The metabolic engineering of microorganisms with elevated organic matter explored for the development of biofuels forms that become the basis for developing fourth-generation biofuels [6]. The third and fourth generations of biofuel production include organic matter technology into biofuels (Table 3.3). Huang et al. [48] evaluated that genetically engineered OsSEX4-knockdown transgenic rice plants with starch accumulation higher than the wildtype forms as a potential source to produce bioethanol. OsSEX4 plays a vital role in the degradation of transitory starch; thus, it increases the plant’s starch content by knockdown. Genetically modified biomass produces bioethanol 50% higher than the wild-type straw in a vertical mass-flow type bioreactor (two-tank type bioreactor) by simultaneous saccharification and fermentation (SSF) [48, 52].
3.3.1.5 Waste Biomass Resources
Biomass waste constitutes both organic and inorganic compounds. It is an abundant bioresource available for gaseous or liquid-based bioenergy generation (hydrogen, methane, and ethanol) and biochemicals (volatile fatty acids, lactic, acetic, propionic, and butyric acid) [53].
3.3.1.5.1 Agricultural and Forest Residues
Biomass residues are produced in excess from the processing of crops. One of the significant fields of emphasis in various countries worldwide is the extraction of electricity from these residues [54]. The biomass residues that have appeared since primary crop harvesting are stalks, stems, leaves, husks, cobs. Stalks, straw, stems and leaves, husks, cobs, and others are the biomass residues that have emerged after primary crop harvesting [54]. They estimated that energy extracted from all these residues of agricultural biomass was 298,955 TJ and 65,491 TJ. Agricultural biomass and animal manure are the cheapest and most possible bioenergy sources (energy crops-wheat, rice, barley, corn, potatoes, apples, grapes, alfalfa, and other agricultural residues) in Iran [16]. It projected that biogas production of 11,523.84 and 16,026 million m3/year was from livestock and slaughter. Forest residues possess a comparatively large concentration of lignin – precursors of bio-phenols and bio-polyols [7].
3.3.1.5.2 Industrial Waste
The tannery industry is a leather processing industry, and mostly it manufactures leather from the skin and hides of sheep, pigs, and cattle. Solid waste, nearly around 850Kg, was disposed of per ton of raw materials (Table 3.4).
The solid wastes of tannery industry waste are rich in collagen and 3 to 5% chromium oxide [23]. This content presence prevents the debris from fast degradation, but the high rate of degradation cause an obnoxious, intolerable smell during summer. Then, chromium accumulation into the soil contaminates the groundwater systems and affects the lives of aquatic animals and humans. Therefore tannery waste shows a high impact on the environment and leads to the world’s ecological problem.
The primary source of industrial biomass comes from fish processing industries, including fish heads, viscera, vertebral column, fin, scales, and meat scraps as the fish processing industrial waste. The fish industry produces around 98g of fish waste per Kg of fish and fish crude oil waste of about 35g/100g of fish waste [24] (Table 3.4). However, these wastes are rich in micronutrients that cause a heavy impact on the environment if left untreated, mainly due to the high organic load.
Table 3.4 List of industrial waste biomass, the process of conversion, and biofuel products.
| Sources of industrial waste | Biomass | Process of conversion | Biofuel products | Reactor | Reference |
| Tannery industry | A mixture of pelletized leather tannery waste and hardwood pellets | Combustion | Ash | Laboratory-scale combustion reactor (Perforated flat grate of combustion test reactor) | [55] |
| Hides, collagen-based solid wastes - shavings and offcuts | Pre-treatment by extrusion and enzymatic degradation | Biogas along with diauxie | Bioreactor | [23] | |
| Fish industry | Fish waste (FW) and Fish crude oil waste (FCOW) extracted from common carp (Cyprinus carpio) viscera | Anaerobic digestion (AD) using VDI 4630 as a reference | Biogas (methane) | Anaerobic mono-digestion system - 2L glass reactor | [24] |
| Fish carcass and viscera | Oil extraction | Biofuel | - | [56] | |
| Combustible industry | Coal-water slurry based on coal processing waste (combustible industry waste) | Gasification by direct light induction through solar radiation (allothermal process) | Syngas | Nanosecond pulse and continuous-wave laser | [57] |
| Agroindustry | Cattle slaughterhouse waste - Slaughtering waste streams like paunch (PA), soft offal (SO) (intestinal residues, fat and meat trimmings, and some blood), dissolved air flotation sludge (DAF) | Anaerobic digestion (AD) at the mesophilic condition | Biogas | - | [25] |
The combustible industry is a fossil fuel industry like the coal processing industry. The waste arising from these industries is rich in hydrocarbon. On earth, the resources from fossils are costly and high in demand, and coal conversion technologies show adverse effects on contaminants’ atmosphere [58]. The animal-based agroindustrial sector releases a high amount of organic waste into the environment. This organic waste mainly consists of animal by-products like blood, paunch, fat and protein, bones of head and limb. It can spread human diseases like Creutzfeld-Jacob and bovine spongiform encephalopathy [25]. Considering these issues, researchers focused on converting industrial waste residues into energy resources (Table 3.4).
3.3.1.5.3 Municipal Solid Waste
Municipal solid waste possesses paper and household wastes, non-degradable plastic waste, and non-flammable materials such as glass and aluminum from various residences [59], [60]. According to several variables, the MSW constitution varies according to household waste, seasonality, housing standards, and the prevalence of measures to reduce waste [60]. Municipal solid waste leads to a significant pollution concern worldwide [61]. All are regulated by dumping rubbish at municipal landfills, recycling to produce valuable products, and
