Renato Iannelli

FITOVERT: A dynamic numerical model of subsurface vertical flow constructed wetlands

This paper introduces a mathematical model (FITOVERT) specifically developed to simulate the behaviour of vertical subsurface flow constructed wetlands (VSSF-CWs). One of the main goals of the development of FITOVERT was to keep the complexity of the model to an acceptable level, so as to provide a practical tool for design and operation optimization. The dynamic formulation of the model allows to simulate the typical non stationary feeding-emptying operation of VSSF-CWs. FITOVERT is able to describe the water flow through porous media in unsaturated conditions, combined with evapotranspiration; its biochemical module describes the degradation of both organic matter and nitrogen; the transport in the liquid phase is implemented for both dissolved and particulate components; the oxygen transport in the gaseous phase of the soil and its exchange with the liquid phase are also considered. As a main advantage, compared to the few currently available dedicated numerical models, FITOVERT is able to handle the porosity reduction due to bacteria growth and accumulation of particulate components, so that the clogging process is also simulated as an effect of the pore size reduction on the hydraulic conductivity of the simulated system. The performance of the model was firstly analyzed by comparison with hydrodynamic tests recorded in an experimental VSSF-CW pilot plant: tracer test were carried out in three different saturation conditions (fully saturated, partially saturated, and completely drained). FITOVERT proved to accurately simulate the hydraulic behaviour of VSSF-CWs in both saturated and unsaturated conditions. The needs for model improvements and further calibration are finally discussed.

Assessment of pollution impact on biological activity and structure of seabed bacterial communities in the Port of Livorno (Italy)

The main objective of this study was to assess the impact of pollution on seabed bacterial diversity, structure and activity in the Port of Livorno. Samples of seabed sediments taken from five selected sites within the port were subjected to chemical analyses, enzymatic activity detection, bacterial count and biomolecular analysis. Five different statistics were used to correlate the level of contamination with the detected biological indicators. The results showed that the port is mainly contaminated by variable levels of petroleum hydrocarbons and heavy metals, which affect the structure and activity of the bacterial population. Irrespective of pollution levels, the bacterial diversity did not diverge significantly among the assessed sites and samples, and no dominance was observed. The type of impact of hydrocarbons and heavy metals was controversial, thus enforcing the supposition that the structure of the bacterial community is mainly driven by the levels of nutrients. The combined use of chemical and biological essays resulted in an in-depth observation and analysis of the existing links between pollution macro-indicators and biological response of seabed bacterial communities.

Bacterial communities in polluted seabed sediments: a molecular biology assay in Leghorn harbor

Seabed sediments of commercial ports are often characterized by high pollution levels. Differences in number and distribution of bacteria in such areas can be related to distribution of pollutants in the port and to sediment conditions. In this study, the bacterial communities of five sites from Leghorn Harbor seabed were characterized, and the main bacterial groups were identified. T-RFLP was used for all samples; two 16S rRNA libraries and in silico digestion of clones were used to identify fingerprint profiles. Library data, phylogenetic analysis, and T-RFLP coupled with in silico digestion of the obtained sequences evidenced the dominance of Proteobacteria and the high percentage of Bacteroidetes in all sites. The approach highlighted similar bacterial communities between samples coming from the five sites, suggesting a modest differentiation among bacterial communities of different harbor seabed sediments and hence the capacity of bacterial communities to adapt to different levels and types of pollution.

Organic matter stabilization in reed bed systems: Danish and Italian examples.

In this study, results about sludge stabilization in reed bed systems (RBSs) after the entire period of operation in two different systems situated in Denmark (Helsinge 42,000 population equivalent (p.e.) - 10 years) and in Italy (La Fontina, 30,000 p.e. - 6 years) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical and chemico-structural properties of organic sludge matter have been determined. The level of total and soluble nutrients, and enzyme activities, parameters related to overall microbial activity, showed that stabilization of the sludge similarly occurred in both RBSs, even though in different landscape ecosystems. The chemical-structural characterization of sludge organic matter highlighted how the processes of stabilization have occurred satisfactorily in both RBSs; in fact, significant levels of pyrolytic indices for mineralization and humification were reached. The successful stabilization of organic matter occurred in both RBSs and was confirmed by the absence of Escherichia coli, and also by the results of organic compounds (polycyclic aromatic hydrocarbons, linear alkyl benzene sulfonates, nonylphenol ethoxylates, di-2-ethylhexyl-phthalate) and heavy metals.

Biofouling of reverse osmosis membranes used in river water purification for drinking purposes: analysis of microbial populations

Biofouling in water treatment processes represents one of the most frequent causes of plant performance decline. Investigation of clogged membranes (reverse osmosis membranes, microfiltration membranes and ultrafiltration membranes) is generally performed on fresh membranes. In the present study, a multidisciplinary autopsy of a reverse osmosis membrane (ROM) was conducted. The membrane, which was used in sulfate-rich river water purification for drinking purposes, had become inoperative after 6 months because of biofouling and was later stored for 18 months in dry conditions before analysis. SSU rRNA gene library construction, clone sequencing, T-RFLP, light microscope, and scanning electron microscope (SEM) observations were used to identify the microorganisms present on the membrane and possibly responsible for biofouling at the time of removal. The microorganisms were mainly represented by bacteria belonging to the phylum Actinobacteria and by a single protozoan species belonging to the Lobosea group. The microbiological analysis was interpreted in the context of the treatment plant operations to hypothesize as to the possible mechanisms used by microorganisms to enter the plant and colonize the ROM surface.

Phytoremediation of contaminated sediments: evaluation of agronomic properties and risk assessment

This study evaluates the possibility of reusing marine sediments in land management. The sediments, dredged from Livorno port (Italy), had previously been phytotreated, using a salt-tolerant plant cover and earthworms, with the aim of reducing the salt level and improving the texture and microbiology. In this study, sediments were investigated in order to: (1) test their capability to be used as a revitalised soil-like substrate (techno-soil), and (2) assess the human exposure risks associated with sediment management. Results obtained after 6 months of experiments performed with biological indicators composed of an association of graminae grass (Paspalum vaginatum), legumes (Trifolium alexandrinum) and earthworms (Eisenia foetida), showed that the substrate behaves like a natural soil capable of supporting biological life (total N=0.2%; total P=0.7%; EC=1.5 mS·cm −1; β−glucosidase=20 μ g PNP·g *h −1). It was also found that plants accumulate small amounts of heavy metals in shoot tissues (120 mg Zn·kg−1; 25 mg Cu·kg−1). In detail, risk analysis was performed considering: (1) sediment storage in a sealed disposal basin inside the Livorno port area, and (2) off-site phyto-remediation. The maximum hazard index was found for workers inside the port area, with values of 1.7 and 25 for dermal contact and vapour inhalation risks, respectively.

Hydraulic and biochemical analyses on full-scale sludge consolidation reed beds in Tuscany (Italy)

The management of sewage sludge has recently become one of the most significant challenges in wastewater management. Reed bed systems appear to be an efficient and economical solution for sludge management in small wastewater treatment plants. Four years ago, one of the holding companies for water and wastewater in central Italy adopted this technology in 6 wastewater treatment plants. Hydraulic and biochemical analyses were performed on the most representative site to asses the behaviour of reed beds with regard to dewatering, mineralization and humification of disposed sludge. Moreover, daily water content analysis were performed in the interval between subsequent sludge loadings. Results indicated a decrease of sludge volume by about 93% on a yearly basis. Biochemical analysis highlighted that mineralization processes decrease over time due to a rapid decrease of microbial activity and labile substrates, such as DHase enzyme and water-soluble carbon and ammonium, respectively. Moreover, a significant interrelationship between the parameters linked with mineralization was found: after two years of operation, the process of mineralization of organic matter is still predominant in the humification of organic matter. Daily water content data were used to define a semi empirical equation describing the dynamics of the dewatering process. Overall, the use of sludge reed beds resulted feasible, ecologically sustainable and cost-effective.

Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H+, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction.

Modelling assessment of carbon supply by different macrophytes for nitrogen removal in pilot vegetated mesocosms

The aim of this study was the evaluation of carbon supply by different macrophytes for nitrogen removal in constructed wetlands, using a dynamic numerical model previously developed by our work group to assess the results of a recently published meso-scale experiment. The experiment consisted of 12 mesocosms (five different macrophytes plus an unvegetated control, two cells each) drained once a week and immediately fed again until complete submersion with a solution of ammonium nitrate. To leave out any external carbon supply, no carbon substrate was added to the feed flux and no organic soil was included in the support media. The numerical simulations were obtained by calibration of the nitrification and denitrification processes driven by the alternate aerobic-anoxic phases generated by the weekly filling–emptying cycles. The carbon supplied by plants was demonstrated to be the main parameter affecting the denitrification rates observed in the experiments. It ranged in summer from 5.76 to 7.02 g/(m2 d), while the control accounted for 5.11 g/(m2 d). A winter test showed a 54% reduction of the summer supply of the same plant. The observed evapotranspiration rates were also simulated, and were shown to significantly affect the behaviour of the mesocosms planted with different species. Finally, the different vertical root-density distributions of the plants were found to play a relevant role in the development of nitrogen removal.

Life Cycle Assessment of Remediation Alternatives for Dredged Sediments

In this study, LCA was used to compare, in terms of their associated environmental burdens, two scenarios for managing the contaminated dredged sediments of the seabed of the Livorno Port area. The compared options were: (i) confined longshore disposal, i.e. placement of dredged material in a confined disposal facility; (ii) phytoremediation treatment, by an association of salt-tolerant shrub and grass species, aimed at turning the polluted sediment an agronomic substrate (techno-soil). The results of the life cycle impact assessment underline that the potential impacts of the two compared options involve different environmental problems. Indeed, for phytoremediation the most significant impacts are related to energy and resources consumption, while for the confined disposal is related to loads in the marine ecotoxicity categories. Therefore, phytoremediation can be considered a promising alternative solution for the management and valorization of contaminated dredged sediments.