Biodegradation of monoaromatic hydrocarbons in aquifer columns amended with hydrogen peroxide and nitrate

The ability of indigenous microorganisms to degrade benzene, toluene, ethylbenzene and xylenes (BTEX) in laboratory scale flow-through aquifer columns was tested separately with hydrogen peroxide (110 mg/l) and nitrate (330 mg/l as NO₃⁻) amendments to air-saturated influent nutrient solution. The continuous removal of individual components from all columns relative to the sterile controls provided evidence for biodegradation. In the presence of hydrogen peroxide, the indigeneous microorganisms degraded benzene and toluene (> 95%), meta- plus para-xylene (80%) and ortho-xylene (70%). Nitrate addition resulted in 90% removal of toluene and 25% removal of ortho-xylene. However, benzene, ethylbenzene, meta- and para-xylene concentrations were not significantly reduced after 42 days of operation. Following this experiment, low dissolved oxygen (< 1 mg/l) conditions were initiated with the nitrate-amended column influent in order to mimic contaminated groundwater conditions distal from a nutrient injection well. Toluene continued to be effectively degraded (> 90%), and more than 25% of the benzene, 40% of the ethylbenzene, 50% of the meta- plus para-xylenes and 60% of the ortho-xylene were removed after several months of operation.     

Preparation of core–shell type nanoparticles of diblock copolymers of poly(L‐lactide)/poly(ethylene glycol) and their characterization in vitro

Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The ¹H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002     

Comparative study of the elimination of toluene vapours in twin biotrickling filters using two microorganisms Bacillus cereus S1 and S2

BACKGROUND: To investigate the microbial degradation performance of organic pollutants in the atmosphere using a biotrickling filter, two microorganism strains, Bacillus cereus S1 and Bacillus cereus S2, were selected, identified and inoculated into a twin biotrickling filter for comparison. RESULTS: Both strains showed good performance towards the degradation of model organic pollutants when gas flow rates ranged from 100 to 600 L h⁻¹. For S1, the total maximum removal efficiency (RE) of toluene was maintained nearly 100% not only at gas flow rates of 100 L h⁻¹ corresponding to empty bed residence time (EBRT) 199.44 s, but also at gas flow rates of 200 L h⁻¹ (EBRT = 99.72 s) and 300 L h⁻¹ (EBRT = 66.48 s). However, S2 had a much lower degradation capability; near 100% removal efficiency was obtained only at the gas flow rate of 100 L h⁻¹ although both bacteria belong to the same Bacillus cereus. With further increase in gas flow rate, the total REs for both S1 and S2 decreased slightly at first and then dropped sharply to 46% and 35%, respectively, at an EBRT of 33.24 s, corresponding to a gas flow rate of 600 L h⁻¹. Starvation for between 2 and 10 days resulted in the re‐acclimation times of both strains ranging between 1.0 and 15.5 h. CONCLUSION: Strain S1 would be a better choice for inoculation into a biotrickling filter than strain S2, because of its much higher toluene removal capacity and rapid recovery to full performance. Copyright © 2008 Society of Chemical Industry     

Aerobic degradation by white‐rot fungi of trichloroethylene (TCE) and mixtures of TCE and perchloroethylene (PCE)

BACKGROUND: Trichloroethylene (TCE) and perchloroethylene (PCE) are considered among the most important groundwater pollutants around the world. These compounds are usually found together in polluted environments but little is known about the ability of microorganisms to simultaneously degrade TCE and PCE. RESULTS: Data showed that several species of white‐rot fungi, including Trametes versicolor, Ganoderma lucidum, and Irpex lacteus, degrade substantial levels of TCE in pure culture. T. versicolor was chosen for further study since it degraded higher levels of TCE than the other organisms. Initial glucose concentration and reoxygenation of samples increased the amount of TCE dechlorination, but no significant difference in percentage TCE degradation was observed. T. versicolor was able to degrade 34.1 and 47.7% of PCE and TCE added as mixtures (containing 5 and 10 mg L⁻¹, respectively). CONCLUSIONS: The degradation ability of TCE was extended to other species of white‐rot fungi. Percentage degradation as well as chloride release from mixtures of TCE and PCE showed that T. versicolor degrades mixtures of TCE and PCE almost as well as its ability to degrade individually added TCE or PCE. The results suggest the potential promise of T. versicolor for bioremediation of TCE and PCE in the environment. Copyright © 2008 Society of Chemical Industry     

Surface tension as a limiting factor for aerobic n-alkane biodegradation

A new mathematical model for n-alkane biodegradation in crude oil, heavy oil and paraffinic mixtures is described. The pattern of n-alkane degradation as a function of the inverse of hydrocarbon chain length reported in this paper can be considered as general behaviour for many aerobic n-alkane biodegradation processes. A new interpretation of n-alkane biodegradation as a function of surface tension, is given. A mathematical expression was obtained starting from the degradation values of n-alkane and relative surface tension, which is a parameter independent of fermentation conditions. An interesting parameter, b, was identified which represented the accelerating conversion factor for n-alkane biodegradation. The findings suggested that the n-alkane biodegradation. The findings suggested that he n-alkane biodegradation rate may be affected by the fermentation condition (agitation, aeration, etc.) and by the strain of microorganism, while the behaviour pattern of n-alkane degradation was essentially linked to the substrate characteristics (molecular structure, molecular weight and density).     

海洋丝状真菌转化石油烃的研究

研究从湄洲湾海域分离的4株丝状真菌MF1，MF2，MF3，MF4的生长特性及去除油污的过程，观察在温度26℃，初始油浓度在3g/l,培养12d的过程中培养液的变化，分析培养液的pH值及原油的去除率与时间的关系，结果表明，丝状真菌去除原油的[过程是生物吸附与生物降解相结合的生物转化过程，比较革兰氏阴性细菌与丝状真菌细胞壁组成，结构，得出海洋微生物的脱油作用与其细胞壁有直接的关系。     

The biodegradability of two primary alcohol ethoxylate nonionic surfactants under practical conditions,and the toxicity of the biodegradation products to rainbow trout

A field trial has been performed to measure the biodegradability of two typical alcohol ethoxylate nonionic surfactants, “Dobanol” 45-7 and “Dobanol” 45-11, by dosing them to biological filters in a mixture with domestic sewage. Influent levels were 10 and 25 mg l^?1 of each surfactant and 96–98% degradation was achieved within a temperature range of 5–10°C. The surfactants had no adverse effects on the filters in terms of the usual sanitary parameters (BOD, COD, TOC and ammoniacal nitrogen). Tests on the effluents indicated no residual acute lethal toxicity to rainbow trout Salmo gairdneri).     

脂肪醇聚氧乙烯醚的厌氧与好氧生物降解性

以脂肪醇聚氧乙烯醚(AEO)为目标污染物，在等同条件下做厌氧消化污泥和好氧活性污泥对其生物降解性能的对比实验，得出了同一系列AEO分子中聚氧乙烯基与整个分子的降解难易程度的关系。表明：①污泥会对AEO分子产生吸附一脱附作用而出现假降解率，克服假降解率的干扰是准确测定AEO生物降解性的关键因素；②厌氧和好氧条件下，AEO均可降解，但厌氧降解要稍优于好氧降解；③AEO中聚氧乙烯基的单元数(n)是影响其生物降解的重要因素，相同碳链的直链烷基，生物降解率随n的增加而明显降低。     

微生物聚酯的合成和应用研究进展

微生物聚酯是由发酵技术生产、具有生物降解性的热塑性高分子材料。本文介绍了３－羟基丁酯均聚物（ＰＨＢ）和共聚物的基本结构、生物降解性能、生物合成及其应用研究的进展。     

溶液共混法制备高强度淀粉基完全生物降解塑料薄膜

利用一步溶液共混法，将预糊化的淀粉糊与PvA溶液共混，用乙二醛进行交联，制备淀粉／聚乙烯醇（PVA）完全生物降解塑料薄膜。研究不同乙二醛和甘油的用量对薄膜性能的影响。薄膜的力学性能、热性能和微观形态表征表明，淀粉／PvA体系具有较好的相容性和较高的力学性能，薄膜的拉伸强度和断裂伸长率分别可达到28．52MPa和307．5％。