Abstract
Biological treatments such as anaerobic digestion and composting are known to be the most widespread methods to deal with Organic Fraction of Municipal Solid Waste (OFMSW). The production of biogas, a mix of methane and carbon dioxide, is worth but alone cannot solve the problems of waste disposal and recovery; moreover, the digestate could be stabilized by aerobic stabilization, which is one of the most widespread methods. The anaerobic digestion + composting integration converts 10% to 14% of the OFMSW into biogas, about 35–40% into compost and 35–40% into leachate. The economic sustainability could be rather increased by integrating the whole system with lactic acid production, because of the high added value and by substituting the composting process with the hydrothermal carbonization process. The assessment of this integrated scenario in term of mass balance demonstrates that the recovery of useful products with a potentially high economic added value increases, at the same time reducing the waste streams outgoing the plant. The economic evaluation of the operating costs for the traditional and the alternative systems confirms that the integration is a valid alternative and the most interesting solution is the utilization of the leachate produced during the anaerobic digestion process instead of fresh water required for the hydrothermal carbonization process.
Highlights
Food waste (FW) represents an important fraction of biowaste posing increasing disposal costs and environmental challenges
By assuming lactic acid (LA) production as a step of a virtuous chain, which should be both economic and environmentally sustainable, the residue needs to be exploited by using other suitable methods; among the possible options to treat the biowaste the best are: (a) the biochemical fermentation under anaerobic conditions, that allows the conversion of a fraction of residual carbon into biogas/biomethane and (b) the thermochemical processes that allow the conversion of the residue into biochar (BC) or HC, depending on operating conditions of the process used and source composition (BC can be produced starting from high lignin biowaste)
Whatever the optimized order of application of LA production and Anaerobic digestion (AD), the further treatment of digestate is a sore point to face; digestate represents more than 65% mass of starting food/biowaste having 60–65% of water and around 17–20% of carbon
Summary
Food waste (FW) represents an important fraction of biowaste posing increasing disposal costs and environmental challenges. By assuming LA production as a step of a virtuous chain, which should be both economic and environmentally sustainable, the residue needs to be exploited by using other suitable methods; among the possible options to treat the biowaste the best are: (a) the biochemical fermentation under anaerobic conditions, that allows the conversion of a fraction of residual carbon into biogas/biomethane and (b) the thermochemical processes that allow the conversion of the residue into biochar (BC) or HC, depending on operating conditions of the process used and source composition (BC can be produced starting from high lignin biowaste). Whatever the optimized order of application of LA production and AD, the further treatment of digestate is a sore point to face; digestate represents more than 65% mass of starting food/biowaste having 60–65% of water and around 17–20% of carbon This “digestate” is generally mineralized under form of compost by using an aerobic treatment requiring 90 days with intense aeration and a cost (only electricity) of about 5 € per ton while the economic value does not overcome. The present study was carried out using FW collected between April and September 2019 and sampled directly as entering the AD plant
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