Aerobic Laboratory Conditions Research Articles

Correlation of Two Biodegradability Indices of PLA-Based Polymers under Thermophilic Aerobic Laboratory Conditions

The biodegradation of bioplastics is a topic of interest worldwide. This work aims to measure the biodegradability of five polylactic acid (PLA)-based bioplastics under aerobic, thermophilic laboratory conditions and correlate their weight loss with their CO2 generation over a 3-month period, as both are considered indexes of biodegradation. The experimental design was based on the simulation of composting conditions by placing the bioplastic samples mixed with compost in sealed glass vessels that were regularly opened. The results showed significant variability in biodegradation, as dry weight losses ranged from 15.1–99.7%, while CO2 generation ranged from 9.2–14.9 g C–CO2/kg dry mixture (bioplastic + inoculum) depending on the sample. Moreover, no significant correlation between the weight losses and the gross CO2 production was calculated (p = 0.656), indicating the importance of carefully selecting the methods to assess biodegradation potential. This lack of correlation also reveals that different pathways are likely involved during the biodegradation of bioplastics and that the weight loss alone cannot indicate the conversion of solid C to CO2. This work proposes the need to develop an optimal degradation index for bioplastics that would provide a better understanding of their biodegradability in composting reactors. This index should combine dry weight loss and CO2 generation to assess the biodegradation of bioplastics with high confidence.

High nitrogen isotope fractionation of nitrate during denitrification in four forest soils and its implications for denitrification rate estimates

Denitrification is a major process contributing to the removal of nitrogen (N) from ecosystems, but its rate is difficult to quantify. The natural abundance of isotopes can be used to identify the occurrence of denitrification and has recently been used to quantify denitrification rates at the ecosystem level. However, the technique requires an understanding of the isotopic enrichment factor associated with denitrification, which few studies have investigated in forest soils. Here, soils collected from two tropical and two temperate forests in China were incubated under anaerobic or aerobic laboratory conditions for two weeks to determine the N and oxygen (O) isotope enrichment factors during denitrification. We found that at room temperature (20°C), NO3− was reduced at a rate of 0.17 to 0.35μgNg−1h−1, accompanied by the isotope fractionation of N (15ε) and O (18ε) of 31‰ to 65‰ (48.3±2.0‰ on average) and 11‰ to 39‰ (18.9±1.7‰ on average), respectively. The N isotope effects were, unexpectedly, much higher than reported in the literature for heterotrophic denitrification (typically ranging from 5‰ to 30‰) and in other environmental settings (e.g., groundwater, marine sediments and agricultural soils). In addition, the ratios of Δδ18O:Δδ15N ranged from 0.28 to 0.60 (0.38±0.02 on average), which were lower than the canonical ratios of 0.5 to 1 for denitrification reported in other terrestrial and freshwater systems. We suggest that the isotope effects of denitrification for soils may vary greatly among regions and soil types and that gaseous N losses may have been overestimated for terrestrial ecosystems in previous studies in which lower fractionation factors were applied.

Oxygen-limited cellobiose fermentation and the characterization of the cellobiase of an industrial Dekkera/Brettanomyces bruxellensis strain

The discovery of a novel yeast with a natural capacity to produce ethanol from lignocellulosic substrates (second-generation ethanol) is of great significance for bioethanol technology. While there are some yeast strains capable of assimilating cellobiose in aerobic laboratory conditions, the predominant sugar in the treatment of lignocellulosic material, little is known about this ability in real industrial conditions. Fermentations designed to simulate industrial conditions were conducted in synthetic medium with glucose, sucrose, cellobiose and hydrolyzed pre-treated cane bagasse as a different carbon source, with the aim of further characterizing the fermentation capacity of a promising Dekkera bruxellensis yeast strain, isolated from the bioethanol process in Brazil. As a result, it was found (for the first time in oxygen-limiting conditions) that the strain Dekkera bruxellensis GDB 248 could produce ethanol from cellobiose. Moreover, it was corroborated that the cellobiase activity characterizes the enzyme candidate in semi-purified extracts (β-glucosidase). In addition, it was demonstrated that GDB 248 strain had the capacity to produce a higher acetic acid concentration than ethanol and glycerol, which confirms the absence of the Custer effect with this strain in oxygen-limiting conditions. Moreover, it is also being suggested that D. bruxellensis could benefit Saccharomyces cerevisiae and outcompete it in the industrial environment. In this way, it was confirmed that D. bruxellensis GDB 248 has the potential to produce ethanol from cellobiose, and is a promising strain for the fermentation of lignocellulosic substrates.

Mineralização de nitrogênio e carbono em solos sob plantações de eucalipto, em uma sequência de idades

A estimativa da mineralização de N e de C é essencial no desenvolvimento de práticas que maximizem a eficiência no uso de N, especialmente no caso do eucalipto, que apresenta baixa magnitude de resposta à fertilização nitrogenada. Foram estimadas as taxas de mineralização de N e de C e avaliados os potenciais de mineralização de N e de C de solos sob plantações de eucalipto de 1, 3, 5 e 13 anos de idade, crescendo sob condições edafoclimáticas semelhantes. Amostras de solo foram coletadas na profundidade de 0-10 cm, em novembro de 2003. Essas amostras foram incubadas por períodos sucessivos de 1, 1, 1, 2, 2, 4, 4 e 4 semanas, totalizando 19 semanas, sob condições aeróbias, em laboratório. O N mineralizado das amostras incubadas foi extraído periodicamente e determinado por colorimetria, e o C mineralizado, por titulação após liberação de C-CO2 a cada período de incubação. O valor médio de N mineralizado acumulado (Nm) foi de 58 mg kg-1 de N no solo e não diferiu significativamente entre as idades. As quantidades de N potencialmente mineralizável (No) variaram de 58 a 87 mg kg-1, o que representou 3,4 a 5,2 % do N total do solo (Nt), tomando por base a razão No:Nt. A forma predominante de N mineral em todas as idades foi o N-NH4+. As quantidades totais de C mineralizado (Cm) diferiram significativamente entre as idades, variando de 606 a 1.122 mg kg-1 de C no solo. O C potencialmente mineralizável (Co) dos solos foi, em média, de 862 mg kg-1 de C-CO2, o que representou 3,4 % do C orgânico do solo (Corg), de acordo com a razão Co:Corg. A taxa e o potencial de mineralização de C e N não foram influenciados pela idade das plantações do eucalipto. As reservas de N potencialmente mineralizável dos solos seriam suficientes para atender à demanda de N pelo eucalipto em rotações futuras.

Release of Isoprene and Monoterpenes during the Aerobic Decomposition of Orange Wastes from Laboratory Incubation Experiments

The release of isoprene and 12 monoterpenes during the decomposition of orange wastes was studied under controlled aerobic conditions in laboratory for a period of 2 months. Monoterpenes (mainly limonene, beta-myrcene, sabinene, and alpha-pinene) dominated among the released volatile organic compounds, but isoprene was only a very minor constituent. Two time windows with peak microbial activity were indicated by CO2 emission fluxes and waste temperature, both of which reached their maximums 3-4 days and 15-20 days after the incubation, respectively. Although isoprene had only one emission peak synchronizing with the first peak microbial activity, monoterpenes had relatively high emission rates, but they decreased at the beginning without correlation to the first peak of microbial activity, due largely to direct volatilization of these monoterpenes primarily present in orange substrates as inherited constituents. However, after the initial decrease the emission rates of monoterpenes rose again in conjunction with the second peak of microbial activity, indicating secondary production of these monoterpenes through microbial activity. On the basis of monitored emission fluxes, the amounts of secondarily formed monoterpenes from microbial activity well surpassed those inherited in the orange wastes. Production of total terpenes reached 1.10 x 10(4) mg kg(-1) (dry weight), of which limonene alone was 63%. For either limonene or total terpenes, about 95% of their emission occurred in the first 30 days, implying that organic wastes might give off considerable amount of terpenes during early disposal under aerobic conditions before the conventional anaerobic landfilling, and emission measurements just in landfills might underestimate the waste-related emissions of reactive organic gases.

Determination of soil biodegradation half-lives from simulation testing under aerobic laboratory conditions: A kinetic model approach

A kinetic model approach for determination of biodegradation half-lives from soil simulation testing is presented. The model describes transformation of the parent compound to metabolites and formation of bound (non-extractable) residues as well as mineralization in soil under aerobic laboratory conditions. Experimental data for several pesticide compounds from various soil simulation tests are used for fitting kinetic rate constants. Formation of bound residues, either from parent or metabolites or from both, can be described by first-order kinetics for all examined compounds. Correlation of kinetic rate constants of primary degradation and formation of bound residues from parent compound suggests a common mechanism, presumably co-metabolic microbial activity, for both processes. Inverse modelling allows for estimation of primary degradation half-life DegT50 instead of disappearance time DT50. Application of the DegT50 approach in PBT assessment might result in a different persistent classification for which the developed model delivers an appropriate evaluation tool.

Degradation of imazosulfuron in different soils-HPLC determination.

Imazosulfuron, 1-(2-chloroimidazo [1,2-a] pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea, is a new sulfonylurea herbicide applied once per growing season. It is highly active at low application levels and is used to control most annual and perennial broad-leaf weeds and some grasses in cereal crop. In this work the degradation of imazosulfuron in four different soils was investigated under aerobic laboratory conditions to evaluate its environmental fate. Test soils were treated with this herbicide in acetonitrile to obtain a final concentration of 0.2 mg kg(-1) (100 g ha(-1)), extracted with methylene chloride and analyzed by reversed-phase liquid chromatography (RP-HPLC) using a C(18) column coupled with UV detection. Recoveries of spiked soils ranged from 84.3 to 99.8% (RDS 0.0-4.9%; n = 4). The limits of quantitation ranged from 0.002 to 0.004 mg kg(-1). Imazosulfuron half-life, t(1/2), was calculated in each of the investigated soil. In aerobic conditions it ranged between 1 and 50 days.

Acid-stimulated phosphate uptake by activated sludge microorganisms under aerobic laboratory conditions

Activated sludge inocula taken from five different wastewater treatment plants were grown aerobically under laboratory conditions on mineral salts medium containing either glucose or skimmed milk powder as carbon source. Cultures showed increases of between 50% and 143% in levels of phosphate uptake from the medium when the growth pH was 5.5 rather than 7.5. Of 100 individual sludge microbial isolates studied, 34 demonstrated such acid-stimulated luxury phosphate uptake; the optimum pH for the process was shown to lie between 5.0 and 6.5. Enhanced phosphate removal by these isolates was accompanied by increases of between 2 and 10.5-fold in their polyphosphate content; this was visualised as intracellular inclusions. Acid-stimulated luxury phosphate uptake by environmental microorganisms is a previously-unrecognised phenomenon that may have application in novel technologies for nutrient removal from wastewaters.

Nitrogen Availability from Surface‐Applied and Soil‐Incorporated Crop Residues

AbstractManagement systems which maintain crop residues on the soil surface have prompted a need for more detailed information regarding crop residue N availability. Such information is needed from both agronomic and environmental standpoints. Our study examined the placement effects of 15N tagged alfalfa (Medicago sativa L.), sorghum [Sorghum bicolor (L.) Moench], and wheat (Triticum aestivum L.) residues on crop residue N availability in association with eight Oklahoma surface soils representing five soil orders. The experiment was conducted under aerobic laboratory conditions, and involved 0.25‐mm crop residue materials and 2‐mm soil particles. Crop residue N availability was determined on the basis of N mineralized during short‐term (14 d) and long‐term (168 d) incubation. Mean amounts of crop residue N mineralized ranged from <18 kg N ha−1 for sorghum and wheat (<28% of residue N) to 55 kg N ha−1 for alfalfa (35% of residue N). Surface placement of crop residue reduced residue N availability compared to soil incorporation, but the differences were only equivalent to 1 to 7 kg N ha−1. Relative to residue type, the influence of soil type on crop residue N mineralization was secondary. Overall, differences in crop residue N availability associated with residue placement should have minor agronomic and environmental impact.

Degradation and mineralization of 3-chlorobiphenyl by a mixed aerobic bacterial culture.

A mixed bacterial culture obtained from polychlorinated-biphenyl-contaminated river sediments proved capable of degrading 3-chlorobiphenyl (3-CB) under aerobic laboratory conditions. Almost total mineralization of 150 mg/l of 3-CB occurred when, after 3 days of incubation, the mineral medium was supplied with benzoic acid as a carbon source. Two strains of Pseudomonas capable of degrading the substrate to 3-chlorobenzoic acid and a strain of Pseudomonas fluorescens capable of co-metabolizing this metabolite were selected from the mixed culture. A nearly stoichiometric amount of chloride, which defines the percentage of total mineralization, was eliminated during mixed culture growth.

Soil Nitrogen Mineralization in the Presence of Surface and Incorporated Crop Residues

AbstractThe increasing adoption of farming practices which maintain crop residues on the soil surface has created a need for more detailed information regarding associated soil N availability. This study examines the effects of crop residue placement and type on soil N availability for a range of soils. Representative field rates of alfalfa (Medicago saliva L.), corn (Zea mays L.), oat (Avena saliva L.), peanut (Arachis hypogaea L.), sorghum, (Sorghum sudanense (Pipe;:) Stapf.), soybean (Glycine max L.), and wheat (Triticum aestivum L.) crop residues were applied to eight Oklahoma surface soils. The experiment was conducted under aerobic laboratory conditions at 35 °C, and involved 2‐mm soil particles and 0.25‐mm crop residue materials. The N availability was measured on the basis of indigenous and fertilizer‐derived soil N mineralized during short‐ (14 d) and long‐ (84 d) term incubation. Short‐term, an initial depression (more than 80% with corn) in net mineralization occurred with nonlegume residue additions. The depression was enhanced when the residues were incorporated rather than left on the soil surface. The relative depression was greater with the newly formed, fertilizer‐derived soil N than the older, indigenous soil N. On the other hand, N mineralization was enhanced more than 50% with the alfalfa addition. Effects of crop residue type on N mineralization showed ranges up to threefold or more and generally proceeded in the order alfalfa > peanut > soybean > oat ≥ sorghum > wheat > com. Long‐term, N mineralization for all systems was more comparable to that without residue additions.