Value-added chemicals from food supply chain wastes: State-of-the-art review and future prospects

Highlights

• Food waste valorization is a profitable and sustainable waste management option.

• Consumer, specialty, commodity, and niche chemicals can be refined or recovered from food waste.

• Physical, chemical, and biological technologies improve outcomes of food waste conversion.

• Integrated biorefinery of food waste into a wide spectrum of value-added products is promising.

Abstract

Food wastes are generated massively across global food supply chains. Conventional treatments of food waste (e.g., landfilling and incineration) cause environmental, economic, and social problems. There is a more sustainable and profitable management option by valorization of food waste into value-added chemicals. Consumer chemicals, including acids, sugars, and their derivatized forms, can be synthesized from food waste. Refined specialty chemicals from food waste ranging from solvents to antioxidant materials can be important for nutraceutical and biomaterial applications. Meanwhile, commodity chemicals derived from food waste such as biofuel, biogas, and biochar help meet the global demand for large-scale reutilization of resources and energy. Niche chemicals (e.g., chitosan, glucose, and free amino nitrogen) converted from food waste also show great prospect in nutrient recycling and use for industrial applications. This paper reviews and discusses the latest technological advances in different physical, chemical, and biological treatments of food waste, such that the productivity of value-added chemicals and cost-effectiveness of these valorization methods can be improved for future scaled-up operations. This paper covers holistic comparison and in-depth discussion regarding the feasibility and sustainability of food waste derived chemicals, together with the market outlook of recycling and valorization of food wastes from state-of-the-art perspectives.

Introduction

As there is a global shortage of energy and resources, which has aroused increasing public attention, research efforts are being made to develop innovative and practical technologies to recycle useful materials from waste streams. Food loss occurs from initial agricultural production to various later steps and procedures across the food supply chain (e.g., harvesting, transport, storage, processing, packing, distribution, marketing, and household consumption). Food waste is generated in the process of these retail and final consumption parts of the food supply chain, according to the Food and Agriculture Organization (FAO) of the United Nations [1], [2].

Food waste generation and disposal is an emerging and critical issue around the world. The per capita annual food loss in North America and Europe amounts to 280–300 kg, while that in sub-Saharan Africa and South/Southeast Asia is 120–170 kg [2]. In 2010, United States had 195 million tons the available food supply, of which 60 million tons were lost at the retail and consumer levels with an estimated total value of US$161.6 billion [3]. As for Europe, a recent study revealed that an annual amount of food waste was approximately 88 million tons in the EU, with an estimated associated cost at 143 billion euros [4]. The costs are expected to rise to about 126 million tons by 2020 unless action is taken. With the increasing global food supply as indicated in the latest biannual report by FAO [5], food waste generation is expected to remain significant, and should be addressed from both technological and managerial perspectives.

Traditional options for food waste treatments such as landfilling, composting, and incineration cannot meet the demand in reducing the adverse impact to the environment while providing sufficient economic merits for resource and energy recovery. In fact, the applicability of these approaches varies with different locations. For example, landfill disposal is not suitable for populated cities while composting is not cost-effective in urbanized areas with limited agricultural activities. As for environmental impacts, disposal of every ton of food waste would emit >4.2 tons of CO₂ to the atmosphere, not to mention secondary emissions to soil and water [6]. While each ton of food waste brought about US$60–200 in economic value for electricity generation or cattle feed, US$1000 could be obtained if food wastes were used for bulk chemical production (e.g., hydroxymethylfurfural and furfural [7]). In a life cycle assessment study, innovative alternatives such as bioconversion and thermochemical conversion were shown to give the best environmental performances, and could cause less energy consumption, secondary pollution, and recovery of more resources, compared with conventional methods such as landfilling and incineration [8], [9], [10]. Such technological innovations could diversify options for food waste treatments. Decision makers could design configuration of a recycling system with a mix of technologies, depending on the local environment and constraints (e.g., space, food culture, industrial activities).

Therefore, recent attention on food waste valorization has drawn great interest from the research community. In the process, food wastes undergo various thermochemical or biological treatments to produce abundant valorized products. This can not only reduce waste disposal but regenerate resources from waste streams. However, existing reviews mainly focus on valorization of certain types of food waste, such as animal, fruit, vegetable, and cereals wastes [6], [11], [12], [13], [14]. Other reviews emphasize specific products such as bio-fertilizers, hydroxymethylfurfural, and levulinic/succinic/lactic acids [15], [16], [17], [18]; or examine particular approaches of food waste processing such as anaerobic digestion, thermal conversion, and fermentation [19], [20], [21], [22]. Little information is available for comparing potential alternatives of food waste valorization. In view of this, an encyclopedic review is needed to cover all the possible synthesized chemicals from the perspective of industrial and commercial applications.

A wide range of value-added chemicals synthesized from food waste can be further categorized for clearer illustration [230]. Specialty chemicals are a group of materials used for achieving particular effects on products to enhance their specific properties or functions, such as solvents and antioxidant chemicals [68], [69]. Consumer chemicals refer to household products directly interacting with customers as the end-user, such as health supplements and detergents [231]. Commodity chemicals refer to chemicals of high global demand that are usually produced at large quantity, including biofuel, biogas and biochar [232]. Niche chemicals (e.g., chitosan, glucose, and free amino nitrogen) are chemical products targeting a particular section of profitable industry or market [233].

In regard to the shortage of global resources, this paper reviews the research advances and scientific knowledge in food waste treatments, with a focus on integrated valorization technologies that convert food wastes into a diverse range of value-added chemicals. These chemicals are categorized into specialty chemicals, consumer chemicals, commodity chemicals, and niche chemicals, of which the formation mechanisms and conditions will be critically discussed. This review will provide a holistic comparison of the feasibility and sustainability of different approaches to food waste valorization. These practices are possible means to realize efficient closed-loop resource utilization and circular bio-economy.