Remediated marine sediment as growing medium for lettuce production: assessment of agronomic performance and food safety in a pilot experiment.

BACKGROUND: The use of reclaimed dredged sediments as growing media may offer a profitable alternative to their disposal as a waste and at the same time meets the need of peat-substitute substrates in horticulture. When sediments are reused to cultivate food crops, issues related to human health rise due to potential accumulation of contaminants in the product. This pilot study aimed at verifying the suitability of a reclaimed dredged port sediment, used pure or mixed with peat, as a growing medium for lettuce cultivation. RESULTS: The pure sediment caused a reduction in crop yield, probably due to its unsuitable physical properties, whereas the mixture sediment-peat and pure peat resulted in the same yield. Although the sediment contained potentially phytotoxic heavy metals and some organic pollutants, no symptoms of plant toxicity were noted. Besides, no organic contaminants were detected in lettuce heads, and heavy metals amounts were not hazardous for consumers. Conversely, plants grown in the sediment were particularly rich in minerals like Ca, Mg and Fe, and showed higher concentrations of organic acids and antioxidants. CONCLUSION: The use of the sediment as a growing medium for lettuce was shown to be safe for both inorganic and organic contaminants. Nevertheless, considering crop yield results, the mixture of the sediment with other materials is recommended in order to produce a substrate with more suitable physicochemical properties for vegetable cultivation. © 2019 Society of Chemical Industry.

Use of phytoremediated sediments dredged in maritime port as plant nursery growing media.

We evaluated the potential of a phytoremediated sediment (TR) dredged from maritime port as peat-free growth substrate for seven ornamental plants, in comparison with an untreated sediment (NT), in a greenhouse experiment. The studied plants were Quercus ilex, Photinia x fraseri, Viburnum tinus, Cistus albidus, Raphiolepis indica, Westringia fruticosa and Teucrium fruticans. Plant growth was monitored for ten months, and the changes in the physico-chemical properties, toxicity, microbial biomass and enzyme activities involved in the C, P and N cycles were also monitored during the plant growth period. The results showed that the studied ornamental plants could grow on both NT and TR sediments, but that the growth was higher on TR sediment. The plant growth induced changes in the sediment chemical functional groups, with clear separation between NT and TR sediments for each of the studied plant. Microbial biomass and enzyme activities significantly increased during the plant growth, more in TR than in NT sediment. Toxicity was detected in NT sediments during the plant growth whereas it was not observed in NT sediments during the whole growth period. We concluded that phytoremediation converted the dredged maritime sediments into suitable substrates for growing ornamental plants, and that the re-use by plant nursery industry can be a sustainable management and valorization for remediated sediments.

Testing decontaminated sediments as a substrate for ornamentals in field nursery plantations.

When canals and harbours are dredged, huge amount of polluted sediments has to be stocked and transported to the landfill with incredibly high costs of management. Among the remediation techniques for the reclamation of polluted sediments and soils, phytoremediation represents a sustainable and effective technique though still not fully promoted or commercialized. In this study we have tested the suitability for plant nursing of a substrate resulting from sediments dredged from a canal and treated with phytoremediation. The experiment was set up in 2014. It aimed to test the physical, chemical and hydrological characteristics of two mixes of remediated sediments and agronomic soil (at 33% and 50% by volume) compared to control soil (100% agronomic soil), and to assess the growth of three ornamental species (Viburnum tinus L., Photinia x fraseri var. red robin, Eleagnus macrophylla Thunb.) together with the suitability for root balling. The mixed substrates produced good results in terms of water drainage, and were similar to the control in terms of soluble nutrients, guaranteeing and enhancing the aboveground and belowground growth of all the three species, especially V. tinus. In contrast, mixed substrates impaired root ball compaction with root ball breakage observed especially in 50% sediment/soil mix. Therefore, the use of remediated sediments in plant nursery can be limited to specific productions or practices.

Sewage sludge and waterworks sludge stabilization in sludge treatment reed bed systems.

In this study, results about sludge stabilization in sludge treatment reed bed (STRB) systems in two different systems, Hanningfield STRB 1 (England), treating waterworks sludge, and Stenlille STRB 2 (Denmark), treating surplus activated sludge, are presented. The study mainly focused on the effectiveness of the STRBs systems in stabilizing sludge organic matter; in fact, parameters correlated to biochemical and chemico-structural properties of organic sludge matter were determined. Dewatering and sludge stabilization were effective in both STRBs, as highlighted by total and volatile dry solids trend. ß-glucosidase, phosphatase, arylsulphatase, leucine amino-peptidase and butyrate esterase activities, enzymes related to C, P, S, N and overall microbial activity, respectively, significantly declined along the profile in both STRBs. The determination of humic carbon highlighted the formation of a stable nucleus of humified organic matter in both STRBs in the deepest layers, thus meaning the successful stabilization of sludge organic matter for both kind of sludges. Similar conclusions can be drawn from pyrolysis gas chromatography analysis (Py-GC), which enables the characterization of soil organic matter quality from a chemical-structural point of view. The pyrolytic indices of mineralization and humification showed that in both STRBs the sludge organic matter is well stabilized.

Stabilisation and mineralisation of sludge in reed bed systems after 10-20 years of operation.

Sludge stabilisation and mineralisation during periods of operation between 10 and 21 years were investigated in three different systems receiving sludge from urban wastewater treatment plants situated in Denmark. Samples were taken along the entire profiles, in order to compare the effectiveness of the sludge stabilisation process. Particular attention was given to the stabilisation process occurring within the reed beds; in fact, parameters correlated to biochemical properties of organic sludge matter were determined. Statistical procedures were used to evaluate how the biochemical processes influence the quality of sludge organic matter. The level of total organic carbon and total nitrogen had a similar trend along the profile: their concentration decreased with increasing depth, reaching very low levels at the deepest layers. The same trend was also observed for the water-soluble carbon, N-NH(3), ß-glucosidase and urease activities, and hydrolytic enzymes linked to C and N cycles: their values decreased dramatically with increasing depth, meaning that the level of mineralisation of the organic matter was higher in the deepest layers. The determination of extracellular enzymes bound to humic substances and humic carbon permitted evaluation of the stabilisation of organic sludge matter, and also allowed individuation of the ways in which the sludge was stabilised, in terms of mineralisation and humification of the organic matter.

A real-scale soil phytoremediation.

In the present investigation, a phytoremediation process with a combination of different plant species (Populus nigra (var.italica), Paulownia tomentosa and Cytisus scoparius), and natural growing vegetation has been proposed at real-scale (10.000 m(2)) to bioremediate and functionally recover a soil historically contaminated by heavy metals and hydrocarbons. In the attempts to assess both effectiveness and evolution of the remediation system towards a natural soil ecosystem, besides the pollution parameters, also parameters describing the efficiency of the microbiological components (enzyme activities), were investigated. In 3 years, the total content of hydrocarbons and heavy metals in soil decreased with time (40 % and 20-40 %, respectively), reaching concentrations under the limit of National legislation and making the site suitable for environmental reusing. The reduction in pollutants was probably the reason of the increase in dehydrogenase (indicator of overall microbial activity), ß-glucosidase and phosphatase activities, enzymes related to C and P cycles, respectively. However, this trend was obviously due also to the increase of chemical nutrients, acting as substrate of these enzymes. Moreover, a phytotest carried out with Raphanus sativus, showed, after 3 years, a significant increase in percentage of plant growth, confirming a reduction in soil toxicity and an improvement in soil nutritional state. Therefore, this phytoremediation system seems very promising to perform both decontamination and functional recovery of a polluted soil at real-scale level.

Short-term performance analysis of sludge treatment reed beds.

Sludge treatment reed beds (STRBs) represent an established technology for managing sludge produced by wastewater treatment plants (WWTPs). In this study, an analysis conducted on sludge stratigraphy in a STRB serving the municipal WWTPs of Helsinge (42,000 person equivalent, Denmark) is presented. The STRB has been in operation since 1996. The analysis was conducted for four months including two consecutive loadings of one of the 10 basins. The amount of dewatering during the short initial phase was significant, and the rehydration of deeper layers was negligible. A clear reduction trend was observed for volatile solids and labile organic matter, which is the first step towards organic matter humification. This hypothesis was also confirmed by water soluble carbon, which decreased with the increasing depth and the time of resting. About the N cycle, ammonification and nitrification showed a reciprocal balancing effect, so as to cause an equilibrium between the stable trends of NH(4)(+) and NO(3)(-) which were similar along the depth and the time of monitoring. The highest values of both parameters were found at the surface, where the combined effect of plant action, direct diffusive oxygen transfer from the atmosphere and high nutrient contents of the freshly loaded sludge was likely more intense.

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.

Bioremediation of polluted soil through the combined application of plants, earthworms and organic matter.

Two plant species (Paulownia tomentosa and Cytisus scoparius), earthworms (Eisenia fetida), and organic matter (horse manure) were used as an ecological approach to bioremediate a soil historically contaminated by heavy metals and hydrocarbons. The experiment was carried out for six months at a mesoscale level using pots containing 90 kg of polluted soil. Three different treatments were performed for each plant: (i) untreated planted soil as a control (C); (ii) planted soil + horse manure (20:1 w/w) (M); (iii) planted soil + horse manure + 15 earthworms (ME). Both the plant species were able to grow in the polluted soil and to improve the soil's bio-chemical conditions, especially when organic matter and earthworms were applied. By comparing the two plant species, few significant differences were observed in the soil characteristics; Cytisus scoparius improved soil nutrient content more than Paulownia tomentosa, which instead stimulated more soil microbial metabolism. Regarding the pollutants, Paulownia tomentosa was more efficient in reducing the heavy metal (Pb, Cr, Cd, Zn, Cu, Ni) content, while earthworms were particularly able to stimulate the processes involved in the decontamination of organic pollutants (hydrocarbons). This ecological approach, validated at a mesoscale level, has recently been transferred to a real scale situation to carry out the bioremediation of polluted soil in San Giuliano Terme Municipality (Pisa, Italy).

Almond tree and organic fertilization for soil quality improvement in southern Italy.

The semi-arid Mediterranean region, characterized by long dry periods followed by heavy bursts of rainfall, is particularly prone to soil erosion. The main goal of this study is to evaluate the soil quality under different practices of bio-physical amelioration which involve the soil-plant system (almond trees) and microorganism-manure. This study, carried out in the South of Italy (Basilicata Region- Pantanello farm), considered two types of fertilization (mineral and organic) and three slope gradients (0, 2 and 6%), in order to evaluate the effects of management practices in resisting soil erosion. Chemical (organic carbon and nitrogen), physical (soil shrinkage and bulk density) and biochemical (dehydrogenase activity and hydrolytic enzyme activities) parameters were selected as markers to follow agro-ecological changes with time. The organic treatment affected soil microbiological and physico-chemical properties by increasing soil nutrient availability, microbial activity, and improving soil structure. The consistently higher values of the hydrolytic enzyme activities (ß-glucosidase, phosphatase, urease and protease) often observed in the presence of plants and on the 0 and 2% slopes, suggested the stimulation of nutrient cycles by tree roots, which improve the conditions for soil microorganisms in carrying out their metabolic activity. In the 6% slope and, in particular, in the mineral fertilizer treatment, soil metabolism was lower as suggested by the dehydrogenase activity which was 50% lower than that found in the 0 and 2% slopes, this seemed to be related to a slowdown in the nutrient cycling and organic carbon metabolism. However, on this slope, in both mineral and organic treatments, a significant stimulation of hydrolytic enzyme activities and an improvement of soil structure (reduction of bulk density of about 10% and increase in total shrinkage from 20 to 60%) were observed with plants compared to the control soil. The combination of organic fertilization and almond trees resulted effective, also in the highest slope, in mitigating the degradation processes through the improvement of chemico-nutritional, biochemical and physical soil properties.

Application of organic wastes on a benzo(a)pyrene polluted soil. Response of soil biochemical properties and role of Eisenia fetida.

In this paper we studied the bioremediation effects of a soil artificially contaminated by benzo(a)pyrene with and without two organic wastes (organic municipal solid waste, MSW, and poultry manure, PM) and with and without worms (Eisenia fetida) over 90 days. For the organic treatments, soil samples were mixed with MSW at a rate of 10% or PM at a rate of 7.6%, in order to apply the same amount of organic matter to the soil. An unamended and non-polluted soil was used as control. Cellulase and glutathione-S-transferase activities in worms and the earthworms' weight were measured at four different incubation times (3, 15, 60 and 90 days). Cocoon numbers, average weight per cocoon and number of juveniles per cocoon were measured 30 days after the benzo(a)pyrene exposure. Extractable benzo(a)pyrene in soils and E. fetida was determined during the incubation period. To observe the effects of bioremediation of the contaminated soil, ATP, urease and phosphatase activities were measured. At the end of the incubation period and when compared with the polluted soil without worms and organic matter, the extractable benzo(a)pyrene decreased by 41.2% for the unamended polluted soil and without worms, by 45.8% for the organic-PM polluted soil and without worms, 48.3% for the organic-MSW polluted soil and without worms, 55.4% for the organic-PM polluted soil and with worms, and 66.3% for the organic-MSW polluted soil and with worms. This meant that worm hydrocarbon absorption was lowest in the contaminated soil amended with MSW and with worms, causing an increase in catabolic activity of the soil. These results suggested that the co-application of organic wastes and E. fetida for the bioremediation of benzo(a)pyrene polluted soil is potentially advantageous.

Landfarming as a sustainable management strategy for fresh and phytoremediated sediment.

The aim of this study was to evaluate the effectiveness of a landfarming process (LP) in recovering sediments at different biodegradation phases: phytoremediated dredged sediments (PDS) and fresh dredged sediments (FDS). The PDS landfarming was applied to (1) reduce residual contamination and (2) improve the biological activities in order to obtain a decontaminated matrix rich in organic matter and enzymatic activity to be reused as agronomic substrate. In 3 months of LP, a microbial activity stimulation (from 7 to 48%) and a decrease in organic contamination (about 15%) were recorded. In addition, no phytotoxicity and the content in total organic carbon and nitrogen make the sediments suitable to be reused in agriculture. The FDS landfarming was carried out to (1) reduce water content, (2) transform the organic matter into a more stable form, and (3) decrease organic contaminant level. Five months of LP led to a considerable reduction in water content (40%) and to the activation of microbial biomass metabolism (from 4 to 50 times higher), which achieved proper mineralization of organic matter and contaminants (polycyclic aromatic hydrocarbons near to zero and a total petroleum hydrocarbon reduction of about 60%). The LP also enhanced the stoichiometric ratios of nutrients and enzymes. In conclusion, the LP was a promising and economical methodology to improve the physical, chemical, and biological properties of polluted sediments at different biodegradation phases, creating a substrate ready for several environmental applications. Notably, the PDS resulted appropriate for agricultural use and FDS for civil applications.

Agronomic performance and food safety of strawberry cultivated on a remediated sediment.

A marine sediment phytoremediated and homogenized by landfarming was tested for its potential recycle as growing media in horticulture. Two strawberry cultivars, Camarosa and Monterey, were grown on remediated sediment alone (TS100), commercial peat/pumice based growing medium (TS0) and a mixture 1:1 in volume of sediment and peat (TS50). Chemical fertility and strawberry production and safety of produced food were monitored for three consecutive productive seasons on the same growing media. During the first year of cultivation, plants grown on sediment-based media showed a significantly lower biomass production and fruit yield compared with peat, mainly due to the sediment low fertility. In the subsequent two years, the plant re-cultivation improved the sediment structure and N mineralization, and on the third cultivation year both strawberry cultivars showed higher fruit productivity and no accumulation of potentially toxic trace metals. The produced fruits did non accumulate high concentrations of trace metals, and risk assessment showed no risks for human health related to the consumption of strawberry produced on sediment-based growing media. We concluded that a phytoremediated sediment could be recycled as an ingredient of soilless growing media for reducing the environmental impact of plant nursery production and posing no risks for human health. These results show that reclaimed sediments could be reconsidered as a component material category in the new EU regulation on fertilizers.

Use of earthworms (Eisenia fetida) to reduce phytotoxicity and promote humification of pre-composted olive oil mill wastewater.

BACKGROUND: Olive mill wastewaters (OMWW) contain a high recalcitrant organic load and an associated toxicity that make their treatment necessary before environmental application. The aim of this study was to evaluate the feasibility of promoting the valorization and reducing the phytotoxicity of OMWW through a pre-composting process together with straw-chip bulking materials followed by the application of earthworms (Eisenia fetida) in the presence of oat seedlings (Avena sativa L.) seedlings. RESULTS: After 3 months, the pre-composted material showed properties similar to a partially digested compost with some significant amelioration of chemical-physical and biochemical properties. The application of earthworms permitted a significant decrease in chemical (total organic carbon, water-extractable organic carbon, total nitrogen) and biological parameters (dehydrogenase enzyme activity), and an increase in humic substances and available nitrogen forms. In the presence of plants a higher C/N ratio and a lower content of nitrates were observed. In addition, the reduction in phenolic compounds observed in treatments with earthworms caused a decrease in phytotoxicity by about 50% with respect to the pre-composted material, which results in an increase in germination index. CONCLUSION: The utilization of earthworms, in particular in the presence of plants, may be an ecologically sound and economically feasible technology to obtain a non-toxic, high-value product useful for agricultural purposes.

Vermicomposting of olive oil mill wastewaters.

The disposal of olive oil mill wastewaters (OMW) represents a substantial environmental problem in Italy. A vermicompost process could be an alternative and valid method for the management of OMW. In a laboratory experiment, the OMW were absorbed onto a ligno-cellulosic solid matrix and 30 adult earthworms of Eisenia fetida specie were added. The experiment was carried out for 13 weeks. The number of earthworms increased throughout the experimental period and after 2 weeks about 90% of the earthworms had become sexually mature. The decrease in total organic carbon (about 35%), C : N ratio (from 31.2 to 12.3) and biochemical parameters (hydrolytic enzymes averagely 40% and dehydrogenase 23%), and the increase in humification rate (pyrophosphate extractable carbon (PEC) from 17.6 to 33.3 mg g(-1), and PEC : water-soluble carbon from 1.76 to 2.97) indicated the mineralization and the stabilization of organic matter at the end of the vermicomposting process. At the end of the experiment, the extracellular beta-glucosidase, phosphatase, urease and protease activities, measured in the pyrophosphate extract of the vermicompost, were found to be always higher or equal to that measured at the beginning of the vermicomposting process, suggesting that the enzymes bound to humic matter resisted biological attack and environmental stress. Moreover, the results obtained from the phyto-test showed that the OMW lose their toxicity and stimulate plant germination and growth.

Monitoring of a long term phytoremediation process of a soil contaminated by heavy metals and hydrocarbons in Tuscany.

The purpose of this study was to monitor and model indicators of soil contamination, organic matter evolution and biochemical processes involved in a long-term phytoremediation process. Populus nigra L., Paulownia tomentosa Steud., Cytisus scoparius L. and natural vegetation were used in differently contaminated areas (high, medium and low levels of contamination). Parameters indicating contamination (total petroleum hydrocarbons (TPH) and heavy metals) and agronomic (C, N and P) and functional (enzyme activities) soil recovery were monitored for 3.5 years. Three subareas with different levels of contamination (high, medium and low) were identified according to the Nemerow Index. A considerable decrease in TPH (52% on average) over time in the whole site was measured, while the metal reduction was only of about 22% at surface level. A stimulation in metabolic soil processes and improvement in the chemical quality of the soil was also observed throughout the experimental site. Statistical analysis modelling showed that the contaminant content decreased following a one-phase decay model, while the dramatic increase in enzyme activities could be represented by an exponential growth equation. On the basis of our data, it is possible to conclude that the initial contamination level affected neither the decontamination process nor the improvement in soil quality, which occurred similarly in the three different contaminated areas.

Metabolic and bacterial diversity in soils historically contaminated by heavy metals and hydrocarbons.

The aim of this study was to characterize soils contaminated by different levels of heavy metals and hydrocarbons (Madonna Dell'Acqua, Pisa, Italy). The soils were chemically and biochemically analysed by measuring the standard chemical properties and some enzyme activities related to microbial activity (dehydrogenase activity) and the soil carbon cycle (total and extracellular beta-glucosidase activities). The metabolic capacities of soil microorganisms to degrade hydrocarbons through catechol 2,3-dioxygenase were also described. The microbial diversity of contaminated and uncontaminated soils was estimated by denaturing gradient gel electrophoresis (DGGE) of amplified 16S rDNA sequences. The PCR/single-strand conformation polymorphism (PCR/SSCP) method was used to estimate the genetic diversity of PAH-degrading genes in both contaminated and uncontaminated soils. A greater bacterial diversity and lower catechol 2,3-dioxygenase activity was detected in unpolluted soils. The complexity of the microbial community (Shannon and Simpson indices) as well as the dehydrogenase soil activity negatively correlated with contamination levels. The greatest PAH-degrading gene diversity and the most intense catechol 2,3-dioxygenase activity were found in the soils with the highest levels of hydrocarbons. Heavy metals and hydrocarbon pollution has caused a genetic and metabolic alteration in microbial communities, corresponding to a reduction in microbial activity. A multi-technique approach combining traditional biochemical methods with molecular-based techniques, along with some methodological improvements, may represent an important tool to expand our knowledge of the role of microbial diversity in contaminated soil.

Phytoremediated marine sediments as suitable peat-free growing media for production of red robin photinia (Photinia x fraseri).

Sediments dredged by an industrial port, slightly contaminated by heavy metals and petroleoum hydrocarbons, were phytoremediated and used as peat-free growing media for the red robin photinia (Photinia x fraseri L.). Plants were grown on sediment only (S), sediment mixed with composted pruning residues (S + PR), sediment fertilized with controlled release fertilizers (S + F) and peat-based growing media as control (C). Plant elongation and dry weight, leaf contents of chlorophyll, malondialdehyde (MDA), macronutrients and heavy metals were determined at the end of one growing season. Environmental impact related to the use of sediment-based as compared to peat-based growing media was assessed by the Life Cycle Analysis (LCA). Sediment-based growing media presented significantly higher bulk density, pH and electrical conductivity values, lower C and N contents, and significantly higher total and available P. Red robin photinia grown on S + F growing media showed morphological and chemical parameters similar to those of control plants (C), whereas plants grown on S and S + PR showed lower growth. Leaf concentration of nutrients and heavy metals varied depending on the considered element and growing media, but were all within the common values for ornamental plants, whereas the highest MDA concentrations were found in plants grown on traditional growing media. The LCA indicated the use of sediments as growing media reduced the C footprint of ornamental plant production and the contribute of growing media to the environmental impact per produced plant. We concluded that sediments phytoremediation and use in plant nursery is a practical alternative re-use option for dredged sediments.

Ornamental plants for micropollutant removal in wetland systems.

The objective of this paper was to evaluate the efficiency of micropollutant removal, such as Cu, Zn, carbamazepine, and linear alkylbenzene sulfonates (LAS), through the use of a subsurface vertical flow constructed wetland system with ornamental plants. Zantedeschia aethiopica, Canna indica, Carex hirta, Miscanthus sinensis, and Phragmites australis were selected and planted in lysimeters filled up with gravel. The lysimeters were completely saturated with synthetic wastewater (N 280 mg L(-1), P 30 mg L(-1), Cu 3.6 mg L(-1), Zn 9 mg L(-1), carbamazepine 5 µg L(-1), linear alkylbenzene sulfonates 14 mg L(-1)), and the leaching water was collected for analysis after 15, 30, and 60 days in winter-spring and spring-summer periods. Nutrients (N and P) and heavy metals decreased greatly due to both plant activity and adsorption. C. indica and P. australis showed the highest metal content in their tissues and also the greatest carbamazepine and LAS removal. In these plants, the adsorption/degradation processes led to particularly high oxidative stress, as evidenced by the significantly high levels of ascorbate peroxidase activity detected. Conversely, Z. aethiopica was the less efficient plant in metal and organic compound removal and was also less stressed in terms of ascorbate peroxidase activity.

Organic matter and pollutants monitoring in reed bed systems for sludge stabilization: a case study.

In this study, results about sludge stabilization and pollutant monitoring in a reed bed system (RBSs) situated in Central Italy (Colle di Compito, 4,000 p.e.) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical, chemical and chemico-structural properties of organic sludge matter have been followed during the entire period of operation (7 years). Moreover, the trend of heavy metals (bioavailable fractions and total content) and toxic organic compounds (LAS, NPE and DEHP) was monitored during all the period. The trend of all parameters related clearly demonstrated that sludge stabilization successfully proceeded in RBS. Moreover, through statistical analysis modelling, it is possible to determine how the stabilization process proceeded in terms of organic matter mineralization and humification, and how these processes influenced the content of pollutant compounds present in the stabilized sludges.