RESUMEN
Organic waste fractions such as sewage sludge, food waste and manure can be stabilized by anaerobic digestion (AD) to produce renewable energy in the form of biogas. Following AD, the digested solid fraction (digestate) is usually dewatered to reduce the volume before transportation. Post-AD treatments such as the Post-AD thermal hydrolysis process (Post-AD THP) have been developed to improve the dewatering, but the mode of action is not well understood. In this study, samples from 32 commercial full-scale plants were used to assess the impact of Post-AD THP on a broad range of raw materials. Maximum dewatered cake solids after Post-AD THP was predicted by thermogravimetric analysis (TGA). Post-AD THP changed the moisture distribution of the samples by increasing the free water fraction. A consistent improvement in predicted dewatered cake solids was achieved across the 32 samples tested, on average increasing the dry solids concentration by 87%. A full-scale trial showed that dewatering Post-AD THP digestate at 80 °C improved dewatered cake solids above the predictions by TGA at 35 °C. In conclusion, dewatered cake solids were significantly improved by Post-AD THP, reducing the volume of dewatered cake for disposal.
Asunto(s)
Alimentos , Eliminación de Residuos , Anaerobiosis , Hidrólisis , Aguas del Alcantarillado , Eliminación de Residuos LíquidosRESUMEN
The use of low field Nuclear Magnetic Resonance (LF-NMR) is shown to be a fast and accurate alternative to the use of drying and solvent extraction, to determine the content of raw or total fat and moisture in a biological system. The proposed NMR method for fat determination in minced meat proves to be a robust method that does not require sophisticated post handling of the experimental data. The calibration procedure is very easy, as a calibration value from a sample of known weight containing 100% oil is the only calibration needed for the proposed experimental set-up. On three sets, each containing 42 samples of minced beef where the fat content varies from less than 1 to 14%, the fat content has been measured either by NMR on fresh tissue, NMR on dried tissue, or by the use of solvent extraction determining the content of raw fat [Foss-let fat analyser (AOAC Official Method 976.21]. Comparison of the three methods for determination of the fat content shows satisfactory agreement between the different methods. On six samples of minced pork meat, the fat and moisture content have been determined. The total fat content was determined by NMR both on fresh and dried tissue. The moisture content was determined by NMR of fresh tissue and by drying of the tissue. The different methods for determining fat and moisture content agreed for the minced pork samples.
RESUMEN
The application range and validity of two new NMR sequences (hereafter called sequence 1 and sequence 2) for the study of water-in-oil emulsions (w/o) has been assessed using model emulsions and comparison with results obtained by a commercial apparatus (Turbiscan). These new NMR sequences allow to determine the brine profile i.e. the vertical variations of the dispersed phase content (brine) in the NMR tube. Measuring these parameters as a function of time allows to monitor the separation (sedimentation and coalescence rate) between oil and water. The results obtained on model water-in-oil emulsions with both NMR sequences are consistent and meaningful for both stable and coalescing emulsions and are similar, even if not strictly identical, to the ones obtained with the Turbiscan. It also appears that the second NMR sequence is faster (30s to obtain a profile compared with 3 min for the 1st one in the conditions used in this article) and has a broader application range. Indeed, for these two methods, the oil phase must have a viscosity higher or equal than values which is around 5 mPas for the sequence 2 and 20-25 mPas for the method 1.