Manuel Jesús Bellido Díaz

New approaches to establish optimum moisture content for compostable materials

Optimum moisture content (MC) for three different compostable materials was estimated through the relationship MC vs. FAS, where FAS is the free air space, which is calculated from the values of both particle and bulk density (method 1). As the determination of particle and bulk density was complicated and tedious, two simplifications of the method 1 were tested to obtain an easier approach to establish the optimum MC. The first one (method 2) assumed that bulk density was a constant value (calculated for dry samples), independent of the moisture content of the sample. The second approach (method 3) was based on the measurement of the porosity of the materials. Independently of the method used for the estimation of FAS, values of MC and FAS were linearly correlated with high determination coefficients. Regression lines of methods 1 and 2 were comparable only for a fibrous material (cotton gin trash) because bulk density increased slightly when MC increased. For the other materials (grape marc and olive press cake) the simplification assumed by method 2 was not valid due to great increases of bulk density when MC increased. However, the comparison of the regression lines showed that methods 1 and 3 were not statistically different for the three materials tested. Thus, the optimum MC (FAS = 30-36%) of compostable materials can be estimated by a simple method that requires only easy measurements of porosity at several moisture contents.

Co-composting of sugarbeet vinasse: influence of the organic matter nature of the bulking agents used

Two composts were obtained by co-composting of a concentrated depotassified beet vinasse and two agricultural solid residues with different organic matter nature: grape marc (GM; lignin waste) and cotton gin trash (C; cellulosic waste). Composting was carried out in aerated piles with mechanical turning, in controlled conditions during 4 months. After 71 days of composting, a new addition of vinasse similar to the initial addition was made. Changes in temperature, pH and inorganic nitrogen followed a similar path for both mixtures. However, organic matter fractions showed different behaviour depending on the material co-composted with vinasse. Lower organic matter degradation was observed when GM was used as bulking agent due to its high lignin content. No phytotoxicity was detected in the end products. The chemical and physical properties of both vinasse composts suggest their possible use as fertiliser.

Analysis of inorganic anions in drainage water and soil solution by single-column ion chromatography

Single-column ion chromatography (SCIC) for anion determination in drainage water and soil solution was tested. The SCIC minimum detection limits (100-microliter sample loop) were 0.75 mg l-1 for Cl-, 0.2 mg l-1 for NO2-N, 0.02 mg l-1 for NO3-N, 1.25 mg l-1 for HPO4-P, and 0.5 mg l-1 for SO4-S. The results showed a high reproducibility. Results for Cl-, NO3-N and SO4-S obtained by the SCIC method were compared with those obtained by traditional methods; Students t-test and regression analysis showed that the methods agree closely.

Influence of control parameters in VOCs evolution during MSW trimming residues composting

The influence of control parameters (aeration, moisture, and C/N ratio) during composting of a municipal solid waste (MSW)-legume-trimming residue (LTR) mixture was studied at a pilot plant scale. Factors measured included the composition of the main volatile organic carbons (VOCs) emitted including limonene, β-pinene, 2-butanone, undecane, phenol, toluene, and dimethyl disulfide. Polynomial models were found to reproduce the experimental results with errors at less than 10%. The relative influence of the independent variables on temperature and selected VOCs followed the order: aeration > moisture > C/N. A high aeration rate results in higher (strong negative effect) values on selected VOCs emissions (41-71% on emitted VOCs variation). Moisture had a positive and negative effect depending on the selected VOCs. A high C/N ratio caused lower production of VOCs except for undecane and 2-butanone. Providing an aerobic environment (0.05 Lair kg(-1) min(-1)), high C/N ratios (>50), and medium moisture (55%) minimize emitted VOCs during MSW composting, ultimately resulting in less odors in the surrounding environment.

Biofiltration of composting gases using different municipal solid waste-pruning residue composts: Monitoring by using an electronic nose

The concentration of volatile organic compounds (VOCs) during the composting of kitchen waste and pruning residues, and the abatement of VOCs by different compost biofilters was studied. VOCs removal efficiencies greater than 90% were obtained using composts of municipal solid waste (MSW) or MSW-pruning residue as biofilter material. An electronic nose identified qualitative differences among the biofilter output gases at very low concentrations of VOCs. These differences were related to compost constituents, compost particle size (2-7 or 7-20mm), and a combination of both factors. The total concentration of VOCs determined by a photoionization analyser and inferred from electronic nose data sets were correlated over an ample range of concentrations of VOCs, showing that these techniques could be specially adapted for the monitoring of these processes.

Cotton fertilization with compost of (sugarbeet) vinasse and agricultural residues

A concentrated depotassified beet vinasse was mixed with each of ten solid agricultural residues. The ten mixtures were composted for 7 months. The composts obtained after this period were used to fertilize a cotton crop. A mineral treatment was used for comparison and a treatment without fertilization was used as control. The nitrate content of petiole determined before the first top dressing revealed significant differences between treatments. All treatments produced higher yields than the control. Analysis of fibre quality did not show significant differences between treatments.

Improving sustainability in the remediation of contaminated soils by the use of compost and energy valorization by Paulownia fortunei

The plantation of fast growing trees in contaminated sites, in combination with the use of organic wastes, could partially solve a dual environmental problem: the disposal of these wastes and the improvement of soil quality in these degraded soils. This study evaluated the effects of two compost on the quantity and quality of Paulownia fortunei biomass and on syngas production by biomass gasification, produced by plants growing on trace elements contaminated soils. Compost increased biomass production to values similar to those produced in non-contaminated soils, due to the improvement in plant nutritional status. Moreover, biomass quality for gasification was increased by compost addition. Trace element accumulation in the biomass was relatively low and not related to biomass production or the gas quality obtained through gasification. Thus, P. fortunei plantations could pose an opportunity to improve the economic balance of the revegetation of contaminated soils, given that other commercial uses such as food or fodder crop production is not recommended in these soils.

The potential of native species as bioenergy crops on trace-element contaminated Mediterranean lands

The establishment of energy crops could be an option for the management of degraded and contaminated lands, where they would not compete with food production for land use. Here, we aimed to explore the potential of certain native Mediterranean species for the revegetation of contaminated lands for energy production purposes. A field survey was conducted in a trace-element (TE) contaminated area from SW Spain, where the patterns of biomass production, TE accumulation and the calorific value of some thistle species were analyzed along a soil contamination gradient. In a greenhouse experiment the response of two thistle species (Cynara cardunculus and Silybum marianum) and the shrub Dittrichia viscosa to soil contamination was assessed, as well as the effects of these species on some soil microbial parameters involved in nutrient cycling (enzyme activities and arbuscular mycorrhizal colonization in roots). Silybum marianum was able to colonize highly contaminated soils. Its aboveground biomass accumulated Cd and had a relatively high calorific value; this value was similar in biomass obtained from both heavily and moderately contaminated soils. Greenhouse experiment confirmed that S. marianum biomass production and calorific value is scarcely affected by soil contamination. In addition, some soil enzyme activities were clearly enhanced in the S. marianum rhizosphere. Dittrichia viscosa is another promising species, given its capacity to produce a high biomass with appreciable calorific value in acid contaminated soils. Germination of both species was hampered in the acid contaminated soil, and therefore soil pH correction would have to be accomplished before establishing these species on extremely acid soils. Further assessment of the risk of transfer of Cd and other TE to the food chain would be needed to confirm the suitability of these species for the revegetation of contaminated lands with energy production purposes.

Logic-Level fast current simulation for digital CMOS circuits

Nowadays, verification of digital integrated circuit has been focused more and more from the timing and area field to current and power estimations. The main problem with this kind of verification is on the lack of precision of current estimations when working at higher levels (logic, RT, architectural levels). To solve this problem it is not only necessary to use good current models for switching activity but, also, it is necessary to calculate this switching activity with high accuracy. In this paper we present an alternative to estimate current consumption using logic-level simulation. To do that, we use a simple but accurate enough current model to calculate the current consumption for each signal transition, and a delay model that obtains high accuracy when it is used to measure the switching activity (the Degradation Delay Model -DDM-). In the paper we present the current model for CMOS inverter, the characterization process and the model implementation in the logic simulator HALOTIS that includes the DDM. Results show a high accuracy in the estimation of current curves when compared to HSPICE, and a potentially large improvement over conventional approaches.

Novel energy crops for Mediterranean contaminated lands: Valorization of Dittrichia viscosa and Silybum marianum biomass by pyrolysis

Establishing energy crops could be a cost-efficient alternative towards the valorization of the plant biomass produced in contaminated lands, where they would not compete with food production for land use. Dittrichia viscosa and Silybum marianum are two native Mediterranean species recently identified as potential energy crops for degraded lands. Here, we present the first characterization of the decomposition of the biomass of these species during thermo-chemical conversion (pyrolysis). Using a greenhouse study we evaluated whether the quality of D.xa0viscosa and S.xa0marianum biomass for energy production through pyrolysis could be substantially influenced by the presence of high concentrations of soluble trace element concentrations in the growing substrate. For each species, biomass produced in two different soil types (with contrasted trace element concentrations and pH) had similar elemental composition. Behavior during thermal decomposition, activation energies and concentrations of pyrolysis gases were also similar between both types of soils. Average activation energy values were 295 and 300xa0kJxa0mol-1 (for a conversion value of αxa0=xa00.5) for S.xa0marianum and D.xa0viscosa, respectively. Results suggest that there were no major effects of soil growing conditions on the properties of the biomass as raw material for pyrolysis, and confirm the interest of these species as energy crops for Mediterranean contaminated lands.