M.J. Díaz

Influence of bulking agent on sewage sludge composting process.

Four types of compost, consisting of mixtures of Acacia dealbata (A) with sewage sludge (SS) were studied in a laboratory reactor. Composting time was 80 days and parameters monitored over this period included temperature, organic matter, pH, CO(2), O(2), C/N ratio, Kjeldahl-N, as well as maturity indexes. All the studied parameters were influenced by the bulking amount used. The highest profile temperature measured was for the A/SS 1/2 (w/w) mixture that reached a maxima temperature of 67 degrees C and lower maximum temperatures of 52, 48 and 46 degrees C were observed for A/SS 1/3, 1/1 and 1/0 composts, respectively. The kinetic model used showed that a descent of sewage sludge in the composting mixtures favored the enzyme-substrate affinity. However, an increase in depending on the parameters of the process factors was observed when the sewage sludge ratio was increased in mixtures. The optimal amounts of sewage sludge for co-composting with Acacia indicate that moderate amounts of sludge (1/1) would be the best compromise.

Hydrothermal and pulp processing of Eucalyptus.

Hydrothermal processing of Eucalyptus wood was performed at operation temperature of 181 degrees C, processing time or 37.5 min and solid water ratio of 1/6 to ensure a maximum loss of xylan recuperation with minimum cellulose fibre degradation. Under those conditions, the loss of xylan was 22% less than that achieved with the conditions 196 degrees C, 50.6 min and 1/8 (solid/water). IN In addition, an experimental design was used to study the influence of process variables: temperature (145-175 degrees C), pulping time (40-120 min) and ethanol concentration (40-70% weight concentration), on the properties of pulps (yield, kappa number, viscosity, cellulose, xylan, lignin acetyl groups contents and brightness) and paper sheets (stretch index, burst index and tear index) obtained from the solid fraction after hydrothermal treatment of Eucalyptus globulus. Pulps with acceptably high physical and chemical properties can be obtained operating at 175 degrees C for 90 min with 55% ethanol concentration.

Optimization of hydrogen peroxide in totally chlorine free bleaching of cellulose pulp from olive tree residues.

The influence of the operating conditions used in the bleaching of olive wood trimmings pulp (viz. hydrogen peroxide concentration and time) on the yield, kappa index and viscosity of the resulting pulp and on strength-related properties of paper sheets was studied to determine the optimal bleaching conditions of this pulp. Hydrogen peroxide bleached pulps at different sequences (oxygen, ozone, chlorine dioxide and alkaline extractions) were compared. Hydrogen peroxide bleaching proved to be suitable for this pulp. Considerable improvements in viscosity were obtained with respect to other bleaching sequences such as oxygen, ozone and chlorine dioxide. Hydrogen peroxide bleaching decreased the kappa index 51.3% less than ozone bleaching, 25.0% less than chlorine dioxide (D) and 6.3% less combined chlorine dioxide-alkaline extraction (DE). To obtain kappa indices 50.9% and 37.9% lower than the index achieved by hydrogen peroxide, oxygen (LaO(p)) and ozone (LaO(LaZ)R) sequences respectively were needed. Lower-medium levels of hydrogen peroxide concentrations (1-3%) and high reaction times (210 min) proved to be suitable for bleaching of pulp olive trimming residues. This approach could be used on this residue to produce adequately bleached pulp.

Modelling vinasse/cotton waste ratio incubation for optimum composting

Abstract A central composite experimental design was used to investigate the influence of incubation conditions (vinasse added and operation time) for vinasse/cotton waste mixtures on the properties of products obtained (pH, electrical conductivity, organic matter, Kjeldahl-N, C/N ratio, biodegradability, Kjeldahl-N losses and germination index) in order to determine the best in-vessel composting conditions. The range of the independent variable measured was 0–80% for vinasse added and 1–50 days for operation time. A second-order polynomial model consisting of two independent process variables was found to accurately describe the vinasse/cotton waste incubation. The differences between the experimental values and those estimated by using the equations never exceeded 10% of the former. Obtaining products with acceptable chemical properties, high biodegradability and minimum N losses entails operating at medium operation time (20–35 days) and 20–30% of vinasse added.

Valorisation of a leguminous specie, Sesbania grandiflora, by means of hydrothermal fractionation

For the purpose of hydrolysing hemicelluloses to oligomers and monomers, Sesbania grandiflora samples were subjected to isothermal autohydrolysis in the temperatures ranging from 145 degrees C to 190 degrees C, using a solid to liquid ratio of 8 and reaction times up to 7.5 h. Kinetic models based on sequential pseudo-homogeneous first order Kinetics with Arrhenius type temperature dependence were employed for describing the time course of the main hemicelluloses compounds and their degradation products. The hydrothermal treatment results show that Sesbania grandiflora can be employed as an alternative raw material for the production of XOS leading to high concentrations of XOS (14.1 g/L in the experiment carried out at 190 degrees C and 0.1 h) and xylan to XOS conversion (62.6% in the experiment carried out at 190 degrees C and 6 min). The model proposed provides a satisfactory interpretation of the experimental data obtained in the hydrothermal treatments of this study.

Biorefinery process for production of paper and oligomers from Leucaena leucocephala K360 with or without prior autohydrolysis.

Lignocellulosic material from Leucaena leucocephala was subjected to a two-stage fractionation process to obtain a valorized effluent containing hemicellulose derivatives and a solid phase for producing cellulose pulp by conventional soda-anthraquinone delignification. This solid phase allows the production of cellulose pulp, under less rigorous conditions from NaOH-AQ process (177 °C, 21%, 120 min) than without pretreatment delignification (185 °C, 25%, 150 min) and better or similar properties in the paper sheets obtained (yield 27.6 and 34.0%, brightness 39.3 and 31.6% ISO, tensile index 7.8 and 10.5 N m/g, burst index 0.43 and 0.29 MPa m(2)/kg with and without previous autohydrolysis) have be found. Also, the first autohydrolysis stage allows up to 46.6% of the initial hemicellulose in the raw material to be extracted as xylooligomers, xylose and furfural into the liquid phase.

Cocomposting of Beet Vinasse and Grape Marc In Windrows and Static Pile Systems

Two composts were obtained by cocomposting a concentrated depotassified beet vinasse and grape marc using an aerated static pile and a windrow system. The composting mixtures comprised grape marc (83%) and vinasse (17%) for the aerated static pile system and grape marc (77%), vinasse (20%) and phosphate rock (3%) for the windrow. Changes in temperature followed a similar path for both mixtures, however the thermophilic phase was longer in the aerated static pile (25 days) than in the windrow (10 days). This fact caused differences in both organic matter degradation, weight losses (21% for static pile and 10% for windrow) and gas losses during the process. Nevertheless, the composts obtained by the two systems had a high fertilizer nutrient value (18.2 g kg−1 N; 3.1 g kg−1 P; 13.6 g kg−1 K, C/N 16.1 for compost obtained in static pile and 20.6 g kg−1 N; 13.7 g kg−1 P; 13.1 g kg−1 K; C/N 18 for compost obtained in windrow). A high degree of stability was reached in both composting systems (124 cmolc kg−1 CEC for static pile and 153 cmolc kg−1 CEC for windrow at 80 days of composting). The chemical and physical properties of both vinasse composts suggest their possible use as soil conditioner.

Selective organic compounds degradation under controlling composting conditions

Organic matter stabilization resulted from the decrease of cellulose, xylan, arabinan, acetyl groups, glucuronic acids, galacturonic acids (easily biodegradable fractions) and the increase of lignin (resistant compound) and humic substances coming from the initial wastes have been studied. A central composite experimental design was used to investigate the influence of environmental composting parameters (moisture, aeration and particle size) on organic matter evolution. The organic matter evolution was clearly influenced by the studied composting parameters. All results were concordant, with an increase of humic substances and lignin and a decrease of the rest of the cellulose and hemicellulose compounds. Lower cellulose, xylan, acetyl groups and glucuronic acids contents (higher degradation) have been observed under low particle size (1cm) and higher moisture content (70%). However lower lignin and higher humic substances under medium (3cm) to low particle size and low moisture content (40%) have been found.

Modelling of parameters for optimization of maturity in composting trimming residues

In this paper, changes in physico-chemical parameters during trimmings residue composting (cation exchange capacity, germination index, self-heated, NH(4)/NO(3) ratio and C(FA)/C(HA) ratio) in relation to environmental composting parameters (time, aeration, moisture and particle size) of the composting process were studied. A central composite experimental design was used to obtain the polynomial model for each dependent variable. Results of the modelling showed that among the studied range, moisture was the highest influenced parameter in maturity evaluation, with respect to aeration and particle size. An exception was found for CEC evolution. In this parameter, the highest influence was found for particle size. Moreover, a product with acceptable chemical properties entails operating at medium moisture content (55%) and medium-to-high particle size (3-5 cm). Moderate to low aeration (0.2 m(3) air kg(-1) d(-1)) would be the best compromise to composting this residue, due to the scarce statistical influence of this independent variable.

Influence of Environmental Parameters on the Composting Kinetic of Lignocellulosic Residues

The kinetic of the thermophilic composting process of trimming residues was studied under several parameters [moisture (40-70%), aeration (0.2-0.6 l air/kg min) and particle size (1-5 cm)] in order to determine the best composting conditions to ensure an optimum composting design. Under those conditions, suitable temperature evolutions have been found for all the reactors. The kinetic model proposed by Whang and Meenaghan was used and two first-order kinetic equations were used for describing the composting process. A central composite experimental design was used and a second-order polynomial model consisting of the three selected independent process variables was found to accurately describe (the differences between the experimental values and those estimated by using the equations never exceeded 10% of the former) the kinetic process. The magnitude of the constants among the studied conditions varies among 5 and 13.9 for 1/K1 and 0.0015 and 0.0035 for K2. Both, moisture and particle size affects positively and negatively the composting process and low effect of aeration (among studied values) was found. The values of 1/K1 and K2 obtained showed higher values for both parameters under 55% moisture content, 5cm particle size and 0.2 lair/min kg.