Digestion | EPFL Graph Search

Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small molecules the body can use. In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication (chewing), a form of mechanical digestion, and the wetting contact of saliva

Assessment of organic waste availability and suitability for the co-digestion of faecal sludge in Vietnam

Adeline Mertenat

This Master thesis comes within the framework of the PURR project (Partnership for Urban Resource Recovery), which is a collaboration between the Department of Water and Sanitation in Developing Countries (Sandec) at the Swiss Federal Institute of Aquatic Science and Technology (Eawag), the Institute of Environmental Science and Engineering (IESE) at the National University of Civil Engineering of Hanoi (HUCE), and the Laboratory for Environmental Biotechnology (LBE) at the Swiss Federal Institute of Technology Lausanne (EPFL). The PURR project is aiming to allow a comprehensive management of faecal sludge (FS) in Vietnamese urban areas. In that perspective, anaerobic co-digestion of FS with other type of organic waste is seen as a very promising technology. As the potential benefit from FS co-digestion is closely linked with the choice of co-substrates, this Master thesis was focusing on assessing the availability and suitability of potential co-substrates produced in the two case study cities Bac Ninh and Son La. By field research and interviews, a better understanding of the actual organic waste management was established. This showed that the actual organic waste management is not in favour of FS co-digestion as such. Indeed, all organic wastes separated at production source and therefore of high quality in terms of absence of impurities with disturbing effects, are already being reused, mainly as livestock feed. The remaining organic wastes are domestic waste, which cannot be used for anaerobic digestion (AD) process due to their high level of impurities related to their mixture with non-organic wastes. However, field research also revealed that rooms for improvements do exist for a better management of organic domestic waste. Nowadays they are most of the time dumped in landfills without any treatment. A segregation step would be really relevant to implement in order to decrease the related pollution and potential resource recovery of these valuable but underexploited wastes. Nevertheless, this would require political support from local authority in order to be efficient. Based on the organic waste assessment, co-treatment scenarios and related pros and constraints for FS co-digestion when considering the local context were developed. The use of segregated organic domestic waste came out to be the most sustainable scenario but is largely compromised by actual policy. The use of unfresh fruits and vegetables from market can be considered as the best compromise between technical and contextual constraints and would require less effort to be effective. In both scenarios, local support is a key factor for their effectiveness. Based on the results of the current report, the following statement can be deduced: If local support is provided, anaerobic co-digestion would be a relevant process for FS treatment. Otherwise, other treatment processes should be investigated.

2014

Energy efficiency in waste water treatments plants: Optimization of activated sludge process coupled with anaerobic digestion

Nicolas Descoins, François Maréchal

This paper presents a study concerning the optimization of a Waste Water Treatment process. The process deals with carbon and nitrogen removal and includes activated sludge reactors coupled with an anaerobic digestion reactor. Nitrification and de-nitrification biochemical reactions are due to the biological activity of heterotrophic and autotrophic micro-organisms occurring inside the reactors. Rigorous Plant-Wide models that represent the main biochemical transformations have been constructed as per the CEIT approach [1]. The energy consumption for each Physical Unit Operation (P.U.O.) involved in the flow-sheet is evaluated and a full link is made between the biological activity and the electrical demand or production. Steady-state mathematical optimizations are then computed and the influence of primary settling efficiency on electrical autonomy is quantified and demonstrated. The ammonium recycling from digestion to activated sludge reactors is also demonstrated to be a limiting factor for the overall energy efficiency, as well as the C-substrate availability for denitrifying. Some conclusions are then drawn to improve the global electrical efficiency of the system. © 2011 Elsevier Ltd.

2012

Energy efficiency in waste water treatments plants: Optimization of activated sludge process coupled with anaerobic digestion

Nicolas Descoins, François Maréchal

2011

Assessment of organic waste availability and suitability for the co-digestion of faecal sludge in Vietnam

Adeline Mertenat

2014