Giorgia De Gioannis

ENHANCED ELECTROKINETIC TREATMENT OF MARINE SEDIMENTS CONTAMINATED BY HEAVY METALS AND PAHS

Dredged sediments contaminated by heavy metals and PAHs were subjected to both unenhanced and enhanced electrokinetic remediation under different operating conditions, obtained by varying the applied voltage and the type of conditioning agent used at the electrode compartments in individual experiments. While metals were not appreciably mobilized as a result of the unenhanced process, metal removal was found to be significantly improved when both the anodic and cathodic reservoirs were conditioned with the chelating agent EDTA, with removal yields ranging from 28% to 84% depending on the contaminant concerned. As for the effect on organic contaminants, under the conditions tested the electrokinetic treatment displayed a poor removal capacity towards PAHs, even when a surfactant (Tween 80) was used to promote contaminant mobilization, indicating the need for further investigation on this issue. Further research on organics removal from this type of materials through electrokinetic remediation is thus required. Furthermore, a number of technical and environmental issues will also require a careful evaluation with a view to full-scale implementation of electrokinetic sediment remediation. These include controlling side effects during the treatment (such as anodic precipitation, oxidation of the conditioning agent, and evolution of toxic gases), as well as evaluating the potential ecotoxicological effects of the chemical agents used.

Acetate-fed aerobic granular sludge for the degradation of 4-chlorophenol.

Chlorinated phenols are considered a critical environmental problem, due to their extreme toxicity and their widespread use both in industrial and agricultural activities. In this study, aerobic granular sludge was initially developed into an acetate-fed Granulated Sequencing Batch Reactor (GSBR) and then used for the degradation of low chlorinated 4-mono-chlorophenol (4CP), with readily biodegradable sodium acetate (NaAc) as co-substrate. Influent 4CP concentration ranged between 0 and 50mg/l, with a maximum volumetric organic loading rate of 0.20 kg(4CP)/m(3)d (0.32 kg(COD-4CP)/m(3)d). Differences in granules shape and size were observed with 4CP dosed in the influent at different concentrations, and the effects of such toxic compound on acetate removal were evaluated, with both unacclimated and acclimated biomass. Aerobic granules grown on acetate as carbon source proved to be an interesting solution for the degradation of 4CP, showing good resistance to high 4CP concentrations in the influent even if unacclimated (short term effects). Moreover, the monitoring of intermediate products and the evaluation of chloride release due to 4CP degradation proved that acclimated granular sludge could completely remove 4CP (long term effects), with high specific removal rates.

Enhanced electrokinetic treatment of different marine sediments contaminated by heavy metals

In the present work, the application of an assisted electrokinetic process for the removal of heavy metals from real contaminated sediments was investigated. The process made use of both chemical and physical methods, including addition of chelating and acid agents, as well as application of a hydraulic gradient. Lab-scale electrokinetic runs were applied on two different dredged sediments varying the applied voltage gradient and the treatment duration. The use of EDTA significantly improved the overall performance of the electrokinetic treatment for sediment V (more than 60% mobilized for each metal), while only aggressive acid conditioning with nitric acid was able to remove significant amounts of heavy metals (up to 40.5% for Pb) from sediment S due to the strong buffering capacity of this material. This clearly assesses that the specific characteristics of the materials under concern and the reactions occurring at the electrodes must be carefully evaluated when applying an electroremediation process.

Energy recovery from one- and two-stage anaerobic digestion of food waste

One- and two-stage anaerobic digestion of food waste aimed at recovering methane (CH4) and hydrogen and methane (H2+CH4), respectively, were compared in order to assess the potential benefits from the two-stage process in terms of overall energy recovery. Results suggest that a two-stage process where the first reactor is properly operated in order to achieve a significant net hydrogen production, may display a 20% comparatively higher energy recovery yield as a result, mainly, of enhanced methane production as well as of the associated hydrogen production. The highest methane production of the two-stage process was due to improved hydrolysis and fermentation of food waste, with increased amounts of volatile fatty acids being readily available to methanogenesis.

Chromate adsorption in a transformed red mud permeable reactive barrier using electrokinesis.

Electrokinetic removal of chromium from artificially contaminated clayey soil in a bench-scale cell was enhanced by a reactive barrier (RB) of transformed Red Mud (TRM, BAUXSOL) fitted near the anode. When using 0.75 wt% of TRM in a soil spiked up to a Cr (VI) concentration of 1000 mg/kg dry weight, about 54 wt% of total Cr was removed after 6 days, as compared to only 36 wt% from the control cell without TRM RB. Increasing the duration of the treatment up to 12 days and using 1.5 wt% of TRM resulted in the increase of the above mentioned removal efficiencies up to 93 wt% and 57 wt%, respectively. The reduction of Cr (VI) into less mobile Cr (III) was limited by the TRM RB; in fact, lower reduction percentages for the tests with TRM RB as compared to the tests without were observed (respectively, 42% versus 72% for 6 days test, and 60% versus 93% for 12 days test). The obtained results show that Cr (VI) removal efficiency is proportional to the duration of the treatment and enhanced by the development of favorable pH conditions caused by the activity of the anodic TRM RB. It is suggested that electrokinesis may increase the efficiency of metal-oxyanion adsorption on TRM, as well as that the use of a TRM RB may improve the efficiency of contaminated soil remediation by means of electrokinesis.

Biomass ash reutilisation as an additive in the composting process of organic fraction of municipal solid waste

In this work the effects of selected types of biomass ash on the composting process and final product quality were studied by conducting a 96-day long experiment where the source separated organic fraction of municipal waste, mixed with wood prunings that served as bulking agent, was added with 0%, 2%, 4% and 8% wt/wt of biomass ash. The evolution over time of the main process parameters was observed, and the final composts were characterised. On the basis of the results, both the composting process and the quality of the final product were improved by ash addition. Enhanced volatile solids reduction and biological stability (up to 32% and 52%, respectively, as compared to the unamended product) were attained when ash was added, since ash favored the aerobic degradation by acting asa physical conditioner. In the final products, higher humification of organic matter (expressed in terms of the humification index, that was 2.25 times higher in the most-enriched compost than in the unamended one) and total Ca, K, Mg and P content were observed when ash was used. The latter aspect may influence the composts marketability positively, particularly with regards to potassium and phosphorus. The heavy metals content, that is regarded as the main environmental disadvantage when using ash asa composting additive, did not negatively affect the final composts quality. However, some other controversial effects of ash, related to the moisture and temperature values attained during the process, pH (8.8-9.2 as compared to 8.2 of the unamended compost) and electrical conductivity levels (up to 53% higher as compared to the unamended compost) in the final composts, were also observed.

A parametric response surface study of fermentative hydrogen production from cheese whey

Batch factorial experiments were performed on cheese whey+wastewater sludge mixtures to evaluate the influence of pH and the inoculum-to-substrate ratio (ISR) on fermentative H2 production and build a related predictive model. ISR and pH affected H2 potential and rate, and the fermentation pathways. The specific H2 yield varied from 61 (ISR=0, pH=7.0) to 371L H2/kg TOCwhey (ISR=1.44gVS/g TOC, pH=5.5). The process duration range was 5.3 (ISR=1.44gVS/g TOC, pH=7.5) - 183h (ISR=0, pH=5.5). The metabolic products included mainly acetate and butyrate followed by ethanol, while propionate was only observed once H2 production had significantly decreased. The multiple metabolic products suggested that the process was governed by several fermentation pathways, presumably overlapping and mutually competing, reducing the conversion yield into H2 compared to that expected with clostridial fermentation.

Preliminary results of the life+ project: CO-ordinated approach for sediment treatment and beneficial reuse in small harbours networks

a ISPRA (Italian Institute for Environmental Protection and Research). Via Vitaliano Brancati, 60 00144 Rome (Italy) b Università di Cagliari – Dipartimento di Geoingegneria e Tecnologie Ambientali. Piazza d’Armi, 1 – 09123 Cagliari (Italy) c ARPA Emilia Romagna (Agenzia Regionale Prevenzione e Ambiente). Largo Caduti del Lavoro, 6 40121 Bologna (Italy) d CNR (Consiglio Nazionale delle Ricerche) – Istituto di Geologia Ambientale e Geoingegneria. Piazza d’Armi, 19 – 09123 Cagliari (Italy) e Università degli Studi di Roma “La Sapienza” – Dipartimento di Ingegneria Civile, Edile ed Ambientale. Via Eudossiana, 18 – 00184 Rome (Italy) raffaella.pomi@uniroma1.it