Specific Degradation Rate Research Articles

Kinetics of thermodegradation of palm kernel oil derived medium‐chain‐length polyhydroxyalkanoates

AbstractOligomeric hydroxyalkanoic acids have potential industrial, medical, and pharmaceutical applications and they can be produced from the degradation of high molecular weight polyhydroxyalkanoates by a number of different ways. Thermal decomposition takes place in the absence of organic solvent and other chemicals and this justified the method of producing low molecular weight PHA as green chemistry. The kinetics for thermal degradation of medium‐chain‐length polyhydroxyalkanoates (mcl‐PHA) prepared from saponified palm kernel oil (SPKO) was studied by thermogravimetric analysis (TGA) technique. Employing the nonisothermal Kissinger's method, the degradation activation energy, Ed, and pre‐exponential factor, A, were 129 kJ mol−1 and 1.15 × 1010 s−1, respectively. Specific degradation rate constant, k was found to increase at higher heating rate. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Development of aerobic granules in sequencing batch reactor with p-nitrophenol as sole carbon source

The present study was aimed at the development of aerobic granules in sequencing batch reactor (SBR) for the biodegradation of p-nitrophenol (PNP). The reactor was started with 50 mg L−1 of PNP. Aerobic granules first appeared within 1 month of the start up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 2–3 mm. The integrity coefficient and granule density was found to be 98% and 1,031 kg m−3 respectively. The settling velocity of granules was found to be in the range of 3 × 10−2 to 4 × 10−2m s−1. The aerobic granules were able to degrade PNP up to 700 mg L−1 at a removal efficiency of 87%. Gas chromatography–mass spectrometry studies confirmed that the biodegradation of PNP occurred by an initial oxygenase attack that resulted in the release of nitrite and the accumulation of hydroquinone. The specific PNP degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific PNP degradation rate up to 0.872 g PNP g−1 VSS−1 d−1 was sustained up to PNP concentration of 200 mg L−1. Higher removal efficiency, good settling characteristics of aerobic granules, makes a SBR suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Biodegradation of 4-methylaniline in a sequencing batch reactor

The biodegradation of the aromatic amine 4-methylaniline (4MA) using an aerobic sequencing batch reactor was evaluated. The specific degradation rate showed an exponential increase during the acclimation of the microorganisms reaching a maximal value of 34 mg 4MA/VSS/h. After the acclimation, the process showed a stable operation. A high similarity index was observed, indicating a low variation in the population diversity. During this period, the physicochemical parameters demonstrated a stable operation of the reactor.

Enhancement of cypermethrin degradation by a coculture of Bacillus cereus ZH-3 and Streptomyces aureus HP-S-01

Degradation of cypermethrin was significantly enhanced in a coculture of Bacillus cereus ZH-3 and Streptomyces aureus HP-S-01. In the pure culture, longer half-lives (t1/2=32.6–43.0h) of cypermethrin were observed, as compared to the mixed cocultures (t1/2=13.0h). The optimal degradation conditions were determined to be 28.2°C and pH 7.5 based on response surface methodology (RSM). Under these conditions, the mixed cultures completely metabolized cypermethrin (50mgL−1) within 72h. Analysis of degradation products of cypermethrin indicated that the microbial consortium converted cypermethrin to α-hydroxy-3-phenoxy-benzeneacetonitrile, 3-phenoxybenzaldehyde and 4-phenoxyphenyl-2,2-dimethyl-propiophenone, and subsequently transformed these compounds with a maximum specific degradation rate (qmax), half-saturation constant (Ks) and inhibition constant (Ki) of 0.1051h−1, 31.2289mgL−1 and 220.5752mgL−1, respectively. This is the first report of a proposed pathway of degradation of cypermethrin by hydrolysis of ester linkage and oxidization of 3-phenoxybenzyl in a coculture. Finally, this coculture is the first described mixed microbial consortium capable of metabolizing cypermethrin.

Kinetics of aerobic phenol biodegradation by the acidophilic and hyperthermophilic archaeon Sulfolobus solfataricus 98/2

Biodegradation of 51–745mgl−1 of phenol by a well-acclimatized strain of Sulfolobus solfataricus, a thermoacidophilic archaeon, was studied in batch experiments at 80°C and pH 3.2. Phenol inhibited growth and specific degradation rates (μ and qS). Fitting the experimental growth data with the Haldane model gave the following kinetic parameters: μ*=0.094h−1,KS=77.7mgl−1, Ki=319.4mgl−1 (R2=0.950). The true μmax, calculated from μ*, was 0.047h−1. A volumetric degradation rate (Vmax) was calculated by fitting the phenol consumption data with the Gompertz model. The value of Vmax increased with initial phenol concentration (Si) up to 14.4mgl−1h−1. The qS values, calculated from Vmax, were fitted with the Haldane equation, yielding qSmax of 0.110gg−1h−1. The yield factor (YX/S) depends on Si and reached a maximum of 0.83gg−1 at Si=93mgl−1.S. solfataricus 98/2 displayed low μmax and qSmax but a good tolerance to phenol (fairly high Ki, K′i, high YX/S). This ability to grow on and degrade phenol (93mgl−1<optimal Si<175mgl−1) at high temperature and low pH is unique and may be useful for removing phenol from hot acidic contaminated effluents. Other possible application could lie in the production of the enzymes involved in the key steps of phenol degradation provided the cloning of the enzymes-related genes in fast-growing mesophiles.

Growth of Trametes Versicolor in Nitro and Hydroxyl Phenol Derivatives

ABSTRACTThis is the first report on the ability of Trametes versicolor to utilize hydroxyl and nitro aromatic compounds as a sole carbon source. The cultivation was carried out in Czapek salt medium supplemented with 0.5 g/l 2-,3-,4-nitrophenol as well as benzene-1,3-diol (resorcinol), benzene-1,2-diol (catechol) and benzene-1,4-diol (hydroquinone), respectively. The hydroxylated phenols were completely utilized for 80–96 hours. The best degradation of the investigated nitrophenols was registered with 2-nitrophenol. The strain was able to degrade it completely in 216 hours.The dynamics of all degradation processes were investigated and characterized by specific growth rate (μmax), metabolic coefficient (k) and rate of degradation (Q). The kinetic parameters established for the best utilized compounds were as follows: benzene-1,3-diol—μmax = 0.065 h−1, k = 9.0, Q = 0.075 h−1; and 2-nitrophenol—μmax = 0.048 h-1, k = 8.5, Q = 0.033 h−1. The intracellular phenol hydroxylase [EC 1.14.13.7], catechol-1,2-dioxygenase [EC 1.13.11.1], and cis, cis-muconate lactonizing enzyme [EC 5.5.1.5] activities were determined in cells cultivated in medium complemented with the best utilized compounds—resorcinol and 2-nitrophenol. The obtained data showed that the substrate specificity of the first enzyme—phenol hydroxylase, is decisive for the rate of degradation of the studied toxic aromatic compounds.

Biodegradation of Paracetamol by Aerobic Granules in a Sequencing Batch Reactor (SBR)

Aerobic granules efficient at degrading paracetamol as the sole carbon and energy resource were successfully developed in a sequencing batch reactor (SBR). Aerobic granules were first observed about 220 days after reactor start-up. The images SEM showed the aerobic granules typically consisted of coccus and bacillus. Meanwhile, the size distribution of aerobic granules was analyzed on day 200. The result indicated that the granules eventually grew to become the dominant form of biomass in the reactor. The granular sludge on day 80 and 200 degraded paracetamol completely in 48 h and 28 h, respectively, indicating that granulation contributed to paracetamol degradation. The specific paracetamol degradation rate was observed to increase with increasing paracetamol initial concentration from 500 to 5000 mg/L, peaked at 1200 mg-MTBE/g-VSS·h, and declined with further increases in MTBE concentration as substrate inhibition effects became significant. This study demonstrates that paracetamol can be effectively degraded by aerobic granules and gives insight into the microorganisms potentially involved in the process.

Penicillium chrysogenum: Phenol Degradation Abilities and Kinetic Model

Phenol is a typical contaminant of the environment generated by many industries. Several fungi had been reported to degrade phenol as the only source of carbon and energy, but many of them are not useful to apply in soil bioremediation process. In this work, we study the dynamics of phenol degradation by a Penicillium chrysogenum, isolated from soil. Degradation of phenol was studied at room temperature and resting mycelium conditions. High specific degradation rates were obtained. Inhibition was observed on the specific growth rate (30 mg l1) and the degradation rate (200 mg l−1). Experimental results were fitted to several models during exponential phase, with the Andrews-Haldane model given the best fit. Dynamic mass balance equations for biomass and phenol during the exponential and stationary growth phases were solved and compared very satisfactorily to experimental outcomes. P. chrysogenum degrades phenol completely during the exponential and stationary growth phases. The results obtained are relevant for its practical applications in soil decontamination processes. Model predictions were satisfactory. This is the first work which describes a kinetic model for phenol biodegradation using a filamentous fungus considering both, exponential and stationary phases, and the first one in which a Penicillium isolate is used.

Isolation and characterization of Rhodococcus sp.BX2 capable of degrading bensulfuron-methyl

Bensulfuron-methyl (BSM) is a widely applicable sulfonylurea herbicides. However, BSM remains in environment for extended period of time (over 100 days) and causes a series of environmental problems. In this study, BX2, a strain presents high BSM degradation abilities, was isolated from an activated sludge sample using a continuous enrichment method and determined to be a member of the genus Rhodococcus based on its physiobiochemical characteristics and 16S rRNA gene sequence. Strain BX2 degradated 92% BSM from an initial concentration of 20 mg/L within a 7- day incubation at 35℃. The specific degradation rate increased with an increase in the initial BSM concentration and the maximum specific degradation rate obtained was 0.146 mg/(mg·d) at 140 mg/L. BSM degradation by strain BX2 can be presented by Haldane’s inhibition equation and the kinetic parameters were: = 16.75 mg/(mg·d), = 7809.36 mg/L and = 2.41 mg/L, respectively. These results indicated that the strain BX2 could be an excellent candidate for bioremediation of BSM-contaminated environments due to its high BSM-degradative ability. Key words: Bensulfuron-methyl (BMS), Rhodococcus sp.BX2, isolation, biodegradation.

Degradation of chlorophenol mixtures in a fed-batch system by two soil bacteria

This work was undertaken to investigate the effect of variations of the feed rate on a fed-batch set-up used to degrade xenobiotics. The mixture of substrates was composed of PCP, 2,4,6 TCP and 2,3,5,6 TeCP (pentachlorophenol, 2,4,6 trichlorophenol and 2,3,5,6 tetrachlorophenol respectively). Two acclimated bacteria isolated from soil were used: Pseudomonas aeruginosa and Achromobacter sp. nov. The different flow rates tested were: I: 0.5 ml∙min -1 , II: 1.67 ml∙min -1 and III: 2.00 ml∙min -1 . Our results show that during fed-batch operation the 2,4,6 TCP exhibits an earlier degradation than the other compounds, for all of the flow rates tested. This indicates that in this case the degradation of the most recalcitrant compounds (PCP and 2,3,5,6 TeCP) is benefited by the increase in biomass of bacteria, due to the metabolisation of a less recalcitrant compound (2,4,6 TCP). The defined parameter, specific degradation rate (SDR), was demonstrated to be very useful for comparing the degradation abilities at different flow rates of a fed-batch system. The degradation efficiencies were shown to be higher than 90% for all of the cases and to decrease as the feed rate increases. However, the SDR, a parameter that involves the rate of degradation and the biomass, increases as the flow rate increases. At a feed flow rate of 2 ml∙min -1 SDR reaches a maximum of 12.476 x 10 -10 mgCP∙h -1 ∙CFU -1 . Finally, among the feed flows tested, taking into account both the degradation efficiency and the SDR, 2 ml∙min -1 is the most convenient flow rate for chlorophenol degradation in fed-batch systems. An even higher degradation efficiency (97%) can be achieved by using the feed rate of 2 ml∙min -1 followed by an additional batch post-treatment of 2 h, with a SDR of 13.136 x 10 -10 mg CP∙h -1 ∙CFU -1 . Keywords: Chlorophenol; fed batch system; aerobic degradation; waste treatment; microbial biocatalysis

Biodegradation dynamics and cell maintenance for the treatment of resorcinol and p-cresol by filamentous fungus Gliomastix indicus

Biodegradation of resorcinol and p-cresol using fungus Gliomastix indicus MTCC 3869 was investigated in batch culture experiments at 28 °C temperature and pH of 6 in the medium up to the initial concentration of 1300 mg/L and 700 mg/L for resorcinol and p-cresol, respectively. Five specific growth kinetic models and five specific degradation rate models were fitted to the experimental data in order to get best fitted kinetic models. The variation of observed growth yield and maintenance energy requirement with the initial substrate concentration was also studied. The model for maintenance energy coefficient was fitted to the experimental data. The model parameters were: m 1 = 0.0135 h −1, k = 0.054, μ max = 0.132 h −1 for resorcinol and m 1 = 0.0229 h −1, k = 0.011, μ max = 0.102 h −1 for p-cresol. Two mathematical models comprising of two sets of ODE were solved simultaneously to get degradation profiles with time. The model with varying growth yield and maintenance energy was found to be most appropriate biodegradation model.

Biodegradation kinetics of 4-fluorocinnamic acid by a consortium of Arthrobacter and Ralstonia strains

Arthrobacter sp. strain G1 is able to grow on 4-fluorocinnamic acid (4-FCA) as sole carbon source. The organism converts 4-FCA into 4-fluorobenzoic acid (4-FBA) and utilizes the two-carbon side-chain for growth with some formation of 4-fluoroacetophenone as a dead-end side product. We also have isolated Ralstonia sp. strain H1, an organism that degrades 4-FBA. A consortium of strains G1 and H1 degraded 4-FCA with Monod kinetics during growth in batch and continuous cultures. Specific growth rates of strain G1 and specific degradation rates of 4-FCA were observed to follow substrate inhibition kinetics, which could be modeled using the kinetic models of Haldane–Andrew and Luong–Levenspiel. The mixed culture showed complete mineralization of 4-FCA with quantitative release of fluoride, both in batch and continuous cultures. Steady-state chemostat cultures that were exposed to shock loadings of substrate responded with rapid degradation and returned to steady-state in 10–15 h, indicating that the mixed culture provided a robust system for continuous 4-FCA degradation.

Improved phenol degradation in high-phenol-fed MBR by membrane-driven containment of non-settling biodegradation microbes

Phenol is one of major pollutants in industrial wastewater with high remediation priority. In this study, the role of membrane in phenol degradation in high-phenol-fed MBR (membrane bioreactor) was explored. Phenol elimination in high-phenol-fed MBRs resulted in complete mineralization and the high-phenol-fed MBR exhibited greater biomass-specific phenol removal rates (0.4–1.5 mg phenol/(mgVSS•d) than the low-phenol-fed MBR. In the high-phenol-fed MBR, filamentous non-settling microbes were more abundant than in the low-phenol-fed MBR. In the following batch experiment, high-acclimated and non-settling microbes were separately collected from the high-phenol-acclimated bioreactor, and their specific phenol degradation was determined at 5.1 mg phenol/(mgVSS•d). The greater specific phenol degradation rate of the non-settling microbes than the observed phenol elimination rate in the high-phenol-fed MBR indicates that the high-phenol-acclimated and non-settling microbes had greater degradation activity than the rest of sludge microbes in the bioreactor. According to these findings, the role of membrane in the high-phenol-fed MBR was identified as the containment of non-settling and biodegradative microbes in bioreactor, and in turn, the membrane-driven increase of non-settling phenol degrading microbes enhanced phenol elimination in the high-phenol-fed MBR.

The acceleration of sludge granulation using the chlamydospores of Phanerochaete sp. HSD

In the present paper, a novel method to accelerate sludge granulation is presented. Inoculation with chlamydospores of Phanerochaete sp. HSD accelerated sludge granulation during the treatment process of phenol wastewater, and the sludge granulation rate reached 66 ± 2% on day 7, 32 days earlier than that of the control inoculated with activated sludge only. Aerobic granule in R1 (AG R1) showed an annual ring-like multilayer structure and a primary core also existed in the nuclear area of the granule. The mechanism of rapid granulation revealed that the chlamydospore could survive in phenol wastewater and form the primary matrix on which aerobic granule was developed layer by layer. In addition, AG R1 developed in a phenol uptake system to counteract the adverse effects of phenol inhibition. Higher tolerance toward wastewater with high phenol strength was exhibited, and the maximum specific phenol degradation rate reached 1.54 g phenol g −1 VSS day −1.

Degradation pathway, toxicity and kinetics of 2,4,6-trichlorophenol with different co-substrate by aerobic granules in SBR

The present study deals with cultivation of 2,4,6-trichlorophenol (TCP) degrading aerobic granules in two SBR systems based on glucose and acetate as co-substrate. Biodegradation of TCP containing wastewater starting from 10 to 360 mg L −1 with more than 90% efficiency was achieved. Sludge volume index decreases as the operation proceeds to stabilize at 35 and 30 mL g −1 while MLVSS increases from 4 to 6.5 and 6.2 g L −1 for R1 (with glucose as co-substrate) and R2 (with sodium acetate as co-substrate), respectively. FTIR, GC and GC/MS spectral studies shows that the biodegradation occurred via chlorocatechol pathway and the cleavage may be at ortho-position. Haldane model for inhibitory substrate was applied to the system and it was observed that glucose fed granules have a high specific degradation rate and efficiency than acetate fed granules. Genotoxicity studies shows that effluent coming from SBRs was non-toxic.

Factors influencing 4-fluorobenzoate degradation in biofilm cultures of Pseudomonas knackmussii B13

Membrane aerated biofilm reactors (MABRs) have potential in wastewater treatment as they permit simultaneous COD minimisation, nitrification and denitrification. Here we report on the application of the MABR to the removal of fluorinated xenobiotics from wastewater, employing a Pseudomonas knackmussii monoculture to degrade the model compound 4-fluorobenzoate. Growth of biofilm in the MABR using the fluorinated compound as the sole carbon source occurred in two distinct phases, with early rapid growth (up to 0.007 h −1) followed by ten-fold slower growth after 200 h operation. Furthermore, the specific 4-fluorobenzoate degradation rate decreased from 1.2 g g −1 h −1 to 0.2 g g −1 h −1, indicating a diminishing effectiveness of the biofilm as thickness increased. In planktonic cultures stoichiometric conversion of substrate to the fluoride ion was observed, however in the MABR, approximately 85% of the fluorine added was recovered as fluoride, suggesting accumulation of ‘fluorine’ in the biofilm might account for the decreasing efficiency. This was investigated by culturing the bacterium in a tubular biofilm reactor (TBR), revealing that there was significant fluoride accumulation within the biofilm (0.25 M), which might be responsible for inhibition of 4-fluorobenzoate degradation. This contention was supported by the observation of the inhibition of biofilm accumulation on glass cover slips in the presence of 40 mM fluoride. These experiments highlight the importance of fluoride ion accumulation on biofilm performance when applied to organofluorine remediation.

Direct ethanol production from cellulosic materials using a diploid strain of Saccharomyces cerevisiaewith optimized cellulase expression

BackgroundHydrolysis of cellulose requires the action of the cellulolytic enzymes endoglucanase, cellobiohydrolase and β-glucosidase. The expression ratios and synergetic effects of these enzymes significantly influence the extent and specific rate of cellulose degradation. In this study, using our previously developed method to optimize cellulase-expression levels in yeast, we constructed a diploid Saccharomyces cerevisiae strain optimized for expression of cellulolytic enzymes, and attempted to improve the cellulose-degradation activity and enable direct ethanol production from rice straw, one of the most abundant sources of lignocellulosic biomass.ResultsThe engineered diploid strain, which contained multiple copies of three cellulase genes integrated into its genome, was precultured in molasses medium (381.4 mU/g wet cell), and displayed approximately six-fold higher phosphoric acid swollen cellulose (PASC) degradation activity than the parent haploid strain (63.5 mU/g wet cell). When used to ferment PASC, the diploid strain produced 7.6 g/l ethanol in 72 hours, with an ethanol yield that achieved 75% of the theoretical value, and also produced 7.5 g/l ethanol from pretreated rice straw in 72 hours.ConclusionsWe have developed diploid yeast strain optimized for expression of cellulolytic enzymes, which is capable of directly fermenting from cellulosic materials. Although this is a proof-of-concept study, it is to our knowledge, the first report of ethanol production from agricultural waste biomass using cellulolytic enzyme-expressing yeast without the addition of exogenous enzymes. Our results suggest that combining multigene expression optimization and diploidization in yeast is a promising approach for enhancing ethanol production from various types of lignocellulosic biomass.

Production of poly-β-hydroxybutyrate (PHB) by Methylobacterium organophilum isolated from a methanotrophic consortium in a two-phase partition bioreactor

The biodegradation of methane, a greenhouse gas, and the accumulation of poly-β-hydroxybutyrate (PHB) were studied using a methanotrophic consortium and an isolated strain thereof. The specific rates for methane consumption were 100 and 17 m g C H 4 g x − 1 h − 1 for the isolate and the consortium, respectively. Also the effect of including 10% (v v −1) of silicone oil in a two-phase partitioning bioreactor (TPPB) was assayed for the elimination of 1% methane in air stream. TPPB allowed a 33–45% increase of methane elimination under growing conditions. Nitrogen limitation was assayed in bioreactors to promote PHB production. Under this condition, the specific methane degradation rate remained unchanged for the consortium and decreased to 36 m g C H 4 g x − 1 h − 1 for the isolated strain. The accumulated PHB in the reactor was 34% and 38% (w w −1) for the consortium and the isolate, respectively. The highest productivity was obtained in the TPPB and was 1 .61 m g PHB g x − 1 h − 1 . The CZ-2 isolate was identified as Methylobacterium organophilum, this is the first study that reports this species as being able to grow on methane and accumulate up to 57% (w w −1) of PHB under nitrogen limitation in microcosm experiments.

Aerobic granular treatment of 2,4‐dichlorophenol

Abstract2,4‐Dichlorophenol (2,4‐DCP) fed aerobic granules were cultivated in a sequencing batch reactor (SBR). Stable and compact granules were obtained in 60 days of SBR operation. Formed granules were compact and strong with closed packed channels. After granulation, effluent chemical oxygen demand and 2,4‐DCP concentrations were 95 and 2.5 mg L−1 with corresponding removal efficiencies of 96% and 95% were achieved. Degradation profile shows a high initial degradation rate which decreases later. Degradation rate was found to be directly proportional to the substrate concentration. Specific degradation rate of 2,4‐DCP was 6.54 mg 2,4‐DCP gVSS−1 h−1 at 60 mg L−1 and specific cell growth rate was 0.042 ± 0.02 day−1. High optical density (OD600) the system shows effective retention of biomass which is the main advantage of present technique.

High-rate biodegradation and metabolic pathways of 4-chloroaniline by aerobic granules

A high-rate degradation of 4-chloroaniline (4-ClA) was achieved by developing mixed-culture microbial granules under aerobic conditions in a sequencing airlift bioreactor (SABR). An essential step in this process was the enrichment of the biomass with improved setting characteristics and high 4-ClA degradation activity by manipulating combined hydraulic and microbial selection pressures via stepwise increases in 4-ClA loading. The seed sludge was conditioned over a 15-day acclimation period to allow the biomass to adapt to the presence of 4-ClA and the preferred short-settling time. Over the subsequent two months, aerobic granular sludge was developed by decreasing the settling time and gradually increasing the 4-ClA loading, and glucose/CH 3COONa was used to facilitate the growth of the 4-ClA-fed biomass. High specific degradation rates of more than 0.27 g gVSS −1 d −1 were sustained for 4-ClA concentrations above 400 mg L −1. At concentrations as high as (8.18 ± 0.06) g L −1, 4-ClA was completely removed, and the biomass concentration was maintained. Degradation kinetics for all tests was described well by the typical substrate-inhibition pattern predicted by the Haldane equation. The aerobic granule primarily degraded 4-ClA via the meta-cleavage pathway.