Endogenous Decay Research Articles

A simple kinetic modeling approach for aerobic stabilization of real waste activated sludge

The objective of this study is to propose a procedure to simplify the modeling of aerobic stabilization process. In order to achieve this, the activated sludge models no. 1 (ASM1) and no. 3 (ASM3) were evaluated based on uncomplicated chemical oxygen demand and volatile suspended solid data gathered from batch aerobic digesters. The aerobic digestion period of real waste activated sludge was modeled and then the modeling results were validated at different volumetric organic loading rates. The uniqueness of given model parameters were confirmed by sensitivity analyses. According to experimental results, at the end of 30days, the maximum volatile suspended solid removal rate was as 51.50%. The model simulations indicated the viability of both models, with regression coefficients of >0.978 without requiring the addition of any process or component to the original model structures contrary to those suggested by prior studies. According to sensitivity analyses used to determine the identifiability of estimated model parameters, the active biomass fraction, production rate of microbial products, endogenous decay rate and heterotrophic yield coefficient are the most sensitive and identifiable parameters in both models. As a result of modeling, the endogenous decay process was determined to be the main microbial mechanism involved in aerobic digestion, while the hydrolysis of particulate organic matter and removal of storage products were found as insignificant mechanisms during aerobic digestion process. Additionally, the modeling studies indicated the importance of the organic loading to achieve satisfactory organic removal since microbial kinetic rates were decreased under a threshold level of organic loading.

Kinetics of batch anaerobic co-digestion of poultry litter and wheat straw including a novel strategy of estimation of endogenous decay and yield coefficients using numerical integration

The kinetics of anaerobic co-digestion of poultry litter and wheat straw has not been widely reported in the literature. Since endogenous decay and yield coefficients are two basic parameters for the design of anaerobic digesters, they are currently estimated only by continues experiments. In this study, numerical integration was employed to develop a novel strategy to estimate endogenous decay and yield coefficients using initial and final liquid data combined with methane volumes produced over time in batch experiments. To verify this method, the kinetics of batch anaerobic co-digestion of poultry litter and wheat straw at different TS and VS levels was investigated, with the corresponding endogenous decay and (non-observed) yield coefficients in the exponential periods determined to be between 0.74×10(-3) and 6.1×10(-3)d(-1), and between 0.0259 and 0.108g VSS (gVS)(-1), respectively. A general Gompertz model developed early for bio-product could be used to simulate the methane volume profile in the co-digestion. The same model parameters obtained from the methane model combined with the corresponding yield coefficients could also be used to describe the VSS generation and VS destruction.

Model development and experimental validation of capnophilic lactic fermentation and hydrogen synthesis by Thermotoga neapolitana

The aim of the present study was to develop a kinetic model for a recently proposed unique and novel metabolic process called capnophilic (CO2-requiring) lactic fermentation (CLF) pathway in Thermotoga neapolitana. The model was based on Monod kinetics and the mathematical expressions were developed to enable the simulation of biomass growth, substrate consumption and product formation. The calibrated kinetic parameters such as maximum specific uptake rate (k), semi-saturation constant (kS), biomass yield coefficient (Y) and endogenous decay rate (kd) were 1.30 h−1, 1.42 g/L, 0.1195 and 0.0205 h−1, respectively. A high correlation (>0.98) was obtained between the experimental data and model predictions for both model validation and cross validation processes. An increase of the lactate production in the range of 40–80% was obtained through CLF pathway compared to the classic dark fermentation model. The proposed kinetic model is the first mechanistically based model for the CLF pathway. This model provides useful information to improve the knowledge about how acetate and CO2 are recycled back by Thermotoga neapolitana to produce lactate without compromising the overall hydrogen yield.

Anaerobic side-stream reactor for excess sludge reduction: 5-year management of a full-scale plant

The long-term performances of a full-scale anaerobic side-stream reactor (ASSR) aimed at sludge reduction have been monitored for the first time, in comparison with a conventional activated sludge process (CAS). The plant was integrated with an ASSR treatment of 2293–3293 m3. Operational parameters in the ASSR were: ORP -250 mV, interchange ratio of 7–10%, hydraulic retention time of 7 d. No worsening of effluent quality was observed in the ASSR configuration and removal efficiency of COD and NH4 was above 95%. A slight increase in the Sludge Volume Index did not cause worsening in effluent solids concentration. The observed sludge yield (Yobs) passed from 0.44 kgTSS/kgCOD in the CAS to 0.35 in the ASSR configuration. The reduction of Yobs by 20% is lower than expected from the literature where sythetic wastewater is used, indicating that sludge reduction efficiency is largely affected by inert mass fed with influent real wastewater. An increase by 45% of the ASSR volume did not promote a further reduction of Yobs, because sludge reduction is affected not solely by endogenous decay but also by other factors such as interchange ratio and aerobiosis/anaerobiosis alternation.

Degradation of the unbiodegradable particulate fraction (XU) from different activated sludges during batch digestion tests at ambient temperature

One strategy for the management of excess sludge in small wastewater treatment plants (WWTPs) consists in minimizing the excess sludge production by operating the WWTP at very long solids retention times (SRTs > 30 days). A number of recent studies have suggested that sludge minimization at very long SRT results from the degradation of the unbiodegradable particulate fraction (XU) (influent unbiodegradable compounds and endogenous decay products). But the biodegradability of the unbiodegradable particulate fraction has only been evaluated during batch digestion test performed at ambient temperature with sludge fed with synthetic wastewaters. It is not clear to what extent observations made for sludge fed with synthetic influents can be transposed to sludge fed with real influent. The current study thus focused on evaluating the biodegradability of the unbiodegradable particulate fraction for sludge fed with real wastewater. Batch digestion tests (400 days, ambient temperature) were conducted with three different sludges fed with either synthetic or real influents and exposed to aerobic or intermittent aeration conditions. Our results indicate that volatile suspended solids (VSS) decreased even after complete decay of the active biomass (i.e., after 30 days of aerobic batch digestion) indicating that the unbiodegradable particulate fraction is biodegradable. However, very low degradation rates of the unbiodegradable particulate fraction were monitored after day 30 of digestion (0.7–1.7·10−3 d−1). These values were in the lower range of previously published values for synthetic wastewaters (1–7.5·10−3 d−1). The low values determined in our study indicate that the rate could decrease over time or that sludge composition influences the degradability of the unbiodegradable particulate fraction. But our results also demonstrate that extracellular polymeric substances (EPS) have a minor impact on the biodegradability of the unbiodegradable particulate fraction. Overall bound EPS were indeed biodegradable under all conditions and thus did not accumulate in the unbiodegradable particulate fraction. Different bound EPS pools (e.g., cation bound EPS) were associated with specific degradation behaviors. Besides improved mechanistic understanding of sludge degradation processes, our results have implications for the development of decentralized wastewater treatment technologies with on-site reduction of excess sludge.

Wide-field medium-repetition-rate multiphoton microscopy reduces photodamage of living cells.

Demands of higher spatial and temporal resolutions in linear and nonlinear imaging keep pushing the limits of optical microscopy. We showed recently that a multiphoton microscope with 200 kHz repetition rate and wide-field illumination has a 2-3 orders of magnitude improved throughput compared to a high repetition rate confocal scanning microscope. Here, we examine the photodamage mechanisms and thresholds in live cell imaging for both systems. We first analyze theoretically the temperature increase in an aqueous solution resulting from illuminating with different repetition rates (keeping the deposited energy and irradiated volume constant). The analysis is complemented with photobleaching experiments of a phenolsulfonphthalein (phenol red) solution. Combining medium repetition rates and wide-field illumination promotes thermal diffusivity, which leads to lower photodamage and allows for higher peak intensities. A three day proliferation assay is also performed on living cells to confirm these results: dwell times can be increased by a factor of 3×10(6) while still preserving cell proliferation. By comparing the proliferation data with the endogenous two-photon fluorescence decay, we propose to use the percentage of the remaining endogenous two-photon fluorescence after exposure as a simple in-situ viability test. These findings enable the possibility of long-term imaging and reduced photodamage.

Activated sludge mass reduction and biodegradability of the endogenous residues by digestion under different aerobic to anaerobic conditions: Comparison and modeling

This study was performed to identify suitable conditions for the in-situ reduction of excess sludge production by intercalated digesters in recycle-activated sludge (RAS) flow. The objective was to compare and model biological sludge mass reduction and the biodegradation of endogenous residues (XP) by digestion under hypoxic, aerobic, anaerobic, and five intermittent-aeration conditions. A mathematical model based on the heterotrophic endogenous decay constant (bH) and including the biodegradation of XP was used to fit the long-term data from the digesters to identify and estimate the parameters. Both the bH constant (0.02–0.05d−1) and the endogenous residue biodegradation constant (bP, 0.001–0.004d−1) were determined across the different mediums. The digesters with intermittent aeration cycles of 12h–12h and 5min–3h (ON/OFF) were the fastest, compared to the aerobic reactor. The study provides a basis for rating RAS-digester volumes to avoid the accumulation of XP in aeration tanks.

Impact of the Anoxic Volume Ratio on the Dynamics of Biological Nitrogen Removal Under Extended Aeration Conditions

The study provided a critical appraisal of the extended aeration process as a single-sludge system for nitrogen removal, emphasizing its inherent deficiencies. For this purpose, the system was designed first using the prescribed procedure in the German practice, ATV A-131. The design used the basic data reported in different studies related to conventional characterization and chemical oxygen demand (COD) fractionation defining the biodegradation characteristics of domestic wastewater. A critical appraisal of the design was made with emphasis on the fate of biodegradable COD and oxidized nitrogen in the anoxic phase by process modeling and evaluation. The results obtained were evaluated using basic stoichiometry and mass balance for major nitrogen fractions. The A-131 design based on a total sludge age of 20 days defined a system with a hydraulic residence time of 1.2 days where half of the volume was operated under anoxic conditions; the effluent nitrate concentration was reduced to 8.3 mg N/L with an internal recycle (nitrate) ratio of 4.9. Model evaluation of the prescribed design indicated that oxidized nitrogen was totally consumed within the first 25–30 % portion of the anoxic volume. The remaining volume was forced to operate under anaerobic conditions, where no appreciable endogenous decay would occur. ATV A-131 procedure, relying on empirical coefficients and expressions, was neither consistent with process stoichiometry nor justifiable by modeling. Evaluations based on modeling and process stoichiometry revealed significant inherent weaknesses of extended aeration for providing a sustainable basis for nitrogen removal.

Anammox endogenous metabolism during long-term starvation: Impacts of intermittent and persistent modes and phosphates

Starvation of anaerobic ammonium oxidation (anammox) bacteria can occur in underloaded bioreactors or during the storage of sludge. In this study, the impacts of intermittent and persistent resting modes and phosphates on the endogenous metabolism of anammox bacteria during long-term starvation were investigated. Batch experiments were performed to evaluate the response of anammox granules to different modes of starvation (persistent-resting and intermittent-resting cells) in the presence and absence of phosphates. The endogenous decay coefficient of anammox granules (based on the decreased biomass) over a 30-d persistent starvation period was 0.0062d−1, while the intermittent starvation by means of providing substrates every 10days accelerated the biomass decay approximately twice (0.0110d−1). Moreover, the intermittent-resting cells displayed exacerbated decreases in specific anammox activity relative to the persistent-resting cells, whereas no significant difference was observed in the heme c contents. Regardless of the physiological status of the cells, the presence of low levels of phosphates may be beneficial; however, a high level of phosphates is not recommended. Although different metabolic strategies were adopted depending on the starvation mode, anammox bacteria possessed a better survival strategy via a relatively low maintenance energy requirement to ensure their survival in nutrient-limited systems. In addition, the variations in extracellular protein-like components were indicative of different intracellular metabolic regulation mechanisms. These results provide a better understanding of the endogenous metabolism of anammox bacteria.

Modeling effects of DO and SRT on activated sludge decay and production

The effect of dissolved oxygen (DO) on the endogenous decay of active heterotrophic biomass and the hydrolysis of cell debris were studied. With the inclusion of a hydrolysis process for the cell debris, mathematical models that are capable of quantifying the effects of DO and sludge retention time (SRT) on concentrations of active biomass and cell debris in activated sludge are presented. By modeling the biomass cultivated with unlimited DO, the values of endogenous decay coefficient for heterotrophic biomass, the hydrolysis constant of cell debris, and the fraction of decayed biomass that became cell debris were determined to be 0.38 d−1, 0.013 d−1, and 0.28, respectively. Results from modeling the biomass cultivated under different DO conditions suggested that the experimental low DO (∼0.2 mg/L) did not inhibit the endogenous decay of heterotrophic biomass, but significantly inhibited the hydrolysis of cell debris with a half-velocity constant value of 2.1 mg/L. Therefore, the increase in sludge production with low DO was mainly contributed by cell debris rather than the active heterotrophic biomass. Maximizing sludge production during aerobic wastewater treatment could reduce aeration energy consumption and improve biogas energy recovery potential.

Anaerobic Digestion Treatment of Soft Drink Wastewater

The aim of this study was to treat soft drink industrial wastewater by anaerobic digestion. Digestion lasted for a hydraulic retention time of 30 days. The total quantity of biogas produced was 80ml. The wastewater was characterized after digestion. The result showed that chloride, total dissolved solid, total suspended solid and chemical oxygen demand met the specifications of the world health organization for the safe disposal of wastewater into the water body. The kinetics of anaerobic digestion of the wastewater was described by first order kinetic model. The net specific growth rate of the wastewater was evaluated and observed to reduce with time. The kinetic parameters such as maximum rate of substrate utilization, half velocity or saturation constant, endogenous decay coefficient, biomass or microbial growth yield and maximum specific microorganism growth rate obtained were 0.350day−1, 204.12mg/l, 0.0222day−1, 0.194day−1 and 0.0679day−1 respectively. This revealed that inoculation would be needed for increased volume of biogas production and for an increased digestion rate to be obtained. Based on the endogenous decay coefficient and biomass yield values, a small sludge handling facility would be required in the absence of inoculation during digestion.

LC/MS Based Monitoring of Endogenous Decay Markers for Quality Assessment of Serum Specimens

Introduction: Preanalytical variations have major impact on most biological assays. Specifically MS-based multiparametric proteomics analyses of blood specimens are seriously affected by limited protein stability due to high intrinsic proteolytic activity of serum and plasma. However, the direct analysis of sample quality (DASQ) for serum specimens is not readily available. Here we propose the mass spectrometry based monitoring of peptide patterns that are ex vivo changing in a time dependent manner to alleviate these constrains. Materials and methods: Serum specimens from healthy controls (n=3) and patients with colorectal cancer were analyzed for a set of endogenous peptides (n=62). The respective proteolytic fragments were monitored with LC/MS at different preanalytical points in time ranging from 1 h to 48 h after blood withdrawal. An algorithm was constructed with a training set of serum specimens from colorectal cancer patients (n=30). An independent test set of patients (n=20) was used for further validation. Results: The coefficient of determination (R2) for the linear regression of true and estimated points in time was 0.89. However, the classification accuracy for specimens with a preanalytical time span below 8 h was higher when compared to older specimens (>8 h). Conclusion: Endogenous peptides are processed in blood specimens in a time dependent manner. This ‘proteomic degradation clock’ can be used to estimate the preanalytical quality of serum specimens. This is specifically relevant prior to in depth proteomic profiling approaches or other laborious analyses in research or diagnostic applications. Accordingly, specimens with low quality can be identified and subsequently be excluded from further analyses to avoid any unwanted preanalytical bias.

Kinetics of Batch Anaerobic Digestion of Vegetable Oil Wastewater

The treatment of vegetable oil industrial wastewater by anaerobic digestion was studied. A hydraulic retention time (HRT) of 35 days was used for the digestion process. The maximum volume of biogas production by downward displacement of water was 150ml. After digestion, the following parameters (chloride, total dissolved solids, total suspended solids, total solids total nitrogen, chemical oxygen demand, biological oxygen demand) fell within the limits prescribed by WHO (World Health Organization). The kinetic parameters such as maximum rate of substrate utilization (K), half velocity or saturation constant (Ks), endogenous decay coefficient (Kd), biomass or microbial growth yield (Y) and maximum specific microorganism growth rate (μmax) were determined as 0.8215 day 1, 163.31mg/l, 0.0838 day 1, 0.2813mg/mg and 0.231 day 1 respectively. The kinetics of anaerobic digestion of the wastewater was described by first order kinetic model. The net specific growth rates (μnet) for the wastewater also was observed to reduce with time. These values indicated that inoculation of the feed with microorganism would be required to increase the rate of digestion and therefore will require a large digester.

Modeling and parameter estimation of two-phase endogenous respirograms and COD measurements during aerobic digestion of biological sludge

Long-term aerobic digestion batch tests were performed on a sludge that contained mainly two fractions, a heterotrophic biomass XH and its endogenous residues XP, which were cultivated in conditions known to favor bio-storage (XSto). The objective was to model the stabilization of the sludge and determine the parameters of the endogenous decay processes, based on simultaneous measurements of the chemical oxygen demand (COD) and oxygen uptake rates (OUR). The respirograms were shown to have a two-phase structure that was describable with activated sludge model 3 (ASM3), but not with ASM1. Comparing the information from the COD and OUR data suggested the presence of two different groups of heterotrophs (XHa and XHb), one that decays with oxygen consumption and another without using O2. A modified ASM3 model was proposed, which was able to fit the OUR and COD data from the digesters, as well as cases from the literature.

Kinetic Modeling for Simultaneous Organic Carbon Oxidation, Nitrification, and Denitrification of Abattoir Wastewater in Sequencing Batch Reactor

ABSTRACTA laboratory-scale study was conducted in a 20.0-L sequencing batch reactor (SBR) to explore the feasibility of simultaneous removal of organic carbon and nitrogen from abattoir wastewater. The reactor was operated under three different combinations of aerobic-anoxic sequence, viz., (4+4), (5+3), and (5+4) h of total react period, with influent soluble chemical oxygen demand (SCOD) and ammonia nitrogen (NH4+-N) level of 2200 ± 50 and 125 ± 5 mg L−1, respectively. In (5+4) h cycle, a maximum 90.27% of ammonia reduction corresponding to initial NH4+-N value of 122.25 mg L−1 and 91.36% of organic carbon removal corresponding to initial SCOD value of 2215.25 mg L−1 have been achieved, respectively. The biokinetic parameters such as yield coefficient (Y), endogenous decay constant (kd), and half-velocity constant (Ks) were also determined to improve the design and operation of package effluent treatment plants comprising SBR units. The specific denitrification rate (qDN) during anoxic condition was estimated as 6.135 mg N/g mixed liquor volatile suspended solid (MLVSS)·h on 4-h average contact period. The value of Y, kd and Ks for carbon oxidation and nitrification were found to be in the range of 0.6225–0.6952 mg VSS/mg SCOD, 0.0481–0.0588 day−1, and 306.56–320.51 mg L−1, and 0.2461–0.2541 mg VSS/mg NH4+-N, 0.0324–0.0565 day−1, and 38.28–50.08 mg L−1, respectively, for different combinations of react periods.

Anaerobic Digestion of Slaughterhouse Wastewater: A Kinetics Study

Anaerobic digestion was used to study the treatment of slaughterhouse industrial wastewater (SHW). Digestion period of 50 days was observed. This hydraulic retention time (HRT) was used because that was when negligible biogas production was obtained with. The gas was collected in a measuring cylinder by the use of downward displacement of water. The maximum volume of biogas produced was 537ml. Some of the characteristics of the wastewater such as chloride, total nitrogen, calcium were within the limit prescribed by WHO (world health organization). The kinetic parameters such as maximum rate of substrate utilization (K), half velocity or saturation constant (KS), endogenous decay coefficient (Kd), biomass or microbial growth yield (Y) and maximum specific microorganism growth rate (μmax) were evaluated as 31.847day 1, 25,347.77mg/l, 0.009day 1, 0.034 mg/mg and 1.073day 1 respectively. The kinetics data of anaerobic digestion of the wastewater fitted first order kinetic model. The net specific growth rates (μnet) reduced with time. The values of the kinetics parameters showed that digestion of SHW did not require inoculation of the feed with microorganism to increase the rate of digestion.

Aerobic stabilization of biological sludge characterized by an extremely low decay rate: modeling, identifiability analysis and parameter estimation.

Aerobic digestion batch tests were run on a sludge model that contained only two fractions, the heterotrophic biomass (XH) and its endogenous residue (XP). The objective was to describe the stabilization of the sludge and estimate the endogenous decay parameters. Modeling was performed with Aquasim, based on long-term data of volatile suspended solids and chemical oxygen demand (VSS, COD). Sensitivity analyses were carried out to determine the conditions for unique identifiability of the parameters. Importantly, it was found that the COD/VSS ratio of the endogenous residues (1.06) was significantly lower than for the active biomass fraction (1.48). The decay rate constant of the studied sludge (low bH, 0.025 d(-1)) was one-tenth that usually observed (0.2d(-1)), which has two main practical significances. Digestion time required is much more long; also the oxygen uptake rate might be <1.5 mg O₂/gTSSh (biosolids standards), without there being significant decline in the biomass.

Effects of sludge retention times on nutrient removal and nitrous oxide emission in biological nutrient removal processes.

Sludge retention time (SRT) is an important factor affecting not only the performance of the nutrient removal and sludge characteristics, but also the production of secondary pollutants such as nitrous oxide (N2O) in biological nutrient removal (BNR) processes. Four laboratory-scale sequencing batch reactors (SBRs), namely, SBR5, SBR10, SBR20 and SBR40 with the SRT of 5 d, 10 d, 20 d and 40 d, respectively, were operated to examine effects of SRT on nutrient removal, activated sludge characteristics and N2O emissions. The removal of chemical oxygen demand or total phosphorus was similar under SRTs of 5–40 d, SRT mainly affected the nitrogen removal and the optimal SRT for BNR was 20 d. The molecular weight distribution of the effluent organic matters was in the range of 500–3,000 Da under SRTs of 5–40 d. The lowest concentration of the effluent soluble microbial products concentration was obtained at the SRT of 5 d. Nitrifier growth was limited at a short SRT and nitrite existed in the effluent of SBR5. With increasing SRTs, mixed liquor suspended solids concentration increased while the excess sludge production was reduced due to the high endogenous decay rate at high SRTs. Endogenous decay coefficients were 0.020 d−1, 0.036 d−1, 0.037 d−1 and 0.039 d−1 under SRTs of 5–40 d, respectively. In BNR, the N2O emission occurred mainly during the aerobic phase and its emission ratio decreased with increasing SRTs. The ratio between the N2O-N emission and the removed ammonium nitrogen in the aerobic phase was 5%, 3%, 1.8% and 0.8% at the SRT of 5 d, 10 d, 20 d and 40 d, respectively. With low concentrations of dissolved oxygen and high concentrations of oxidized nitrogen, the N2O emission was significantly accelerated due to heterotrophic denitrification activities.

Kinetic Modeling of cometabolic degradation of ethanethiol and phenol by Ralstonia eutropha

Cometabolism, as a complex phenomenon in microbial world, is a special mechanism for transformation of many compounds of environmental and toxicological significance. Several models have been proposed to describe the cometabolic transformations of non-growth substrates in the absence or presence of growth substrates. In this study, a model was proposed to simulate the degradation kinetics of phenol and ethanethiol (ET) by a pure culture of Ralstonia eutropha, including the effects of cell growth, endogenous cell decay, loss of transformation activity, competitive inhibition between growth and non-growth substrates, and self-inhibition of non-growth substrate. The model parameters were determined independently and were then used for evaluating the applicability of the model by comparing experimental data with model predictions. The model successfully predicted ET transformation and phenol utilization for a wide range of concentrations of ET (0 ∼ 40 mg/L) and phenol (0 ∼ 100 mg/L).

Effect of a direct electric current on the activity of a hydrocarbon-degrading microorganism culture used as the flushing liquid in soil remediation processes

This work aims to obtain more fundamentals for the development of novel electrokinetically enhanced bioremediation processes. It is focused on the effects of direct electric field (DC) on the microbial communities used to bioremediate soils. To evaluate this parameter, two experimental setups were used. A stirred tank reactor and a lab scale soil column. Results show that when a DC electric field (in the range 0.0–2.0Vcm−1) is applied to a diesel-degrading microbial culture, the diesel degradation rate increases. It is also demonstrated that prolonged periods of exposure to electric fields have no significant negative effects on the viability of the microorganisms. The values of the endogenous decay constant were maintained in the range 0.02–0.05h−1. No significant differences were found between viability of microorganisms stressed under an electric field in a soil remediation process or in a single tank reactor.