics with the Addition of Avocado Seed Extract as an Inhibitor in Olive Oil

Free fatty acids are compounds resulting from the hydrolysis of triglycerides catalyzed by the enzyme lipase. Free fatty acids harm health if they enter the body in large amounts. Avocado seed extract can reduce free fatty acid levels by inhibiting lipase activity. This research is a type of true-experimental research that aims to determine the effect of variations in substrate concentration on lipase enzyme activity with the addition of avocado seed extract and to determine the impact of the addition of avocado seed extract as an inhibitor on lipase enzyme kinetics. Lipase activity was determined based on the amount of oleic acid formed using Cu acetate pyridine reagent by Uv-Vis spectrophotometry at a wavelength of 715 nm. Lipase enzyme kinetics were determined using the Lineweaver-Burk curve equation, a transformed form of the Michaelis-Menten equation. The results showed that 60% substrate concentration was the most effective in reducing lipase enzyme activity by 60%. In addition, the addition of avocado seed extract proved to act as a competitive inhibitor, with the KM value decreasing from 0.014 M to 0.004 M and Vmaks remaining relatively stable at 23.2 µM. This shows that avocado seed extract effectively reduces lipase enzyme activity, which has implications for reducing FFA levels in olive oil. Thus, this study concludes that avocado seed extract has great potential as a natural inhibitor agent in reducing lipase enzyme activity.

Non-Invasive Characterization of Different Saccharomyces Suspensions with Ultrasound.

In fermentation processes, changes in yeast cell count and substrate concentration are indicators of yeast performance. Therefore, monitoring the composition of the biological suspension, particularly the dispersed solid phase (i.e., yeast cells) and the continuous liquid phase (i.e., medium), is a prerequisite to ensure favorable process conditions. However, the available monitoring methods are often invasive or restricted by detection limits, sampling requirements, or susceptibility to masking effects from interfering signals. In contrast, ultrasound measurements are non-invasive and provide real-time data. In this study, the suitability to characterize the dispersed and the liquid phase of yeast suspensions with ultrasound was investigated. The ultrasound signals collected from three commercially available Saccharomyces yeast were evaluated and compared. For all three yeasts, the attenuation coefficient and speed of sound increased linearly with increasing yeast concentrations (0.0-1.0 wt%) and cell counts (R2 > 0.95). Further characterization of the dispersed phase revealed that cell diameter and volume density influence the attenuation of the ultrasound signal, whereas changes in the speed of sound were partially attributed to compositional variations in the liquid phase. This demonstrates the ability of ultrasound to monitor industrial fermentations and the feasibility of developing targeted control strategies.

Characterisation of Pseudomonas mosselii H6 for aerobic denitrification: stoichiometry and reaction kinetics

The application of aerobic denitrifying bacteria in biological nitrogen removal has been of great interest. However, the mechanism of nitrogen conversion by aerobic denitrifying bacteria is unclear due to the lack of stoichiometry and kinetic studies. Therefore, this study aimed to investigate the stoichiometry and kinetics of aerobic denitrification using Pseudomonas mosselii H6 as a model strain. The results showed that the stoichiometric equations of strain H6 under different nitrogen source conditions were obtained by nitrogen balance analysis; the concentrations of different limiting substrates were set and combined with the multi-substrate Monod kinetic equation to fit the half-saturation constants of COD, ammonia, nitrate and nitrite nitrogen for strain H6, which were 230.1008, 25.3435, 4.1009 and 23.4601 mg/L, respectively; based on the model of “two-step denitrification”, the numerical simulation of the growth and aerobic denitrification of strain H6 under different limiting substrate concentrations was carried out by using AQUASIM software to test the validity of stoichiometric coefficients and kinetic constants and perfect fitting results were obtained. These parameters will help to simulate the growth and denitrification performance of aerobic denitrifying bacteria and provide an experimental basis for further quantitatively elucidating the mechanism of action in the aerobic denitrification process.

Combining systems and synthetic biology for in vivo enzymology

Enzymatic parameters are classically determined in vitro, under conditions that are far from those encountered in cells, casting doubt on their physiological relevance. We developed a generic approach combining tools from synthetic and systems biology to measure enzymatic parameters in vivo. In the context of a synthetic carotenoid pathway in Saccharomyces cerevisiae, we focused on a phytoene synthase and three phytoene desaturases, which are difficult to study in vitro. We designed, built, and analyzed a collection of yeast strains mimicking substantial variations in substrate concentration by strategically manipulating the expression of geranyl-geranyl pyrophosphate (GGPP) synthase. We successfully determined in vivo Michaelis-Menten parameters (KM, Vmax, and kcat) for GGPP-converting phytoene synthase from absolute metabolomics, fluxomics and proteomics data, highlighting differences between in vivo and in vitro parameters. Leveraging the versatility of the same set of strains, we then extracted enzymatic parameters for two of the three phytoene desaturases. Our approach demonstrates the feasibility of assessing enzymatic parameters directly in vivo, providing a novel perspective on the kinetic characteristics of enzymes in real cellular conditions.

Efficient synthesis of salidroside from tyrosol based on UDPG recycling system

Salidroside is a functional ingredient with wide applications in food and pharmaceutical fields. It is conventionally produced by extraction from plants, the application of which is limited by the scarcity of raw materials and cumbersome process. This study achieved the efficient production of salidroside by biosynthesis with tyrosol as the substrate. While utilizing glycosyltransferases for tyrosol glycosylation, we introduced sucrose synthase to construct the uridine diphosphate glucose (UDPG) recycling system. The glycosyltransferase UGT33 and sucrose synthase AtSUS were screened out by comparison, and the recombinant strain Escherichia coli BL21/pETDuet-AtSUS-UGT33 was constructed. The copy number of the gene was optimized and the optimal copy number ratio of glycosyltransferase to sucrose synthase was determined to be 3:1. The whole-cell transformation conditions (temperature, pH, inoculum amount, substrate concentration, and concentrations of metal ions) of the recombinant strain were optimized, and the highest yield of salidroside reached 8.17 g/L after fermentation under the optimal conditions in a 5 L fermenter for 24 h. This study provides a reference for the efficient production of salidroside by microorganisms.

Efficient cleavage of Cα[sbnd]Cβ bonds in lignin using tetrabutylammonium tetrafluoroborate as both the catalyst and auxiliary electrolyte

Lignin is a promising alternative to fossil resources due to its abundance of benzene ring monomers. However, the stability of the CαCβ bond in lignin has hindered its efficient depolymerization. Electrochemical methods for breaking this bond are not well-studied. This paper presents a novel approach for catalytic depolymerization of lignin to produce acetals under mild conditions, without the need for additional catalysts. Under room temperature and in an air atmosphere, the combination of tetrabutylammonium tetrafluoroborate (TBABF4) as an auxiliary electrolyte and methanol (MeOH) as a solvent has shown high selectivity in catalyzing the cleavage of CαCβ bonds in lignin. Over 90.0 % of the resulting products are acetals, with the optimal conditions being a substrate concentration of 0.02 M, TBABF4 concentration of 0.008 M, a constant current of 30 mA, and a reaction time of 3 h. This led to a substrate conversion rate of 95.8 % and a product yield of 98.0 % for benzaldehyde dimethyl acetal (Bda). The mechanism study reveals that the tributyl ammonium radical cation decomposed by TBABF4 is adsorbed on the electrode surface. Subsequently, the adsorbed O2 is activated to form superoxide anion radical active species through single electron transfer, which plays a crucial catalytic role. TBABF4 acts as both an auxiliary electrolyte and a catalyst in this process. This research introduces a novel approach for electrocatalytic depolymerization of inert CαCβ bonds in lignin, leading to the selective conversion into acetal chemicals.

Oxidative Stress Markers and Na,K-ATPase Enzyme Kinetics Are Altered in the Cerebellum of Zucker Diabetic Fatty fa/fa Rats: A Comparison with Lean fa/+ and Wistar Rats.

Type 2 diabetes mellitus has been referred to as being closely related to oxidative stress, which may affect brain functions and brain glucose metabolism due to its high metabolic activity and lipid-rich content. Na,K-ATPase is an essential enzyme maintaining intracellular homeostasis, with properties that can sensitively mirror various pathophysiological conditions such as diabetes. The goal of this study was to determine oxidative stress markers as well as Na,K-ATPase activities in the cerebellum of Zucker diabetic fatty (ZDF) rats depending on diabetes severity. The following groups of male rats were used: Wistar, ZDF Lean (fa/+), and ZDF (fa/fa) rats, arbitrarily divided according to glycemia into ZDF obese (ZO, less severe diabetes) and ZDF diabetic (ZOD, advanced diabetes) groups. In addition to basic biometry and biochemistry, oxidative stress markers were assessed in plasma and cerebellar tissues. The Na, K-ATPase enzyme activity was measured at varying ATP substrate concentrations. The results indicate significant differences in basic biometric and biochemical parameters within all the studied groups. Furthermore, oxidative damage was greater in the cerebellum of both ZDF (fa/fa) groups compared with the controls. Interestingly, Na,K-ATPase enzyme activity was highest to lowest in the following order: ZOD > ZO > Wistar > ZDF lean rats. In conclusion, an increase in systemic oxidative stress resulting from diabetic conditions has a significant impact on the cerebellar tissue independently of diabetes severity. The increased cerebellar Na,K-ATPase activity may reflect compensatory mechanisms in aged ZDF (fa/fa) animals, rather than indicating cerebellar neurodegeneration: a phenomenon that warrants further investigation.

Efficient whole-cell biosynthesis of D-mannose by recombinant Bacillus subtilis

D-mannose is a natural hexose with great economic and application values in the food, medicine, and cosmetic fields. However, most biosynthesis methods of D-mannose rely on Escherichia coli as the host, which poses safety issues during the production process and imposes limitations on subsequent applications. This study compared the enzyme properties of mannose isomerases from multiple sources to select the most suitable source. B. subtilis 168/pMA5-EcMIaseA was constructed with "generally recognized as safe" (GRAS) Bacillus subtilis as the host and used as a whole-cell catalyst to synthesize D-mannose from d-fructose. Optimizing the conversion conditions such as culture temperature, pH, and substrate concentration increased the yield of D-mannose. The results showed that the conversion rates reached 27.75% and 27.22% and the yields of D-mannose were 138.74 g/L and 163.30 g/L after 6 h whole-cell transformation with d-fructose at the concentrations of 500 g/L and 600 g/L, respectively, in a 5 L fermentor. This study achieves the highest yield of D-mannose produced under the catalysis by recombinant B. subtilis that has ever been reported and provides a basis for the industrial production and application of D-mannose.

PRODUCTION AND CHARACTERIZATION OF CELLULASES FROM ASPERGILLUS NIGER UNDER STATIC FERMENTATION

The ever-increasing uses of cellulase in various industries have made it popular among researchers. Annually, a large amount of fruit wastes go into vain, which is a great source of cellulases. The objective of this study is to use grape wastes as substrate for production of cellulases from Aspergillus niger using static fermentation. CMCase and FPase assays were performed to characterize the cellulases. The cellulases’ CMCase and FPase activities and stabilities were analyzed for optimum temperature and pH. The effect of substrate concentration and kinetic constants Km and Vmax, along with thermodynamic analysis, were determined. The effects of several metals on the activity of the enzyme were observed. The optimal temperatures were found as 40 °C and 50 °C for CMCase and FPase activity, respectively. CMCase activity shows stability at 20 °C-60 °C, FPase shows low thermal stability as its activity starts to decrease after 50 °C. CMCase and FPase both show maximum activity at pH 6, and maintain their stability at pH 6-7. The values of Km and Vmax obtained from Lineweaver and Burk plot for CMCase are 0.648 mM and 12.953 mM/min, and for FPase are 0.975 mM and 41.493 mM/min. The Arrhenius plot was used to calculate activation energy (Ea) as -19 kJ/mol, and enthalpy of reaction (ΔH) as 16.4 kJ/mol, while entropy ΔS -16.4 kJ/mol was obtained from the plot of ln(Vmax/T) versus the inverse of temperature (1/T). Most metals induce enzyme activities, whereas EDTA inhibits enzyme activities. The findings suggest A. niger has remarkable cellulase production potential from grape wastes in static fermentation, at optimum temperature and pH levels for achieving enzyme activity and stability.

Boosting Fructosyl Transferase's Thermostability and Catalytic Performance for Highly Efficient Fructooligosaccharides (FOS) Production.

Achieving enzymatic food processing at high substrate concentrations can significantly enhance production efficiency; however, related studies are notably insufficient. This study focused on the enzymatic synthesis of fructooligosaccharides (FOS) at high temperature and high substrate concentration. Results revealed that increased viscosity and limited substrate solubility in high-concentration systems could be alleviated by raising the reaction temperature, provided it aligned with the enzyme's thermostability. Further analysis of enzyme thermostability in real sucrose solutions demonstrates that the enzyme's thermostability was remarkedly improved at higher sucrose concentrations, evidenced by a 10.3 °C increase in melting temperature (Tm) in an 800 g/L sucrose solution. Building upon these findings, we developed a novel method for enzymatic FOS synthesis at elevated temperatures and high sucrose concentrations. Compared to existing commercial methods, the initial transglycosylation rate and volumetric productivity for FOS synthesis increased by 155.9% and 113.5%, respectively, at 65 °C in an 800 g/L sucrose solution. This study underscores the pivotal role of substrate concentration, incubation temperature, and the enzyme's actual status in advancing enzyme-catalyzed processes and demonstrates the potential of enzymatic applications in enhancing food processing technologies, providing innovative strategies for the food industry.

Calibration-Free and Highly Sensitive Potentiometric Enzyme-Based Biosensors.

Enzyme-based amperometric biosensors have become popular for healthcare applications. However, they have been under constant pressure for technological innovation to improve their sensitivity and usability. An ideal biosensor has high sensitivity and calibration-free characteristics. This study aims to report enzyme-based glucose and lactate sensors that utilize a proposed "time-derivative of potential (dOCP/dt)" method, with a further aim being to prove theoretically and experimentally that dOCP/dt values are proportional to substrate concentration. High sensitivity is obtained regardless of the electrode size because the electrode potential is independent of the electrode area in the biosensor. Importantly, because the substrate diffusion determines the enzyme reaction rate on the sensors, the dOCP/dt biosensors can essentially eliminate external influences such as temperature and pH. The result is the successful realization of a biosensor that is calibration-free, making it a much more practical option.

Differences in the physiology of Pichia pastoris grown on glycerol/glucose using polyurethane foam slabs as solid support

AbstractBACKGROUNDGrowth physiology and metabolic flux of Pichia pastoris were analyzed using glass columns containing slabs of polyurethane foam as a solid support and culture medium with glycerol or glucose as a carbon source.RESULTSMedia with glycerol produced an average of 30.91% more biomass than media where glucose was used. However, the specific growth rate registered higher values for media with glucose than those with glycerol at low substrate concentrations: 0.46 versus 0.22 h−1. Media with glycerol produced a large amount of d‐arabitol, whereas ethanol and citrate were the predominant metabolites in media with glucose. Both types of culture systems generated biphasic curves in terms of the respiratory quotient value, whose inflection point coincided with the transition from aerobic metabolism to a mixed one.CONCLUSIONAdequate oxygen transfer occurred in both culture systems; therefore, the differences found in growth physiology can be explained by the transport mechanism that internalizes glycerol, the access point to primary metabolism, and the degree of glycerol oxidation. The arrangement of cells in the polyurethane matrix allowed an attenuation of the repression phenomenon due to excess substrate for both carbon sources. This is the first work to study metabolic flux comparisons using this system. © 2024 Society of Chemical Industry (SCI).

Influences and mechanisms of iron input for methane productions in peatlands.

Atmospheric deposition provides a stable iron source for peatlands. The influences of Fe input on methane (CH4) productions and the underlying mechanisms remain unclear. We conducted a microcosm experiment with peat sediments collected from the Qinghai-Tibet Plateau of China to explore the effects of ferrihydrite reductionfor CH4 productions in peatlands by using geochemical analyses including 57Fe Mössbauer spectroscopy and three-dimensional fluorescence spectroscopy (3D-EEM) in combination with high-throughput sequencing of 16S rRNA and real-time fluorescence quantitative PCR (qPCR). Results showed that ferrihydrite reduction significantly increased CH4 production, being 30 times of that under the control. Selective extractions for iron oxides and 57Fe Mössbauer spectroscopy measurements revealed that no crystalline secondary iron minerals were formed during the ferrihydrite reduction process. The addition of ferrihydrite enhanced the degradation of dissolved organic matter (DOM) in peat soil, resulting in a reduction in the concentration of dissolved organic carbon (DOC). Furthermore, the relative abundance of typical fermentative microorganisms in peat sediments, including Acidobacteriota and Bacteroidota, significantly increased. Such a result indicated that reduction of ferrihydrite accelerated organic matter decomposition and increased substrate concentration required for methanogenesis. Furthermore, a co-increase in relative abundance of Geobacter, Geothrix, and Methanobacterium in the ferrihydrite-amended group suggested a potential synergistic interaction that may promote the CH4 production. Our results demonstrated that ferrihydrite reduction could significantly enhance CH4 production and play a vital role in regulating CH4 emissions in peatlands.

Understanding Cytochrome P450 Enzyme Substrate Inhibition and Prospects for Elimination Strategies.

Cytochrome P450 (CYP450) enzymes, which are widely distributed and pivotal in various biochemical reactions, catalyze diverse processes such as hydroxylation, epoxidation, dehydrogenation, dealkylation, nitrification, and bond formation. These enzymes have been applied in drug metabolism, antibiotic production, bioremediation, and fine chemical synthesis. Recent research revealed that CYP450 catalytic kinetics deviated from the classic Michaelis-Menten model. A notable substrate inhibition phenomenon that affects the catalytic efficiency of CYP450 at high substrate concentrations was identified. However, the substrate inhibition of various reactions catalyzed by CYP450 enzymes have not been comprehensively reviewed. This review describes CYP450 substrate inhibition examples and atypical Michaelis-Menten kinetic models, and provides insight into mechanisms of these enzymes. We also reviewed 3D structure and dynamics of CYP450 with substrate binding. Outline methods for alleviating substrate inhibition in CYP450 and other enzymes, including traditional fermentation approaches and protein engineering modifications. The comprehensive analysis presented in this study lays the foundation for enhancing the catalytic efficiency of CYP450 by deregulating substrate inhibition.

Bio-process optimization for developing a turmeric (Curcuma longa Linn.) beverage fermented with functional lactic acid starter cultures

Turmeric, scientifically known as Curcuma longa, is a herbaceous plant characterized by its rhizomatous nature with remarkable chemical composition and biologically active compounds. Lactic acid bacteria (LAB) have been observed to break down complex polyphenols into simpler, more bioactive compounds through fermentation. The success of the fermentation process relies on various factors to achieve the desired end product. This study's main goal was to assess the feasibility of using turmeric as a fermentable substrate for LAB, with the intention of creating a non-dairy fermented beverage. The investigation delved into the impact of several fermentation parameters, namely Fermentation Temperature, pH (Lemon juice concentration), Inoculum concentration, and Substrate concentration (Turmeric concentration), on the phytochemical and antioxidant properties of the lactic acid-fermented turmeric beverage (FTB). Statistical analysis revealed that a quadratic polynomial model could effectively illustrate how these fermentation parameters influenced the beverage's phytochemical and antioxidant qualities. Visualization through response surface plots revealed that these independent variables significantly influenced the beverage's total phenolic content, total flavonoid content, and antioxidant properties. Optimal fermentation conditions were identified to yield the highest levels of phenolic, flavonoid, and antioxidant content. These conditions included a Fermentation Temperature of 37.45 °C, a pH of 5.62, an Inoculum concentration of 5.12%v/v, and a Substrate (turmeric) concentration of 2.28%w/v. Under these precise conditions, experimental results closely aligned with predicted values for total phenolic content (57.46mg/100 ml), total flavonoid content (51.48mg/100 ml), and total antioxidant activity (72.24%). The overall acceptability of the fermented turmeric beverage reached a high 98.10%. Notably, the FTB exhibited significantly improved attributes such as astringency, flavor, taste, and overall acceptability when compared to the non-fermented turmeric beverage (NFTB), with statistical significance (P < 0.05).

Screening of oxytetracycline-degrading strains in the intestine of the black soldier fly larvae and their degradation characteristics

The presence of excessive antibiotic residues poses a significant threat to human health and the environment. This study was designed to identify an effective oxytetracycline (OTC)-degrading strain through the screening of the intestine of black soldier fly larvae (BSFL). A strain designated “B2” was selected using a series of traditional microbial screening methods. It could be identified as Enterococcus faecalis by Gram staining and 16S rDNA sequencing, with a similarity of 99.93%. Its ability to degrade OTC was then assessed using high-performance liquid chromatography (HPLC). The degradation of the strain was characterized using a one-way test to assess the effects of the substrate concentration, inoculum amount, and initial pH on the degrading bacteria. The results indicate that strain B2 exhibited optimal OTC-degrading performance at a substrate concentration of 50 mg/L, with an inoculum amount of 6% and a pH value of 5.0. Specifically, strain B2 achieved degradation rates of 71.11%, 56.14%, and 45.03%. These findings demonstrate the effectiveness of strain B2 in degrading OTC, indicating its potential for use in environmental remediation efforts.

A Urease-Based pH Photoswitch: A General Route to Light-to-pH Transduction.

New approaches for the integration of chemical and physical stimuli to control the dynamics of artificial enzymatic reaction networks (ERNs) are needed. Here, we present a general approach to convert a light stimulus into a time-programmed pH response. We developed and characterized a panel of photoswitchable inhibitors of urease. Urease activity, now regulated by light via the photoinhibitors, leads to an increase in pH upon hydrolysis of urea into ammonia. Careful choice of characteristics of light, and concentrations of enzyme, substrate, and photoinhibitor, allowed us to control the timing of the pH transition. Furthermore, as all enzymes have an activity-pH profile, the urease photoinhibitor system can be used to regulate the activities of other enzymes in small reaction networks.

Effective sludge activation in a sequencing batch reactor (SBR) towards aerobic granular sludge (AGS) technology

Activated sludge is a biological treatment that commonly deals with the problem of excess sludge production. As advanced technology, aerobic granular sludge is expected to address the drawbacks of the activated sludge system, including the excess sludge issue. This study aims to investigate the characteristics and performance of the activation process of excess sludge. The study was conducted in a sequencing batch reactor with different substrate compositions in three phases. The activation process with biodegradable substrate supported by nutrients and micronutrients consisting of cations successfully enhanced the growth of microorganisms to 6720 mg/L of MLSS and 5450 mg/L of MLVSS. The settling performance of the sludge increased, marked by a low average of SVI5 of 63.89 mL/gTSS and SVI30 of 45.16 mL/gTSS. The treatment improved COD removal to 90 % and ammonia, nitrate, and phosphate removal to 98 %, 47 %, and 37 %, respectively. The granulation process with micronutrients as cation addition in 25 mg/L has not been achieved through the experiment in 18 days indicated by the ratio of SVI30 to SVI5 on the average of 0.71. Therefore, the findings suggest that the study of substrate and cation concentration to accelerate the granulation is proposed towards AGS technology and its application to achieve a sustainable environment.