Anaerobic co-digestion of organic wastes

Abstract

Over the last years anaerobic digestion has been successfully established as technology to treat organic wastes. The perspective of turning, through a low-cost process, organic wastes into biogas, a source of renewable energy and profit, has certainly increased the interest around this technology and has required several studies aimed to develop methods that could improve the performance as well as the efficiency of this process. The present work reviews the most interesting results achieved through such studies, mainly focusing on the following three aspects: (1) the analysis of the organic substrates typically co-digested to exploit their complementary characteristics; (2) the need of pre-treating the substrates before their digestion in order to change their physical and/or chemical characteristics; (3) the usefulness of mathematical models simulating the anaerobic co-digestion process. In particular these studies have demonstrated that combining different organic wastes results in a substrate better balanced and assorted in terms of nutrients, pre-treatments make organic solids more accessible and degradable to microorganisms, whereas mathematical models are extremely useful to predict the co-digestion process performance and therefore can be successfully used to choose the best substrates to mix as well as the most suitable pre-treatments to be applied

Development of optimum substrate compositions in the methane fermentation process

“…For some time now one can observe a significant increase in the amount of organic wastes and contaminants produced in agriculture and related branches. Those wastes are rich in components necessary for the growth and development of microorganisms, such as carbohydrates, lipids, proteins, microelements, biogenic elements and vitamins (Esposito et al, 2012). They may appear in solid, semi-liquid and liquid forms.…”

“…The use of methane fermentation process for organic waste degradation is attractive for several reasons (Barton et al, 2008;Esposito et al, 2012;Lettinga, 2001), this technology not only reduces the volume of organic waste to be disposed and avoids soil and groundwater pollution, but also makes available renewable and low-cost energy, for example biogas, that, unlike the fossil fuels, keeps stable the balance of greenhouse gases, such as CO 2 , in the atmosphere. Moreover, methane fermentation process of organic waste represents a reasonably low-cost and lowtechnology system to supply energy for rural areas in developing as well as underdeveloped countries where the main cause of their economic and social backwardness can be reasonably attributed to the lack of suitable energy.…”

“…Moreover, methane fermentation process of organic waste represents a reasonably low-cost and lowtechnology system to supply energy for rural areas in developing as well as underdeveloped countries where the main cause of their economic and social backwardness can be reasonably attributed to the lack of suitable energy. Biogas is already effectively used to produce electricity and heat, and to feed gas networks (Bekkering et al, 2010;Esposito et al, 2012). A further source of income produced by the process of methane fermentation of organic solids is represented by the semi-solid by-product of this process -post-fermentation sludge -that thanks to its high content of nutrients can be used in agriculture directly as a fertilizer or processed into compost to increase its quality (Esposito et al, 2012;Rehl and Müller, 2011;Tambone et al, 2009).…”

“…Biogas is already effectively used to produce electricity and heat, and to feed gas networks (Bekkering et al, 2010;Esposito et al, 2012). A further source of income produced by the process of methane fermentation of organic solids is represented by the semi-solid by-product of this process -post-fermentation sludge -that thanks to its high content of nutrients can be used in agriculture directly as a fertilizer or processed into compost to increase its quality (Esposito et al, 2012;Rehl and Müller, 2011;Tambone et al, 2009). Unfortunately, methane fermentation process has substantial drawbacks.…”

Co-digestion of sewage sludge from external small WWTP’s in a large plant

“…sewage sludge, swine manure) and the others are additional material (e.g. food waste, grease trap sludge) [4,5]. A specific case of co-digestion is situation when basis and additional materials are both sewage sludge, for example basis material form large WWTP and additional material are form transported from medium and small WWTPs located near a large plant.…”