Endogenous Decay Research Articles

Impact of acute and chronic exposure to sulfamethoxazole on the kinetics and microbial structure of an activated sludge community

The aim of this study was to reveal the microbial and kinetic impacts of acute and chronic exposure to one of the frequently administered antibiotics, i.e., sulfamethoxazole, on an activated sludge biomass. Respirometric analysis and model evaluation of the oxygen utilization rate profiles were the backbone of this study. The results showed that continuous exposure to sulfamethoxazole resulted in the inhibition of substrate storage and an increase in the endogenous decay rates by twofold, which was supported by analysis of the resistance genes. A mild inhibition on the growth and hydrolysis kinetics was also observed. Moreover, sulfamethoxazole had a binding impact with available organic carbon, resulting in a slightly less oxygen consumption. DNA sequencing and antibiotic resistance gene analyses showed that continuous exposure to sulfamethoxazole caused a change in the community structure at the species level. Resistant bacteria including Arthrobacter sp. and members of the Chitinophagaceae and Intrasporangiaceae families were found to have dominated the bacterial community. The impact of intermittent exposure was also investigated, and the results indicated a drop in the severity of the impact after 20 days of intermittence.

Aerobic digestibility of waste aerobic granular sludge (AGS) assessed by respirometry, physical-chemical analyses, modeling and 16S rRNA gene sequencing

Research has evolved on aerobic granular sludge (AGS) process, but still there are very few studies on the treatment of excess AGS sludge, with almost none considering its aerobic digestion. Here therefore, the aerobic digestibility of typical AGS sludge was assessed. Granules were produced from acetate-based synthetic wastewater (WW) and were subjected to aerobic digestion for 64 d. The stabilization process was monitored over time through physical-chemical parameters, oxygen uptake rates (OUR) and 16S rRNA gene sequencing. The microbial analyses revealed that the cultivated granules were dominated by slow-growing bacteria, mainly ordinary heterotrophic organisms with potential for polyhydroxyalkanoates (PHA) aerobic storage (PHA-OHOs), polyphosphate and glycogen accumulating organisms (PAOs and GAOs), fermentative anaerobes and nitrifiers (AOB and NOB). Differential abundance analysis of the bacterial data (before versus after digestion) discriminated between the most vulnerable microbiome genera and those most resistant to aerobic digestion. Furthermore, modeling of the stabilization process determined that the endogenous decay rate constant (bH) for the heterotrophs present in the granules was notably low; bH = 0.05 d−1 (average), four times less than for common activated sludge (AS), which is rated at 0.2 d−1. For first time, the research reveals another important feature of AGS sludge, i.e. the slow-decaying character of its bacteria (along with their known slow-growing character). This results in slower stabilization, need of bigger digesters and reconsideration of the specific OUR limits in biosolids regulations (SOUR limit of 1.5 mg/gTSS.h), for waste AGS compared to conventional waste AS. The study suggests that aerobic digestion of waste AGS (fully-granulated) could differ from that of conventional AS. Future work is needed on aerobic digestibility of real AGS sludges from municipal and industrial WWs, compared to synthetic WWs.

The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization

Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields.To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Yobs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10–60 %) with the increase of the AET (7.9–13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Yobs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Yobs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=−0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process.

Improving BioWin Modeling of Phosphorus Solubilization in Acid-Phase Digesters

BioWin 6.0 does not accurately predict phosphorus (P) speciation in acidogenic anaerobic digesters under default kinetics characterization and parameterization. The accurate modeling of acid-phase digestion is needed to predict the performance of novel nutrient recovery technologies that act on these digester effluents. The main thrust of this work was to identify and correct the causes of inaccurate P partitioning and precipitation within BioWin models of acid-phase digestion reactors. A BioWin configuration including an organic acid digester was parameterized and recalibrated based on the known traits of acid-phase digestion and then validated against a full-scale digester in a municipal wastewater treatment plant. This digester, with pH 5.14 and 61–74% solubilized P, was predicted by BioWin default parameters to have only 27% soluble P and a net formation of P precipitates. Corrections to the polyphosphate-accumulating organism decay, endogenous product decay, hydrolysis rate, and brushite behavior resulted in 67% solubilization with no precipitate formation. Cabinet configurations showed similar behavior when modified to include an acid-phase digester under default parameters, but predictions were similarly amended by our parameter changes. This improved modeling technique should allow operators to effectively characterize acid digesters for their own treatment trains and allow engineers to predict the performance of novel nutrient recovery technologies acting on acidogenic digest.

Fibre-based fluorescence-lifetime imaging microscopy: a real-time biopsy guidance tool for suspected lung cancer.

Lung cancer is the most common cause of cancer-related deaths worldwide. Early detection improves outcomes, however, existing sampling techniques are associated with suboptimal diagnostic yield and procedure-related complications. Autofluorescence-based fluorescence-lifetime imaging microscopy (FLIM), a technique which measures endogenous fluorophore decay rates, may aid identification of optimal biopsy sites in suspected lung cancer. Our fibre-based fluorescence-lifetime imaging system, utilising 488 nm excitation, which is deliverable via existing diagnostic platforms, enables real-time visualisation and lifetime analysis of distal alveolar lung structure. We evaluated the diagnostic accuracy of the fibre-based fluorescence-lifetime imaging system to detect changes in fluorescence lifetime in freshly resected ex vivo lung cancer and adjacent healthy tissue as a first step towards future translation. The study compares paired non-small cell lung cancer (NSCLC) and non-cancerous tissues with gold standard diagnostic pathology to assess the performance of the technique. Paired NSCLC and non-cancerous lung tissues were obtained from thoracic resection patients (N=21). A clinically compatible 488 nm fluorescence-lifetime endomicroscopy platform was used to acquire simultaneous fluorescence intensity and lifetime images. Fluorescence lifetimes were calculated using a computationally-lightweight, rapid lifetime determination method. Fluorescence lifetime was significantly reduced in ex vivo lung cancer, compared with non-cancerous lung tissue [mean ± standard deviation (SD), 1.79±0.40 vs. 2.15±0.26 ns, P<0.0001], and fluorescence intensity images demonstrated distortion of alveolar elastin autofluorescence structure. Fibre-based fluorescence-lifetime imaging demonstrated good performance characteristics for distinguishing lung cancer, from adjacent non-cancerous tissue, with 81.0% sensitivity and 71.4% specificity. Our novel fibre-based fluorescence-lifetime imaging system, which enables label-free imaging and quantitative lifetime analysis, discriminates ex vivo lung cancer from adjacent healthy tissue. This minimally invasive technique has potential to be translated as a real-time biopsy guidance tool, capable of optimising diagnostic accuracy in lung cancer.

Decay or Erosion? The Role of Informal Institutions in Challenges Faced by Democratic Judiciaries

AbstractDe-democratization may take the form of executive-led attacks as well as incremental decrepitude, gradual emptying of underlying constitutional values, and state inertia. Contrary to general wisdom, both exogenous erosion and endogenous decay are heavily affected by informality. As courts are often the first institutions affected by de-democratization, this Article analyzes informality in erosion and decay of judicial institutions. It argues that such institutions interact with democracy in two core directions. The first one is endogenous and describes the decay of democratic judiciaries as a result of a long-term incongruence between formal and informal judicial institutions. The second direction captures the gradual erosion of informal institutions that have positive effects on judicial democratic resilience. These two processes, decay and erosion of informal judicial institutions, should not be overlooked. While they are less visible, slower, and often unintentional, they are as dangerous as frontal executive-led attacks on courts, because they significantly increase the window of opportunity for politicians who wish to downgrade the substance of democracy or even implement a regime change.

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).

Radical in the Peroxide-Produced F-Type Ferryl Form of Bovine Cytochrome c Oxidase.

The reduction of O2 in respiratory cytochrome c oxidases (CcO) is associated with the generation of the transmembrane proton gradient by two mechanisms. In one of them, the proton pumping, two different types of the ferryl intermediates of the catalytic heme a3-CuB center P and F forms, participate. Equivalent ferryl states can be also formed by the reaction of the oxidized CcO (O) with H2O2. Interestingly, in acidic solutions a single molecule of H2O2 can generate from the O an additional F-type ferryl form (F•) that should contain, in contrast to the catalytic F intermediate, a free radical at the heme a3-CuB center. In this work, the formation and the endogenous decay of both the ferryl iron of heme a3 and the radical in F• intermediate were examined by the combination of four experimental approaches, isothermal titration calorimetry, electron paramagnetic resonance, and electronic absorption spectroscopy together with the reduction of this form by the defined number of electrons. The results are consistent with the generation of radicals in F• form. However, the radical at the catalytic center is more rapidly quenched than the accompanying ferryl state of heme a3, very likely by the intrinsic oxidation of the enzyme itself.

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.

Cytosolic microRNA-inducible nuclear translocation of Cas9 protein for disease-specific genome modification.

MicroRNA-dependent mRNA decay plays an important role in gene silencing by facilitating posttranscriptional and translational repression. Inspired by this intrinsic nature of microRNA-mediated mRNA cleavage, here, we describe a microRNA-targeting mRNA as a switch platform called mRNA bridge mimetics to regulate the translocation of proteins. We applied the mRNA bridge mimetics platform to Cas9 protein to confer it the ability to translocate into the nucleus via cleavage of the nuclear export signal. This system performed programmed gene editing in vitro and in vivo. Combinatorial treatment with cisplatin and miR-21-EZH2 axis-targeting CRISPR Self Check-In improved sensitivity to chemotherapeutic drugs in vivo. Using the endogenous microRNA-mediated mRNA decay mechanism, our platform is able to remodel a cell's natural biology to allow the entry of precise drugs into the nucleus, devoid of non-specific translocation. The mRNA bridge mimetics strategy is promising for applications in which the reaction must be controlled via intracellular stimuli and modulates Cas9 proteins to ensure safe genome modification in diseased conditions.

Prediction of co-metabolic degradation of bisphenol A and phenol by kinetic modeling

In this work, a model was proposed to describe the ability of Ralstonia eutropha for co-metabolic transformation kinetic of bisphenol A (BPA) as a non-growth substrate in the absence or presence of phenol as a growth substrate. The effects of cell growth, loss of transformation activity, endogenous cell decay, self-inhibition of BPA, loss of transformation activity, and competitive inhibition between BPA and phenol were included in the proposed model. The model then was validated by comparing the predicated and the experimental data. To evaluate the model predictions under different combinations of phenol/BPA concentrations, the kinetic parameters were individually determined. Therefore, BPA transformation and phenol utilization were predicted successfully by the model for a defined range of concentrations of phenol (15–100 mg.l −1 ) and BPA (5–40 mg.l −1 ). • Co-metabolic transformation of BPA and phenol by Ralstonia eutropha was studied. • Kinetic model was successfully developed to predict co-metabolic degradation. • 44% of the initial BPA was mineralized to CO 2 . • Intermediate compounds were detected by LC-MS.

Linking endogenous decay and sludge bulking in the microbial community to membrane fouling at sub-critical flux

This study examined membrane fouling and associated microbial taxa in a membrane bioreactor operating at a sub-critical flux condition using next-generation amplicon sequencing. The membrane was operated at a sub-critical flux, thus, fouling was not observed until endogenous decay. The observed fouling could be attributed to endogenous decay which was driven by nutrient deficiency at high sludge age and low food-to-microorganisms ratio (decreasing from 0.15 to 0.09 gBOD/gMLVSS.d). Endogenous decay resulted in a sharp decrease of the number of species and evenness between different species (49.7 and 58.9% compared to the inoculum, respectively). The release of dissolved organic matters and cell debris from endogenous decay as well as the excessive growth of filamentous bacteria, e.g. Thiotrichales were the main contributors to membrane fouling. The relative abundance of Thiotrichales significantly correlated with TMP (Pearson R = 0.996, p-value <0.001), indicating this order's contribution to membrane fouling. Other dominant orders in the mixed liquor after endogenous decay such as Rhizobiales, Burkholderiales, Rhodospirillales and Myxococcales, Flavobacteriales can produce extracellular polymeric substances and aggravating membrane fouling. Fouling layers possess highly similar microbial composition with the mixed liquor, with some filamentous microbial orders, e.g. Corynebacteriales and Oligoflexales showing increased relative abundance by 6.83 and 5.64 folds, respectively.

O1 - Temperature Impacts on Streptococcus Mutans Growth and Substrate Utilization Kinetics

Streptococcus mutans has been studied as a model cariogenic bacterium for decades. In spite of myriad studies, growth and substrate utilization kinetics studies have been largely limited to human body temperature (37 C). This makes it difficult to quantitatively assess the impact of temperature on metabolic kinetics. The objective of this study is to evaluate the effect of temperature, substrate, and nutrient conditions on S. mutans biokinetic parameters to provide comparability between biokinetic studies. S. mutans UA159 from ATCC (700610) was maintained on brain heart infusion (BHI) agar plates. S. mutans was grown in a chemostat fed BHI with either sucrose or glucose to calculate yield, maximal substrate utilization rate, endogenous decay, and half saturation constant from cellmass and substrate data assuming Monod kinetics. Pseudo-first order growth rates were determined in batch culture grown on sucrose or glucose with rich (100% BHI) and diluted (10% BHI) media at different temperatures (20-37 C). An Arrhenius plot was used to assess the impact of temperature on growth. Statistical significance was determined at the 95% confidence interval. Cell yield was statistically significantly greater on sucrose compared to glucose (0.2 g biomass/g sucrose compared to 0.1 g biomass/g glucose) at 37 C. The maximal substrate utilization rate was greater on glucose-amended media compared to sucrose. At lower temperatures, cell growth rate was statistically significantly greater on glucose compared to sucrose, but at 37 C, the growth rate was statistically significantly greater for sucrose-amended diluted media. This indicates that growth on sucrose is more strongly impacted by changes in temperature under nutrient-limited conditions, as confirmed by Arrhenius slope for S. mutans at 65 +/- 15 kJ/mol while growing on glucose and 84 +/- 20 kJ/mol on sucrose. Growth on glucose under nutrient rich conditions had the greatest Arrhenius slope of 132 +/- 8 kJ/mol. These findings enhance the understanding of S. mutans biokinetics and provide useful data for comparing studies under different environmental conditions. S. mutans has a greater cell growth yield on sucrose compared to glucose. Further, growth at lower temperatures is more strongly dependent on having rich media regardless of substrate, as growth rate was approximately double in rich media compared to either sucrose or glucose in diluted media at 20 C. At greater temperatures, these nutritional requirements were less important, as kinetic rates were only 10-20% greater when grown in rich media at human body temperature.

Testing an aerobic fluidized biofilm process to treat intermittent flows of oil polluted wastewater

An aerobic fluidized biofilm process of treating oil-polluted wastewater has been studied. A series of batch experiments were conducted using synthetic wastewater and the kinetic coefficients were evaluated. The maximum rate of substrate utilization per unit mass microorganisms (K) was 1.6 days-1, the substrate concentration at one-half the maximum growth rate (Ks) was 26 mg/L, the maximum specific growth rate (m) was 1.0 days-1, the ratio of the mass cells formed to the mass of substrate consumed (Y) was 0.61, and the endogenous decay coefficient (Kd ) was 0.044 days-1. The kinetic coefficients obtained were within the range of municipal wastewater. It was observed that up to 1500 mg/L oil (Motor oil SAE–40) could be degraded in a fluidized bed bioreactor (FBBR). The experiments, however, were limited to the oil concentration within a range of 1000-2600 mg/L. Average biofilm thickness () under specific conditions was found to be 22 m and average oil degradation rate of 0.053 mg oil/mg biomass/hour was measured in the FBBR. The results also support that the increase in the concentration of oil in the treatment process reduced significantly the degradation rate of non-oil carbon.

Kinetics of Cometabolic Transformation of 4-chlorophenol and Phenol Degradation by Pseudomonas putida Cells in Batch and Biofilm Reactors

The biodegradation kinetics of 4-chlorophenol (4-CP) and phenol and microbial growth of Pseudomonas putida (P. putida) cells were estimated in batch and biofilm reactors. The kinetic parameters of cells on phenol were determined using the Haldane formula. The maximum specific growth rate of P. putida on phenol, the half-saturation constant of phenol and the self-inhibition constant of phenol were 0.512 h−1, 78.38 mg/L and 228.5 mg/L, respectively. The yield growth of cells on phenol (YP) was 0.618 mg phenol/mg cell. The batch experimental results for the specific transformation rate of 4-CP by resting P. putida cells were fitted with Haldane kinetics to evaluate the maximum specific utilization rate of 4-CP, half-saturation constant of 4-CP, and self-inhibition constant of 4-CP, which were 0.246 h−1, 1.048 mg/L and 53.40 mg/L, respectively. The negative specific growth rates of cells on 4-CP obtained were fitted using a kinetic equation to investigate the true transformation capacity and first-order endogenous decay coefficient, which were 4.34 mg 4-CP/mg cell and 5.99 × 10−3 h−1, respectively. The competitive inhibition coefficients of phenol to 4-CP transformation and 4-CP to phenol degradation were 6.75 and 9.27 mg/L, respectively; therefore, phenol had a higher competitive inhibition of 4-CP transformation than the converse. The predicted model examining cometabolic transformation of 4-CP and phenol degradation showed good agreement with the experimental observations. The removal efficiencies for phenol and 4-CP were 94.56–98.45% and 96.09–98.85%, respectively, for steady-state performance.

Characterization and modelling of soluble microbial products in activated sludge systems treating municipal wastewater with special emphasis on temperature effect.

Soluble microbial products (SMP) classified as utilization-associated products (UAP) and biomass-associated products (BAP) are the predominant foulants determining fouling in tertiary filtration. However, the exact mechanisms of BAP and UAP generation when treating real wastewaters under cold temperatures remain unrevealed. This paper presents the first study linking biological processes and SMP formation when treating real wastewaters through a combination of bioprocess modelling and advanced SMP characterization. Further, the impact of low operating temperatures on SMP production which has received relatively little attention was studied in detail. The use of liquid chromatography-organic carbon detection (LC-OCD) revealed a significant increase in protein and polysaccharide concentrations in the treated effluents as temperature decreased with a more sensitive impact on polysaccharides. The generation of SMP from biomass decay (BAP) and substrate utilization (UAP) was derived from the LC-OCD data on the basis of protein and polysaccharide mass balances. UAP and BAP yields were estimated as the ratios of the observed generation rates to the rates of substrate utilization and endogenous decay respectively, which both declined as temperature increased. A strong correlation was observed between temperature and BAP/UAP yields whereas the generation of BAP was more temperature sensitive than UAP. Such process modelling can be employed to assist with the optimization of the design and operation of membrane processes when treating wastewaters under challenging conditions like low temperature.

Identifying the mechanisms of sludge reduction in the sulfidogenic oxic-settling anaerobic (SOSA) process: Side-stream sulfidogenesis-intensified sludge decay and mainstream extended aeration

An energy-/cost-efficient and environment-friendly in-situ sludge reduction process, called the sulfidogenic oxic-settling anaerobic (SOSA) was developed recently. However, the underpinning mechanism of sludge reduction by the SOSA process remains elusive. This paper investigated the possible mechanisms of sludge reduction through biomass cultivation in three lab-scale experimental systems: one anoxic-oxic CAS process with a long sludge retention time (SRT) and extended aeration (EAO) process, and two EAO-based in-situ sludge reduction processes, i.e., the conventional oxic-settling anaerobic (COSA) process and the new SOSA process. These three comparative biosystems were operated with identical influent and reactor configurations as well as the same biomass concentrations and SRTs (approximately 5 g/L and 46 days, respectively), and the sludge interchange ratios (between the CAS and side-stream reactors) in COSA and SOSA were both 10% per day. Three systems all achieved high organic (>93%) and total nitrogen (TN) (>74%) removal efficiencies. SOSA produced 29% and 20% less sludge than EAO and COSA, respectively, simultaneously consumed 14% and 8% more oxygen than EAO and COSA, indicating that the sludge reduction in SOSA was not only caused by EAO-based aerobic digestion in the mainstream and conventional anaerobic reactions in the side-stream, but more importantly due to the bioaugmentation of sulfidogenesis. The roles of sulfidogenesis were further studied in batch tests, and the key findings were as follows: i) the SOSA biomass had a faster endogenous decay rate (0.097 d−1) than that of the COSA biomass (0.045 d−1), and ii) sulfidogenesis accelerated anaerobic solubilization, hydrolysis, acidogenesis and acetogenesis by 2.3 – 3.1 times, 6 – 22 %, 22 – 60% and 6 – 22%, respectively. Overall, the mechanisms of sludge reduction in SOSA were unraveled in this study which will help promote its full-scale application in future.

Evaluation of nitrification kinetics for treating ammonium nitrogen enriched wastewater in moving bed hybrid bioreactor

Nitrification kinetics of wastewater characterized by high nitrogen and very low organic carbon was evaluated using a moving bed hybrid bioreactor (MBHBR) in batch mode by varying initial ammonium nitrogen (NH4+-N) concentration in the range of (500–1000) mg L−1 at a pH of 7.8 ± 0.15 and temperature around 28 ± 2°C. A maximum removal efficiency of 89 % in terms of ammonium nitrogen was achieved with initial NH4+-N concentration of 900 mg L−1 having a total biomass concentration around 2000 mg L−1 and at a batch period of 5 days. The experimental results were analyzed in the light of Monod’s kinetic theory and coefficients for nitrification were obtained as maximum substrate removal rate coefficient (μmax) = 0.52 day−1, yield coefficient (Y) = 0.63 mg VSS/mg NH4+-N, half saturation constant (Ks) =603.11 mg NH4+-NL−1 and endogenous decay constant (kd) = 0.008 day−1. The study confirms better nitrification efficiency in presence of attached biomass as compared to suspended growth condition. An interesting observation from the nitrate nitrogen profile establishes the possibility of denitrification, occurring simultaneously even in absence of organic carbon in the wastewater in aerobic MBHBR. This can be supported by the fact that the suspended flocs and/or attached biofilms in hybrid reactor was deep enough for creating necessary conditions for denitrification and the required organic carbon was partially obtained from endogenous degradation of the microorganisms.

Soft part preservation in hyolithids from the lower Cambrian (Stage 4) Guanshan Biota of South China and its implications

Hyoliths, known globally from the Cambrian to the Permian are generally recognized as early lophotrochozoan animals of uncertain phylogenetic position. The calcareous exoskeleton of hyolithids, one of the two subgroups of hyoliths, consist of four elements including a conical conch, an external operculum, and a pair of curved enigmatic helens, but their ecology and internal morphology have long been considered controversial. Here we present for the first time, remarkably preserved hyolithids with helens and interior soft tissues from the Guanshan Biota (Cambrian, Stage 4) of Shijiangjun section, Wuding County in eastern Yunnan Province of South China. Preserved soft tissues and organs encompass the digestive tract, muscle scars and connective tissues between the operculum and conch. Three modes of soft part preservation in hyolithids from the Guanshan Biota are described: (1) preservation through pyritization, (2) sediment-infilling of guts, and (3) bacterial biofilm pseudomorphs (expressed as large internal hollow cavities), resulting from endogenous bacterial decay of soft parts. Such differential preservation of hyolith guts indicates different taphonomic modes for the soft parts of Cambrian animals in the Guanshan Biota. The newly collected material yields the oldest preserved guts in hyolithids from Konservat-biotas, and reveals new evidence for reconstructing hyolithid anatomy, such as the articulation mechanism of the opercula and the internal structures in the conch. Comparisons with younger well-preserved hyolithid specimens indicate that the gut anatomy of hyolithids was evolutionarily conservative from the early Cambrian through to at least the Ordovician.

Kinetics of Anaerobic Digestion of Unripe Plantain Peels

This study was carried out to investigate the biogas production obtained from anaerobic digestion of unripe plantain peels (PP) and the kinetics of the digestion process. 400 g of dried and shredded unripe plantain peels were mixed with 200 ml of water and put into 1 L digester and observed for biogas for hydraulic retention time (HRT) of 15 days by the method of downwards displacement. The cumulative biogas volume obtained after digestion was 285 ml. The COD removal efficiency of 72.5% was achieved. The kinetics of PP digestion was evaluated using first order, Monod, Contois and, Grau second-order models. Results showed that the kinetics of anaerobic digestion of PP followed the first-order model with a constant (K) of 0.095 day-1. Monod kinetics was evaluated and the maximum rate of substrate utilization (K), the half velocity constant (KS), endogenous decay coefficient (Kd), biomass growth yield (Y) and, maximum specific microorganism growth rate (µmax) obtained were 0.7615 day-1, 16.20 mg/l, 0.0047 day-1, 0.0112 mgVSS mgCOD-1 and, 0.009 day-1 respectively. These results revealed that inoculation would be required to increase the rate and volume of biogas production. Both first-order and Monod models gave a high coefficient of determination indicating that first order and Monod models can be used to model the digestion of PP. Contois model gave values of µmax and β as 0.011 day-1 and 0.644 mgCOD mgVSS-1 respectively. The result obtained has shown that the digestion of PP did not follow second-order kinetics.