Factors controlling carbon metabolism and humification in different soil agroecosystems.

The aim of this study was to describe the processes that control humic carbon sequestration in soil. Three experimental sites differing in terms of management system and climate were selected: (i) Abanilla-Spain, soil treated with municipal solid wastes in Mediterranean semiarid climate; (ii) Puch-Germany, soil under intensive tillage and conventional agriculture in continental climate; and (iii) Alberese-Italy, soil under organic and conventional agriculture in Mediterranean subarid climate. The chemical-structural and biochemical soil properties at the initial sampling time and one year later were evaluated. The soils under organic (Alberese, soil cultivated with Triticum durum Desf.) and nonintensive management practices (Puch, soil cultivated with Triticum aestivum L. and Avena sativa L.) showed higher enzymatically active humic carbon, total organic carbon, humification index (B/E(3)s), and metabolic potential (dehydrogenase activity/water soluble carbon) if compared with conventional agriculture and plough-based tillage, respectively. In Abanilla, the application of municipal solid wastes stimulated the specific ß-glucosidase activity (extracellular ß-glucosidase activity/extractable humic carbon) and promoted the increase of humic substances with respect to untreated soil. The evolution of the chemical and biochemical status of the soils along a climatic gradient suggested that the adoption of certain management practices could be very promising in increasing SOC sequestration potential.

Decontamination and functional reclamation of dredged brackish sediments.

The continuous stream of sediments, dredged from harbors and waterways for keeping shipping traffic efficiency, is a considerable ongoing problem recognized worldwide. This problem gets worse as most of the sediments dredged from commercial ports and waterways turn out to be polluted by a wide range of organic and inorganic contaminants. In this study, phytoremediation was explored as a sustainable reclamation technology for turning slightly-polluted brackish dredged sediments into a matrix feasible for productive use. To test this possibility, a phytoremediation experimentation was carried out in containers of about 0.7 m(3) each, filled with brackish dredged sediments contaminated by heavy metals and hydrocarbons. The sediments were pre-conditioned by adding an agronomic soil (30 % v/v) to improve their clayey granulometric composition, and by topping the mixture with high quality compost (4 kg m(-2)) to favour the initial adaptation of the selected vegetal species. The following plant treatments were tested: (1) Paspalum vaginatum, (2) Phragmites australis, (3) Spartium junceum + P. vaginatum, (4) Nerium oleander + P. vaginatum, (5) Tamarix gallica + P. vaginatum, and (6) unplanted control. Eighteen months after the beginning of the experimentation, all the plant species were found in healthy condition and well developed. Throughout the whole experiment, the monitored biological parameters (total microbial population and dehydrogenase activity) were generally observed as constantly increasing in all the planted sediments more than in the control, pointing out an improvement of the chemico-physical conditions of both microorganisms and plants. The concentration decrease of organic and inorganic contaminants (>35 and 20 %, respectively) in the treatments with plants, particularly in the T. gallica + P. vaginatum, confirmed the importance of the root-microorganism interaction in activating the decontamination processes. Finally, the healthy state of the plants and the sediment characteristics, approaching those of an uncontaminated natural soil (technosoil), indicated the efficiency and success of this technology for brackish sediments reclamation.

In situ phytoremediation of a soil historically contaminated by metals, hydrocarbons and polychlorobiphenyls.

In the past several years, industrial and agricultural activities have led to serious environmental pollution, resulting in a large number of contaminated sites. As a result, much recent research activity has focused on the application of bioremediation technologies as an environmentally friendly and economically feasible means for decontamination of polluted soil. In this study horse manure and Populus nigra (var. italica) (HM + P treatment) have been used, at real scale level, as an approach for bioremediation of a soil historically contaminated by metals (Pb, Cr, Cd, Zn, Cu and Ni) and organic contaminants, such as polychlorobiphenyls and petroleum hydrocarbon. After one year, the HM + P phytotreatment was effective in the reclamation of the polluted soil from both organic and inorganic contaminants. A reduction of about 80% in total petroleum hydrocarbon (TPH), and 60% in polychlorobiphenyls (PCBs) and total metals was observed in the HM + P treatment. In contrast, in the horse manure (HM) treatment, used as control, a reduction of only about 30% of TPH was obtained. In order to assess both effectiveness and evolution of the remediation system to a biologically active soil ecosystem, together with the pollution parameters, the parameters describing the evolution of the soil functionality (enzymatic activities and protein SDS-PAGE pattern) were investigated. A stimulation of the metabolic soil processes (increase in dehydrogenase activity) was observed in the HM + P compared to the HM treatment. Finally, preliminary protein SDS-PAGE results have permitted the identification of proteins that have been recovered in the HM + P soil with respect to the HM; this may become a basic tool for improving the biogeochemical status of soil during the decontamination through the identification of microbial populations that are active in soil decontamination.

Pollutant monitoring in sludge treatment wetlands.

Phragmites australis for sludge dewatering and stabilization processes have been widely proved. The presence of reeds, indeed, efficiently allows solids dewatering and organic matter stabilization in order to obtain a stabilised product that can be suitable for land application, even if its environmental impact has to be considered. The actual revision of the European Union's Working Document on Sludge (2000), in fact, seems to be addressed to detect two principal categories of pollutants in sludge for agricultural use: heavy metals and toxic organic compounds. In this study are presented results about sludge stabilization and monitoring of heavy metal fractionation and organic compounds in four urban wastewater treatment plants managed by Acque S.p.A., (Tuscany, Italy). To evaluate the process of sludge stabilization parameters were determined that highlight the biochemical and chemico-structural properties of sludge organic matter. The results showed that stabilization of the sludge over time occurred as shown by the low content of water soluble carbon and dehydrogenase activity, and by the re-synthesis of humic-like matter highlighted by the pyrolytic indices of mineralization and humification. Results about fractionation showed that heavy metals were retained in fractions related to the stabilized organic matter. Moreover, toxic organic compounds showed a drastic reduction at the end of the monitoring period.

Phytotreatment of sludges (Phragmites australis) for their reuse in the environment.

The aim of this study is the evaluation of the agronomic characteristics acquired by a phytotreated sludge coming from a wastewater treatment plant (WWTP) located in Tuscany (central Italy). The chemical characterization showed values which are within the Italian legislation limits for mixed composts. From an agronomic point of view, the sludge did not present a level of phytotoxicity, as shown by the germination index (GI% = 77). Furthermore, pathogen compounds are inexistent (Escherichia coli < 1,000 CFU/g). Different substrates (obtained by mixing the sludge with sandy agronomic soil - 0.5% w/w, 1% w/w, 2.5% w/w and 5% w/w) were prepared in order to evaluate the best mixture performance in terms of water retention capacity and plant growth. No significant differences were observed for all sludge mixtures. Different plants were tested in plots (Lepidium sativum, Cucumis sativus and Avena sativa). The best plant adaptation, measured as dry biomass production, was observed for Avena sativa. The results obtained underlined that the phytotreatment of sludge can bring about the transformation of sewage sludges into organic products that are reusable in agriculture, if previously mixed with other appropriate materials and taking into account their heavy metal content.

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.

Evolution of soil organic matter changes using pyrolysis and metabolic indices: a comparison between organic and mineral fertilization.

The aim of this study was to evaluate chemical and biochemical changes of organic matter in fertilized (ammonium nitrate) and amended (vermicompost and manure) soils using pyrolysis and metabolic indices. The metabolic potential [dehydrogenase (DH-ase)/water soluble organic carbon (WSOC)], the metabolic quotient (qCO2) and the microbial quotient (Cmic:Corg) were calculated as indices of soil organic matter evolution. Pyrolysis-gas chromatography (Py-GC) was used to study structural changes in the organic matter. Carbon forms and microbial biomass have been measured by dichromate oxidation and fumigation-extraction methods, respectively. Dehydrogenase activity has been tested using INT (p-Iodonitrotetrazolium violet) as substrate. The results showed that organic amendment increased soil microbial biomass and its activity which were strictly related to pyrolytic mineralization and humification indices (N/O, B/E3). Mineral fertilization caused a greater alteration of native soil organic matter than the organic amendments, in that a high release of WSOC and relatively large amounts of aliphatic pyrolytic products, were observed. Therefore, the pyrolysis and metabolic indices provided similar and complementary information on soil organic matter changes after mineral and organic fertilization.

A microcosm approach to assessing the effects of earthworm inoculation and oat cover cropping on CO2 fluxes and biological properties in an amended semiarid soil.

We designed a microcosm experiment to assess the influence of inoculation with Eisenia foetida earthworms and the establishment of an Avena sativa cover crop on biological (enzyme activities and labile carbon fractions) soil quality indicators in a soil treated with a composted organic residue, and to determine the contribution of these treatments to carbon dioxide emissions from the soil to the atmosphere of the microcosm. The microcosms were incubated for 53 days under 28 degrees C/18 degrees C day/night temperatures. The addition of earthworms and the planting of A. sativa increased dehydrogenase activity of compost amended soil by about 44% after 23 days of incubation. The metabolic potential, calculated as the ratio dehydrogenase activity/water soluble C, was higher in the compost amended soil planted with A. sativa. The highest total amount of CO2-C evolved occurred in the soil treated with composted residue and earthworms (about 40% of the total amount of CO2 evolved came from earthworm activity). The planting of A. sativa increased the decomposition rate constant of organic matter in the amended soil but decreased the potentially mineralizable C pool. In conclusion, the establishment of an A. sativa cover crop and the addition of E. foetida to a degraded agricultural soil treated with composted residue were effective treatments for improving the biological and biochemical quality and the metabolic potential of the soil.