WP 8 Up-scaling, Risk and Sustainability

Large scale experiments are a crucial step from the lab to a field application. Three large scale experiments have been set up in VEGAS to investigate the applicability of oxidized iron nanoparticles to enhance microbial degradation of BTEX and of nZVI and Carbo-Iron to chemically reduce a PCE source.

The step from (small) laboratory experiments to a field size application is an extremely challenging task. NanoRem is attempting to bridge the gap between laboratory and field application via large scale experiments. Such experiments must be contained to allow for the use of noxious model contaminants and to sustain an exact mass balance. While these experiments are similar in size to the field application and their artificial aquifers show realistic heterogeneities, their instrumentation is much denser and sampling intervals are much smaller than anticipated in the field. Furthermore, instrumentation tested in these experiments may be extrapolated to field applications. 

Three large scale experiments using large contained tank systems (see Photos 1-3) are being carried out by USTUTT inside the VEGAS laboratory to better understand up-scaling effects to assist planning for field scale deployments. These containers offer a maximum flexibility with contaminants and a highly disaggregated monitoring grid which will allow for conclusions with respect to improving the real field sites.

1. The Large Scale Container 

In a large heterogeneous, unconfined aquifer (L x W x H = 9 x 6 x 4.5m) steady state groundwater flow was established. Then a BTEX plume was introduced. The goal of the experiment was to inject Goethite nanoparticles to enhance the microbial degradation of this plume.

The container is equipped with 378 groundwater sampling ports, thus a highly defined spatial analysis of the plume was possible. A numerical model (MODFLOW) was set up to model flow and transport in the aquifer. This model was also used to optimize the location of an injection well for the nanoparticles. Requirement for the injection was that the particles are “homogeneously” distributed throughout the pathway of the contaminant. At the same time it had to be ensured that the injection flowrate would allow for a maximum particle transport while daylighting was prevented.

Based on these calculations, 6 m³ of a slurry containing 20 kg/m³ goethite nanoparticles was injected at t a rate of Q=0.7 m³/h. Water samples were taken to delineate the spreading of the nanoparticles: it had to be shown that the particles reach the target zone and that they do not migrate beyond this zone. Subsequently, the groundwater was sampled at regular time intervals to determine the effect of the nanoparticle injection on BTEX degradation.

2. The large Scale Flume I 

The first large scale flume experiment was set up to chemically reduce a chlorinated hydrocarbon (CHC; PCE) source using nano zero valent iron (nZVI) produced by Nanoiron (CZ). The artificial aquifer in the flume has dimensions of L x W x H = 6 x 1 x 3m. The unconfined aquifer (WT = 1.7 m) is homogeneous and a steady state groundwater flow (q = 0.2 m/d) was established to simulate field conditions. In this aquifer 2 kg of PCE were injected in 20 mL increments to create a residual contaminant source of about 0.7 m³.

At 32 sampling ports water samples were taken at regular intervals to prove that the source was spatially stable (no remobilization) and that a steady state plume was established. After establishment of the plume, Nanofer 25s particles were injected using a direct push rod. The injected slurry was prepared using the AQUATEST Vulcanus mixing unit which allows for a continuous addition of concentrated nZVI slurry into the injection stream. A total of 1 m³ suspension with a concentration of c_nZVI = 10 kg/m³ was injected at different locations throughout the contaminant source. The spreading of the nanoparticles was monitored using susceptibility probes as well as micro pumps. Again the injection pressure and flowrates were limited to prevent daylighting. First preliminary results indicate that the injection rate chosen (Q = 0.1 m³/h) was not sufficient to provide a flow field sufficient to transport the nanoparticles for an appreciable distance. Currently, the particle suspension is being improved to obtain better migration results in the next injection.

3. The Large Scale Flume II

The aquifer in the second large scale flume is identical to the one in the first flume, but the monitoring equipment installed is slightly different. Where the first flume sports a series of susceptibility spools, these have been omitted in the second flume as Carbo-Iron® is to be injected. Carbo-Iron® contains of approx. 60w% activated carbon (AC) and both 25w% nZVI 15wt% iron oxide inside the AC grain. To obtain an injectable suspension, 20kg Carbo-Iron® powder and a minimal amount of CMC (5 wt% compared to particle mass) are mixed in tap water. CMC is used to prevent agglomeration of Carbo-Iron® particles and, thus, to ensure controlled migration of the reactant in the aquifer. While the flume experiment has been set up and steady state base flow has been obtained the Carbo-Iron® suspension is being optimized.

Data derived from these experiments will not only yield a profound understanding of the “real” field situation, but will also allow the design of a cost effective sampling and monitoring strategy for NanoRem pilot and demonstration projects. Furthermore, all aspects relevant for the application of nanoparticles can be investigated, i.e. the transport behaviour of the particles, the reactivity of the particles with the contaminants as well as (unwanted) side reactions and, finally, the ultimate fate of the particles. 

Photos 1 & 2 -  Large scale experiments at VEGAS  left: large flume (16 x 3 x 1m)  right: large container (18 x 6 x 4.5m)

Photo 3 – Large scale tank experiments (© VEGAS/University of Stuttgart, Germany)

NanoRem is using various large scale tank experiments of the VEGAS facility to provide: 

•   Representative scale testing of emerging nanoparticle applications in contained facilities. The VEGAS facility is unique in Europe in allowing in-situ testing under controlled boundary conditions in large contained tanks (approx. 250 m³). This provides three major benefits: precise mass balance, capacity for comprehensive instrumentation not possible in the field, and also – if necessary – assurance of no potential for release of nanoparticles into the wider environment. 
   
•   Optimisation of nanoparticles and tools (WPs 2-7) via feedback from large scale performance testing. Injection in the laboratory (VEGAS facility) will improve nanoparticle design (WP2, WP3), understanding of transport (WP4) and monitoring equipment (WP6). 
•   Knowledge on degradation products under field relevant conditions. Nanoparticle transformation products and contaminant degradation products will be monitored to ensure efficiency of degradation, and the potential of microbiological enhancement will be assessed (WP5).
•  Testing appropriate injection technologies for varying hydrogeology including gravitational porous media flow, high pressure injection etc. 
•   Developing an understanding of nanoparticle deployment risks for in-situ remediation. WP8 will integrate NanoRem’s technical and field project findings, with an initial opinion based on stakeholder and expert views gathered in WP9, to provide a more substantial basis for assessing and (if necessary) managing risks from nanoparticle deployment for remediation. 
•   Assessing the sustainability of nanoremediation compared with alternate (remediation) strategies. Contemporary tools for understanding sustainability in remediation will be applied to the field tests (not only the large scale laboratory tanks) in NanoRem to provide case study based comparative sustainability assessments and considering a range of stakeholder opinions where possible. Sustainability will be considered across a system boundary and a life-cycle relevant for the remediation work being undertaken.
• A thorough validation and verification of the numerical tool (WP7) will be possible based on these large scale experiments.

Sustainability appraisal and life cycle assessment approaches are in preparation. A preliminary sustainability assessment approach for case study sites has been developed and a bulletin has been produced (for more information, see: http://www.nanorem.eu/displayfaq.aspx?id=16). Explanatory documents on purposes/advantages of LCI (Life cycle inventory) for nanoparticle production and on how to deal with confidentiality issues have been produced. Relevant NPs for the LCI have been identified and initial data collection has begun, including production data on NPs NANOFER 25S and NANOFER STAR (produced by WP2).