Microbial nitrogen transformation in constructed wetlands

Oksana Coban explores within ADVOCATE Project the role of aerobic and anaerobic microbial processes for the removal of ammonium from contaminated groundwater in constructed wetlands (CWs) downstream of the chemical industrial area in Leuna, Germany. In this video she shows us an overview about how CWs works.

If you would like to learn more about this topic, please don’t miss our previous post on this blog about Oksana research topic titled “Constructed Wetlands: A promising system”

 

ResearchBlogging.org

Coban, O., Kuschk, P., Kappelmeyer, U., Spott, O., Martienssen, M., Jetten, M., & Knoeller, K. (2015). Nitrogen transforming community in a horizontal subsurface-flow constructed wetland Water Research, 74, 203-212 DOI: 10.1016/j.watres.2015.02.018

ResearchBlogging.org

Coban, O., Kuschk, P., Wells, N., Strauch, G., & Knoeller, K. (2014). Microbial nitrogen transformation in constructed wetlands treating contaminated groundwater Environmental Science and Pollution Research DOI: 10.1007/s11356-014-3575-3

The importance of protecting aquifers from contaminated plumes

Do you know how many people depend directly on aquifers for drinking water? And the water used on irrigation for food production? No, right? The answer is that two billion people depend directly upon aquifers for drinking water, and 40 per cent of the world’s food is produced by irrigated agriculture that relies largely on groundwater according to The United Nations Environment Association.

Have you ever stopped a minute and thought about this? The real situation is that water stored in the ground beneath our feet is invisible and so its depletion or degradation due to contamination proceeds unnoticed for us.

So, what should we do about it? Over the years hundreds of studies have been carried out from all different angles to try and solve this problem, however, the industrial legacy and the current industrially dependent world where we live does not make it easy to get a solution. The realistic situation is that the world consumes beyond its resources generating non stop contamination and not taking enough decisions to stop them .

With this introduction, the scene is set up for the next step, what are we really doing to get a solution? Well, projects like ADVOCATE, NanoRem, SuRF-UK, CLARINET, etc. in the framework of Europe are looking for sustainable remediation practices, assessments, etc.

Technologies that range from natural attenuation to advanced oxidation processes such as wet air oxidation or supercritical CO2 extraction, etc., have been studied to date, however, this time, I would like to draw your attention to “Permeable Reactive Barriers (PRBs)” being one of the most promising remediation technologies to intercept and decontaminate plumes in the subsurface.

But, how do these barriers work? Why is it a promising technology? Johana Grajales and Franklin Obiri Nyarko, ADVOCATE’s fellows, are specialized in this topic and recently have published a detailed overview about it in the paper “An overview of permeable reactive barriers for in situ sustainable groundwater remediation”.

The PRB can be defined as a groundwater remediation technology that consists of introducing a wall of reactive material perpendicular to the groundwater flow path to intercept and treat the contaminants. The contaminants in the plume react with the media leading to either their transformation to less harmful compounds or fixation to the reactive materials. The challenge is to match the reactive material and the removal process to the contaminant.

In this paper, Johana and Franklin have carried out a detailed study of the state-of-art explaining the reactive media used so far and the mechanisms employed to transform or immobilize contaminants.

Although this is a promising low cost remediation technology there is still a lot to be done regarding the long-term performance of PRBs and improving their treatment of a broad spectrum of contaminants, and thereby expand their remit.

If you would like to know more about this paper, please click here:

ResearchBlogging.org

Obiri-Nyarko F, Grajales-Mesa SJ, & Malina G (2014). An overview of permeable reactive barriers for in situ sustainable groundwater remediation. Chemosphere, 111, 243-59 PMID: 24997925

A sample restoration project at the Chriesbach river in Dübendorf, Switzerland to explain the features of a restored river

Link

Prof. Dr. Mario Schimmer is involved in ADVOCATE Network. He works at EAWAG Research Institute in Switzerland. His work on numerical modelling, laboratory and field work concerning biodegradation processes of industrial and urban contaminants in the subsurface involves several research areas, such as contaminant hydrogeology, geochemistry, microbiology, engineering, social sciences and numerical methods.

He gives us through this video an introduction about a sample restoration project at the Chriesbach river in Dübendorf, Switzerland to explain the features of a restored river.

Developing in situ treatment strategies for mixed contaminants from contaminated groundwater megasites

Link

Naomi Wells is working on developing better ways of measuring where water pollution comes from, and how long it’s going to stick around for. She uses light stable isotopes to improve the understanding of the fate and transport of key nutrients across biomes, landscapes, and scales.

Check out this video and knowing a bit more how the industrial legacy is harmful to us and our environment. Don’t miss it !

Stimulating bacterial growth to enhance natural biodegradation processes – a low cost treatment option for environmental pollutant removal

                                                           “No amount of experimentation can ever prove me right; a single experiment can prove me wrong.”

Albert Einstein

Naturally occurring bacteria found in soil, groundwater, water and sediments may be a key for environmental pollutant removal. This so-called biodegradation is a part of natural attenuation, which according to the US Environmental Protection Agency could be defined as “The effect of naturally occurring physical, chemical and biological processes, or any combination of those processes to reduce the load, concentration, flux or toxicity of polluting substances without human intervention”. The effectiveness of biodegradation depends on the type of contaminant present as well as on the complex environmental conditions that determine microbial community structure, electron donor availability (the electron donors could be defined as releasing an electron during cellular respiration, resulting in the release of energy. Microorganisms, such as bacteria, obtain energy in the electron transfer processes) and degradation reactions in the subsurface.  Under natural conditions, biodegradation of many contaminants is often a slow process and long timeframes may be required to achieve a remediation objective. Because of this, scientists lately focus more and more on stimulating the growth of that part of the site-specific microbial community that demonstrates the largest degradation potential. Here the idea is to study natural biodegradation processes occurring at a contaminated site in the lab to understand the microbial community structure, kinetics and determine the maximum degradation potential. Once these aspects are sufficiently understood and the site´s hydrogeology has been characterized, a growth-stimulating medium can be injected at certain locations to enhance biodegradation.

Although many studies have been carried over several decades, to improve our understanding of natural attenuation processes there is still a great deal to be learned regarding the mechanisms governing natural attenuation processes and their ability to address different types of contamination problems.

For example, chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE), represent a common class of contaminants used for degreasing in the dry cleaning, electronic manufacturing and machine maintenance industries. Where these contaminants had been used excessively in the past they often have leaked into the subsurface from storage tanks and machinery and have formed large plumes in the groundwater that often shows chlorinated ethene concentrations, which have been proven unhealthy.

The bacterium Dehalococcoides mccartyi is an organic halide-respiring anaerobic bacterium that uses chlorinated compounds for its dehalogenation activity. In other words, this bacterium is specialized to grow with halogenated compounds such as chlorinated aliphatic hydrocarbons as electron acceptor via a respiratory process, i.e. an electron-consuming process, and in most of the cases hydrogen is used as the final electron donor.

The removal of chlorinated ethenes by Dehalococcoides mccartyi via dehalogenation follows the sequential degradation of PCE to TCE to the dichloroethene isomers (cis-DCE, trans-DCE, 1,1-DCE), then to vinyl chloride (VC) and finally to ethene/ethane. However, a complete dechlorination always depends on the environmental conditions and other limiting factors. During the last two decades, several studies have been carried out based on the addition of electron donors for achieving a complete removal of chlorinated compounds, nevertheless, no convincing conclusions have yet been drawn.

declhoronation sequential

As a precursor to an in-situ stimulation of the natural biodegradation potential, Uwe Schneidewind and his colleagues from VITO evaluated the dechlorination reaction occurring at an aquifer contaminated with TCE and its daughter products, discharging into the Zenne River, Belgium, in their article titled “Kinetics of dechlorination by dehalococcoides mccartyi using different carbon sources”.

Sediment material was collected from three locations of the aquifer as well as from the riverbed and used in microcosm studies (measurement of microbial activity). The growth of the microbial community was stimulated by using different carbon sources (i.e. external supply of energy in the form of food) such as lactate (C3H6O3) or molasses (C6H12NNaO3S) and the dechlorination reaction in each microcosm was monitored. Afterwards, the observed reactions were modelled using first order, Michaelis-Menten and Monod kinetics.

Reductive dechlorination of TCE took place only when external carbon sources were added to microcosms, and occurred concomitant with a pronounced increase in the Dehalococcoides mccartyi cell count as determined by 16S rRNA gene-targeted qPCR (i.e. growth measurements and bioremediation monitoring method). This indicates that native dechlorinating bacteria are present in the aquifer of the Zenne site and that the oligotrophic nature of the aquifer prevents a complete degradation to ethene. The type of carbon source, the cell number of D. mccartyi or the reductive dehalogenase genes, however, did not unequivocally explain the observed differences in degradation rates or the extent of dechlorination. Results point to the role of the supporting microbial community but it remains to be verified how the complexity of the microbial (inter)actions should be represented in a model framework.

ResearchBlogging.org

Schneidewind, U., Haest, P., Atashgahi, S., Maphosa, F., Hamonts, K., Maesen, M., Calderer, M., Seuntjens, P., Smidt, H., Springael, D., & Dejonghe, W. (2014). Kinetics of dechlorination by Dehalococcoides mccartyi using different carbon sources Journal of Contaminant Hydrology, 157, 25-36 DOI: 10.1016/j.jconhyd.2013.10.006

What a Marie Curie Fellow does?

Link

Lukasz’s topic within the ADVOCATE project is about “Microbial dynamics and biodegradation at the bioreactive fringe of contaminant plumes in groundwater”, difficult to understand, isn’t it? Lukasz shows us what he does by means of a simple and easy understood video. Don’t miss it!

Can carbon and chlorine stable isotope (δ13C – δ37Cl) act as indicators of treatment performance for groundwater remediation?

First of all, we need to understand what an isotope is. Easy answer? Let us give it a try… the atoms of a particular element must have the same number of protons and electrons, but they can have a different number of neutrons. When atoms differ only in the number of neutrons, they are referred to as isotopes of each other. In addition, if a particular isotope is not radioactive, it is called a stable isotope.

The key issue that we need to provide an answer for is how the isotopes may act as indicators of treatment efficiency and performance for natural biological processes such as bioremediation or natural attenuation, which can remove organic contaminants in the environment. What is helpful is that when organic contaminants are degraded in the environment, the ratio of stable isotopes will change, and the extent of degradation can be recognized and predicted from the change in the ratio of the stable isotopes. Recent advances in analytical chemistry make it possible to perform Compound Specific Isotope Analysis (CSIA) on dissolved organic contaminants such as chlorinated solvents, aromatic petroleum hydrocarbons, fuel oxygenates and many other organic chemicals, at concentrations in water that are near their regulatory standards.

Once we understood this, we can go one step further, and approach the research topic of Alice Badin, a Marie Curie Fellow in the ADVOCATE network. Alice is working at the University of Neuchatel in Switzerland. Her research looks at the variability of carbon and stables isotope ratios in chlorinated ethenes, which are common groundwater contaminants, for various applications such as source identification and characterisation of biodegradation. The isotopic signature measurement of such solvents might be a great help in providing a rigorous basis to identify the source, timing and fate of chemicals released to soil and groundwater.

According to a previous research, the isotopic signatures (i.e. combination of isotopic ratios of chlorine, noted δ37Cl and carbon, noted δ13C in the solvent molecule) of pure compounds from different manufacturers were measured, it could be observed that the signatures varied depending on the manufacturer. Hence, in the field, neighbour spills might have different signatures, so when we don’t know which spill is responsible for further downstream contamination, a comparison between the downstream signature and the suspected sources signatures might help delineating the responsible source (see drawing). However, there are few detailed case studies on the potential application, and the lack of signature variability at a country scale might be a brake to its use. This is the key reason why Alice’s research is partly evaluating the variability in stable isotopic signature of these organic chemicals in Switzerland.

Scheme 1

Based on this, Alice first completed field studies where she measured the isotopic signature of tetrachloroethene (PCE) at 10 different contaminated sites in Switzerland.

molecure

Tetrachloroethene (PCE)

The question that Alice had to contend with was: “Do sites contaminated with PCE in Switzerland have similar stable isotopic signatures?” Although the sites were distributed throughout the country and represented different industrial activities, the PCE examined had very similar isotopic signatures. This thus limits the use of isotopic signature measurement for PCE source delineation in Switzerland. On the other hand, an average value of the stable isotopic signatures determined in these sites could represent a starting point for the assessment of PCE biodegradation at contaminated sites in Switzerland.

The next step in Alice’s research was to assess the relationship between the δ13C and δ37Cl composition of chlorinated ethenes during PCE biodegradation, as this can further help assessing the extent of biodegradation in the field (see multistep biodegradation chain) Currently, the interpretation of this compound specific isotope data set is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl were determined in the lab for biodegradation of PCE to TCE, using microbial enrichment cultures originating from an aquifer contaminated with chlorinated ethenes, which contains members of the bacterial genus Sulfurospirillum.

scheme 2

Multistep biodegradation: the most toxic compound vinyl chloride can eventually be degraded into not harmful ethene or inorganic carbon

These lab experiments are also intended to help understanding better the mechanisms involved during degradation by looking at trends in the stable isotopic ratios. The aim is to relate these changes to some possible degradation pathways or mechanisms, but this part is still under discussion.

After a painstaking and extensive study, Alice recently presented her results at the Isotopes 2013 conference in Sopot (Poland) under the heading “Carbon and chlorine isotopic trend in fingerprinting and anaerobic dechlorination of tetrachloroethene”

 

ResearchBlogging.org

Badin A, Buttet G, Maillard J, Holliger C, & Hunkeler D (2014). Multiple dual C-Cl isotope patterns associated with reductive dechlorination of tetrachloroethene. Environmental science & technology, 48 (16), 9179-86 PMID: 25000152

The installation of the Vadose Monitoring System (VMS) was carried out successfully in Belgium last June

The installation of the Vadose Monitoring System (VMS) was carried out successfully in Belgium last June

I am pleased to announce that Natalia Fernandez together with her research group, HGeo³-Hydrogéologie et Géologie de l’Environnement, proceeded with the installation of the Vadose Monitoring System (VMS) in Belgium in June. The objective is to develop a methodology that is able to quantify contaminant fluxes, identify their sources and pathways and understand the various reactive processes in soil and groundwater.

The combined experiment consisted of a tracer test performed directly in the vadose zone via infiltration rings, located within an infiltration pond. To do this, a flexible sleeve was installed in a slanted borehole with the aim of capturing a tracer infiltrated throughout undisturbed material above the borehole. To measure water content, Flexible Time Domain Reflectometry probes (FTDR), which contain stainless steel waveguides, were installed in the outer wall of the flexible sleeve. As well, Vadose Sampling Ports (VSP) were placed in the inner wall of the flexible sleeve for sampling pore water in the vadose zone. Finally, additional boreholes were installed in the unsaturated zone to conduct cross-hole geophysics with the aim of monitoring contaminants and tracers as they move into the saturated zone (see it in the pictures).

The outlook of this experiment is to use the advantages of the combination of the Vadose Monitoring System and geophysical techniques with the aim of developing a conceptual model that better characterizes the transport of pollutants in the vadose zone of industrial sites. The objective is to use such a methodology as an approach to improve risk assessment and remediation measures for the vadose zone.

Natalia experiment 0 Natalia experiment 1Natalia experiment 2  Natalia experiment 2b Natalia experiment 3aNatalia experiment 3bNatalia experiment 4aNatalia experiment 4b   Natalia experiment 5

How much impact has climate change on contaminated land and pollutants?

How much impact has climate change on contaminated land and pollutants? 

How much impact has climate change on contaminated land and pollutants is an excellent question with a blank answer currently. The impact of climate change factors on the risk assessment, design of future remediation systems and management of current and future contaminated sites will be likely a key point that we should take into account or consider.

On the one hand, sustainability indicators in terms of environmental, economic and social are the basis for the sustainable remediation assessment of contaminated soils and groundwater. In this way, the UK Sustainable Remediation Forum (SuRF-UK) has developed a framework for assessing their sustainability, and for incorporating sustainable development criteria in land contamination management strategies, setting up in this sense a series of sustainability indicators for their remediation. These indicators are indicative of the range of issues that may be relevant, and are provided to help assessors identify the most critical issues to evaluate further in a project. As well, they highlight which are the challenges at global, national or local level.

On the other hand, in readiness for our future climate and its changes, there is a need to evaluate the risks of climate change and to predict how it is going to affect our future. In this way, some European projects have tried to give a response since 2000. PRUDENCE, Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects, was a European scale investigation project which aimed to quantify the confidence and the uncertainties in predictions of future climate and its impacts, using an array of climate models and impact models and expert judgement on their performance. Continuing the theme of this investigation, the project ENSEMBLES was carried out, based on Predictions of Climate Changes and their Impacts. This project aimed to build a common ensemble climate forecast system which would be developed for use across a range of timescales (seasonal, decadal and longer) and spatial scales (global, regional and local). So, this model system would be used to construct integrated scenarios of future climate change, including both non-intervention and stabilisation scenarios. ENSEMBLES ended in 2009 and immediately a new major project was started up, CORDEX, COordinated Regional climate Downscaling Experiment, which is an international project to produce an improved generation of regional climate change projections world-wide for input into impact and adaptation studies.

All this effort provides us a quantitative risk assessment of climate change and climate variability. On this basis, the next step would be to quantify the impact of climate change on contaminated land and to examine technical evidence of this impact and potential technical adaptation strategies that should be followed.

Although, all projects identified in this document have done extremely respectable and useful work, there is currently very little published work providing experimental evidence of potential direct impacts of climate change on contaminated land and remediation systems. The closest work is that which investigates and compares the impacts of different climatic regions on biological and chemical properties of contaminated soils and contaminant behaviour. Consequently there is a need for effort in this area to ensure that remediation choices being made now are the right ones by future land use, climatic conditions and societal demographics. 

So, in the United Kingdom, in 2007, a multi-institutional and multi-disciplinary research consortium was involved in a project called SUBR:IM, Sustainable Urban Brownfield Regeneration: Integrated Management, whose aim was producing integrated and sustainable solutions for the development of brownfield land in urban areas. They concluded that from the evidence available in the literature and collected as part of the study, it is clear that certain climate change scenarios are expected to have significant impacts on current and future contaminated land and remediation systems. These impacts will have major effects on the future management of contaminated and remediated sites and are expected to influence the way risk is managed on those sites and the design of future remediation strategies. 

However, this project is only the beginning of an emerging area of research. We still have a long way to go. It is important to set up a good correlation between the climate change and the current soil remediation technologies so that their implementation will not be a complete waste of time in the future when the environmental conditions change, in particular, those systems that required long time scales.