Abstract
Abstract A box-type reactor system with liquid inoculum has been studied for the dry anaerobic digestion of food waste. The food waste was processed without any pre-treatment to remove physical impurities, neither water addition to dilute and slurry the feedstock. The experiment was carried out with inoculum to substrate ratios of 1:1 (w/w) and 0.08:1 (VS basis). Previous acclimation of liquid inoculum enhanced the process, assuring a fast start up of the box digester and preventing from process failure by volatile fatty acids accumulation. The percolate recirculation strategy was shown to have a relevant effect on the progress of the process. The results suggest that the process can be optimized by providing low percolate recirculation rate during the start-up of the box digester followed by an increase in the percolate recirculation rate when volatile fatty acids decrease and methane content in the biogas increases. The methane yield obtained in the box digester from the food waste was in the range 460–477 L CH4 kg−1 VS, being the VS removal efficiency between 91.1 and 91.4%. Globally, the process operated at an organic loading rate of 2.5 kg VS m−3 d−1 and yielded a volumetric methane production rate of 1.0 m3 CH4 m3 d−1. These results show the high potential of food waste for its conversion in renewable energy by using the dry batch anaerobic technology.
Highlights
The socio-economic changes that have occurred in the last decades due to urban population increase, the development of the food industry and the rise of consumption trends, have resulted in an increase of the generation of food waste, in areas of high population density
The daily methane yield followed the typical curve of an anaerobic batch process (Fig. 2b), characterized by a peak in daily methane production rate that depends in extension and time on the substrate and inoculum characteristics and its ratio
The evolution of pH, volatile fatty acids (VFA) and daily methane yield can be interpreted as a signal for correct decision-making on the percolate recirculation strategy
Summary
The socio-economic changes that have occurred in the last decades due to urban population increase, the development of the food industry and the rise of consumption trends, have resulted in an increase of the generation of food waste, in areas of high population density. In the European Union, approximately 88 million tons of food waste are generated each year (Scherhaufer et al, 2018). About one-third of the food produced is wasted globally, which amounts to about 1.3 billion metric tons each year (Brunklaus et al, 2018). Food waste is a problematic waste because of the huge amounts generated, and because the broad range of environmental impacts that its management causes, such as water and air pollution, as well as greenhouse gas emissions (Schanes et al, 2018). Landfilling, the most used disposal method for food waste, contributes to the release of high organic load leachates and greenhouse gases. The amount of biowaste landfilled is restricted in the European Union by the European Council Directive on the landfill of waste (Council Directive 1999/31/EC)
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