Mineralization of phenanthrene and fluoranthene in yardwaste compost

Biodegradation performance and diversity of enriched bacterial consortia capable of degrading high-molecular-weight polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are key organic pollutants in the environment that pose threats to the ecosystem and human health. The degradation of high molecular weight (HMW) PAHs by enriched bacterial consortia has been previously studied, while the involved metabolisms and microbial communities are still unclear and warrant further investigations. In this study, five bacterial consortia capable of utilizing different PAHs (naphthalene, anthracene, and pyrene) as the sole carbon and energy sources were enriched from PAH-contaminated soil samples. Among the five consortia, consortium TC exhibited the highest pyrene degradation efficiency (91%) after 19 d of incubation. The degradation efficiency was further enhanced up to 99% by supplementing yeast extract. Besides, consortium TC showed tolerances to high concentrations of pyrene (up to 1000 mg/L) and different heavy metal stresses (including Zn²⁺, Cd²⁺, and Pb²⁺). The dominant genus in consortium TC, GS, and PL showing relatively higher degradation efficiency for anthracene and pyrene was Pseudomonas, whereas consortium PG and GD were predominated by genus Achromobacter and class Enterobacteriaceae, respectively. Consortium TC, as a highly efficient HMW PAH-degrading consortium, could be applied for synergistic biodegradation of HMW PAHs and in situ bioremediation of the sites contaminated with both PAHs and heavy metals.

Loading and removal of PAHs, fragrance compounds, triclosan and toxicity by composting process from sewage sludge

Although the production of compost from sewage sludge is well established in developed countries, the use of sludge-based compost may represent a source of pollutants. The present study assessed the levels of potentially harmful compounds in compost as well as their rates of decrease during composting. The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs), three fragrance compounds (OTNE, HHCB and AHTN) and triclosan were determined in the initial sewage sludge and in compost over the span of 1year. Simultaneously, the toxicity to luminescent bacteria (Aliivibrio fischeri) and aryl hydrocarbon receptor reactivity of organic solvent extracts of sludge and compost samples were assessed. Higher PAH, fragrance compounds, and triclosan concentrations were found in sewage sludge from urban areas compared with rural regions, and the urban sludge was also more toxic than the rural sludge. The high pollutant concentrations in urban sludge raised the concentrations of these compounds in the raw materials for composting and in the resulting composts. The organic matter was decomposed by 65% during the composting process, and the measured toxic substances were decreased by a similar amount, with the exception of triclosan, which decreased by only 35%. The toxicity to A. fischeri decreased to a greater extent (90%) than did the organic matter, while the aryl hydrocarbon receptor reactivity decreased by only 35%. This lower decrease coincided with that of the aryl hydrocarbon receptor-reactive PAHs (37%).

Pollution of Flooded Arable Soils with Heavy Metals and Polycyclic Aromatic Hydrocarbons (PAHs)

Soils that are exposed to floodwaters because of shallow groundwater and periodical wetlands are, to a large extent, exposed to contamination by organic and inorganic compounds. These are mainly compounds that have drifted along with the inflow of heavily laden floodwater and are produced within the soil profile by the anaerobic transformation of organic matter. Heavy metals and polycyclic aromatic hydrocarbon (PAH) compounds are absorbed by the soil of the floodwaters, and moving in the soil profile, they pose a threat to groundwater. What is more, after a flood, they may be absorbed by the crops. This paper focuses on the effects of Odra River (Poland) floods, heavy metals, and PAHs on soil and the possibilities of the migration of these pollutants into the soil profile. In the tested sludge samples of floodwater and soil, there were no abnormal concentrations of heavy metals, but the flooding time positively affected the amount listed in the test samples. Concentrations of PAHs increased, but they also exceeded the standards for arable soils in the case of single compounds.

Ozone oxidation and aerobic biodegradation with spent mushroom compost for detoxification and benzo(a)pyrene removal from contaminated soil

The combination of ozonation and spent mushroom compost (SMC)-mediated aerobic biological treatment was investigated in the removal of benzo(a)pyrene from contaminated soil. The performances of the process alone and combined were evaluated in terms of benzo(a)pyrene removal efficiency, mineralization efficiency (as total organic carbon removal), and soil residual toxicity (phytotoxicity to Lepidium Sativum and toxicity to Vibrio fischeri). In spite of the removal efficiency (35%) obtained by SMC-mediated biological process as a stand-alone treatment, the combined process showed a benzo(a)pyrene concentration reduction higher than 75%; the best removal (82%) was observed after 10 min pre-ozonation treatment. In particular, ozonation improved the biodegradability of the contaminant, as confirmed by the increase of CO(2) production (close to 70% compared to the control), mineralization (greater than 60%) and bacterial density (which increased by two orders of magnitude). Moreover, according to phytotoxicity tests on L. Sativum, the aerobic biological process of pre-ozonated soil decreased toxicity. According to the results achieved in the present study, ozonation pre-treatment showed an high potential to overcome the limitation of bioremediation of recalcitrant compound, but it should be carefully operated in order to maximize PAH removal efficiency as well as to minimize soil residual toxicity which can result from the formation of the oxidation intermediates.

Sorption and mineralization of organic pollutants during different stages of composting

The organic pollutant (OP) content is a key factor when determining compost quality. The OPs present in feedstock materials may either be degraded during composting or stabilized in the compost by sorption interactions with organic matter (OM), which may reduce the availability of OP to microorganism degradation. It is particularly important to identify the key stages during composting that are involved in OP mineralization so as to be able to optimize the composting process and determine whether OP sorption on OM is a limiting factor to OP mineralization. Four (14)C-labeled OPs were used during the study: a polycyclic aromatic hydrocarbon (fluoranthene), two surfactants (4-n-nonylphenol - NP and sodium linear dodecylbenzene sulfonate - LAS) and a herbicide (glyphosate). The potential for compost microflora to degrade OP, and compost sorption properties, were characterized at different stages of composting. The highest levels of LAS and glyphosate mineralization were found during the thermophilic stage, at the beginning of maturation for NP and at the end of maturation for fluoranthene. A specific microflora was probably involved in the biodegradation of fluoranthene while NP, LAS and glyphosate mineralization were linked to total microbial activity. OP sorption on compost was linked to their hydrophobicity, decreasing in the order: fluoranthene>NP>LAS>glyphosate. Moreover, sorption decreased as compost maturity increased, except for glyphosate. The sorption coefficients were positively correlated to mineralization kinetics parameters for NP, LAS and glyphosate, suggesting a positive effect of sorption on increasing mineralization rates.

Effects of soil amendment with different carbon sources and other factors on the bioremediation of an aged PAH-contaminated soil

Carbon supplementation, soil moisture and soil aeration are believed to enhance in situ bioremediation of PAH-contaminated soils by stimulating the growth of indigenous microorganisms. However, the effects of added carbon and nitrogen together with soil moisture and soil aeration on the dissipation of PAHs and on associated microbial counts have yet to be fully assessed. In this study the effects on bioremediation of carbon source, carbon-to-nitrogen ratio, soil moisture and aeration on an aged PAH-contaminated agricultural soil were studied in microcosms over a 90-day period. Additions of starch, glucose and sodium succinate increased soil bacterial and fungal counts and accelerated the dissipation of phenanthrene and benzo(a)pyrene in soil. Decreases in phenanthrene and benzo(a)pyrene concentrations were effective in soil supplemented with glucose and sodium succinate (both 0.2 g C kg(-1) dry soil) and starch (1.0 g C kg(-1) dry soil). The bioremediation effect at a C/N ratio of 10:1 was significantly higher (P < 0.05) than at a C/N of either 25:1 or 40:1. Soil microbial counts and PAH dissipation were lower in the submerged soil but soil aeration increased bacterial and fungal counts, enhanced indigenous microbial metabolic activities, and accelerated the natural degradation of phenanthrene and benzo(a)pyrene. The results suggest that optimizing carbon source, C/N ratio, soil moisture and aeration conditions may be a feasible remediation strategy in certain PAH contaminated soils with large active microbial populations.

Biodegradation of phenanthrene and pyrene in compost-amended soil

This study investigated the biodegradation of the polycyclic aromatic hydrocarbons (PAHs) phenanthrene and pyrene in compost and compost-amended soil. The degradation rates of the two PAHs were phenanthrene>pyrene. The degradation of PAH was enhanced when the two PAHs were present simultaneously in the soil. The addition of either of the two types of compost (straw and animal manure) individually enhanced PAH degradation. Compost samples were separated into fractions with various particle size ranges, which spanned 2-50 microm, 50-105 microm, 105-500 microm, and 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAH degradation rates. However, when the different compost fractions were added to soil, compost particle size had no significant effect on the rate of PAH degradation. Of the micro-organisms isolated from the soil-compost mixtures, strains S1, S2, and S8, which were identified as Arthrobacter nicotianae, Pseudomonas fluorescens, and Bordetella Petrii, respectively, demonstrated the best degradation ability.

Biodegradation of phthalate esters in compost-amended soil

In this study, we investigated the biodegradation of the phthalate acid esters (PAEs) di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl) phthalate (DEHP) in compost and compost-amended soil. DBP (50 mg kg(-1)) and DEHP (50 mg kg(-1)) were added to the two types of compost (straw and animal manure) and subsequently added to the soil; they were tested as a single compound and in combination. Optimal PAE degradation in soil was at pH 7 and 30 degrees C. The degradation of PAE was enhanced when DBP and DEHP were simultaneously present in the soil. The addition of either of the two types of compost individually also improved the rate of PAE degradation. Compost samples were separated into fractions with various particle size ranges, which spanned from 0.1-0.45 to 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAE degradation rates. When the different compost fractions were added to soil, however, compost particle size had no significant effect on the rate of PAE degradation.

Fate of polycyclic aromatic hydrocarbons during composting of activated sewage sludge with green waste

The level and fate of 16 polycyclic aromatic hydrocarbons (PAHs), targeted by the US Environmental Protection Agency (USEPA), has been studied over 90 days of composting of activated sludge with green waste, under a semi-arid climate. The total PAH calculated from the sum of the amounts of the 16 PAHs in the initial mixture of activated sludge and green waste, was lower than accepted European Union cut-off limits by about 0.48mgkg(-1). The treatment by composting led to a decrease of all PAHs mainly in the stabilization phase, but some differences could be observed between PAHs with three or fewer aromatic rings (N< or = 3) and those with four or more (N> or = 4). The former (except phenanthrene) exhibited a continuous decrease, while the latter PAHs with N of four or more and phenanthrene showed increases in the intermediate stages (30-60 days). This indicates the high potential sorption mainly of PAH with high molecular weight (> or = N4) plus phenanthrene, their tight adsorption makes them inaccessible for microbial attack. The high molecular weight PAHs showed a greater reduction of their bioavailability than those of low molecular weight. Naphthalene, with the lowest molecular weight, showed the smallest decrease (about 67.8%) compared to other PAHs of higher molecular weight (decrease reaching 100%). This is in agreement with the fact that the adsorption is less reversible with increased numbers of fused aromatic rings or an increase of their hydrophobicity.

Anaerobic degradation of nonylphenol in soil

This study investigated the effects of various factors on the anaerobic degradation of nonylphenol (NP) in soil. The results show that the optimal pH for NP degradation was 7.0 and that the degradation rate was enhanced when the temperature was increased. The addition of compost enhanced NP degradation. The individual addition of the electron donors lactate, acetate, and pyruvate inhibited NP degradation. The high-to-low order of NP degradation rates under three anaerobic conditions was sulfate-reducing conditions > methanogenic conditions > nitrate-reducing conditions. The results show that sulfate-reducing bacteria, methanogen, and eubacteria are involved in the anaerobic degradation of NP, with sulfate-reducing bacteria being a major component of the soil. Of the anaerobic strains isolated from the soil samples, strain AT3 expressed the best ability to biodegrade NP.

Biodegradation of nonylphenol in soil

We investigated the effects of various factors (brij 30, brij 35, yeast extract, hydrogen peroxide and compost) on the aerobic degradation of nonylphenol (NP) in soil and characterized the structure of the microbial community in that soil. Residues of NP were measured using gas chromatography-mass spectrometry (GC-MS) and a change of microbial communities was demonstrated using denaturing gradient gel electrophoresis (DGGE). The results showed that Taichung sandy clay loam had higher NP degradation rate than Kaoshiung silty clay. The addition of compost, yeast extract (0.5 mg/l), brij 30 (55 microM), or brij 35 (91 microM) enhanced NP degradation, while the addition of hydrogen peroxide (1.0 mg/l) inhibited its degradation. We also found that the addition of various substrates changed the microbial community in the soils. Cytophaga sp. and Ochrobactrum sp. were constantly dominant bacteria under various conditions in the soil.

Polycyclic aromatic hydrocarbons degradation by composting in a soot-contaminated alkaline soil

This study deals with the biodegradation of the polycyclic aromatic hydrocarbons (PAH)s present in a soil contaminated by soot waste, characterised by a total PAHs content in the 200 mg kg(-1) range. A challenging characteristic of the waste soil treated was its high alkalinity, with a pH of about 12.8. The waste came from a soot-contaminated area located in the industrial zone of Porto Marghera, Venice (Italy). The biodegradation process employed was the composting of the waste with sewage sludge and yard waste. The process was carried out on a pilot scale using a closed tank with forced aeration for a period of 60 days, followed by 70 days with natural aeration. The time evolution of the process was monitored by following the time change in the concentration of the 16 US-EPA PAHs, as well as temperature, pH, electrical conductivity, C and N contents. Also phytotoxicity parameters, such as the growth and respiration indexes, were monitored. An induction time of about 30 days was observed, which corresponded to the time required before observing a significant self-drop in the waste pH and an increase in mass temperature. Afterward, a progressive drop in the PAHs concentration was observed, up to reaching after 130 days an overall degradation percentage in the order of 68%. The degradation was more effective on rather low molecular weight PAHs (2-4 rings).

Persistent organic pollutants in source-separated compost and its feedstock materials--a review of field studies

Composting and the application of compost to the soil follow the principle of recycling and sustainability. Compost can also have a positive effect on physical, chemical, and biological soil parameters. However, little is known about the origin, concentration, and transformation of persistent organic pollutants (POPs) in compost. We therefore compiled literature data on some priority POPs in compost and its main feedstock materials from more than 60 reports. Our data evaluation suggests the following findings. First, median concentrations of Sigma 16 polycyclic aromatic hydrocarbons (PAHs), Sigma 6 polychlorinated biphenyls (PCBs), and Sigma 17 polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) were higher in green waste (1803, 15.6 microg/kg dry wt., and 2.5 ng international toxicity equivalent [I-TEQ]/kg dry wt.) than in organic household waste (635, 14.6 microg/kg dry wt., and 2.2 ng I-TEQ/kg dry wt.) and kitchen waste (not available [NA], 14.9 microg/kg dry wt., 0.4 ng I-TEQ/kg dry wt.). The POP concentrations in foliage were up to 12 times higher than in other feedstock materials. Second, in contrast, compost from organic household waste and green waste contained similar amounts of Sigma 16 PAHs, Sigma 6 PCBs, and Sigma 17 PCDD/Fs (1915, 39.8 microg/kg dry wt., and 9.5 ng I-TEQ/kg dry wt., and 1715, 30.6 microg/kg dry wt., and 8.5 ng I-TEQ/kg dry wt., respectively). Third, concentrations of three-ring PAHs were reduced during the composting process, whereas five- to six-ring PAHs and Sigma 6 PCBs increased by roughly a factor of two due to mass reduction during composting. Sigma 17 PCDD/Fs had accumulated by up to a factor of 14. Fourth, urban feedstock and compost had higher POP concentrations than rural material. Fifth, the highest concentrations of POPs were usually observed in summer samples. Finally, median compost concentrations of POPs were greater by up to one order of magnitude than in arable soils, as the primary recipients of compost, but were well within the range of many urban soils. In conclusion, this work provides a basis for the further improvement of composting and for future risk assessments of compost application.

Fate of polycyclic aromatic hydrocarbons during composting of lagooning sewage sludge

The fate of 16 polycyclic aromatic hydrocarbons (PAHs), targeted by the USEPA agency, has been investigated during composting of lagooning sludge. Composting shows efficient decrease of the content and the bioavailability of each PAH. Biodegradation and sorption are suggested as the main mechanisms contributing to this decrease. During the stabilization phase of composting, extensive microbial degradation of PAHs, mainly those with a low number of aromatic rings, was achieved following development of intense thermophilic communities. However, partial sorption of PAH to non-accessible sites temporarily limits the mobility mainly of PAHs with a high number of aromatic rings plus acenaphthene and acenaphthylene, and allows them to escape microbial attack. During the maturation phase, the development of a mesophilic population could play an important role in the degradation of the remaining PAH. During this phase of composting, PAH sequestration and binding of their oxidative metabolites within new-formed humic substances might also explain PAH decrease at the end of composting. The tendency of change of content or bioavailability of various PAH compounds during composting is found to be strongly related to the number of their aromatic rings, their molecular weight and structure.