Effects of community-accessible biochar and compost on diesel-contaminated soil

Petroleum pollution is a global problem that requires effective and accessible remediation strategies that takes ecosystem functioning into serious consideration. Bioremediation can be an effective tool to address the challenge. In this study, we used a mesocosm experiment to evaluate the effects of locally sourced and community produced biochar and compost amendments on diesel-contaminated soil. At the end of the 90-day experiment, we quantified the effects of the amendments on total petroleum hydrocarbons (C9-C40) (TPH) and soil pH, organic matter, aggregate stability, soil respiration, extractable phosphorus, extractable potassium, and micronutrients (Mg, Fe, Mn, and Zn). We observed significantly higher TPH degradation in compost-amended soils than in controls and soils amended with biochar. We propose that the addition of compost improved TPH biodegradation by augmenting soil nutrient content and microbial activity. Our results suggest that community-accessible compost can improve TPH biodegradation, and that implementation is possible at the community level.     

Detection of catabolic genes in indigenous microbial consortia isolated from a diesel-contaminated soil

Bioremediation is often used for in situ remediation of petroleum-contaminated sites. The primary focus of this study was on understanding the indigenous microbial community which can survive in contaminated environment and is responsible for the degradation. Diesel. toluene and naphthalene-degrading microbial consortia were isolated from diesel-contaminated soil by growing on selective hydrocarbon substrates. The presence and frequency of the catabolic genes responsible for aromatic hydrocarbon biodegradation (xylE, ndoB) within the isolated consortia were screened using polymerase chain reaction PCR and DNA DNA colony hybridization. The diesel DNA-extract possessed both the xy/E catabolic gene for toluene, and the nah catabolic gene for polynuclear aromatic hydrocarbon degradation. The toluene DNA-extract possessed only the xylE catabolic gene, while the naphthalene DNA-extract only the ndoB gene. Restriction enzyme analysis with HaeIII indicated similar restriction patterns for the xylE gene fragment between toluene DNA-extract and a type strain, Pseudomonas putida ATCC 23973. A substantial proportion (74%) of the colonies from the diesel-consortium possessed the xylE gene, and the ndoB gene (78%), while a minority (29%) of the toluene-consortium harbored the xylE gene. 59% of the colonies from the naphthalene-consortium had the ndoB gene, and did not have the xylE gene. These results indicate that the microbial population has been naturally enriched in organisms carrying genes for aromatic hydrocarbon degradation and that significant aromatic biodegradative potential exists at the site. Characterization of the population genotype constitutes a molecular diagnosis which permits the determination of the catabolic potential of the site to degrade the contaminant present.     

Effects of soil organic matter and bacterial community shift on bioremediation of diesel-contaminated soil

Bioremediation of diesel-contaminated soils were applied to investigating effects of soil organic matter (SOM) and bacterial community shift. Soil samples were artificially contaminated with diesel oil, ranging from 4000 to 12000 mg/kg soil, remediated with laboratory-scale landfarming batch applications. The SOM levels in our experiment were 2.3% (presented as SOM15), 8.9% (SOM092), and 11.8% (SOM125). Based on each of the SOM levels, bioremediation approaches of bioaugmentation (BA015, BA092, and BA125) and using indigenous microorganisms as control groups (CT015, CT092, and CT125) were tested. After about 300-day operation, total petroleum hydrocarbon (TPH) degradation efficiency became 73%, 63%, and 59% in SOM015, SOM092, and SOM125, respectively. Their 1st order degradation rates also reduced with the increase of SOM. We preliminarily concluded that SOM affected the TPH degradation efficiency and 1st degradation rates. With a logarithm transformation, the degradation pattern of SOM092 and SOM125 found to resemble each other. No apparent improvement was found from the BA batches. Our Intergenic spacer (ITS) microarray result indicated the existence of diesel-degrading bacteria in the indigenous communities. Nonmetric multidimensional scaling (MDS) based on terminal restriction fragment length polymorphism (T-RFLP) data indicated that 1) CT community became similar to BA community, once the 1st degradation stage started, impling an activation of the indigenous bacteria; 2) the degradation stage affected the community dynamics more than the SOM or the remediation approaches could do, and 3) both BA092 and BA125 located in the same cluster on the MDS plot all the time, revealing the similar communities. The similar communities might cause the comparable degradation patterns in SOM092 and SOM125. The bacteria community shift found useful in explaining the TPH degradation performance.     

A model study of pesticide biodegradation in soil

This study addresses the efficiency of microbial preparations to degrade pesticide residues in soil. A method to degrade pesticides DNOC and pendimethalin using Pseudomonas and Arthrobacter bacteria with a fertilizer is described.     

On-line estimation of biodegradation in an unsaturated soil

The objective of this study was to develop a model-based estimator of biodegradation in unsaturated soil. This would allow real-time assessment of the efficiency of treatment bioprocesses, such as bioventilation and biopile, and eventually permit optimization through the implementation of control strategies. Based on a reduced-order model, an asymptotic observer was designed to estimate on-line the contaminant concentration, using carbon dioxide measurement. Two observer-based estimators were built to approximate: (1) the specific microbial growth rate; and (2) the biocontact kinetics representing the soil resistance to contaminant biodegradation. State observers and parameter estimators were confronted with the experimental results of biodegradation in microcosms. Hexadecane was used as the model compound, representing petroleum hydrocarbons. Three water contents, corresponding to 20%, 50% and 80% of the water-holding capacity, were tested. The asymptotic observer is able to predict hexadecane depletion with an error on the overall time trajectories of 13%, 8% and 4% for the dry, intermediate and wet soils, respectively, which is acceptable given that all the biokinetic parameters were identified from a biodegradation experiment in liquid phase. The observer-based estimator of the specific microbial growth rate, based on the CO₂ measurement, was successfully calibrated using the off-line measurements of hexadecane as validation data, and allowed estimation of the time when biodegradation switched from a microbial to a biocontact limitation. The biocontact kinetics was also identified on-line, using an estimator based on the hexadecane not in biocontact. These results are very encouraging with respect to the potential for on-line assessment of the performance of treatment bioprocesses in unsaturated soils.     

Enhanced crude oil biodegradation in soil via biostimulation

Research on feasible methods for the enhancement of bioremediation in soil contaminated by crude oil is vital in oil-exporting countries such as Kuwait, where crude oil is a major pollutant and the environment is hostile to biodegradation. This study investigated the possibility of enhancing crude oil bioremediation by supplementing soil with cost-effective organic materials derived from two widespread locally grown trees, Conocarpus and Tamarix. Amendments in soils increased the counts of soil microbiota by up to 98% and enhanced their activity by up to 95.5%. The increase in the biodegradation of crude oil (75%) and high levels of alkB expression substantiated the efficiency of the proposed amendment technology for the bioremediation of hydrocarbon-contaminated sites. The identification of crude-oil-degrading bacteria revealed the dominance of the genus Microbacterium (39.6%), Sphingopyxis soli (19.3%), and Bordetella petrii (19.6%) in unamended, Conocarpus-amended, and Tamarix-amended contaminated soils, respectively. Although soil amendments favored the growth of Gram-negative bacteria and reduced bacterial diversity, the structures of bacterial communities were not significantly altered.     

Rapid biodegradation of metsulfuron-methyl by a soil fungus in pure cultures and soil

Summary Four strains of bacteria, 9 strains of fungi and 20 strains of actinomycetes capable of utilizing metsulfuron-methyl as sole carbon and energy source were isolated from a metsulfuron-methyl-treated soil by the enrichment culture method. A fungus named DS11F was selected as the most highly effective one according to the maximum tolerance concentration of 1,200 mg l⁻¹ and metsulfuron-methyl-degrading rate of 0.0716 g g⁻¹ cells h⁻¹, and was identified as an unknown strain of Penicillium sp. on the basis of colony growth, morphology and biochemical characteristics.␣Through liquid pure culture, the optimal metsulfuron-methyl-degrading conditions of DS11F were determined to be metsulfuron-methyl concentration 22.6 mg l⁻¹, inoculum concentration 12.25 mg l⁻¹, pH 7.0 and temperature 30°C. As additional C sources, supernatant of soaked compost could increase metsulfuron-methyl degradation by 8%, but glucose was ineffective. DS11F inoculation was found to significantly enhance the degradation of metsulfuron-methyl in soil, with the reduction of the concentration reaching 50% in 6 days. Admixture of compost could promote metsulfuron-methyl degradation to some extent. The growth of the inocula in the soils remained dominant and degradation resumed immediately when metsulfuron-methyl was applied again. The results show that addition of the isolated Penicillium sp. enhances the degradation of metsulfuron-methyl in water and soil.     

Porous biocarrier-enhanced biodegradation of crude oil contaminated soil

Soil contamination with crude oil from petrochemicals and oil exploitation is an important worldwide issue. Comparing available remediation techniques, bioremediation is widely considered to be a cost-effective choice; however, slow degradation of crude oil is a common problem due to the low numbers of bacteria capable of degrading petroleum hydrocarbons and the low bioavailability of contaminants in soil. To promote crude oil removal, biocarrier for immobilization of indigenous hydrocarbon-degrading bacteria was developed using porous materials such as activated carbon and zeolite. Microbial biomass reached 10¹⁰ cells g^?1 on activated carbon and 10⁶ cells g^?1 on zeolite. Total microbial and dehydrogenase activities were approximately 12 times and 3 times higher, respectively, in activated carbon than in zeolite. High microbial colonization by spherical and rod shapes were observed for the 5–20 μm thick biofilm on the outer surface of both biocarriers using electronic microscopy. Based on batch-scale experiments containing free-living bacterial cultures and activated carbon biocarrier into crude oil contaminated soil, biocarrier enhanced the biodegradation of crude oil, with 48.89% removal, compared to natural attenuation with 13.0% removal, biostimulation (nutrient supplement only) with 26.3% removal, and bioaugmentation (free-living bacteria) with 37.4% removal. In addition, the biocarrier increased the bacterial population to 10⁸ cells g^?1 dry soil and total microbial activity to 3.5 A₄₉₀. A hypothesis model was proposed to explain the mechanism: the biocarrier improved the oxygen, nutrient mass transfer and water holding capacity of the soil, which were the limiting factors for biodegradation of non-aqueous phase liquid (NAPL) contaminants such as crude oil in soil.Scientific relevanceThis study explored the role of biocarrier in enhancing biodegradation of hydrophobic contaminants such as crude oil, and discussed the function of biocarrier in improving oxygen mass transfer and soil water holding capacity, etc.     

High-temperature hydrocarbon biodegradation activities in Kuwaiti desert soil samples

Soil samples taken monthly from the Burgan South oil field of Kuwait for one year degraded crude oil, phenanthrene, and hexadecane. Bacteria were better degraders at high-temperature (55°C) than fungi, especially in the drier, hotter months. Depending on the period of sampling, bacteria degraded hydrocarbons in the range of 46–86% (crude oil), 42–100% (hexadecane) and 5–58% (phenanthrene). Fungi alone accounted for degradation by 20–81% (crude oil), 30–95% (hexadecane) and less than 55% (phenanthrene).     

Aerobic biodegradation of propylene glycol by soil bacteria

Propylene glycol (PG) is a main component of aircraft deicing fluids and its extensive use in Northern airports is a source of soil and groundwater contamination. Bacterial consortia able to grow on PG as sole carbon and energy source were selected from soil samples taken along the runways of Oslo Airport Gardermoen site (Norway). DGGE analysis of enrichment cultures showed that PG-degrading populations were mainly composed by Pseudomonas species, although Bacteroidetes were found, as well. Nineteen bacterial strains, able to grow on PG as sole carbon and energy source, were isolated and identified as different Pseudomonas species. Maximum specific growth rate of mixed cultures in the absence of nutrient limitation was 0.014 h^?1 at 4 °C. Substrate C:N:P molar ratios calculated on the basis of measured growth yields are in good agreement with the suggested values for biostimulation reported in literature. Therefore, the addition of nutrients is suggested as a suitable technique to sustain PG aerobic degradation at the maximum rate by autochthonous microorganisms of unsaturated soil profile.     

污染土壤中多环芳烃生物降解的调控研究

选用温度、湿度、表面活性剂ＴＷ８０和ＣＮＰ比４个因素为调控因子,采用正交法进行周期为１５０天的实验研究．结果表明,３０天后,土壤中ＰＡＨｓ的降解率可达４４．５～７４．６％,６０天后,达７０．４～９３．７％,降解率的不同与调控条件显著相关．在此期间,降解最佳条件为４０℃,湿度２５％,ＣＮＰ比为１２０１０１,ＴＷ８０分别为２００～５００ｍｇ·ｋｇ－１．实验结束时,土壤中ＰＡＨｓ的降解率达９１．２～９９．８％．降解的最佳条件是４０℃,湿度１５％．经Ｒ值判别表明,不同时期各因子对ＰＡＨｓ降解影响有所不同．温度对ＰＡＨｓ降解影响较大,表面活性剂对土壤中ＰＡＨｓ的生物降解有调控作用．     

表面活性剂TW-80对土壤中多环芳烃生物降解的影响

以表面活性剂TW80为供试物,进行了为期150d的实验研究,并分别在30、60和150d间隔采样监测PAHs降解率。结果表明,30d后,土壤中PAHs的降解率达90%,比对照提高约30%.60d后,浓度为10000mg·kg^-1表面活性剂的土壤和对照中,PAHs降解率从65.1%和60%迅速提高到93.8%和79.2%.其它处理中,PAHs的平均降解率仅比30d的结果提高4%.150d后,所有处理中PAHs的降解率均达到90%以上。可以认为,表面活性剂能提高PAHs的生物可利用性,加快PAHs的降解速率,从而减少污染暴露时间。但表面活性剂浓度过高可抑制微生物活性。研究还发现,TW80土壤中含有优势真菌。经鉴定为常见青霉、蠕形青霉、淡紫青霉和顶孢头孢霉。它们是土壤PAHs迅速降解的动因.     

Anaerobic biodegradation of no. 2 diesel fuel in soil: a soil column study

Soil and sediments are contaminated with petroleum hydrocarbons in many parts of the world. Anaerobic degradation of petroleum hydrocarbon is very relevant in removing oil spills in the anaerobic zones of soil and sediments. This research investigates the possibility of degrading no. diesel fuel under anaerobic conditions. Anaerobic packed soil columns were used to simulate and study in situ bioremediation of soil contaminated with diesel fuel. Several anaerobic conditions were evaluated in soil columns, including sulfate reducing, nitrate reducing, methanogenic, and mixed electron acceptor conditions. The objectives were to determine the extent of diesel fuel degradation in soil columns under various anaerobic conditions and identify the best conditions for efficient removal of diesel fuel. Diesel fuels were degraded significantly under all conditions compared to no electron supplemented soil column (natural attenuation). However, the rate of diesel degradation was the highest under mixed electron acceptor conditions followed in order by sulfate reducing, nitrate reducing, and methanogenic conditions. Under mixed electron acceptor condition 81% of diesel fuel was degraded within 310 days. While under sulfate reducing condition 54.5% degradation of diesel fuel was observed for the same period. This study showed evidence for diesel fuel metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.     

Plant and soil enantioselective biodegradation of racemic phenoxyalkanoic herbicides

The biodegradation of the chiral phenoxyalkanoic herbicides 2-(2,4-dichlorophenoxy)propionic aid (2,4-DP) and 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) was investigated using enantioselective HPLC and chiroptical detection. Racemic mixtures of 2,4-DP and MCPP were applied to three species of turf grass, four species of broadleaf weeds, and soil. Preferential degradation of the S-(-) enantiomer of each herbicide was observed in most species of broadleaf weeds and soil, while the degradation in all species of grass occurred without enantioselectivity. The biodegradation in all systems appeared to follow pseudo first-order kinetics with the fastest degradation occurring in broadleaf weeds, followed by the grasses. The slowest degradation was observed in soil. The results of this work illustrate the need to characterize both enantiomers of chiral agrochemicals in order to have an accurate understanding of their distribution and fate in the environment.     

Horizontal transfer of catabolic plasmids and naphthalene biodegradation in open soil

The horizontal transfer of naphthalene biodegradation plasmids and the parallel process of its microbial degradation were studied for the first time. The tagged naphthalene-degrading strains bearing labeled biodegradation plasmids were used for the monitoring of horizontal plasmid transfer in open soil. The population kinetics of microorganisms, the survival rate and competitiveness of introduced strains, and the transfer of biodegradation plasmids to indigenous strains were investigated. The transfer of the labeled plasmid pNF142::TnMod-OTc to the introduced plasmid-free recipient P. putida KT2442 and to indigenous soil microorganisms of the genus Pseudomonas was shown both under selection pressure (in the presence of naphthalene) and in its absence. The 16S rRNA gene sequencing showed that the soil strains that had acquired plasmids were close to the species P. lini, P. frederiksbergensis, P. jessenii, P. graminis, P. putida, and P. alcaligenes. Thus, direct evidence of dissemination of the naphthalene biodegradation plasmids in microbial populations in open soil under selective and nonselective conditions has been obtained.     

Enhanced biodegradation of methoxychlor in soil under sequential environmental conditions.

Ring-U-[14C]methoxychlor [1,1-bis(p-methoxyphenyl)-2,2,2-trichloroethane] was incubated in soil under aerobic and anaerobic conditions. Primary degradation of methoxychlor occurred under anaerobic conditions, but not under aerobic conditions, after 3 months of incubation. Analysis of soil extracts, using gas chromatography, demonstrated that only 10% of the compound remained at initial concentrations of 10 and 100 ppm (wt/wt) of methoxychlor. Evidence is presented that a dechlorination reaction was responsible for primary degradation of methoxychlor. Analysis of soils treated with 100 ppm of methoxychlor in the presence of 2% HgCl2 showed that 100% of the compound remained after 3 months, indicating that degradation in the unpoisoned flasks was biologically mediated. Methanogenic organisms, however, are probably not involved, as strong inhibition of methane production was observed in all soils treated with methoxychlor. During the 3-month incubation period, little or no evaluation of 14CO2 or 14CH4 occurred under either aerobic or anaerobic conditions. Cometabolic processes may be responsible for the extensive molecular changes which occurred with methoxychlor because the rate of its disappearance from soil was observed to level off after exhaustion of soil organic matter. After this incubation period, soils previously incubated under anaerobic conditions were converted to aerobic conditions. The rates of 14CO2 evolution from soils exposed to anaerobic and aerobic sequences of environments ranged from 10- to 70-fold greater than that observed for soils exposed solely to an aerobic environment.     

Mass transfer and hydrocarbon biodegradation of aged soil in slurry phase

Addition of toluene into slurry phase laboratory microcosm is proposed in order to increase desorption rate of hydrocarbons and as an alternative to improve bioavailability of hydrocarbon in aged soils. Our studies showed that toluene has a positive effect on desorption of total petroleum hydrocarbons (TPH). Addition of 14,000 mg toluene/kg of soil, in highly polluted soil, increased the consumption rate of hydrocarbons three times in comparison to control without solvent. In 30 days the initial TPH concentration in soil, 292,000 mg/kg, diminished 45%. Although toluene was able to dissolve complex organic compounds such as asphaltene fraction, it probably yielded a highly toxic toluene-hydrocarbons phase. The inhibitory effect of toluene-TPH was also studied. A substrate inhibition model was used: the k(m) and k(i) constants were 57 and 490 mg TPH/L liquid phase, respectively. Experimental data were well described when the proposed model included sequential desorption and biodegradation phenomena. Damk?hler number evaluation showed that rate of mass transfer was the limiting step in overall biodegradation in nonsolvent control. When high concentration of toluene was added, then bioreaction was the limiting step, but inhibitory effect should be considered. However, toluene addition at low concentrations facilitates the biodegradation of aromatic compounds.