M.E. Sánchez

Hydrogen production: Two stage processes for waste degradation

The dark fermentation process generates hydrogen by biological means. It presents two main advantages: fulfilling requirements for mild operational conditions and gaining benefit from the residual biomass. The process itself may be seen as a pre-treatment step in a complete stabilisation chain, with the aim of attaining the valorisation of residual biomass. However, increasing the yield of H2 production is an imperative task. In this manuscript, a review of recent work in the field of fermentative hydrogen production is presented. As dark fermentation has a maximum yield of 33% (on sugars), a description is also presented of possible second stage processes for the degradation of dark fermentation effluents. Alternatives considered were photofermentation and bioelectrochemical systems (BES) as processes capable of converting fermentation sub-products into H2. Anaerobic digestion as a final stabilisation stage was also considered owing to the wide application of this technology in the treatment of bio-wastes.

Co-firing of coal and manure biomass: A TG–MS approach

Manure is a rich organic waste which, apart from its traditional use as a fertilizer, could be used as a bioenergy feedstock. In this sense, its utilization as a sole fuel or its co-combustion together with coal would be a choice for the management of this sort of biowaste. However, little is known about the behavior of this biowaste when submitted to high-temperature energy-conversion processes. Thus, the separate combustion of swine manure and coal and their co-combustion (10% dried weight of manure) were studied by simultaneous TG/MS dynamic runs. TG-MS analysis was successfully used as an easy rapid tool to assess the combustion of manure, alone or together with coal. Furthermore, non-isothermal kinetic analysis showed that the Arrhenius activation energy corresponding to the combustion of the blend (125.8-138.9 kJ/mol) was only slightly higher than that of manure (106.4-114.4 kJ/mol) or coal (107.0-119.6 kJ/mol).

TG-MS as a technique for a better monitoring of the pyrolysis, gasification and combustion of two kinds of sewage sludge

Sewage sludge disposal is a difficult task owing to increasingly restrictive re-use policies. Its final destination will obviously depend on its nature and composition but the generation of energy is a significant option. The thermochemical conversion requires exhaustive gas emission controls. In this regard, this paper offers the results of the use of mass spectrometry together with a thermogravimetric analysis system used to study the thermal conversion processes of two kinds of sewage sludge under different atmospheres simulating pyrolysis, gasification and combustion. This TG-MS combination indicates that gasification is the best process for one kind of sludge while a co-combustion process is more suitable for the other.

Thermogravimetric analysis of biowastes during combustion

The combustion of sewage sludge (SS), animal manure (AM) and the organic fraction of municipal solid waste (OFMSW) was assessed and compared with that of a semianthracite coal (SC) and of a PET waste by thermogravimetric (TG) analysis. Differences were found in the TG curves obtained for the combustion of these materials accordingly to their respective proximate analysis. Non-isothermal thermogravimetric data were used to assess the kinetics of the combustion of these biowastes. The present paper reports on the application of the Vyazovkin model-free isoconversional method for the evaluation of the activation energy necessary for the combustion of these biowastes. The activation energy related to SS combustion (129.1 kJ/mol) was similar to that corresponding to AM (132.5 kJ/mol) while the OFMSW showed a higher value (159.3 kJ/mol). These values are quite higher than the one determined in the same way for the combustion of SC (49.2 kJ/mol) but lower than that for the combustion of a PET waste (165.6 kJ/mol).

Digestion of cattle manure: thermogravimetric kinetic analysis for the evaluation of organic matter conversion.

Anaerobic digestion of cattle manure was studied under thermophilic and mesophilic conditions with the purpose of evaluating the effect of temperature on the quality of the final digestate. Non-isothermal thermogravimetric kinetic analysis was applied for assessing organic matter conversion of biological stabilization. The mathematical approximation proves to be a useful tool for evaluating the differences attained during biological degradation. The anaerobic digestion of the organic substrate resulted in a reduction of the activation energy value obtained from the different applied kinetic models. Results obtained from thermal kinetic analysis were in accordance with those from the monitoring of the anaerobic digestion process. The higher values of methane yield reported for the mesophilic digestion in comparison to that of the thermophilic indicated a greater capability of the former process in the utilization of substrate and thus a higher conversion of organic matter which can be quantified by the activation energy value.

Determination of Diazinon and Fenitrothion in Environmental Water and Soil Samples by HPLC

Abstract High performance liquid chromatography (HPLC) methods have been developed for the determination of the organophosphorus pesticides, diazinon, and fenitrothion in environmental water and soil samples; a simple and rapid sample preparation procedure using solid‐phase extraction being developed in the case of water samples. In soil samples, the analytical procedure proposed consisted of a 10‐min ultrasonic extraction of the target compounds from a 20 g soil sample with 20 mL of acetonitrile and, after centrifugation, the filtering and concentration of the supernatant in an SC110H Speed Vac Plus concentrator to evaporate solvents. The quantification of diazinon and fenitrothion was performed using UV photodiode detection at 245 and 267 nm, respectively. The average recoveries from spiked water and soil samples at various concentration levels exceeded 86% with relative standard deviations of 1.8–5.1%. It was possible to determine concentrations of these pesticides in the range 0.1–2 ng/g in water and soil samples with a good level of reproducibility and accuracy.

Solid‐Phase Extraction for the Determination of Dimethoate in Environmental Water and Soil Samples by Micellar Electrokinetic Capillary Chromatography (MEKC)

Abstract A micellar electrokinetic chromatography (MEKC) procedure has been developed for the analysis of dimethoate (DM) in environmental water and soil samples, using solid phase extraction (SPE) as a clean‐up and pre‐concentration technique to improve selectivity and DM detection limits. The limit of quantification (LOQ) was 1 µg/mL for direct injection and 3 ng/mL after the SPE pre‐concentration procedure. Within‐run and between‐day reproducibility studies performed at 0.02, 0.05, and 0.2 µg/mL indicated that the procedure was indeed reproducible. Quantification was by UV detection at 200 nm. The capillary electrophoresis (CE) method proposed uses sodium borate 100 mM with sodium dodecyl sulfate 50 mM, pH 8.4 as a buffer. The method was simple and fast, with good recoveries, which on average ranged from 82 to 92% with a relative standard deviation of 7% or less for water and soil samples fortified at 10, 20, 30, and 300 ng/mL. Our results show CE to be a powerful analytical tool for the determination of DM in environmental water and soil samples.

Modelling and kinetics studies of a corn-rape blend combustion in an oxy-fuel atmosphere.

A kinetic oxy-combustion study of a previously optimized lignocellulose blend is proposed. Kinetic and diffusion control mechanism are considered. The proposed correlations fit properly with the experimental results and diffusion effects are identified as be important enough to be taken into account. Afterwards, with the results obtained in the kinetic study, a detailed consecutive and parallel kinetic scheme is proposed for modelling the oxy-combustion of the blend. A discussion of the temperature and concentration profiles are included. Variation of products final distribution is considered. Smaller particles than 0.001 m are proposed for reducing temperature and concentration profiles and obtaining a good final product distribution. CO2-char reaction is identified as one of the most important step to be optimized for obtaining the lowest final residue. In this study, char is mainly oxidised at 950 K and this situation is attributed to an optimized blending of the bioresidues.