Percolate Water Research Articles

Investigation of Dynamic Water Cluster and Droplet Interactions in Polymer Electrolyte Fuel Cells using Operando X-ray Tomographic Microscopy

Efficient removal of the electrochemically produced water from the gas diffusion layer (GDL) in polymer electrolyte fuel cells is crucial for reducing mass transport losses and improving the efficiency at high current densities. Understanding the relationship between the water percolation through the GDL and droplet formation in the gas channel will allow the design of advanced GDL materials, which provide optimal water management. In this study, a catalyst-coated membrane with 8 individual active areas (0.06 mm2 each) is investigated using operando X-ray tomographic microscopy to study the transient development and interaction of multiple percolating water clusters in a GDL and droplet formation in the channel. The 4D imaging results at a time resolution of 1 Hz showed transient instabilities in the developed percolating water networks at various frequencies associated with break-through and spontaneous water drainage.

Bulk Nanostructure of Mixtures of Choline Arginate, Choline Lysinate, and Water.

Neutron diffraction with empirical potential structure refinement was used to investigate the bulk liquid nanostructure of mixtures of choline arginate (Ch[Arg]), choline lysinate (Ch[Lys]), and water at mole ratios of 1Ch[Arg]:1Ch[Lys]:6H2O (balanced), 1Ch[Arg]:1Ch[Lys]:20H2O (balanced dilute), 3Ch[Arg]:1Ch[Lys]:12H2O (Arg- rich), and 1Ch[Arg]:3Ch[Lys]:12H2O (Lys- rich). The Arg- and Lys- anions tend not to associate due to electrostatic repulsion between charge groups and weak anion-anion attractions. This means that the local ion structures around the anions in these mixtures resemble the parent single-component systems. The bulk liquid nanostructure varies with the Arg-:Lys- ratio. In the Lys--rich mixture (1Ch[Arg]:3Ch[Lys]:12H2O), Lys- side chains cluster into a continuous apolar domain separated from a charged domain of polar groups. In the balanced mixture (1Ch[Arg]:1Ch[Lys]:6H2O), Lys- side chains form discrete apolar aggregates within a continuous polar domain of Arg-, Ch+, and water, and in the Arg--rich mixture (3Ch[Arg]:1Ch[Lys]:12H2O), the distribution of Lys- and Arg- is nearly homogeneous. Finally, in the balance dilute system (1Ch[Arg]:1Ch[Lys]:20H2O), a percolating water domain forms.

Molecular Structure and Dynamics in Wet Gecko β-Keratin.

Molecular dynamics simulations are performed to investigate the molecular picture of water sorption in gecko keratin and the influence of relative humidity (RH) on the local structure and dynamics in water-swollen keratin. At low RHs, water sorption occurs through hydrogen bonding of water with the hydrophilic groups of keratin. At high RHs (>80%), additional water molecules connect to the first "layer" of amide-connected water molecules (multimolecular sorption) through hydrogen bonds, giving rise to a sigmoidal shape of the sorption isotherm. This causes the formation of large chain-like clusters surrounding the hydrophilic groups of keratin, which upon a further increase of the RH form a percolating water network. An examination of the dynamics of water molecules sorbed in keratin demonstrates that there are two states, bound and free, for water. The dynamics of water in these states depends on the RH. At low RHs, large-scale translational motions of tightly bound water molecules to keratin are needed to remake the entire hydration shell of the keratin. At high RHs (>80%), the water molecules more quickly exchange between the two states. The center-of-mass mean-square displacement of water molecules indicates a hopping motion of water molecules in the keratin solvation shell. The hopping mechanism is more pronounced at RHs < 80%. At higher RHs, water translation through water clusters (water network) dominates. We have observed two regimes for the dependence of dynamical properties on the RH: a regime of gradual increase of the dynamics over 10% < RH < 80% and a regime of drastic dynamic acceleration at RH > 80%. The latter regime begins exactly where the water uptake and the volume swelling also increase much more and where a drastic change in the elastic properties of gecko keratin has been observed. A nearly linear relation between the relaxation times for all dynamical processes and the water content of gecko keratin is observed.

Sidestream materials show potential as top-dressed soil improvers for peatland forests.

The effects of top-dressing of several industrial and farming sidestream materials on the growth of downy birch (Betula pubescens Ehrh.) and Scots pine (Pinus sylvestris L.) seedlings in natural sphagnum peat soil were evaluated. Wood fly ash, industrial filter cake waste, mine tailings sand (quartz feldspar from lithium orebody), and digestate and liquid reject of cow manure from a biogas plant were studied for their physical and chemical properties, as well as for their effects as soil ameliorants on seedling growth during one growing period in a greenhouse. Each material was top-dressed on unfertilised peat in pots in quantities that corresponded to the amounts of ash used in Finnish peatland forest fertilisation (2-6tha-1). During growing, the pH of percolate water from the growing pots was below 4, and in the treatments with filter cake even below 3. However, no clear impairment of seedling growth due to acidity was observed. In all treatments, birch and pine seedlings grew at least as well as in the unfertilised peat (control treatment). Growth was strongest in the peat top-dressed with additives originating from cow manure, in which the high N and P contents promoted growth so much that foliar N was found to be diluted with respect to a high P content in the birch seedlings. No harmful concentrations of heavy metal residues were observed from the materials used. Overall, the results suggest that all the used sidestream materials show potential as soil improvers on forested peatlands.

Bioenergy from forests: Impact of logging residues on the carbon and nitrogen cycles

Sustainable forest management practices are crucial for minimizing environmental impacts, and to keep forests and the underlying soils healthy to maintain productivity, and to improve adaptability to climate change and mitigate it in the long-term. There, carbon and nitrogen cycling play crucial roles in proper functioning of forest ecosystems. The overall aim of this thesis was to explore the effects of logging residues on the early-stage dynamics of the main nitrogen and carbon cycling processes in upland forest soils after final felling. A specific aim was to compare the effects of logging residue piles consisting of different tree species, i.e., Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and silver birch (Betula pendula Roth). A special attention was given to the response of soil to different amounts of residues. The effect of logging residues on soil chemical properties and processes was stronger in the organic layer than in the mineral soil layer. Logging residue piles stimulated carbon and nitrogen cycling, especially net nitrification within the first year after the residue treatment. Subsequently, nitrogen was lost via leaching as nitrate and gaseous emission as nitrous oxide. Nitrous oxide fluxes were generally low, although higher in the plots containing logging residues. Spruce residues tended to stimulate nitrous oxide emissions for longer than the residues of the other tree species. Depending on the tree species, nitrous oxide production originated from both autotrophic nitrification and denitrification. Nitrogen concentrations in the soil percolate water already accelerated one year after the establishment of the residue piles. Logging residues increased nitrate and ammonium concentrations, which were highest under birch residues. The effect of logging residue piles on soil was stronger when compared to milder tree species effects. Biological nitrogen fixation activity tended to be higher in branches than in needles or leaves, and higher in coniferous residues. The results of this study raise the importance of more even distribution of logging residues on the forest floor instead of piling them to avoid harmful environmental effects and to maintain soil nutrient balance. The ability of soils to retain nitrogen needs additional attention in forest management practices, especially in boreal areas where nitrogen limits the growth of forests.

Insights into the Stability and Formation of Water Droplets Using Operando X-Ray Tomographic Microscopy

Efficient removal of the electrochemically produced water from the gas diffusion layer (GDL) in polymer electrolyte fuel cells (PEFC) is crucial for reducing the mass transport losses and enabling the technology to become a viable energy solution. Understanding the interaction between the water cluster percolation through the GDL and the droplet formation and detachment in the gas channel could enable the design of advanced GDL materials, which provide optimal water management. In this study, a catalyst-coated membrane (CCM) with 8 small, independent active areas (0.0625 mm2 each) is investigated using operando X-ray tomographic microscopy (XTM) to study the transient development and interaction of multiple percolating water clusters in a GDL and droplet formation and detachment in the channel. The results of the study provide insights into the water removal in PEFC through the development of percolating networks in the GDL. Transient instabilities in the developed percolating water networks associated with break-through and droplet detachment were also observed.

Carcinogenic trace metals in ground water of Bathinda district, Punjab, India

Water is the second important source for surviving of human being on the earth because of it plays the major role in functioning of the body. in some decades decline the water quality due to the threatening of the environmental conditions and disposed untreated waste water in the water bodies which generate during the different activity in industries and human activities, which causes of increases of contamination of carcinogenic metals Include, mercury, cadmium, Arsenic, chromium, Selenium, Beryllium, Cobalt and nickel in ground water. These toxic metals Cancer causing to human being. Metals found in combined form of other element in the water. Carcinogenic metals Hg, Cr, As, Co, Cd, etc. also constituents of the earth crust. These were soluble in the percolate water, merged in the ground water. we have Evidences of carcinogens metals in the ground water of Bathinda district of Punjab. The present study attempt has been made to identify the types and concentration of different carcinogenic metallic ions present in ground water of South-Western, Bathinda district of Punjab. The pH was ranged from 6.5 -7.4 which were within the permissible limit of drinking ground water. Cr and Hg is above the permissible limit of drinking water quality guideline of WHO and BIS. Cr ranged from 70-360 ppb in ground water and highest level of Cr was observed at Lehra Mohabbat. The permissible limit in drinking water of Hg is 1ppb, all the sample have the Hg concentration level is above the limit. Expect three sites (JWS2-17.6 ppb, Bhambhia-11.9 ppb and Ganga-10.7 ppb) the concentration of Se and As was below the permissible limit.

Water migration through fat-based semi solid heterogeneous materials

• Water migration through fat-based composites is mediated by percolation process. • Permeating water network is provided by hydrophilic inclusions. • Size of percolating water cluster diverges with percolation exponent. • Water bridges between hydrophilic inclusions lead to mechanical stiffening. • Percolating moisture network enhances water loss in the heterogeneous material. Water migration through heterogeneous soft materials is central to many applications including oil recovery and consumer product stability of foods and cosmetics. This slow water transport affects all material properties such as mechanical, optical and electrical, but its understanding and modelling remains challenging due to complex wetting and diffusion processes across the heterogeneous material. Here, we study experimentally the penetration of water through a soft composite with hydrophobic (fat) and hydrophilic (salt) components. Conductivity measurements indicate the emergence of a percolating water network above critical water and salt volume fractions. This is corroborated by mechanical measurements revealing a concomitant stiffening of the material due to proliferating water bridges. Simulations of water absorption at spherical inclusions confirm this scenario and show the underlying cluster growth and percolation process.

A modelling approach and module for salinity management in drip irrigation

The article describes a new modelling approach and module for soil salinity management. The two major objectives of the module are to simulate the seasonal course of the salinity of the soil solution in the active root zone of drip-irrigated crops to assist irrigators to optimise irrigation and salt leaching, and to help evaluate the salt fluxes in the deep percolating water for assessing the longer-term salt load of the irrigated crops on the regional ground and surface water resources. The module is based on the solutions of the DIDAS program for quasi-steady water flow and uptake for various drip irrigation scenarios, and on differentiating the applied water to evaporation from the soil surface, uptake by the plant roots, deep percolation through the root zone that leaches salt out of it, and deep percolation outside of the root zone that does not leach salts. After laying out the rationale behind the suggested approach and outlining the expressions used in the module for evaluating the salinity of the root zone, several sample computations, in silico experiments, are performed to illustrate the module functionality and its potential application, and to serve for sensitivity analysis of the system parameters. Additional investigation is needed into the adequacy of the suggested modelling approach and the developed module to simulate soil salinity in the active root zone. • The module evaluates seasonal courses of root zone salinity in drip-irrigated fields. • It simulates root system development but does not predict plant growth and yields. • It is based on modelling quasi-steady water flow and uptake and salt mass balance. • The deep percolating water are partitioned into two fractions. • One that flows through the root zone and leaches salt out of it, and one that flows around it.

Modelling of Soil Moisture Movement and Solute Transport in Parts of Malaprabha Command

Abstract Infiltration is one of the most important hydrological process through which water enters the soil surface and plays a significant role in controlling soil water storage, crop yields, irrigation efficiency and solute entry into the soil profile. In agriculture fields, generally, the top soils are enriched with high organic matter and clay, particularly in black soils that promotes sorption, biological degradation and transformation of contaminants. During the process some of the chemicals applied to farm land, move down with the deep percolating water from the root zone and there are likely chances to pollute the underlying ground water. Such instances are reported by locals in areas dominated by black soils of Malaprabha command area. In order to understand the extent of groundwater contamination through chemical fertilizers, insecticides and manures, two agricultural plots (sugarcane and banana plantation) have been identified in parts of Malaprabha command area covering parts of Saundatti, Ramdurg (Belagavi district) and Nargund taluks (Gadag district). Hydraulic properties such as infiltration and hydraulic conductivity were determined in the field. Soil samples were collected and analysed in the laboratory for texture and porosity. The study indicated that the soils of the region are layered in structure. Further, it is noticed that the coarse textured loamy soil is present below the fine textured soils (such as silty loam or clayey loam). Due to the presence of fine soils at the top, the irrigated water get accumulated and the evaporation takes place relatively faster and results in the accumulation of excess salt. It is also noticed that the layered soils have obvious effects on solute transport and salt accumulation in the clay rich soil layer at the interface. The average salt accumulation (Total Nitrogen) observed in the study area within soil profile is 18.7g/kg. The maximum salt accumulation (21.38 g/kg) occurred in the top layer of sugarcane plots followed by banana plantation (19.85 g/kg). It is also noticed that there are remarkable changes in the interlayered soils with reference to water infiltration characteristics and salt leaching intensities. Study revealed the fact that the properties of the soil profile with a silty loam interlayer is better than with a silty clay loam interlayer.

Simple Derivatization-Gas Chromatography-Mass Spectrometry for Fatty Acids Profiling in Soil Dissolved Organic Matter.

Dissolved organic matter is an important component of the global carbon cycle that allows the distribution of carbon and nutrients. Therefore, analysis of soil dissolved organic matter helps us to better understand climate change impacts as it is the most dynamic and reactive fraction in terrestrial ecosystems. Its characterization at the molecular level is still challenging due to complex mixtures of hundreds of compounds at low concentration levels in percolating water. This work presents simple methods, such as thermochemolysis– or derivatization–gas chromatography, as an alternative for the analysis of fatty acids in dissolved organic matter without any purification step. The variables of the protocols were examined to optimize the processing conditions for the C9–C18 range. As a proof of concept, fatty acid distributions of soil percolating water samples from a long-term field experiment were successfully assessed. The variability of dissolved organic acid distributions was pronounced through depth profile and soil treatment but no major change in composition was observed. However, although the optimization was done from C9 to C18, detection within the C6-C32 fatty acids range was performed for all samples.

Estimation of Groundwater Quality in and Around Dumpsites of Cuddalore District, Tamil Nadu, India

Land filling of urban solid desecrate is a universal dissipate care and one of the economical technique for organizing waste in several parts of the globe. Landfill poses serious threats to the worth of the surroundings if imperfectly safe and indecently managed. The stages of different physicochemical parameters are investigated including Total Dissolved Solids (TDS), alkalinity, pH, Electrical Conductivity (EC), and hardness. The mixture of physical, chemical and microbial practice in the waste shifts the contaminant from the misuse matter to the percolating water. The study asses ground water quality of samples near the dumping area and characterized. The effects are evaluated with the world health organization (WHO) and Bureau of Indian Standard (BIS) index. Also attempt will be made by the aggregate index method to assess the excellence of ground water in Chidambaram and Cuddalore SIPCOT dumpsites.

Calcium carbonate accumulations in Technosols of Moscow city

Complex phenomena of the precipitation and accumulation of calcium carbonate in urban soils and sediments have been studied. They are linked to the interactions between the lithosphere, the biosphere, and the atmosphere. Calcium and its compounds are among the main elements determining soil’s morphological, physical, and chemical characteristics. This study was aimed at summarizing information about calcium carbonate concentrations in soils and finding evidence for the formation of carbonate micronodules by pedogenetic processes in Urbic Technosols under automorphic conditions. Moscow is located within the southern taiga belt, with a humid temperate climate and a percolative water regime. The city’s technogenic deposits contain significant amounts of carbonates due to inclusions of construction waste and additions of airborne dust. Contemporary humus-accumulative horizons of Urbic Technosols were found to contain carbonate accumulations (rounded or isomorphic nodules). Samples from such horizons were studied using a polarizing microscope (analysis of thin sections) and a scanning electron microscope with an energy-dispersive X-ray analyzer (element mapping to detect carbonate accumulations). Laboratory analyses of main chemical and physical soil properties were performed. The analyzed samples contained both primary (i.e., inherited from parent materials) and secondary (i.e., newly formed in soils) calcium carbonates in various forms. Inclusions of solidified mortar (carbonate building solutions) contained dolomite. Although the studied carbonates underwent recrystallization processes, they remained in soils for a long time. Fibrous Mg silicate films deposited at the surface of recrystallization areas were observed. The formation of carbonate micronodules at depths of 15–40 cm in slightly and moderately calcareous humus horizons was investigated. Newly formed calcite was distinguished by a homogeneous composition, a microsparitic size of crystals, and a compact packing within the groundmass. Newly formed calcite was observed within microzones that were free from carbonate inclusions with dissolution features. The dissolution of primary carbonates in soils under humid climate conditions triggers pedogenetic processes of the carbonate heritage redistribution and the mineral matrix transformation. Recrystallized carbonates are the main forms of secondary carbonate accumulations in automorphic Technosols. The presence of compact carbonate nodules composed of microsparitic calcite within the bulk of silicate material may be indicative of carbonate neoformation as a result of interactions between the dissolved CO2 from root respiration and the soil absorbing complex saturated by Ca from soil solution. This is confirmed by a number of studies on the carbonate isotopic composition in urban soils.

Logging residue piles of Norway spruce, Scots pine and silver birch in a clear-cut: Effects on nitrous oxide emissions and soil percolate water nitrogen

We analysed how logging residue (LR) piles of common tree species in Finland, Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth), affect nitrogen (N) losses in forest soil after final felling. A Norway spruce dominated stand was clear-cut and followed by two experimental setups to study the nitrous oxide (N2O) emissions and leaching of carbon (C) and N. Experiments consisted of four treatments: tree species treatments consisting of 40 kg m−2 of LR and a control treatment without residues. The C losses were monitored as dissolved organic carbon (DOC), the N losses as ammonium (NH4-N), nitrate (NO3-N) and dissolved organic nitrogen (DON) fluxes and concentrations in soil percolation waters and the N2O emissions as fluxes from the forest soil to the atmosphere. In addition the soil temperatures, the molecular size distribution of the DOC from the soil percolation waters and the origin of the N2O production were determined. The LR piles lowered the soil temperatures and, especially those of birch, increased the concentrations of NO3-N in the soil percolation waters already 1 year after the establishment of the piles. The LR piles increased the NH4-N concentrations. The smallest molecular size fraction (<1 kD) of DOC predominated in all treatments. The N2O fluxes peaked under the piles during the second and third growing seasons; however, the inconsistent fluxes tended to be low. The production of N2O was driven by both nitrification and denitrification processes, the proportion depending on the tree species. Our results indicate that LR piles accelerate N losses 1 year after the clear-cutting, especially NO3-N, which predominates in the soil percolation waters under the birch residues, whereas spruce residues tend to stimulate N2O emissions longer. These results have implications for sustainable forest management practices and nutrition of regrowing vegetation.

On plate tectonics and ocean temperatures

Abstract Plate tectonics, the principal vehicle for dissipation of planetary energy, is believed to buffer the δ18O of seawater at its near-modern value of 0‰ SMOW (Standard Mean Ocean Water) because the hot and cold cells of hydrothermal circulation at oceanic ridges cancel each other. The persistence of plate tectonics over eons apparently favors attribution of the well-documented oxygen isotope secular trends for carbonates (cherts, phosphates) to progressively warmer oceans, from 40–70 °C in the early Paleozoic to 60–100 °C in the Archean. We argue that these oceanic hydrothermal systems are dominated by low-temperature (&lt;350 °C) cells that deplete the percolating water in 18O. Seawater δ18O is therefore a proxy for, rather than being buffered by, the intensity of plate tectonics. Detrending the Phanerozoic carbonate δ18Oc secular trend for its “tectonic” component yields a stationary time series that, interpreted as a proxy for Phanerozoic climate, indicates low-latitude shallow ocean temperatures oscillating between 10 and 30 °C around a baseline of 17 °C, attributes comparable to modern temperature values.

Dynamics of soil nitrogen cycling and losses under Norway spruce logging residues on a clear-cut

This study aimed to determine the effects of Norway spruce logging residues on the early-stage dynamics of N cycling processes on a clear cut and how this is related to N losses via leaching or nitrous oxide emissions. We compared N cycling processes in soil under spruce logging residues (fresh residues 40 kg m−2) and in corresponding soil without the residues for four growing seasons on a clear-cut in southern Finland. In addition, two other sites were studied in the same region six years after clear-cutting in plots with three different amounts of spruce logging residues (0, 10, 40 kg m−2). Logging residues strongly stimulated net nitrification within the first three months after the residue treatment, and this stimulation continued over the whole study period, although NO3-N concentrations in the soil decreased. Residues increased the pH, rate of net N mineralization and microbial C-to-N ratio. N2O production in the laboratory and fluxes in the field were both studied after four growing seasons. N2O production was higher in the humus layer under the residues and originated from both autotrophic nitrification and denitrification. N2O fluxes in the field were low but were also higher in the residue-containing plots. N concentrations in percolate water were monitored for four years at the same site. Logging residues increased NO3-N and NH4-N concentrations; the highest concentrations were found during the second and third years after clear-cutting. After that the concentrations of dissolved organic N increased. Both the percolate water study at this site and the N cycling studies at the two other sites six years after clear-cutting showed that the largest amount of residues resulted in the highest rates of net N mineralization and net nitrification and the highest concentrations of mineral N forms in the percolate water. The amount and decomposition stage of the logging residues as well as the development of ground vegetation may together determine the dynamics of soil N cycling processes and losses.

Spatial and temporal dynamics of deep percolation, lag time and recharge in an irrigated semi-arid region

The time required for deep percolating water to reach the water table can be considerable in areas with a thick vadose zone. Sustainable groundwater management, therefore, has to consider the spatial and temporal dynamics of groundwater recharge. The key parameters that control the lag time have been widely examined in soil physics using small-scale lysimeters and modeling studies. However, only a small number of studies have analyzed how deep-percolation rates affect groundwater recharge dynamics over large spatial scales. This study examined how the parameters influencing lag time affect groundwater recharge in a semi-arid catchment under irrigation (in northeastern Iran) using a numerical modeling approach. Flow simulations were performed by the MODFLOW-NWT code with the Vadose-Zone Flow (UZF) Package. Calibration of the groundwater model was based on data from 48 observation wells. Flow simulations showed that lag times vary from 1 to more than 100 months. A sensitivity analysis demonstrated that during drought conditions, the lag time was highly sensitive to the rate of deep percolation. The study illustrated two critical points: (1) the importance of providing estimates of the lag time as a basis for sustainable groundwater management, and (2) lag time not only depends on factors such as soil hydraulic conductivity or vadose zone depth but also depends on the deep-percolation rates and the antecedent soil-moisture condition. Therefore, estimates of the lag time have to be associated with specific percolation rates, in addition to depth to groundwater and soil properties.

Incorporation of biomass fly ash and biological sludge in the soil: effects along the soil profile and in the leachate water

This work aimed to study the effect of the application of biomass fly ash in the soil profile and percolate water, which is a novel feature. The results produced by this work pose a useful contribute for by-products’ valorization for the pulp and paper industry, namely fly ash and sludge, diverting them from landfills and achieving significant savings. Soil profiles (0.60 m) were collected in the field and into laboratory-scale vessels. Four soil profiles were used in this work. One of the profiles was used as control. To each of the other three, 7.5 Mg ha−1 of biomass fly ash, fly ash combined with sludge (50:50%wt.), or a conventional liming agent (CaO) were added. A simulation of the daily natural watering of the soils has been made throughout 1 month, with collection of the daily percolating from the bottom of the vessels. After this period, soil profiles were divided into three equal-sized depth layers (0.20 m each). Soil pH, electrical conductivity, and available Ca, Mg, K, P, Na, Mn, Fe, Zn, and Cu contents were determined in the three layers for each of the four soil profiles used. A parallel experiment was conducted in which additional pots of soil were prepared with the same amendment. Ryegrass (Lolium perenne) was sown in order to evaluate the effect on biomass growth and possible phytotoxicity. Amendment with biomass fly ash elevated soil pH slightly, to values within the most adequate range for plant growth. Results showed small raises in the availability of the essential plant macronutrients Ca, K, and Mg, especially in the top layer of the soils, where the amendment materials were applied. The mobilization of cations to the groundwater was always minimal, which is promising since it means little contamination to the groundwater. Ash and ash + sludge amendments produced similar plant growth results when compared to the control. However, biomass grown in Cao-amended pots showed the higher root size. Incorporation in the soil proved to be a viable way to manage fly ash and sludge from pulp and paper industry, which could mean considerable savings. The effect on soil fertilization was similar to the conventional liming agent. No obvious hazardous effect on the soil or groundwater was found.

Ecotoxicological and microbiological assessment of sewage sludge associated with sugarcane bagasse

Sewage sludge (SS) obtained after sewage treatment process may contain several toxic substances. Bioremediation can decrease the toxicity of the sludge, mainly when it is associated with stimulant agents, such as sugarcane bagasse (B). Samples of pure SS (SSP); SS+B; SS+Soil; and SS+B+Soil were bioremediated for 1, 3, and 6 months (T1, T2, and T3, respectively). After each period, the cytotoxic, genotoxic, and mutagenic potentials of the solid samples and their respective aqueous extracts (aqueous eluate and percolate water) were evaluated by the Allium cepa test. A microbiological analysis of the samples was also performed after each period tested. All solid samples of SS+B (in T1, T2, and T3) and the solid sample of SSP (treatment T3) showed a significant decrease of cell division (cytotoxic effects). The aqueous eluate extracts of SS+B (T1 and T3) and SSP (T2 and T3) induced cytotoxic effect. The solid sample of SS+B (T2 and T3) and aqueous extracts of SSP (T1) were genotoxic, indicating a harmful effect of SS on A. cepa, even after 6 months of bioremediation. There was an alternation in the microbial community both in diversity and in abundance, with the predominance of nonfermenting gram-negative bacilli. The tested bioremediation periods were not sufficient for the complete detoxification of SS, and the use of B did not seem to contribute to the degradation of the pollutants to inert compounds. These data emphasize that a specific relationship should exist between the sludge characteristic and the biostimulating agent used to promote a more efficient bioremediation. These results suggest the necessity to study longer periods of biodegradation and the use of other decomposing agents for greater safety and sustainability for the agricultural use of this residue.

Ecotoxicity and fate of a silver nanomaterial in an outdoor lysimeter study

Sewage sludge is repeatedly applied as fertilizer on farmland due to its high nutrient content. This may lead to a significant increase of silver nanomaterials (AgNM) in soil over years. Therefore, our aim was to investigate the ecotoxicity and fate of AgNM under environmentally relevant conditions in outdoor lysimeters over 25 months. Two AgNM concentrations (1.7 and 8.0 mg/kg dry matter soil) were applied via sewage sludge into soil. In subsamples of the soil, incubated under laboratory conditions for 180 days, the comparability of outdoor and laboratory results regarding ecotoxicity was determined. The results from our long term lysimeter experiments show no detectable horizontal displacement in combination with very low remobilization to the percolate water. Thus, indicate that the sludge applied AgNM remains nearly immobile in the pathway between soils and leachate. However, Ag uptake to the roots of wheat and canola suggests that the chemical conditions in the rhizosphere induce AgNM remobilization from the incorporated sewage sludge even after two harvesting cycles. At the higher AgNM concentration a steady inhibition of the soil microflora was observed over 25 month in the lysimeter study, while there was no effect at the lower AgNM concentration. The results of the laboratory experiment reflect the findings of the lysimeter study and indicate that a risk assessment for AgNM based on data from laboratory tests is acceptable.