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Technologies for Converting Food Waste to Energy: Current State and Prospects

A. Asha Monicka1*, M. Suguna Devakumari2 and G. Jeevarathinam3

1Division of Agricultural Engineering, School of Agricultural Sciences, Karunya Institute of Technology and Sciences, Coimbatore, Tamil Nadu, India

2Division of Soil Sciences, School of Agricultural Sciences, Karunya Institute of Technology and Sciences, Coimbatore, Tamil Nadu, India

3Department of Food Technology, Hindusthan College of Engineering and Technology, Coimbatore, Tamil Nadu, India

Abstract

One of the basic needs for the mankind is food. In the journey from harvest to consumer a significant amount of food is lost and wasted. Similarly after reaching the consumer 17% of total food available is thrown into bins by the consumers, retailers and restaurants according to the data given by the United Nations environmental program (UNEP). Food waste index report 2024 estimates that, around US$1 trillion worth of food is wasted every year. However income can be generated through food waste by converting it into a gaseous fuels, bio based liquids, enzymes or fertilizers. On this basis, this chapter reviews the scope, technical, social, and economic challenges of existing technologies available for the food waste treatment like pyrolysis, landfill, incineration, composting, anaerobic digestion, and biochemical conversion. Also elucidate the emerging techniques on the hydrogen production from food waste through various techniques like dark fermentation and hydrothermal gasification process. Hydrothermal carbonization, hydrothermal liquefaction, and integrated biological food waste management are also discussed in this chapter.

Keywords: Hydrogen production, hydrochar, bio oil, biofertilizer, food waste management

1.1 Introduction

In the year 2022, around 1.05 billion tons of food has been wasted globally. This accounts to 19 % of food that are available to the consumers in the retail market, food service and household are being wasted. The majority of the foods are being wasted in the household level (631 million tons) according to the food waste index report 2022. Every single man throws 79 kg of edible food annually. It is estimated that in next 25 years the food waste may increase still higher due to the increase in the population and economic growth mainly in the Asian countries. The World Bank and FAO estimate that about 1.33 billion tons of foods are lost or wasted year worldwide, and that amount of waste would increase to 2.2 billion tons. The reasons behind food waste differ from nation to nation in terms of supply chain inefficiencies, high consumer standards, agricultural conditions, manufacturing inefficiencies, and policy restraints [2]. Even though there is enough food produced daily to feed most of the world's population, process technology and appropriate waste management and recycling are still an issue.

Discarding the food waste is again a huge problem in the general public life. This rise in the food waste directly contributes the carbon foot prints and greenhouse gas emissions. Traditionally the food wastes are being just dumped in the open area or in particular sites called as landfills. However landfills sites are not acceptable by the public since there is a huge release of methane gas and also the groundwater gets contaminated in the long term effect. Also it creates the unpleasant odor and gases due the chemical reactions.

Food waste includes the loss or disposal of food that would otherwise be fit for human consumption. This problem has significant economic ramifications on a global scale in addition to having extensive environmental and social repercussions. Food waste happens at several stages of the supply chain, from the farming stage to the consumption phase. There are several factors contributing to this waste, such as over production, ineffective distribution networks, and consumer behavior. Importantly, food waste has a significant negative influence on the environment by causing greenhouse gas emissions and needless usage of energy and water resources [33]. On the other hand, the problem of food waste in less developed areas frequently originates in the supply chain's early phases. Food loss in this case is mostly caused by elements like inadequate infrastructure, a lack of technology, and inadequate post-harvest procedures. These difficulties show that in order to enhance food processing, storage, and transportation in these areas, infrastructure, and technological expenditures are required. Food waste has consequences that go beyond the environment; it also affects economic stability and food security. There is a matter of ethics and morals when food that may have been used to feed the hungry is lost. Furthermore, food waste results in significant financial losses for farmers, merchants, and consumers alike.

Reducing food waste necessitates a multifaceted strategy that includes behavioral adjustments, technology improvements, and policy changes. Around the world, governments and organizations are putting policies into place to decrease food waste, such as public awareness campaigns, better food supply chain management, and the encouragement of sustainable consumption habits. Possibility for sustainable waste management is presented by the investigation of circular economy models, in which food waste is converted into novel products or energy. Therefore, eliminating food waste necessitates an all-encompassing approach that involves supply chain stakeholders and makes use of technology, policy, and social change to promote a sustainable food system [17].

1.2 Characterization of Food Waste

The composition of food waste depends on the type of the food waste, e.g., food waste with rice, vegetables, pasta will have high carbohydrate whereas the food waste from the fish, meat, and egg will be rich in protein and also lipids. However, generally the moisture content of the food waste ranges from 75-90 percent with acidic pH of 5.1, proteins ranging from 15-25 %, carbohydrates from 41 to 60 % and lipids with 13-30 % [6]. The total solid content may vary between 20 to 30 % w.b. Also the C/N ratio is less (13.2-24.5) than the optimal range. Also, micronutrient present in the food waste influence play an important role in the development of microorganisms.

1.3 Existing Technologies for Food Waste to Energy Conversion

1.3.1 Pyrolysis

It is one of the well-known process of anaerobic digestion that is the thermochemical conversion technique that takes place in the absence of the air. Generally the pyrolysis process was employed for the production of charcoal, syngas, and bio-oils from different biomass like crop residues, municipal waste, and waste biomass. The process of the pyrolysis takes place at high temperature greater than 400 °C and at atmospheric pressure. Pyrolysis can be classified into different types according to the process conditions and parameters. The fast and slow pyrolysis are discussed since it the most commonly employed process [29].

1.3.1.1 Fast Pyrolysis

The biomass medium is heated between 800 and 1300 °C at a rate of 10 to 200 °C during a relatively short period of 1 to 10 s in the fast pyrolysis process. Fast pyrolysis is mostly used to make bio-oil since the oil product yield is greater than the char and gas product yield [32]. Fast pyrolysis yields between 60 to 75 percent liquid biofuel products, 10 to 20 percent non-condensable vapor products, and 15 to 20 percent solid form biochars. The main objective of the fast pyrolysis process is to expose the biomass feedstock to a temperature high enough to achieve thermal cracking while minimizing the exposure time, which promotes the formation of chars. Reactors that are frequently utilized for quick pyrolysis processes include fluidized beds, spinning cones, ablative reactors, vacuum, and entrained flow reactors [27].

1.3.1.2 Slow Pyrolysis

Slow pyrolysis, the conventional type, often involves low heating rates and a long residence time. Biomass is pyrolyzed for a reasonable amount of time (5-30 minutes) at a heating rate of 0.1-1 °C/s to reach an approximate temperature of 400-500 °C. Although the generation of solid carbonaceous char is aided by the slow pyrolysis process, relatively tiny amounts of liquid fuel and gas products are also created [29].

1.3.1.3 Effects of the Pyrolysis Process on the Environment

Food waste and other biomasses undergo pyrolysis to produce fuel gas and fuel oil, which are composed of lower hydrocarbons, lower olefins, carbon dioxide, carbon monoxide, and water vapor. The addition of biochars for arid soils in particular has shown to have several advantages like increase in water holding capacity, removing the cations from the soil and crop yield improvement.

Few researchers believe that producing and using biochar made from biomass for agricultural purposes has highly good effects on global warming. The use of biochars is a direct sequestration method; their carbon concentrations typically range from 10% to 50%. However, a number of studies have found that the microbial growth on the biochar's labile carbon is mostly responsible for the early release of carbon dioxide [26].

1.3.2 Incineration

The incineration procedure is regarded as one of the waste treatment methods with the least demand. Waste is burned in order to generate energy and heat. In...