► A new process of sewage sludge management using CaO as dryer is presented. ► The chemical energy in the reagents is enough for the moisture to evaporate. ► The process is more energy-efficient than ...others, in which fossil fuels are used. ► The obtained product is highly suitable for use as a prime material in cement raw meals. ► The mixes manufactured with it exhibited higher reactivity than the reference mix.
This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Lime not only stabilised the sludge, raised the temperature of the mix to 80–100°C, furthering water evaporation, portlandite formation and the partial oxidation of the organic matter present in the sludge.
Process mass and energy balances were determined. Neutral, a white powder consisting of portlandite (49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to be technologically apt for inclusion as a component in cement raw mixes. In this study, it was used instead of limestone in raw mixes clinkerised at 1400, 1450 and 1500°C. These raw meals exhibited greater reactivity at high temperatures than the limestone product and their calcination at 1500°C yielded clinker containing over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of raw meal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size and distribution.
Seismic‐noise tomography is routinely applied for imaging geological structures at different spatial scales. The frequently used time‐domain approach presents two limitations. First, extracting ...surface‐wave group velocities from time‐domain cross‐correlations requires interstation distances of at least three wavelengths, which may be problematic when working at local or regional scales. Second, the presence of higher modes of surface waves in the cross‐correlation functions is often disregarded, which may cause loss of valuable information about the shear‐wave velocity structure. In this work, we present a complete inversion scheme that avoids these limitations and use it to obtain a 3D shear‐wave velocity model of the Basque‐Cantabrian Zone (N Spain), a structurally complex area affected by multiple tectonic events. The resulting model agrees with the existing geological and geophysical knowledge and significantly extends the area for which high‐resolution information is available.
Key Points
We present a complete inversion scheme for seismic‐noise tomography that accounts for the contribution of higher modes of Rayleigh waves to the observed dispersion
We apply our proposed inversion scheme to data acquired by a dense seismic network deployed in the Basque‐Cantabrian Zone (N Spain)
The final result is a 3D shear‐wave velocity model of the crustal structure that significantly extends the area for which detailed information is available in the region
•Siloxanes cause adverse effects on biogas utilisation for energetic purposes.•Sampling and quantification of siloxanes in biogas were assessed.•Reliable and robust analytical methodology was ...developed.•Biogas from different WWTPs of different European countries was analysed.•Siloxanes were over the limit of tolerance for most of energy recovery technologies.
Siloxanes and trimethylsilanol belong to a family of organic silicone compounds that are currently used extensively in industry. Those that are prone to volatilisation become minor compounds in biogas adversely affecting energetic applications. However, non-standard analytical methodologies are available to analyse biogas-based gaseous matrixes. To this end, different sampling techniques (adsorbent tubes, impingers and tedlar bags) were compared using two different configurations: sampling directly from the biogas source or from a 200L tedlar bag filled with biogas and homogenised. No significant differences were apparent between the two sampling configurations. The adsorbent tubes performed better than the tedlar bags and impingers, particularly for quantifying low concentrations. A method for the speciation of silicon compounds in biogas was developed using gas chromatography coupled with mass spectrometry working in dual scan/single ion monitoring mode. The optimised conditions could separate and quantify eight siloxane compounds (L2, L3, L4, L5, D3, D4, D5 and D6) and trimethylsilanol within fourteen minutes. Biogas from five waste water treatment plants located in Spain, France and England was sampled and analysed using the developed methodology. The siloxane concentrations in the biogas samples were influenced by the anaerobic digestion temperature, as well as the nature and composition of the sewage inlet. Siloxanes D4 and D5 were the most abundant, ranging in concentration from 1.5 to 10.1 and 10.8 to 124.0mgNm−3, respectively, and exceeding the tolerance limit of most energy conversion systems.
In this study, two mixtures of municipal compost, limestone and, optionally, zero-valent iron were assessed in two column experiments on acid mine treatment. The effluent solution was systematically ...analysed throughout the experiment and precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry analysis and, from the column containing zero-valent iron, solid digestion and sequential extraction analysis. The results showed that waters were cleaned of arsenic, metals and acidity, but chemical and morphological analysis suggested that metal removal was not due predominantly to biogenic sulphide generation but to pH increase, i.e. metal (oxy)hydroxide and carbonate precipitation. Retained arsenic and metal removal were clearly associated to co-precipitation with and/or sorption on iron and aluminum (oxy)hydroxides. An improvement on the arsenic removal efficiency was achieved when the filling mixture contained zero-valent iron. Values of arsenic concentrations were then always below 10 μg/L.
The feasibility of continuous phosphate recovery, by adsorption on powdered Ca-activated zeolite (PAZ), was assessed in a hybrid sorption–membrane ultrafiltration (UF) system. The objective was to ...explore the influence of process parameters such as initial P(V) concentration, pH, and PAZ dose on P(V) recovery from a tertiary treatment effluent. The hydrodynamic parameters of the UF operation were also evaluated as a function of the PAZ dose. The P(V) recovery profiles as a function of the initial P(V) concentrations, at pH 8 and 2.5 gPAZ/L, indicated that the sorbent was not saturated, and recoveries reported were 1.8 ± 0.2, 5.7 ± 0.3, and 47.2 ± 2 mg P(V)/gPAZ for 10 ± 1, 25 ± 2, and 100 ± 6 mg P(V)/L, respectively. The increase of the pH of the feed solution from 8 to 9 increased the P(V) recovery up to 70 ± 4%. A P(V) fractionation protocol of the loaded samples confirmed that the phosphate-sorption process involves the formation of calcium phosphate mineral forms.
Woody patches in semiarid environments favor the establishment of other plants. Facilitation may be favored by an increase in soil fertility. Dissolved organic matter (DOM), is the most active ...fraction of soil organic matter and may contain compounds affecting plant establishment, as allelochemicals, hormone-like substances and metal carriers. However, information on DOM contents and composition in these environments is scarce. In this paper, we study the impact of woody patches on DOM in Stipa tenacissima L. steppes and discuss its implications for community dynamics. DOM under patch- and inter-patch areas, was analyzed for elemental composition, UV–Vis indices and organic acid content. Element concentration and composition in DOM, and organic acid concentration were similar in patch- and inter-patch areas. Yet, soils under patches were richer in DOC, aromatic species and organic acids (particularly fumaric acid) than soils in inter-patch areas. Dominant species affected organic matter concentration and quality in complex ways. Thus, patches dominated by Ephedra fragilis showed higher concentrations of TOC and aromatics than those dominated by other species. Rhamnus lycioides patches showed the highest accumulation of fumaric acid, which may contribute to its successful recruitment rate and expansion in the area. Our results show substantial differences in the amount and composition of DOM and specific compounds affecting soil functionality and plant dynamics. Further studies on the effects of such changes on seedling performance are needed to increase our understanding of plant–plant interactions in semiarid environments.
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•Vegetation patches have different ability to recruit new individuals.•Dissolved organic matter plays an important role and is analyzed by UV–Vis and HPLC.•Dissolved organic matter quality is influenced by soil, climatic and biotic factors.•E. fragilis patches are the richest in organic matter.•R. lycioides patches accumulate fumaric acid and are the most abundant in the area.
The success of forest plantations in areas subjected to seasonal drought is strongly dependent on seedling traits. However, there is no consensus on the set of plant traits determining establishment ...success in these environments. We hypothesize that traits associated with nutritional stress, such as reduced biomass allocation and changes in root morphology, may promote seedling resistance to drought. We tested this hypothesis by assessing the effect of different fertilizer types and doses on the morphology and field survival of
Q. suber seedlings. This hypothesis had been previously tested with five Mediterranean species in a semi-arid environment. Nutrient deprivation decreased total biomass accumulation and slenderness ratio (ratio between stem height and root collar diameter). Nitrogen deprivation increased biomass allocation and decreased root growth potential. Short-term seedling survival was not related to nutritional regimes, seedling size or root growth potential. Differences in stem height between control seedlings and those subjected to nutrient manipulations increased in the field as a result of shoot dieback and scarce growth. In contrast, differences in root collar diameter gradually vanished. Nutrient management in the nursery showed a strong potential for modifying the morphology of
Q. suber seedlings but the relationship between these changes and seedling survival remains elusive.
Despite low growth rates, plants in arid areas have a strong ability to modify soil surface properties affecting ecosystem processes and community dynamics. But our knowledge on species effects on ...soil properties in these areas comes largely from observational studies, increasing the risk of confounding factors and precluding estimations of rates of change. We evaluated changes in soil surface properties underneath
Acacia salicina,
Pinus halepensis and
Eucalyptus occidentalis in a 10-year-old common garden experiment established on a degraded
Stipa tenacissima steppe in southern Tunisia. The three species tested improved soil properties compared to those of open areas.
Acacia salicina ranked first as soil modifier as the soil underneath this species showed higher total organic carbon, total nitrogen, available phosphorus, soil CO
2 efflux and infiltration rate, and lower soil hydrophobicity than soil in open areas. The richness of vascular plants was higher under
A. salicina than under the other types of cover. This species showed higher ability to improve microsite conditions and foster succession. Short rotations of
A. salicina could thus be employed for the restoration of degraded
S. tenacissima steppes provided that other aspects of its ecology are controlled.
Pinus halepensis represents a good alternative when native species are a priority, albeit facilitative ability is lower.
The current approach of the biological treatment of acid mine drainage by means of a passive remediation system involves the choice of an appropriate organic substrate as electron donor for sulphate ...reducers. Nowadays this selection is one of the critical steps in the performance of such treatment, as this depends to a great extent on the degradability of the organic substrate. Thus, a prior characterisation of the organic substrate predicting its biodegradability would be desirable before embarking on an extensive large-scale application. The aim of this study was to correlate the chemical composition (lignin content) of four different natural organic substrates (compost, sheep and poultry manures, oak leaf) and their capacity to sustain bacterial activity in an attempt to predict biodegradation from chemical characterisation. The results showed that the lower the content of lignin in the organic substrate, the higher its biodegradability and capacity for developing bacterial activity. Of the four organic materials, sheep and poultry manures and oak leaf evolved reducing conditions and sustained active sulphidogenesis, which coupled with the decrease in sulphate concentration indicated bacterial activity. Sheep manure was clearly the most successful organic material as electron donor (sulphate removal >99%), followed by poultry manure and oak leaf (sulphate removal of 80%). Compost appeared to be too poor in carbon to promote sulphate-reducing bacteria activity by itself. Column experiments emphasised the importance of considering the residence time as a key factor in the performance of continuous systems. With a residence time of 0.73 days, sheep manure did not promote sulphidogenesis. However, extending residence time to 2.4 and 9.0 days resulted in an increase in the sulphate removal to 18% and 27%, respectively.
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