Anaerobic bioremediation of marine sediment artificially contaminated with anthracene and naphthalene

Dose–Response Effect of Nitrogen on Microbial Community during Hydrocarbon Biodegradation in Simplified Model System

Knowledge about the influence of C:N ratio on the biodegradation process of hydrocarbon compounds is of significant importance in the development of biostimulation techniques. The purpose of this study was to assess the impact of nitrogen compounds on the environmental consortium during the process of biological decomposition of hydrocarbons. The experimental variants represented low, moderate, and excessive biostimulation with nitrogen compounds. The metabolic activity of the consortium was tested using the flow cytometry technique. The efficiency of the biodegradation of hydrocarbons of the consortium, based on the gas chromatography method, and metapopulation changes, based on the analysis of V4 16srRNA sequencing data, were assessed. The results of the research confirm the positive effect of properly optimized biostimulation with nitrogen compounds on the biological decomposition of polycyclic aromatic hydrocarbons. The negative impact of excessive biostimulation on the biodegradation efficiency and metabolic activity of microorganisms is also proven. Low resistance to changes in the supply of nitrogen compounds is demonstrated among the orders Xanthomonadales, Burkholderiales, Sphingomonadales, Flavobacteriales, and Sphingobacteriales. It is proven that quantitative analysis of the order of Rhizobiales, characterized by a high-predicted potential for the decomposition of polycyclic aromatic hydrocarbons, may be helpful during biostimulation optimization processes in areas with a high nitrogen deficiency.

Co-metabolic Effect of Glucose on Methane Production and Phenanthrene Removal in an Enriched Phenanthrene-Degrading Consortium Under Methanogenesis

Anaerobic digestion is used to treat diverse waste classes, and polycyclic aromatic hydrocarbons (PAHs) are a class of refractory compounds that common in wastes treated using anaerobic digestion. In this study, a microbial consortium with the ability to degrade phenanthrene under methanogenesis was enriched from paddy soil to investigate the cometabolic effect of glucose on methane (CH₄) production and phenanthrene (a representative PAH) degradation under methanogenic conditions. The addition of glucose enhanced the CH₄ production rate (from 0.37 to 2.25mg⋅L^-1⋅d^-1) but had no influence on the degradation rate of phenanthrene. Moreover, glucose addition significantly decreased the microbial α-diversity (from 2.59 to 1.30) of the enriched consortium but showed no significant effect on the microbial community (R ²=0.39, p=0.10), archaeal community (R ²=0.48, p=0.10), or functional profile (R ²=0.48, p=0.10). The relative abundance of genes involved in the degradation of aromatic compounds showed a decreasing tendency with the addition of glucose, whereas that of genes related to CH₄ synthesis was not affected. Additionally, the abundance of genes related to the acetate pathway was the highest among the four types of CH₄ synthesis pathways detected in the enriched consortium, which averagely accounted for 48.24% of the total CH₄ synthesis pathway, indicating that the acetate pathway is dominant in this phenanthrene-degrading system during methanogenesis. Our results reveal that achieving an ideal effect is diffcult via co-metabolism in a single-stage digestion system of PAH under methanogenesis; thus, other anaerobic systems with higher PAH removal efficiency should be combined with methanogenic digestion, assembling a multistage pattern to enhance the PAH removal rate and CH₄ production in anaerobic digestion.

Biodegradation potential of polycyclic aromatic hydrocarbons in Taihu Lake sediments

ABSTRACTTo assess the biodegradation potential of polycyclic aromatic hydrocarbons (PAHs) in sediments, sediment microcosms were constructed with sediments collected from six lake zones with different trophic statuses in Taihu Lake. The presence and concentration of PAH-degrading bacteria (PDB) were estimated by the most probable number (MPN) method. After 85 d of aerobic and anaerobic incubation, spiked PAHs (phenanthrene, pyrene, and benzo[a]pyrene) were partially degraded by indigenous sediment microorganisms. Large differences in PAH degradation were observed depending on the molecular size of the PAHs. The PAH removal efficiency in sediments under aerobic conditions was higher than that under anaerobic conditions. MPN analyses showed a higher abundance of degrading microflora in the high PAH-contaminated sites than in the low PAH-contaminated sites. Moreover, the anaerobic PDB populations in the sediments from the six different sites were much higher than those of aerobic PDB. The PAH biodegradation capability in sediments was associated with the geochemical conditions and bacterial populations. PDB showed a broad spatial distribution, thereby implying that they played an important role in the natural attenuation and cycling of PAHs in Taihu Lake. This work indicates that PAHs remain a concern in Taihu Lake sediments and can provide useful information for further bioremediation of PAH-contaminated sediments.

Comparing performances, costs and energy balance of ex situ remediation processes for PAH-contaminated marine sediments

This study proposes a comparison of different ex situ technologies aimed at the removal of polycyclic aromatic hydrocarbons from marine sediments in terms of performances, costs and energy balance. In accordance with the principles of water-energy nexus, anaerobic bioremediation, soil washing and thermal desorption were investigated under low liquid phase and temperature conditions using phenanthrene (PHE) as model compound. After 42 days of anaerobic bioremediation, the highest PHE biodegradation of 68 and 64% was observed under denitrifying and methanogenic conditions, respectively, accompanied by N₂ and CH₄ production and volatile fatty acid accumulation. During soil washing, more than 97% of PHE was removed after 60 min using a solid-to-liquid ratio of 1:3. Along the same treatment time, low-temperature thermal desorption (LTTD) allowed a PHE removal of 88% at 200 °C. The economic analysis indicated that LTTD resulted in a higher cost (i.e. 1782 € m^-3) than bioremediation and soil washing (228 and 371 € m^-3, respectively). The energy balance also suggested that bioremediation and soil washing are more sustainable technologies as a lower required energy (i.e. 16 and 14 kWh m^-3, respectively) than LTTD (i.e. 417 kWh m^-3) is needed.

Removal of polycyclic aromatic hydrocarbons during anaerobic biostimulation of marine sediments

This study proposes the supplementation of digestate, fresh organic fraction of municipal solid waste (OFMSW) and a nutrient solution during the anaerobic biostimulation of marine sediments contaminated by polycyclic aromatic hydrocarbons (PAHs). The experimental activity was conducted with four PAHs (i.e. phenanthrene, anthracene, fluoranthene and pyrene) under controlled mesophilic conditions (37 ± 1 °C) in 100 mL serum bottles maintained at 130 rpm. After 120 days of incubation, the highest total PAH degradation of 53 and 55% was observed in the experiments with digestate + nutrients and OFMSW + nutrients, respectively. Phenanthrene was the most degraded PAH and the highest removal of 69% was achieved with OFMSW + nutrients. The anaerobic PAH degradation proceeded through the accumulation of volatile fatty acids and the production of hydrogen and methane as biogas constituents. The highest cumulative biohydrogen production of 80 mL H₂·g VS^-1 was obtained when OFMSW was used as the sole amendment, whereas the highest biomethane yield of 140 mL CH₄·g VS^-1 was obtained with OFMSW + nutrients. The evolution of PAH removal during anaerobic digestion revealed a higher impact of the methanogenic phase rather than acidogenic phase on PAH degradation.

Anaerobic Microbial Degradation of Polycyclic Aromatic Hydrocarbons: A Comprehensive Review

Polycyclic aromatic hydrocarbons (PAHs) are a class of hazardous organic contaminants that are widely distributed in nature, and many of them are potentially toxic to humans and other living organisms. Biodegradation is the major route of detoxification and removal of PAHs from the environment. Aerobic biodegradation of PAHs has been the subject of extensive research; however, reports on anaerobic biodegradation of PAHs are so far limited. Microbial degradation of PAHs under anaerobic conditions is difficult because of the slow growth rate of anaerobes and low energy yield in the metabolic processes. Despite the limitations, some anaerobic bacteria degrade PAHs under nitrate-reducing, sulfate-reducing, iron-reducing, and methanogenic conditions. Anaerobic biodegradation, though relatively slow, is a significant process of natural attenuation of PAHs from the impacted anoxic environments such as sediments, subsurface soils, and aquifers. This review is intended to provide comprehensive details on microbial degradation of PAHs under various reducing conditions, to describe the degradation mechanisms, and to identify the areas that should receive due attention in further investigations.

Biotechnologies for Marine Oil Spill Cleanup: Indissoluble Ties with Microorganisms

The ubiquitous exploitation of petroleum hydrocarbons (HCs) has been accompanied by accidental spills and chronic pollution in marine ecosystems, including the deep ocean. Physicochemical technologies are available for oil spill cleanup, but HCs must ultimately be mineralized by microorganisms. How environmental factors drive the assembly and activity of HC-degrading microbial communities remains unknown, limiting our capacity to integrate microorganism-based cleanup strategies with current physicochemical remediation technologies. In this review, we summarize recent findings about microbial physiology, metabolism and ecology and describe how microbes can be exploited to create improved biotechnological solutions to clean up marine surface and deep waters, sediments and beaches.

Changes of benthic bacteria and meiofauna assemblages during bio-treatments of anthracene-contaminated sediments from Bizerta lagoon (Tunisia)

Sediments from Bizerta lagoon were used in an experimental microcosm setup involving three scenarios for the bioremediation of anthracene-polluted sediments, namely bioaugmentation, biostimulation, and a combination of both bioaugmentation and biostimulation. In order to investigate the effect of the biotreatments on the benthic biosphere, 16S rRNA gene-based T-RFLP bacterial community structure and the abundance and diversity of the meiofauna were determined throughout the experiment period. Addition of fresh anthracene drastically reduced the benthic bacterial and meiofaunal abundances. The treatment combining biostimulation and bioaugmentation was most efficient in eliminating anthracene, resulting in a less toxic sedimentary environment, which restored meiofaunal abundance and diversity. Furthermore, canonical correspondence analysis showed that the biostimulation treatment promoted a bacterial community favorable to the development of nematodes while the treatment combining biostimulation and bioaugmentation resulted in a bacterial community that advantaged the development of the other meiofauna taxa (copepods, oligochaetes, polychaetes, and other) restoring thus the meiofaunal structure. The results highlight the importance to take into account the bacteria/meiofauna interactions during the implementation of bioremediation treatment.

Impacts of bioremediation schemes for the mitigation of a low-dose anthracene contamination on free-living marine benthic nematodes

A microcosm experiment was used to examine (1) the effects of different bioremediation schemes on degradation of anthracene and the structure of free-living marine nematodes in a lightly contaminated (4.5 μg g(-1)) sediment from Bizerte lagoon and (2) the responses of the nematode community upon an artificial spiking of a low dose anthracene (1 μg g(-1)). For that purpose sediment microcosms were incubated in laboratory for 40 days. Bioremediation techniques decreased the anthracene contamination, and interestingly, biodegradation were more efficient when anthracene was artificial supplied into the sediment suggesting that the addition of bioavailable anthracene stimulated the bacterial community to adjust towards a PAH-degrading community. Spiking with this low dose of anthracene provoked significant changes in the nematode community structure and abundance, with the elimination of specific species such as Mesacanthion diplechma, the decrease of the dominant species Oncholaimus campylocercoides and the increase in abundance of opportunistic species such as Spirinia parasitifera. This would suggest a low tolerance of the nematode community despite the presence of a weak anthracene contamination in the sediment that could have allow dominance of an anthracene tolerant nematode species. Anthracene toxicity was alleviated in biostimulation treatments, leading to a strong increase in nematode abundance, concomitantly with changes in the nematode community structure; Prochromadorella neapolitana became the most abundant species.