Reviewing the Anaerobic Digestion of Food Waste: From Waste Generation and Anaerobic Process to Its Perspectives

Abstract

Discharge of waste in general, and food waste, in particular, is considered one of the major environmental problems today, as waste generation increases continuously, reaching values of 32% of all food produced worldwide. There are many different options that can be applied to the management and evaluation of waste treatment, and Anaerobic Digestion seems to be one of the most suitable solutions because of its benefits, including renewable energy generation in form of biogas. Moreover, if FW (food waste) is digested in anaerobic digesters from Waste Water Treatment Plants, a common solution is provided for both residues. Furthermore, co-digestion of food waste and sewage sludge provides benefits in terms of anaerobic process stability enhancing the buffer capacity of ammonia (for example) and biogas formation, which can be increased up to 80% when compared with monodigestion. The present paper reviews food waste anaerobic digestion from its generation, characteristics and different options for its management, and it does focus specifically on the anaerobic digestion and co-digestion process, stages, limiting rates and parameters, utilizing numerous experiences, strictly related to food waste. Pre-treatments are also considered as they are important and innovative for enhancing biogas production and its methane yield. The paper shows an extensive collection of pre-treatments, its basics, improving factors, and numerical data of biogas formation improvements that are related both to substrate modification and to the synergistic effect of co-digestion, which could lead to an increase of methane production from 11% to 180%.

Pleurotus spp. Cultivation on Different Agri-Food By-Products: Example of Biotechnological Application

“…Therefore, different strategies have been already adopted [5] to manage these existing accumulated food wastes. Some examples are the industrial reuse of food wastes in the biomaterials production and energy generation in the form of biogas [6], though anaerobic digestion and anaerobic co-digestion of food waste seem to be among the best waste management strategies since they can be considered a renewable energy source with low emissions [6]. In 2012 the European Union alone generated approximately 88 million tons of food wastes, 9 million tons arising from primary production and 17 million tons coming from processing sector [3].…”

A Review of Sludge-to-Energy Recovery Methods

“…The combination of different energy technologies such as anaerobic digestion followed with pyrolysis has been presented by Cao and Pawlowski [46] for maximisation of energy efficiency in comparison to the use of the technologies independently. The use of anaerobic digestion is particularly attractive as it fulfils most of the requirements in European Waste reuse and recovery hierarchy and its use in combination with food waste has been proposed by Morales-Polo et al [47] due to the added benefit of nutrient enrichment, increase in alkalinity, reduced ammonia and enhanced stability of the process. Furthermore,~20-40% increase in production of bio-methane was obtained from the co-digesting of mixed sludge and organic food waste by boosting the decomposition of acetate during methanogenesis [48].…”

The Future Agricultural Biogas Plant in Germany: A Vision

“…These feedstocks are highly variable as their composition differs between rural and urbanized areas and undergoes seasonal changes [97][98][99]101,102]. Before they can be fed to an anaerobic digester, pre-processing is required, for example, to remove plastics, metals, glass, and other impurities, to reduce/homogenize the particle size, to improve the solubilization of the organic material and to eliminate pathogens [97,98,103,104]. In Germany, thermal pretreatment for hygienization is mandatory per legislation [105].…”

“…However, the chemical variability of these feedstocks remains high and is the major challenge for anaerobic digestion. For example, fruit and vegetable wastes, with their high contents of volatile solids, often lead to an acidification [102,104], while slaughterhouse or dairy residues with their high protein and lipid contents carry the risk of accumulating process-inhibiting metabolites such as ammonium/ammonia, hydrogen sulphide or long chain fatty acids [102,103]. To avoid these problems, co-digestion of organic waste with animal manure or sewage sludge or the usage of multi-stage anaerobic digestions systems are commonly applied [99,101,102].…”