Microbial Degradation of the Natural Rubber in Tire Tread Compound by a Strain of Nocardia

Tread compound of truck tires is based primarily on natural rubber or blends of natural rubber (NR) and synthetic polymers in combination with high grade carbon black. When the tread compound is attacked by a strain of Nocardia capable of degrading NR, part of the NR in the compound is mineralized, and part is disintegrated to very small black particles. The small black particles consist of the residual rubber and inorganic fillers. At higher NR content, large and deep cavities are formed on the surface of the pieces of the tread compound after microbial disintegration. At lower content of NR, large but very shallow cavities or very small pits can be seen on the tread surface. During microbial growth on the tread compound, isoprene oligomers with molecular weight of about two thousand are produced. Not only the isoprene oligomers, but also butadiene oligomers are produced during microbial disintegration of the tread compound of NR/synthetic rubber blend.     

Investigation of physico-chemical properties and microbial community during poultry manure cocomposting process

Co-composting of poultry manure and rubber wood sawdust was performed with the ratio of 2:1 (V/V) for a period of 60 days. An investigation was carried out to study the extracellular enzymatic activities and structural degradation utilizing Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM). The microbial succession was also determined by using denaturing gel gradient electrophoresis (DGGE). The compost was able to reach its highest temperature of 71 ℃ at day 3 and stabilized between 30 and 40 ℃ for 8 weeks. CMCase, FPase and β-glucosidase acted synergistically in order to degrade the cellulosic substrate. The xylanase activities increased gradually during the composting and reached the peak value of 11.637 U/g on day 35, followed by a sharp decline. Both LiP and MnP activities reached their peak values on day 35 with 0.431 and 0.132 U/g respectively. The FT-IR spectra revealed an increase in aromaticity and a decrease in aliphatic compounds such as carbohydrates as decomposition proceeded. TGA/DTG data exhibited significant changes in weight loss in compost samples, indicating degradation of organic matter. SEM micrographs showed higher amounts of parenchyma exposed on the surface of rubber wood sawdust at day 60, showing significant degradation. DGGE and 16S rDNA analyses showed that Burkholderia sp., Pandoraea sp., and Pseudomonas sp. were present throughout the composting process. Ornithinibacillus sp. and Castellaniella ginsengisoli were only found in the initial stage of the composting, while different strains of Burkholderia sp. also occurred in the later stage of composting.     

Biodegradation of Endosulfan by a Soil Bacterium

A bacterium capable of metabolizing endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine3-oxide) was isolated from cotton-growing soil and effectively shown to degrade endosulfan into endosulfan sulfate. The bacterium degraded 50% of the compound within 3 days of incubation. Endosulfan sulfate was the only terminal product and no other metabolites were formed during the incubation. Endosulfan and its metabolites were analyzed by gas chromatography. The metabolites formed indicated that the organism follows an oxidative pathway for metabolism of this pesticide. Therefore, the present study, microbial degradation of endosulfan by a soil bacterium, may provide a basis for the development of bioremediation strategies to remediate the pollutants in the environment.     

Individual-based modelling of carbon and nitrogen dynamics in soils: Parameterization and sensitivity analysis of microbial components

The fate of soil carbon and nitrogen compounds in soils in response to climate change is currently the object of significant research. In particular, there is much interest in the development of a new generation of micro-scale models of soil ecosystems processes. Crucial to the elaboration of such models is the ability to describe the growth and metabolism of small numbers of individual microorganisms, distributed in a highly heterogeneous environment. In this context, the key objective of the research described in this article was to further develop an individual-based soil organic matter model, INDISIM-SOM, first proposed a few years ago, and to assess its performance with a broader experimental data set than previously considered. INDISIM-SOM models the dynamics and evolution of carbon and nitrogen associated with organic matter in soils. The model involves a number of state variables and parameters related to soil organic matter and microbial activity, including growth and decay of microbial biomass, temporal evolutions of easily hydrolysable N, mineral N in ammonium and nitrate, CO₂ and O₂. The present article concentrates on the biotic components of the model. Simulation results demonstrate that the model can be calibrated to provide good fit to experimental data from laboratory incubation experiments performed on three different types of Mediterranean soils. In addition, analysis of the sensitivity toward its biotic parameters shows that the model is far more sensitive to some parameters, i.e., the microbial maintenance energy and the probability of random microbial death, than to others. These results suggest that, in the future, research should focus on securing better measurements of these parameters, on environmental determinants of the switch from active to dormant states, and on the causes of random cell death in soil ecosystems.     

Moist Olive Husks Addition to a Silty Clay Soil: Influence on Microbial and Biochemical Parameters

To investigate the effects of moist olive husks (MOH-residues) on soil respiration, microbial biomass, and enzymatic (o-diphenoloxidase, β-glucosidase, dehydrogenase and alkaline phosphatase) activities, a silty clay soil was incubated with 0 (control), 8 × 10³ (D), 16 × 10³ (2D) and 80 × 10³ (10D) kg ha^?1 of MOH-residues on a dry weight basis. Soil respiration and microbial biomass data indicated that the addition of MOH-residues strongly increased microbial activity proportionally to the amounts added. Data of qCO₂ suggested that the respiration to biomass ratio of the microbial population was strongly modified by MOH-residues additions during the first 90 days of incubation. The qCO₂ data suggested a low efficiency in energy yields from C oxidation during the first 2 months of soil incubation. qFDA seemed to be relatively unaffected for treatments D and 2D as compared to the control, but was significantly lowered by the application of 10D, showing the lowest hydrolytic activity of microbial biomass in this treatment up to 360 days of incubation.

o-Diphenoloxidase activity was delayed, and this delay was extended with the addition of larger quantities of MOH-residues. Alkaline phosphatase, β-glucosidase and dehydrogenase activities were in line with the findings on microbial biomass changes and activities. The biological and biochemical data suggest that the addition of a large quantity of MOH-residues (80 × 10³ kg ha^?1) strongly modifies the soil characteristics affecting the r- and K-strategist populations, and that these changes last for at least the 360 days of incubation. The data also suggest that application rates exceeding 16 × 10³ kg ha^?1 are not recommended until the agro-chemical and -physical functions of the soil are further studied.     

Alteration of sediment organic matter in sediment microbial fuel cells

The alteration of physico-chemical properties of sediment organic matter (SOM) incubated under current-harvesting conditions as well as no-current producing conditions over 120 days using sediment microbial fuel cell systems was examined. The SOM was microbially oxidized under anaerobic conditions with an electrode serving as a terminal electron acceptor. It was found that SOM around the electrochemically-active electrodes became more humified, aromatic, and polydispersed, and had a higher average molecular weight, along with its partial degradation and electricity generation compared to that for the original sediment. These changes in SOM properties were analogous to those commonly observed in the early stages of the SOM diagenetic process (i.e. humification). Such a humification-like process was evidently more stimulated when electrical current was produced than no-current condition. These new findings associated with microbially-catalyzed electricity generation may present a potential for the energy-efficient remediation, monitoring, and/or management of the geo-environment.     

Anaerobic oxidation of methane coupled to sulfate reduction: Consortium characteristics and application in co-removal of H2S and methane

Anaerobic sludge from a sewage treatment plant was used to acclimatize microbial colonies capable of anaerobic oxidation of methane (AOM) coupled to sulfate reduction. Clone libraries and fluorescence in situ hybridization were used to investigate the microbial population. Sulfate-reducing bacteria (SRB) (e.g., Desulfotomaculum arcticum and Desulfobulbus propionicus) and anaerobic methanotrophic archaea (ANME) (e.g., Methanosaeta sp. and Methanolinea sp.) coexisted in the enrichment. The archaeal and bacterial cells were randomly or evenly distributed throughout the consortia. Accompanied by sulfate reduction, methane was oxidized anaerobically by the consortia of methane-oxidizing archaea and SRB. Moreover, CH₄ and SO₄^2 ? were consumed by methanotrophs and sulfate reducers with CO₂ and H₂S as products. The H₃CSH produced by methanotrophy was an intermediate product during the process. The methanotrophic enrichment was inoculated in a down-flow biofilter for the treatment of methane and H₂S from a landfill site. On average, 93.33% of H₂S and 10.71% of methane was successfully reduced in the biofilter. This study tries to provide effective method for the synergistic treatment of waste gas containing sulfur compounds and CH₄.     

Hybrid microbial electrolytic/UV system for highly efficient organic pollutants removal

This study for the first time proposed an efficient microbial electrolyte/UV system for Methyl Orange decomposition. With an external applied voltage of 0.2 V and cathode aeration of20 mL/min, H_2O_2 could be in-situ generated from two-electron reduction of oxygen in cathode, reaching to 8.1 mg/L in 2 hr and continued to increase. The pollutant removal efficiency of approximate 94.7% was achieved at initial neutral pH, with the activation of ·OH in the presence of UV illumination. Although the nature of its guiding principles remain on the vista of practical exploration, this proof-of-concept study provides an alternative operation pattern of solar–microbial hybrid technology for future wastewater treatment from a basic but multidisciplinary view.     

Microbial aerosol particles in four seasons of sanitary landfill site: Molecular approaches, traceability and risk assessment

Landfill sites are regarded as prominent sources of bioaerosols for the surrounding atmosphere. The present study focused on the emission of airborne bacteria and fungi in four seasons of a sanitary landfill site. The main species found in bioaerosols were assayed using high-throughput sequencing. The SourceTracker method was utilized to identify the sources of the bioaerosols present at the boundary of the landfill site. Furthermore, the health consequences of the exposure to bioaerosols were evaluated based on the average daily dose rates. Results showed that the concentrations of airborne bacteria in the operation area (OPA) and the leakage treatment area (LTA) were in the range of (4684 ± 477)–(10883 ± 1395) CFU/m³ and (3179 ± 453)–(9051 ± 738) CFU/m³, respectively. The average emission levels of fungal aerosols were 4026 CFU/m³ for OPA and 1295 CFU/m³ for LTA. The landfill site received the maximum bioaerosol load during summer and the minimum during winter. Approximately 41.39%– 86.24% of the airborne bacteria had a particle size of 1.1 to 4.7 µm, whereas 48.27%– 66.45% of the airborne fungi had a particle size of more than 4.7 µm. Bacillus sp., Brevibacillus sp., and Paenibacillus sp. were abundant in the bacterial population, whereas Penicillium sp. and Aspergillus sp. dominated the fungal population. Bioaerosols released from the working area and treatment of leachate were the two main sources that emerged in the surrounding air of the landfill site boundary. The exposure risks during summer and autumn were higher than those in spring and winter.     

Nitrification performance evaluation of activated sludge under high potassium ion stress during high-ammonia nitrogen organic wastewater treatment

The recycling reverse osmosis（RO） membrane concentrate of some high-ammonia nitrogen（NH₄⁺-N） organic wastewater to the biological unit could cause potassium ion（K⁺） accumulation, thereby affecting the removal of NH₄⁺-N by activated sludge. Thus, the effects of high K⁺ stress on activated sludge nitrification performance was studied. The results showed that the high K⁺ stress promoted the floc sludge to produce more extr...