Francesco Garbo

Lab-scale phytotreatment of old landfill leachate using different energy crops.

Old landfill leachate was treated in lab-scale phytotreatment units using three oleaginous species: sunflower (H), soybean (S) and rapeseed (R). The specific objectives of this study were to identify the effects of plant species combinations with two different soil textures on the reduction of COD, total N (nitrogen) and total P (phosphorous); to identify the correlation between biomass growth and removal efficiency; to assess the potential of oily seeds for the production of biodiesel. The experimental test was carried out using 20L volume pots installed in a greenhouse under different leachate percentages in the feeding and subsequent COD, N and P loads. Significant removal efficiencies were achieved: COD (ɳ>80%), total N (ɳ>70%) and total P (ɳ>95%). Better performances were displayed by the clayey soil. Plants irrigated with leachate, when compared to control units fed only with water and nutrient solution (Hoagland solution), developed a larger plant mass. Sunflower was the best performing species.

Numerical Investigation of Laminar to Turbulent Boundary Layer Transition on a Naca 0012 Airfoil for Vertical-Axis Wind Turbine Applications

Laminar to turbulent transition in vertical-axis wind turbines has a dramatic effect on overall rotor performance, especially in fast rotating machines, where reliable prediction of the total drag coefficient for high values of tip speed ratio is one of the most critical topic in CFD simulations. This paper presents a 2D numerical investigation of the capability of the γ–θ transition model to predict the laminar to turbulent transition and consequent friction drag over a NACA 0012 airfoil for a Reynolds number of 360,000, which is typical of vertical-axis wind turbine blades during operation. The analized range of angles of attack varies from 0 deg to 10 deg. The commercial CFD solver ANSYS FLUENT® is used. In particular, the sensitivity to grid resolution is investigated for four different architectures: a completely unstructured mesh, a hybrid structured-triangular one and two distinct hybrid structured-triangular meshes where the wake region behind the airfoil is discretized using a fully structured grid. The effect of freestream turbulence intensity on the transition onset is also analyzed. Finally, CFD results are compared to experimental data, although affected by some uncertainty, and to the predictions of an interactive program for the design and analysis of subsonic isolated airfoils (XFOIL), showing a very good agreement provided that the value of freestream turbulence intensity is known.

Use of oleaginous plants in phytotreatment of grey water and yellow water from source separation of sewage

Efficient and economic reuse of waste is one of the pillars of modern environmental engineering. In the field of domestic sewage management, source separation of yellow (urine), brown (faecal matter) and grey waters aims to recover the organic substances concentrated in brown water, the nutrients (nitrogen and phosphorous) in the urine and to ensure an easier treatment and recycling of grey waters. With the objective of emphasizing the potential of recovery of resources from sewage management, a lab-scale research study was carried out at the University of Padova in order to evaluate the performances of oleaginous plants (suitable for biodiesel production) in the phytotreatment of source separated yellow and grey waters. The plant species used were Brassica napus (rapeseed), Glycine max (soybean) and Helianthus annuus (sunflower). Phytotreatment tests were carried out using 20L pots. Different testing runs were performed at an increasing nitrogen concentration in the feedstock. The results proved that oleaginous species can conveniently be used for the phytotreatment of grey and yellow waters from source separation of domestic sewage, displaying high removal efficiencies of nutrients and organic substances (nitrogen>80%; phosphorous >90%; COD nearly 90%). No inhibition was registered in the growth of plants irrigated with different mixtures of yellow and grey waters, where the characteristics of the two streams were reciprocally and beneficially integrated.

Different leachate phytotreatment systems using sunflowers.

The use of energy crops in the treatment of wastewaters is of increasing interest, particularly in view of the widespread scarcity of water in many countries and the possibility of obtaining renewable fuels of vegetable origin. The aim of this study was to evaluate the feasibility of landfill leachate phytotreatment using sunflowers, particularly as seeds from this crop are suitable for use in biodiesel production. Two different irrigation systems were tested: vertical flow and horizontal subsurface flow, with or without effluent recirculation. Plants were grown in 130L rectangular tanks placed in a special climatic chamber. Leachate irrigated units were submitted to increasing nitrogen concentrations up to 372mgN/L. Leachate was successfully tested as an alternative fertilizer for plants and was not found to inhibit biomass development. The experiment revealed good removal efficiencies for COD (η>50%) up until flowering, while phosphorous removal invariably exceeded 60%. Nitrogen removal rates decreased over time in all experimental units, particularly in vertical flow tanks. In general, horizontal flow units showed the best performances in terms of contaminant removal capacity; the effluent recirculation procedure did not improve performance. Significant evapo-transpiration was observed, particularly in vertical flow units, promoting removal of up to 80% of the inlet irrigation volume.

PLASMIX management: LCA of six possible scenarios

Only a small percentage of the separately collected plastic is recycled. The mechanical selection process of source segregated plastic materials generates considerable amounts of residues that are commonly named as Plasmix. By means of a life cycle assessment (LCA) modelling, the environmental performances of the main Plasmix management options (thermal treatment, energy recovery, and landfilling) were compared. Six treatment scenarios, with different pre-treatment alternatives, were evaluated. Landfilling after waste washing and Plasmix substitution of coke in a blast furnace represent the most favorable options, since the performances of thermal treatment and energy recovery are worsened by specific emissions of a variety of toxic compounds and heavy metals within plastic materials as additives.

Assessment of the ecotoxicity of phytotreatment substrate soil as landfill cover material for in-situ leachate management

Phytotreatment capping in closed landfills is a promising, cost-effective, in situ option for sustainable leachate treatment and might be synergistically coupled with energy crops to produce renewable energy (e.g.: biodiesel or bioethanol). This study proposes to use 0.30 m of soil as growing substrate for plants cultivated on the temporary cover of closed landfills. Once the leachate phytotreatment process is no longer required, 0.70 m of the same soil would be added to attain the final top cover configuration. This solution would entail saving the costs of excavation and backfilling. However, worsening of the initial soil quality due to potential contaminant transfer from the liquid to the solid matrix must be avoided because EU legislation (such as that in Italy) fixes concentration limits for contaminants in soil. In this research, samples of soil used as substrate in a lab-scale leachate phytotreatment test with sunflowers were analysed to provide chemical characterization before, during, and at the end of the experiment. The results showed that the phytotreatment activity did not increase initial contaminant concentrations. These results are reinforced by those from ecotoxicological bioassays in which Eisenia fetida (earthworms), Lepidium sativum (cress), Folsomia candida (collembola), and Caenorhabditis elegans and Steinernema carpocapsae (nematodes) were used. It was observed that, by the end of the experiment, the substrate soil did not affect the earthworms, collembola and nematode behaviour, or the growth of cress.

Energy crops on landfills: functional, environmental, and costs analysis of different landfill configurations

The cultivation of energy crops on landfills represents an important challenge for the near future, as the possibility to use devalued sites for energy production is very attractive. In this study, four scenarios have been assessed and compared with respect to a reference case defined for northern Italy. The scenarios were defined taking into consideration current energy crops issues. In particular, the first three scenarios were based on energy maximisation, phytotreatment ability, and environmental impact, respectively. The fourth scenario was a combination of these characteristics emphasised by the previous scenarios. A multi-criteria analysis, based on economic, energetic, and environmental aspects, was performed. From the analysis, the best scenario resulted to be the fourth, with its ability to pursue several objectives simultaneously and obtain the best score relatively to both environmental and energetic criteria. On the contrary, the economic criterion emerges as weak, as all the considered scenarios showed some limits from this point of view. Important indications for future designs can be derived. The decrease of leachate production due to the presence of energy crops on the top cover, which enhances evapotranspiration, represents a favourable but critical aspect in the definition of the results.