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A Glance on Biorefinery of Chemical Substitutes from Agriculture and Industrial By-products

Suraini Abd-Aziz1, Misri Gozan2, Mohamad F. Ibrahim1, Lai-Yee Phang1 and Mohd A. Jenol1

1Universiti Putra Malaysia, Faculty of Biotechnology and Biomolecular Sciences, Department of Bioprocess Technology, Serdang, 43400, Selangor, Malaysia

2Universitas Indonesia, Kampus UI, Faculty of Engineering, Bioprocess Engineering Program, Department of Chemical Engineering, Depok, 16424, Indonesia

1.1 Introduction

The agricultural sector is among the important biological sectors that contributed to the production of biomass. This is vital to the bioeconomy development as the biomass produced is used as feedstock for various processes of value-added products. Koul et al. [1] characterized and listed the various sources of agricultural waste as shown in Figure 1.1:

Figure 1.1 Various sources of agricultural waste.

Source: Adapted from Koul et al. [1].

The emerging field on the utilization of agricultural wastes and industrial by-products is the alternative way to find potential feedstocks for chemical substitutes. Chemical substitution focuses on finding new and less hazardous solutions for a particular process or product through advanced biorefinery approach. Due to the exponential rise in the demand for worldwide energy, the depletion of existing fossil fuel reserves is deemed as the vital issue, thus increasing the global interest in creating a new energy pathway via the bioprocessing of agricultural wastes as well as agro-industrial biomass [2]. Agricultural waste is defined as unwanted waste as a result of agricultural activities. Industrial biomass is known to be a solid inorganic residue, which may come from various sources, including mining and metal industry, chemical industry or building industry, energy production, and forest industry [3]. These biomass are potential feedstocks with abundant organic and inorganic nutrient composition.

Every year agricultural-based industries contribute a huge amount of residues, which may result in various environmental problems due to improper waste management. This situation will further have a negative impact on animal and human health. Unfortunately, the disposal of untreated agro-industrial wastes has been reported [4] to create other concerning problems associated with climate change. The common waste management procedures applied by the related agro-industry sectors, including burning, open dumping, and improper landfilling, should be improved with the availability and advancement of current technology.

The by-product from an industrial, commercial, mining, or agricultural operation is known as an "industrial by-product" if it is not a primary product and was not created independently throughout the process. The determination of the inorganic industrial by-product's composition and generic properties is specified by factors such as type of industry and the process. In depth, the environmental and technical properties of by-products are influenced by the equipment, process condition, and the feedstock. This further implies the suitability of the by-product for recycling material. As an example, reclaimed asphalt, waste concrete, and slag are recyclable materials, which have been used all over the world. However, the recycling rates of certain by-products vary among nations, and it can be challenging to locate precise data on the rates. The latter issue is likely caused by inadequate documentation of the amounts and end locations of by-products as well as differences in how trash is classified and how it is managed (e.g. whether filling mines is considered recycling) [5].

The evolution of the biorefinery concept was started during the late 1990s. Biorefinery covers spectrum of processes, as it defines as an overall concept of biomass processing plant conversion and/or extraction into various valuable products [6]. National Renewable Energy Laboratory (NREL) describes a biorefinery concept as the integration of biomass conversion processes as well as equipment to refine value-added products, including chemicals, fuels, and power. The International Energy Agency (IEA) Bioenergy Task 42 has defined a biorefinery as "the sustainable processing of biomass into a spectrum of marketable products (food, feed, materials, chemicals) and energy (fuels, power, heat)." Thus, a biorefinery can be a process, a facility, a plant, or a cluster of facilities for the biomass conversion [7].

An inventive and effective method of using biomass resources for the synergistic co-production of power, heat, and biofuels alongside ingredients for food and feed, pharmaceuticals, chemicals, materials, minerals, and short-cycle CO2 is biorefining. This process involves processing biomass sustainably to create a variety of marketable biobased products and bioenergy/biofuels. Biorefining is one of the vital technologies of the circular economy, closing loops of raw biomass materials, minerals, water, and carbon. Biorefining is the optimal strategy for large-scale sustainable utilization of biomass in the bioeconomy [8].

1.2 Analysis of Feedstocks for Composition and Potential for Chemical Substitutes

Agricultural wastes are vast, which cover the by-products generated from various agricultural products, including crops, dairy products, fruits, meat, poultry, and vegetables. They are the non-product outputs of the production and processing of agricultural products that may contain material that can benefit humans but whose economic value is less than the cost of collection, transportation, and processing for beneficial use. The physicochemical composition of the wastes varies based on the type of agricultural activities as well as the system, which further results in a different form of wastes, such as solid, liquid, and slurry [1].

Agricultural-based residues can be classified into two distinct types based on the point of waste generated, such as field waste and process waste. The field wastes are mainly generated from harvesting activity, which includes leaves, stems, seedpods, and stalks. Meanwhile, the process wastes are generally the by-products produced during processing activity of the harvested products into alternate valuable products [8].

Nowadays, the raising public concern toward major categories of agricultural waste has been deemed to be the main issue. Concurrently, these wastes also have been recognized to threaten the sustainability of agricultural regimes. In fact, several agricultural activities that are affected include livestock wastes (dung, urine, residual milk, wash water, and waste feed), slaughterhouse wastes (blood, bones, flesh, hair, hides, etc.), crop residues (leaf litter, seed pods, stalks, stems, straws, husks, and weeds), poultry wastes (bedding material, droppings, spilled feed, and feathers), agro-industrial wastes (bagasse, molasses, peels [cassava, orange, and potato], pulps [apple, orange, guava, mango, papaya, pineapple, pomegranate, tomato, etc.], oil-seed cakes (coconut, groundnut, palm kernel cake, soybean, mustard, etc.), and aquaculture wastes (fecal waste, uneaten feed) [9, 10].

Through advancement in bioprocessing technology, agricultural wastes, which is also known as biomass, have been determined to be the promising feedstock and alternative renewable resource that helps to reduce existing high dependence on fossil fuel-based sector. This is deemed as impactful approach as it can help in conserving the natural resources as well as alleviate the environmental impact. The major component of agricultural biomass is lignocellulosic biomass that has shown a promising platform in various bioprocesses, including biofuels, platform chemicals, and bioproducts [11]. Lignocellulosic biomass is made up of cellulose, hemicellulose, and lignin, as cellulose is identified as the most abundant biopolymer. Cellulose is accounted to make up 30-50% of the total biomass, which is determined to be a vital substrate in microbial transformation. Various efforts have been explored to provide the strategic management and valorization of lignocellulosic biomass for the production of value-added products, which further resulted in elevating the value chain of the biomass.

1.2.1 Different Types of Agricultural Wastes and Associated Risks

The agricultural sector is urge to discover well sustainable waste management due to its vital impact on the biodiversity, human societies and world economy [12]. Due to the rapidly increasing demand, sustainable resource management is mandatory. Agricultural waste production is not only limited to farming activities, but it also covers other activities associated with food chain and farming. In each and every stage, the waste generated poses a significant risk to the environment and humans, generally, due to poor management. Oluseun Adejumo and Adebiyi [13] explained that there are seven associated agricultural wastes, which are animal wastes, food and meat processing wastes, crop production wastes, on-farm medical wastes, horticultural production wastes, industrial agricultural wastes, and chemical wastes.

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