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Agricultural Waste as a Resource: The Lesser Travelled Road to Sustainability

Avinash Pratap Gupta1, Prachi Upadhyay2, Tirthankar Sen3, and Joystu Dutta1

1 Department of Environmental Science, Sant Gahira Guru University, Sarguja, Chhattisgarh, India

2 Forest Ecology and Environment Management Division, Forest Research Institute (Deemed-to-be) University, Dehradun, Uttarakhand, India

3 Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India

CHAPTER OUTLINE

• 1.1 Introduction
• 1.2 Sources of Agricultural Waste Generation
• 1.2.1 Lignocellulosic Waste
• 1.2.2 Proteinaceous Waste
• 1.3 Agricultural Waste Characterization
• 1.3.1 Food Processing
• 1.3.2 Meat and Poultry Processing Industry
• 1.3.3 Livestock Waste
• 1.4 Waste to Wealth: Agricultural Waste Management Approaches
• 1.4.1 Natural Fibres
• 1.4.2 Agriculture
• 1.4.3 Bioenergy Production
• 1.4.4 Biofertilizer Production
• 1.4.5 Value-Added Products
• 1.4.6 As Adsorbents for the Removal of Heavy Metals
• 1.4.7 Animal Feed
• 1.5 Challenges in Agricultural Waste Management
• 1.6 Conclusion
• References

1.1 Introduction

With the expansion of agricultural activities, the amount and type of wastes being produced from them have increased. As per the Organization for Economic Cooperation and Development and the Food and Agriculture Organization (OECD-FAO), 39.35 million tons of natural fibres are annually being obtained from plants by the farmers, which also contribute to waste production. China reportedly produces 56.2 million tons of agricultural wastes. The types of wastes and their amount are dependent on the country and their management (Nagalakshmaiah et al. 2016; Letcher and Vallero 2019; Kamel et al. 2020). Agricultural wastes are basically the outputs that are not utilized in products or residues produced from the harvest/rearing and processing of raw agricultural products. Although many agricultural wastes contain substances of human value or benefit, it is mostly the case that the economic value of these processed substances is lower than the cost of collection, transportation, and processing of the feedstock. Therefore, wastes are generated due to the economic infeasibility of processing or reusing discarded agricultural by-products.

Agricultural wastes may be in the many forms like solids, slurries, or liquids and can have both plant and animal origins. For example, agricultural wastes encompass

• animal wastes such as manure, carcasses and bones;
• food processing wastes such as corn stalks, fruit peels cores pits pulp stems and seeds, twigs, spoiled fruits, sugarcane bagasse, and molasses;
• crop discards such as corn stalks, fruit/vegetable drops, culls, and pruning;
• toxic agricultural wastes such as pesticides, herbicides, herbicides, and antifungals.

The composition of agricultural wastes can be different from location to location and is dependent on the particulars of the point of origin like the agricultural activities carried out and the regional specialization. Interestingly, the challenges in waste management as well as the opportunities faced by a region because of the primary residues generated are also related to the regional specialization. For example, in locations specifically used for animal husbandry, vast quantities of organic matter rich in nitrogen and nutrient-rich waste materials are generated alongside repugnant odours, microbial contamination, and greenhouse gas (methane) emissions. Manure production is therefore among the most feasible waste management routes for these regions in comparison with the regions devoted to crop production where nutrients and the organic matter deplete because of the nutritional demands exerted by the growing crops on the soil (Gontard et al. 2018).

During the past several decades, significant scientific and technological advancements have resulted in a gradual increase of agricultural yield and productivity throughout the world. This, however, has also resulted in a steady increase in the quantity of waste from livestock, agricultural crop residues, and by-products of agro-industries. Although highly accurate estimates of agricultural waste production are rare, it is believed that agricultural waste contributes significantly to the global total waste production. Over a decade ago, the world was estimated to produce nearly 1000 million tons of waste from agriculture (Agamuthu 2009). Organic wastes have been documented to account for up to 80% of the total solid waste being produced in a farm (Brown and Root Environmental Consultancy Group 1997). In 2012, organic wastes accounted for more than half of the fresh waste of the harvested crops representing a potential of 90 Million Tons Oil Equivalent (MTOE) which was far higher than the energy potential of other wastes such as round wood, municipal wastes, and tertiary forest residues (Elbersen et al. 2012). This scenario is likely to worsen if proper interventions are not put in place.

In this modern age of industrialization and globalization, economic progress is heavily intertwined with non-renewable resource utilization which adversely impacts environmental balance and biodiversity, jeopardizes global food security, and depletes our planet's non-renewable energy reserves (UNEP 2011). Agricultural waste can be transformed into economically valuable products, such as fertilizers, energy, and chemicals, by using specialized conversion processes. This is of critical importance so as to promote a sustainable bioeconomy and consequently decouple non-renewable resource utilization and economic progress from human well-being and environmental sustainability.

As per Indian Ministry of New and Renewable Energy (MNRE), on average, India generates half a billion metric tons (Mt) of crop residue every year. Although a significant fraction of this crop residue is used as fodder, fuel and for other domestic and industrial purposes, there still is an unutilized surplus of 140?Mt each year and 92?Mt of that are incinerated (NPMCR 2019). More agricultural wastes are generated in India than Bangladesh, Indonesia, and Myanmar combined. In fact, the agricultural waste volume that is incinerated in India is more than the net volume of agricultural waste produced by other countries in the region (Bhuvaneshwari et al. 2019).

In this review, we aim at constructing a picture of the state of agricultural waste and its generation. Agricultural wastes, their different types, and their characteristics have also been discussed. Apart from that, the key challenges and most promising opportunities in developing smart, sustainable, and efficient agricultural waste conversion mechanisms and residue management strategies are described.

1.2 Sources of Agricultural Waste Generation

Waste produced from agriculture can be broadly divided into two groups based on their composition namely:

• Lignocellulosic waste
• Proteinaceous waste

1.2.1 Lignocellulosic Waste

Lignocellulosic biomass is about 50% of the world's total biomass. Its annual production is around 10-50 billion tons (Mood et al. 2013; Kumar et al. 2018). It is the main constituent of the cell walls in plants and contains cellulose (40-60%), hemicellulose (20-40%), and lignin (10-25%) (Dionisi et al. 2015). The plant residues produced in agricultural field also come under this and are known as agricultural residues.

They can be grouped into two categories: field residues and process residues. Agricultural wastes which remain in the field after the process of crop harvesting has been concluded are referred to as field residues. Field residues function as feedstock for a number of processes designed to transform agricultural waste into economically valuable products such as animal feed, organic manure, raw materials for different manufacturing industries, and even various biochemicals of clinical and industrial significance. However, these processes also produce by-products which are known as process residues. Field residues and process residues can include a variety of waste products like molasses, husks, bagasse, seeds and seed pods, leaves, stems, straws, stalks, shells, and pulp. India being an agrarian nation produces nearly 686 million tons of lignocellulosic waste and 234 million tons of that are agricultural residues (Kapoor et al. 2020). But because of the current inefficiencies in plaguing agricultural waste management processes, a significant portion of the agricultural residues produced in India is underutilized. This also presents an opportunity for future initiatives aimed at processing agricultural waste and turning waste into wealth.

1.2.2 Proteinaceous Waste

Proteins are known part of our daily nutrition and biochemical function. They also are promising sources of raw material for polymers. The protein obtained from agricultural waste has a huge potential for various utilities. The waste produced from aquaculture and livestock are abundant in protein and can be utilized to derive novel ways to produce value-added products (Barone...