**4. Scaling from TRL 1 to TRL 6: VDM**

—Constructed wetland systems:

From the remediation conceptual tests at the laboratory corresponding to technology readiness level (TRL) 1–2 to their applications in the territory (TRL 7), a long way of calibration and adjustments must be executed. Generally, a significant economic loss is given by poor evidence of adaptation and adjustment when technology proceeds from TRL 3 to TRL 7 [51].

In the study by Scotti et al. [34], a constructed wetland system called vegetable depuration module (VDM) is proposed as a calibrator of variables in MAP tests (**Figure 2A**). The use of VDM allows to determining the balance mass and the metal(loid) partition between soil, fungal structures, mycorrhizal roots, and aboveground plant tissues. The VDM allows the leaching of different HMs under particular conditions of pH-Eh, organic matter and other amendments and coenzymatic factors (among other elements) taking to account the hydraulic variables such as type of irrigation (vertical, horizontal, continuous, interrupted, laminar, or turbulent), dynamics flow, and constant of hydraulic retention (Kh physical constant dependent on filling). Partitioning among different media usually relies on an equilibrium between the contaminant adsorbed on solid surfaces and the contaminant dissolved in a liquid (or gaseous) phases, controlled by the chemical characteristics of the contaminant (e.g., hydrophobicity, volatility). Several distribution coefficients have been developed over the years (e.g., partitioning coefficient between soil and water: Kd, organic carbon and water: Koc, or octanol-water partition coefficient: Kow) to elucidate processes in nature, but these are usually simple models that do not consider the specificity of sorption sites or competition among molecules and elements [1]. Thermodynamic processes that determine the

#### **Figure 2.**

*A: The Vegetable Depuration Module (VDM) under construction, B: Vertical flow beds (VFB) under construction in Lima, Peru; C: VFB under construction in Bayawan City, Philippines; D: From left to right: three VFBs (filters) for pre-treatment and two VFBs for secondary treatment in Albondón, Spain (photos by (photos from [57]).*

bioavailability of trace elements are complex, and VDM allows to calibrate some of these processes. Once the calibration of these parameters has been obtained, the system can be scaled up to territory by adapting the engineering practices. The description of the VDM [34] shows it as a modified subsurface constructed wetland that allows designing the type and quantity of underground filter, its granulometry, type of substrate, and amendments besides the hydraulic system.

The VDM (located at *Centro de Desarrollo Regional Los Reyunos* of *Universidad Tecnológica Nacional* in Mendoza province, Argentina; 34°35′46″S 68°38′25″W at 702 m elevation) consists of modules with two pools connected to collection chambers through a hydraulic system. Each pool was 2.80 m wide and 5.00 m long, and ranged from 0.6 m (bottom depth) to 0.9 m (top depth), resulting in a difference in height of 0.3 m and a slope of 6%. The collection chambers were 1 m long, 2.8 m wide, and 1 m deep. The VDM is isolated from the external environment by using a waterproofing system and a greenhouse covered with a metal net with a polyethylene film against hail. VDM behaves like a modified subsurface artificial wetland, with vertical/horizontal irrigation flow and regulated inflow and outflow water. Water enters the system through pipes connected to a reserve tank and a water pump that drives vertical/horizontal flow to both pools. The remaining water that is not incorporated into the biosystem is allowed to drain into the collection chambers. When the water enters the chambers, it can eventually be recycled by reintroducing it into the reserve tank or released to the environment if it is sufficiently free of contaminants. The pool is filled as follows: depth layer of 10 cm with large gravel (approximately 10 cm in diameter), covered by 15 cm of gravel of medium size (approximately 5 cm in diameter), and 20 cm of small-size gravel (about 1 cm in diameter). The last 15-cm surface layer consisted of the growth substrate of the bioremediation system.

#### *Scale-up of Mycorrhizal-Assisted Phytoremediation System from Technology Readiness… DOI: http://dx.doi.org/10.5772/intechopen.101584*

The VDM is a technological development adaptable to different designs and methodologies with a scale of TRL 6 as a simulated environment. The output of the VDM calibration corresponds to the first engineering cycle of a design to be taken to field scale. Under the experimental conditions in the VDM, the HMs in multicontaminated soils with high leaching properties pass to the collecting chamber to be recycled and treated in another VDM with different physical-chemical and biological conditions. Consequently, those HMs translocated to plant biomass are considered bio-extracted and the elements retained in the substrate without entering biomass are considered stabilized. Furthermore, the VDM allows calibration of the capacity of phytoextraction or phytostabilization of a given system under certain conditions. The differential behavior between phytoextraction and phytostabilization is mainly given by the soil conditions and the plant-microorganism association. The mycorrhizal plants can retain HMs in soil substrate by physicalchemical fixation, redox reactions, absorption and adsorption in the extra-radical mycelium and spores, and by releasing glomalin, a complex of glycoproteins that acts as a carbon reservoir in soils and is involved in the sequestration of HMs [53]. Recent studies have demonstrated that AM symbiosis performance can fluctuate between phytostabilization and/or phytoextraction depending on certain HMs, the environmental conditions, and the types of plant and fungal partners [54]. As it is known, the bioavailability of HMs is related to the solubility of these elements, which intimately depends on the temperature, pH, and Eh parameters (Pourbaix) [55], among other factors. The VDM allows modifying the retention capacity in the substrate or the leaching rates of HMs by controlling the pH-Eh values according to the soil-plant-microorganisms system applied.

Recently, different modular constructed wetland systems in series were designed with different numbers of vertical flow bed (VFB). In the system designed in **Figure 2B**, the entire surface is used as an inlet area to greywater influents through connected pipes with uniform holes that later are covered with gravel to complete the testing performances. In **Figure 2C**, another example of a VFB is constructed for the treatment of wastewater from a landfill. **Figure 2D** shows modular constructed wetland systems in series without electricity supply as it is built on a slope. It consists of three VFBs for pre-treatment as a filtration step and two VFBs for secondary treatment.
