Anaerobic co-digestion of dairy raw by-products and Ulva sp. macroalgae: effect of organic and inorganic additives

An investigation has been carried out for biogas production from dairy raw materials (DRM) and Ulva sp. macroalgae as a co-substrate in order to find a usefulness for these species. Some nutrient media have been selected to optimize methane yield. The effect of the mineral additive medium (medium I), based on bicarbonate compound, and the organic additive one (medium II), based on glucose, on the anaerobic digestibility of DRM has been assessed by using a single-stage anaerobic process. Four batch experiments (batch 1, batch 2, batch 3 and batch 4) have been performed and correspond respectively to DRM without inoculum, DRM with additive medium I, DRM with additive medium II and DRM and Ulva sp. with additive medium I. Measurements of methane produced, chemical oxygen demand (COD), proteins, lipids, carbohydrates and volatile fatty acids have been carried out. It has been found that the mineral additive medium provided a higher specific methane yield compared to the organic additive one, the methane yield was about 0.208 $\mathrm{L}_{\mathrm{CH}_4}/\mathrm{g}_{\mathrm{VS}}$. The co-digestion of DRM with Ulva sp. showed that the methane yield reached was about 0.118 $\mathrm{L}_{\mathrm{CH}_4}/\mathrm{g}_{\mathrm{VS}}$, and revealed that the use of Ulva sp. as co-substrate reduces the concentration of volatile fatty acids, and enhances the biogas quality which contains 96% of methane and only 0.5 to 2% of hydrogen sulphide. Furthermore, a first-order kinetic model has been applied to describe proteins, lipids and carbohydrates biodegradation and showed that these three compounds follow a different kinetics according to the composition of the medium and the presence or not of additive medium

Caractérisation hydrodynamique de la structure des écoulements dans les lignes de transformation des industries agroalimentaires et conséquences sur le nettoyage de souillures bactériennes (étude exploratoire sur l'intérêt des écoulements pulsés)

Les travaux présentés dans ce manuscrit traitent de l effet de la géométrie et de l écoulement sur le décrochement de spores de B. cereus de surfaces inertes au cours d une opération de nettoyage en place. Étant donnée leur forte adhésion à la paroi des équipements et leur aptitude à résister au nettoyage, ces spores présentent un risque sanitaire majeur pour l agro-industrie. Les objectifs visés consistent à étudier l effet de la géométrie sur la répartition des forces de cisaillement pariétal et à comprendre quelles sont les répercutions de la forme de l écoulement sur la contamination bactérienne avant et après nettoyage. Pour ce faire, la caractérisation de l écoulement dans plusieurs configurations composées de différentes géométries, couramment utilisées en industrie laitière, a été effectuée par des mesures de profils de vitesses (méthode de vélocimétrie ultrasonore pulsée) et des composantes moyenne et fluctuante du cisaillement pariétal (méthode polarographique). Par la suite, les niveaux de contamination bactérienne initiale et résiduelle, avant et après nettoyage, ont été déterminés au sein des différentes géométries testées. L effet des interactions entre les accidents hydrauliques sur l écoulement a permis d expliquer les différences de niveaux de contaminations initiale et résiduelle. Les analyses effectuées aux niveaux des soudures et des raccords ont montré que l adhésion et le décrochement des spores dans ces zones sont indépendants de la contrainte de cisaillement, ils sont plutôt liés à l état de surface du support d adhésion. Les interactions entre les tourbillons de différentes échelles et les spores en suspension ou adhérées à une surface ont été discutées. Les phénomènes de décrochement et de redéposition des spores ont été reliés à la taille et à l activité des structures tourbillonnaires en proche paroi.La seconde partie de ce travail concerne l application des écoulements pulsés aux procédures de nettoyage en place. Un nouveau système de génération de pulsations a été étudié. Les mesures réalisées par la méthode polarographique ont montré une nette augmentation de la contrainte moyenne de cisaillement pariétal, alors que l analyse spectrale a mis en exergue l effet des pulsations sur l énergie fluctuante du gradient pariétal de vitesse. La comparaison avec un écoulement stationnaire a montré la contribution de chacun des paramètres caractéristiques des pulsations dans le décrochement des spores de B. cereus. Enfin, une étude cinétique a révélé une augmentation de la vitesse de décrochement des spores en présence d un écoulement pulsé qui pourrait permettre de mieux gérer la durée de l opération de nettoyage.The present work deals with both effects of the geometry and the flow field on the removal of B. cereus spores from inert surfaces during a cleaning in place (CIP) procedure. Due to their strong ability to adhere to the equipment surfaces and their high resistance to cleaning process, these spores present a major sanitary hazard in the food industry. The objectives of this work were to study the effect of the geometry arrangements on the distribution of the local wall shear stress and to understand consequences of flow pattern on the bacterial soiling before and after a cleaning procedure. Flow characterisation of different loops containing several pieces of equipment used in dairy processing lines was carried out by means of instantaneous velocity profiles (Ultrasonic Doppler Velocimetry method) and wall shear stress components (electrochemical method). Initial and residual soiling levels, before and after cleaning, were determined for each geometry and explained by the effect of various interacting geometrical elements on the flow. Cleanability analysis at welding zones and gaskets has shown that the adhesion and the removal of spores in these zones are independent of the shear stress, they are rather related to the surface properties. Interaction between eddies of different sizes and suspended or adhered spores were studied. The removal and the deposition phenomena of spores were related to the size of the eddies and their activity near the wall. The second part of this work concerned pulsed flows application in CIP procedure. A new pulsations generator was used. Electrochemical measurements showed a significant increase in mean wall shear stress, whereas spectral analysis put forward pulsations effect on fluctuation energy of shear stress. Comparison with a steady flow showed the contribution of each pulsation parameter in the removal of adhered B. cereus spores. Lastly, the study of the cleaning kinetics has shown the increase of the removal constant rate of spores using pulsed flow, which allows controlling the cleaning duration.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Effect of VS organic loads and buckwheat husk on methane production by anaerobic co-digestion of primary sludge and wheat straw

International audienceAn environmentally acceptable disposal of sewage sludge and agro-wastes presents an urgent problem facing many countries. Anaerobic digestion (AD) is a robust and suitable technique for producing renewable energy from wastes. This study aims to improve methane production from anaerobic co-digestion of primary sludge (PS) and wheat straw (WS) depending on their volatile solids (VS) organic load and by adding a proposed waste material of buckwheat husk (BH) based on their carbon to nitrogen (C/N) ratio. Mesophilic anaerobic batch tests were carried out in 500-mL digesters. Individual and six mixtures of PS and WS at different VS organic loads were anaerobically digested to optimize VS load for the greatest gas production. The highest cumulative methane yield (CMYs) occurred with combined substrates at a VS load of 7.50 gVS/L. In general, the optimized organic loads that gave the highest cumulative biogas yield (CBYs) and CMYs were in the range of 6-8 gVS/L. In addition, AD of individual substrates of PS, WS, and BH and of their mixture at different C/N ratios was investigated regarding to the methane yields. Multi-component substrates produced the greatest CMY at a C/N ratio of 10.07. The CMYs was increased by 39.26% when the proposed waste material of buckwheat husk (BH) was added to the different mixtures of PS and WS compared to the co-digestion of PS and WS. Experimental results were approved using statistical analysis by ANOVA test at P-value less than 0.05. Purification of methane and biodegradation of VS were evaluated. The results emphasized positive synergy of anaerobic co-digestion for improving CMY and best feedstock utilization. (C) 2016 Elsevier Ltd. All rights reserved