The expected public results of GRABGAS project are:

  • Waste gas characterization
  • DEMO solar photocatalytic reactor
  • GRABGAS DEMO prototype
  • Rhizodegradation maintenance protocol
  • GRABGAS webpage
  • Internal dissemination and training

Deliverables

Project deliverables are the tangible products generated from a project. For GRABGAS, the following deliverables are defined at every important step of the project.

DONE

  1. D1.1 Waste gas characterization
  2. D8.1 GRABGAS webpage
  3. D9.1 Consortium Agreement
  4. D1.2 Selection of plant and rhizosphere
  5. D1.3 Rhizodegrading substrate and lab-scale operation
  6. D1.4 Rhizodegradation lab-scale setup
  7. D2.1 Previous studies for the Developement of a solar Photocatalytic pre-treatement
  8. D8.2 Interim Exploitation Plan of GRABGAS

ONGOING

  1. D3.1 Biological rhizodegradation
  2. D6.2 CFD Simulations
  3. D5.1 Control system
  4. D2.2 Solar Photocatalytic pre-treatment
  5. D4.1 Labscale studies of resilience of rhizodegradating filter
  6. D7.1 DEMO solar photocatalytic reactor
  7. D7.2 GRABGAS DEMO prototype

Some ongoing results

Target industries : For solvents selection, a review of emitted gases by targeted industries has been done. The emitted gases have been identified by industry and activity. Different industries have been analyzed, as for examples industries dealing with Coating of wooden surfaces.

Solvents selection : A total of 27 different organic compounds have been identified as potential organic compound to be studied, such as Toluene, Xylene, Acetone. These organic compounds are representative of parental compounds in the same chemical family. These compounds have been identified as potential compounds to be studied in GRABGAS project These organic compounds can be classified into six different chemical families: ketones, esters, alcohols, aromatic hydrocarbons, halogenated non aromatic hydrocarbons and non-aromatic hydrocarbons.

To choose the solvents, it was considered to have at least:

  • components of aromatic, ester, and ketone families,
  • solvents with higher molecular weight,
  • by-products from photocatalysis,
  • lower molecular weight and higher reactivity solvants.

The action of plants and bacteria : Plants can have several actions to remediate VOC from the soil. It can be Phytoremediation(1), Biostimulation(2) or Phytodegradation(3). All these phenomenas have been evaluated during the project.

(1) Phytoremediation : " Phytoremediation is the direct use of green plants and their associated microorganisms to stabilize or reduce contamination in soils, sludges, sediments, surface water, or ground water ... Sites with low concentrations of contaminants over large cleanup areas and at shallow depths present especially favorable conditions for phytoremediation." - U.S. Environmental Protection Agency, 2011.

(2) Biostimulation : Addition of nutrients and oxygen to increase natural bacterial growth and stimulate contaminant degradation. In this study, nutrients are provided by plant roots by means of exudates, and is so called phytostimulation.

(3) Phytodegradation : The uptake of contaminants, which, through metabolic processes within the plant, are subsequently broken down. Phytodegradation also encompasses the breakdown of contaminants in the soil through the effects of enzymes and other compounds produced by plant tissues other than the roots.

Plants selection : Among the thousands plant species of interest either for the phytoremediation or the capacity to grow on green roofs, 27 have been deeply assessed a short list of 9 plant species have been selected to be used for GRAGAS experiments, for exemple Alium tuberosum, Armeria maritime, Sedum Lineare thunb, . The biology of the plants has been collected and their growing conditions were evaluated. The selection relies on the ability of plants to stimulate the degradation of organic contaminants (biostimulation).

A mix of plants will be used on the GRABGAS solution. Experimental evidence indicates a positive relationship between plant species richness and ecosystem functioning (Aarssen, 1997a, Aarssen, 1997b; Naeem et al., 1998, Naeem et al., 1994). A diverse plant mix is more advantageous than a monoculture in terms of survival and visual rating under dry conditions. It was shown that combinations of species differing in functional diversity and complexity achieved their functions more effectively.

Substrate definition : The characterization and the study of substrate behavior at laboratory allows to perform the selection of a suitable material (mixture of soil and / or additional materials). In order to achieve optimal growth of plant species proposed and the biodegradation of contaminants mixtures of gases, several tests are done.

Eight substrate components have been assessed, such as Sand, Pozzolan, Peatin order to improve the limiting factors identified below. Then 10 substrate mixtures have been tested and compared.

Limiting factors :

  • Optimal substrate for green roofs
  • Optimal substrate for VOC degradation

The critical factors to take into account are defined as follows:

  • To control moisture and nutrient reserves
  • Improve aeration minimizing substrate compaction
  • Decrease bulk density (low weight substrates)

Microbial activity of the substrate : Extraction of microbial DNA of the substrate proved that the microbial activity is fully present and is not limiting the bioremediation.

Substrate degradation : The lab-scale filter designed for GRABGAS project is a modular bioreactor. This bioreactor allows the evaluation of the substrate-plant system operating with a synthetic mixture of gases generated by evaporation systems (bubbling).

In the modules sampling points are available in order to enhance the evolution of the contaminants concentration throughout the entire height of the bioreactor and therefore determine the overall efficiency of the process. The 1rst degradation results were made with substrate only (no plants). Results have shown that the substrate started-up degradating VOC, giving an idea of the start up period (time for the microorganisms to starts having a benefic action). The substrate alone removed part of the pollutants. The removal efficiency is now assessed in the bioreactor.