Advantages and limits of co-digestion in wastewater treatment plants – comparison to co-digestion in agriculture

The Master Project offers a survey on several aspects of co-digestion in wastewater treatment plants (WWTP) and in agriculture. The description of the legal context and the technical processes present the basis for the subsequent analysis of the co-digestion at the WWTP in Bern and in four agricultural installations. For the ecological evaluation a material flow analysis was made to determine the nutrient loss due to co-digestion in WWTP. In addition, the energy and CO2 balances were established to understand environmental impacts. For the economical evaluation financial indicators were calculated in order to judge profitability and efficiency of the installations. The social impacts analyzed include worker security, financial risk, employments and regional economy. Considering the loss of nutrient, a threshold for co-digestion in WWTP is proposed: if energy loss by the nutrients exceeds the net energy production of a co-substrate, it should not be digested in WWTP. The study shows that sustainability of co-digestion does not depend on the sector but on the modalities of each plant. The main factors determining sustainability are size and degree of capacity utilization of the plant, the degree of utilization of produced energy, transport distance of co-substrates, and, in agriculture, the storage and deploying of the digestion end product.

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

Urban District Energy Futures: A Dynamic Material Flow Analysis (MFA) Model

Nataliya Filchakova, Darren Robinson, Jean-Louis Scartezzini

With more than half the world population now urbanised, urban metabolism – defined as the throughput and transformation of material and energy flows to sustain human life in urban settlements – is responsible for consuming the majority of global resources and the impact that this has on the environment. The identification, quantification and analysis of the main stocks and flows of energy and matter can support decision-making for a more sustainable urban resource use. Material Flow Analysis (MFA) is a method that has been widely used to study the metabolism of anthropogenic systems at a variety of scales. Yet the scale of the urban district has been addressed only scarcely. Often an established municipal unit for the purpose of planning, decision making and implementation, it is this district scale which is the subject of our study. In this we first present a mathematical MFA model (MMFA) for the simulation of energy and matter flows within our chosen urban district (Matthäus, Basle). We then go on to describe how this model was calibrated to this district. Various scenarios (with a special focus on energy) for the future optimisation of this status quo are discussed. We conclude by suggesting some promising strategies for the more sustainable development of Matthäus during the next fifteen years.

EPFL2007

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

Adeline Mertenat

2014