Effort to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies

Purpose - In order to provide highly effective yet relatively inexpensive strategies for the remediation of recalcitrant organic contaminants, research has focused on in situ treatment technologies. Recent investigation has shown that coupling two common treatments-in situ chemical oxidation (ISCO) and in situ bioremediation-is not only feasible but in many cases provides more efficient and extensive cleanup of contaminated subsurfaces. However, the combination of aggressive chemical oxidants with delicate microbial activity requires a thorough understanding of the impact of each step on soil geochemistry, biota, and contaminant dynamics. In an attempt to optimize coupled chemical and biological remediation, investigations have focused on elucidating parameters that are necessary to successful treatment. In the case of ISCO, the impacts of chemical oxidant type and quantity on bacterial populations and contaminant biodegradability have been considered. Similarly, biostimulation, that is, the adjustment of redox conditions and amendment with electron donors, acceptors, and nutrients, and bioaugmentation have been used to expedite the regeneration of biodegradation following oxidation. The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized biphasic treatment and areas that require additional focus. Conclusions and recommendations - Although a biphasic treatment consisting of ISCO and bioremediation is a feasible in situ remediation technology, a thorough understanding of the impact of chemical oxidation on subsequent microbial activity is required. Such an understanding is essential as coupled chemical and biological remediation technologies are further optimize

Isolation and characterization of Alicycliphilus denitrificans strain BC, which grows on benzene with chlorate as the electron acceptor

A bacterium, strain BC, was isolated from a benzene-degrading chlorate-reducing enrichment culture. Strain BC degrades benzene in conjunction with chlorate reduction. Cells of strain BC are short rods that are 0.6 microm wide and 1 to 2 microm long, are motile, and stain gram negative. Strain BC grows on benzene and some other aromatic compounds with oxygen or in the absence of oxygen with chlorate as the electron acceptor. Strain BC is a denitrifying bacterium, but it is not able to grow on benzene with nitrate. The closest cultured relative is Alicycliphilus denitrificans type strain K601, a cyclohexanol-degrading nitrate-reducing betaproteobacterium. Chlorate reductase (0.4 U/mg protein) and chlorite dismutase (5.7 U/mg protein) activities in cell extracts of strain BC were determined. Gene sequences encoding a known chlorite dismutase (cld) were not detected in strain BC by using the PCR primers described in previous studies. As physiological and biochemical data indicated that there was oxygenation of benzene during growth with chlorate, a strategy was developed to detect genes encoding monooxygenase and dioxygenase enzymes potentially involved in benzene degradation in strain BC. Using primer sets designed to amplify members of distinct evolutionary branches in the catabolic families involved in benzene biodegradation, two oxygenase genes putatively encoding the enzymes performing the initial successive monooxygenations (BC-BMOa) and the cleavage of catechol (BC-C23O) were detected. Our findings suggest that oxygen formed by dismutation of chlorite can be used to attack organic molecules by means of oxygenases, as exemplified with benzene. Thus, aerobic pathways can be employed under conditions in which no external oxygen is supplie

Bioremediation of petroleum-contaminated soils: mathematical modelling as a tool for the simulation of alternative strategies

POCI-01-0145-FEDER-016575; ERC Grant n.º 323009; UID/BIO/04469/2013; POCI -01-0145-FEDER-006684; NORTE-01-0145-FEDER-000004; FCOMP-01-0124- FEDER-027462; SFRH/BPD/80528/2011info:eu-repo/semantics/publishedVersio

Novel anaerobe obtained from a hexadecane-degrading consortium

Background: Aliphatic hydrocarbons (AHC) are abundant in crude oil and fuels, and are frequent contaminants of water, soil and sediments. There is potential for AHC bioremediation using sulfate as electron acceptor, due to its abundance in marine environments and natural presence in soils and groundwater. Objectives: In this work sulfate-reducing anaerobic microorganisms involved in AHC biodegradation were studied. Methods: Anaerobic sludge was incubated at 37ºC with hexadecane (1mM) and sulfate (20mM) in serum vials. Cultures were successively transferred to fresh medium until a stable enrichment was obtained (monitored by microscopy and PCR-DGGE of 16S rRNA gene). For isolation of AHC-degrading bacteria, serial dilutions and successive transfers are now running using palmitate (1mM) as an easier substrate. Conclusions: Cultures growing on palmitate show two main bacterial cell types: a rod-shaped bacterium closely related to Desulfomonile limimaris (94% identity) was predominant in the first 30 days of incubation, when 83% of the added palmitate was degraded coupled to 4 mM sulfate reduction (suggesting stoichiometric palmitate conversion to acetate); and an oval-shaped bacterium related to Desulforhabdus amnigena (99% identity) that mainly developed when incubations where extended and a total of 11.5 mM sulfate was reduced. Growth of Desulforhabdus was stimulated when incubated with acetate. The role of the Desulfomonile in AHC degradation will be further discussed in the presentation, as well as its halorespiring ability, a characteristic of the Desulfomonile genera. Further characterization of this novel bacterium is important due to its high potential for bioremediation of hydrocarbons, fats and halogenated pollutants

Addition of co-substrates stimulates hexadecene conversion to methane by an enriched microbial consortium

ICBM-3 - 3rd International Conference on Biogas MicrobiologyLinear olefins with 16 to 18 carbon atoms are frequently used as hydrophobic groups in oil soluble surfactants and as lubricating fluids. The production of olefins in petrochemical plants generates olefin contaminated wastewater that can be treated anaerobically in methanogenic bioreactors, coupling degradation to energy recovery. However, this conversion is generally slow, due to olefins ́ insolubility in water and poor bioavailability for microorganisms. Addition of an easy degradable carbon source may enhance the growth of hydrocarbon degrading methanogenic communities. In this study, hexadecene degradation by a methanogenic enrichment was stimulated by addition of yeast extract (0.5 g·L-1), lactate (4.5 mmol·L-1) or crotonate (4.5 mmol·L-1) as co-substrates. After stimulation with yeast extract or lactate, the microbial communities were able to convert hexadecene to methane 5 and 2.5 times faster, respectively, than non-stimulated cultures. Hexadecene conversion to methane was not enhanced by crotonate addition. Further incubations with fermented yeast extract did not improve methane production from hexadecene, which suggests that the positive stimulatory effect of yeast extract was due to the extra carbon source and not to the supply of essential co-factors. The microbial community composition of the hexadecene degrading enrichments was studied by 16S rRNA sequencing. Bacteria from the Chloroflexi, Firmicutes, Proteobacteria(Deltaproteobacteria), Spirochaetes, Synergistetes and Thermotogaephyla were identified, with Syntrophobacterales, Spirochaetales and Synergistales as the most abundant orders. Hydrogenotrophic methanogens predominated over acetoclastic methanogens. Currently the isolation and identification of key microbial players involved in hexadecene degradation are ongoing. This study can be useful for improving the treatment of olefin contaminated wastewater using methanogenic conditionsinfo:eu-repo/semantics/publishedVersio

Facts and challenges on hydrocarbons bioremediation

Book of Abstracts of CEB Annual Meeting 2017[Excerpt] The intense activity of the oil industry generates substantial amounts of contaminated wastes and wastewaters. Moreover, accidental oil spills occur frequently, causing severe damages in the marine environment and in the soil. Subsurface soil contamination is generally caused by oil leakages from underground storage tanks and transport pipelines that can further lead to groundwater contamination. To date, common techniques for remediation of petroleum-contaminated environments include physical removal, washing by cosolvents or surfactants, thermal desorption, electrokinetic movement of contaminants and oxidation/reduction via chemical agents. Biological technologies can be an alternative to the more aggressive physicochemical methods, as bioremediation exploits the metabolic diversity of microorganisms and their ability to degrade organic contaminants. Aerobic bioremediation is frequently preferred over anaerobic processes, due to faster rates of hydrocarbons activation and biodegradation [1]. However, in subsurface environments oxygen is generally scarce and anoxic conditions prevail. Anaerobic microorganisms can biodegrade hydrocarbons coupled to the reduction of nitrate, iron(III), sulfate or under methanogenic conditions [2]. In situ bioremediation of hydrocarbons at anoxic conditions has not been extensively studied, despite the broad occurrence of these contaminants in the subsurface. Reduced knowledge on the catabolic mechanisms and microbial communities involved in anaerobic hydrocarbons biodegradation has limited this approach, and needs further research. [...]info:eu-repo/semantics/publishedVersio

Unraveling who is who in methanogenic oil degradation

2015 Gulf of Mexico Oil Spill and Ecosystem ConferenceMethanogenesis from hydrocarbons is a potentially important component of attenuation in water and sediments impacted by oil spills. The largest fraction of crude oil consists of aliphatic hydrocarbons (AHC). Current knowledge on key microorganisms degrading alkenes is scarce and is a central question addressed in our research. A methanogenic hexadecene (Hxd)-degrading consortium was obtained from laboratory microcosms inoculated with anaerobic granular sludge, and characterized by 16S rRNA gene amplification, cloning and sequencing. We have learned by community analysis that the present bacteria belong mainly to Syntrophaceae and Synergistaceae families. A Syntrophus-like microorganism (96% similarity at genera level) is possibly involved in Hxd degradation. Known methanogens utilizing acetate and H2/CO2 were identified, namely Methanosaeta-, Methanobacterium- and Methanolinea-related microorganisms, and were likely the syntrophic partners in Hxd degradation. With these results we find hints for similar pathways involved in alkenes and alkanes biodegradation. For alkanes, complete degradation to methane can occur through syntrophic interactions between bacteria and methanogens. This is the first time that an alkene-degrading methanogenic mixed community is characterized. Novel microorganisms involved in AHC degradation could be identified. This information is useful for understanding who is doing what, and at what rate. It can be used for innovative biotechnological solutions for deep contaminated sites clean-up.info:eu-repo/semantics/publishedVersio

Who is who in anaerobic oil biodegradation?

[Excerpt] Anaerobic bioremediation is an important alternative for the common aerobic cleanup of subsurface petroleum-contaminated soil and water. Microbial communities involved in anaerobic oil biodegradation are scarcely studied, and only few mechanisms of anaerobic hydrocarbons degradation are described. In this work, microbial degradation of aliphatic hydrocarbons (AHC) was studied by using culture-dependent and culture-independent approaches. Hexadecane and hexadecene-degrading microbial communities were enriched under sulfate-reducing and methanogenic conditions. The microorganisms present in the enriched cultures were identified by 16S rRNA gene sequencing. (...

Disagreement prompts young children’s metacognitive reflection

From Galileo to Gandhi, and from Plato to Piaget, influential thinkers throughout history have highlighted the benefits of disagreement for science, society, and the individual. Despite the rich theoretical interest, the specific individual benefits of disagreement have often remained unclear. To address this gap, the current dissertation explores one particular individual psychological consequence of disagreement: how it prompts metacognitive reflection during early childhood. The ability to metacognitively reflect on one’s own knowledge plays a critical role in learning, as well as in individual and joint decision-making. Yet, young children’s metacognitive capacities are often still limited in significant ways. By middle childhood, however, children’s metacognitive competence has significantly improved. What explains this striking change? This dissertation argues that metacognitive development is centrally driven by young children’s social experiences of disagreement.To begin to test this hypothesis, the effects of disagreement on young children’s metacognition are explored across three chapters, each focusing on a distinct, frequently studied dimension of metacognition: reason-giving, confidence ratings, and rational belief revision. Chapter 2 uses a cross-cultural approach, finding that experiencing disagreement (more so than agreement) leads children from three diverse cultural backgrounds to reflect on their reasons for their beliefs when making joint decisions. Chapter 3 demonstrates that disagreeing (versus agreeing) with another individual reduces young children's overconfidence and increases their motivation to search for the correct answer. Finally, Chapter 4 finds that children flexibly revise their initial beliefs, or suspend judgment until they have acquired additional evidence, depending on the strength of the evidence supporting their own belief versus that of a disagreeing other. Together, these findings provide clear evidence that experiencing disagreement prompts young children’s metacognitive reflection. Theoretically, these insights are significant as they bridge the gap between prior theoretical perspectives that have emphasized the role of social interaction in cognitive development, such as constructivist learning theories and cultural evolutionary accounts of metacognition, refines them, and makes them empirically testable. Moreover, the current work has important practical implications, and could inform interventions aimed at fostering learning and reasoning, as well as promoting mutual understanding