Bio-Based Materials and Waste for Energy Generation and Resource Management: Volume 5 of Advanced Zero Waste Tools: Present and Emerging Waste Management Practices

By Chaudhery Mustansar Hussain

Bio-Based Materials and Wastes for Energy Generation and Resource Management is the fifth and final volume in the series, Advanced Zero Waste Tools: Present and Emerging Waste Management Practices. It addresses processes and practices for utilizing bio-based materials and wastes to support efforts to promote a more sustainable society and provide readers with a better understanding of the major mechanisms required to achieve zero waste in different fields. This book covers numerous mechanisms supported by scientific evidence and case studies, as well as in-depth flowcharts and process diagrams to allow for readers to adopt these processes.

Summarizing present and emerging zero waste tools on the scale of both experimental and theoretical models, Advanced Zero Waste Tools is the first step toward understanding the state-of-the-art practices in making the zero waste goal a reality. In addition to environmental and engineering principles, it also covers economic, toxicologic, and regulatory issues, making it an important resource for researchers, engineers, and policymakers working toward environmental sustainability.

• Uses fundamental, interdisciplinary, and state-of-the-art coverage of zero waste research to provide an integrated approach to tools, methodology, and indicators for bio-based resource management
• Presents strategies for treatment of biological waste to contribute to sustainable management and development
• Includes numerous case studies to illustrate the management of biowaste for generation of economy and energy

• Language: English
• Publisher: Elsevier Science
• Release date: May 8, 2023
• ISBN: 9780323913270

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Chapter 1: Valorization of water hyacinth: A sustainable route for bioenergy generation and other value-added products

Anamika Kushwahaa; Nidhi Hansb; Neha Upadhyayc; Shivani Goswamid; Preeti Pale; Asmaa Benettayebf; Yoseok Choia; Lalit Goswamia; Beom Soo Kima    a Department of Chemical Engineering, Chungbuk National University, Cheongju, Chungbuk, Republic of Korea

b Centre for Rural Development and Technology, Indian Institute of Technology Delhi, New Delhi, India

c Department of Biotechnology, Motilal Nehru National Institute of Technology Allahabad, Prayagraj, Uttar Pradesh, India

d Department of Science, Upper Primary School Mundera, Unnao, Uttar Pradesh, India

e Accelerated Cleaning Systems India Private Limited, Mumbai, Maharashtra, India

f Laboratoire de Génie Chimique et de catalyse hétérogène, département de Génie Chimique, Université de Sciences et de la Technologie-Mohamed Boudiaf, Oran, Algeria

Abstract

Water hyacinth (WH) is considered a harmful weed worldwide as it breeds rapidly and reduces nutrients and oxygen from water bodies, severely disturbing the growth of flora and fauna. Growing oil prices and exhaustion of current fossil fuel assets, together with the incessant increase in greenhouse gas release, have raised the necessity to discover and develop novel renewable bioenergy resources that do not need cultivable land and freshwater. Henceforth, transforming this weed into value-added products and fuels aid in self-sustainability, particularly for emerging nations. Thus, the inexhaustible biomass of invasive WH has gained much consideration in recent years in exploiting them as a potential resource for bioenergy generation. WHs have remarkably high growth rates and contain a high amount of cellulose and hemicellulose with very little lignin, making them effective for next-generation bioenergy crops. The current chapter deliberates the numerous value-added products and biofuels produced from WH, the current research and developmental processes on the WH bioconversion for the biofuel production and value-added products, and its potentials and challenges in commercialization. Furthermore, a comprehensive discussion was conducted on techno-economic and ecological analysis by a mathematical model, techno-economic analysis, life cycle assessment, and circular economy toward sustainable development.

Keywords

Value-added products; Biorefinery; Biowaste; Environmental sustainability; Circular bioeconomy; Waste-to-energy

1: Introduction

Growing apprehensions over global warming due to the exploitation of fossil fuels and the enervation of nonrenewable assets have driven international attention to finding alternate, sustainable, renewable, economic, and green energy sources (Kushwaha, Bajgai, et al., 2022; Lata et al., 2021). Lately, biomass-driven energy (i.e., bioenergy) has been perceived as the promising substitute for ecologically destructive fossil fuels (Goswami, Kushwaha, et al., 2022; Hussain et al., 2022a, 2022b). Biofuel is a supreme substitute for outmoded fossil fuels as they can be generated in massive volume from plentiful renewable biomass materials with low greenhouse gas (GHG) release. Presently, there is an increasing momentum for uncovering potential biomass for biofuel generation by depicting the biomass feedstock's qualitative and quantitative characteristics.

In this respect, the study has now switched on the exploitation of nonedible feedstock such as algae biomass or lignocellulosic biomass instead of cellulose-based food crops (first-generation) owing to serious ecological and humanoid sustenance safety jeopardies linked with the first-generation bioenergy (Deshavath et al., 2022). The lignocellulosic-derived biomass is comparatively cost-effective to other crops as it comprises agricultural residues, woody crops, and municipal and industrial wastes (Mallick et al., 2022). But, lignocellulosic-based biofuel has few constraints, such as its multifaceted structure, making it recalcitrant toward chemical and biochemical reactions. It needs immense pretreatment to decrease the crystallinity of cellulose, making it vulnerable to enzymatic hydrolysis. Thus, discovering new, inexpensive, and ecological-friendly, carbohydrate-rich biomass is of prodigious importance.

To overcome cropland and food safety problems, lately, several studies have been carried out on using aquatic weeds (AW) as alternate biomass for the generation of biofuel. AW contains a high amount of lipid, carbohydrate, and protein content, and exploiting them for the generation of biofuel would offer an advantage in monitoring their propagation in water physiques while concurrently overcoming the existing energy demand (S. Goswami et al., 2021). Their capability to attain increased biomass yield by impounding nutrients in wastewater makes them suitable for a unified arrangement for wastewater treatment, environmental sustainability, and energy generation (Bajgai et al., 2022; Gautam et al., 2021, 2022; Sathe et al., 2021). Globally, the furthermost invasive AW is water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes), Salvinia (Salvinia molesta), and Myriophyllum spicatum. They are dispersed worldwide and can be effortlessly present in varied temperature zones (Sindhu et al., 2017). The primary AW found in India is E. crassipes, P. stratiotes, S. molesta, and Alternanthera philoxeroides.

With the growing irrigation amenities in India to increase the production of food, these wearisome weeds flourish fast in the water and severely disturb farming by hindering water current in irrigation canals. Currently, in India, ∼1 million ha of domestic canals are jeopardized by the interference of lethal AW. In India, ∼15.3 m ha of the area is covered by wetlands, of which ∼1.32 m ha wetland area is covered by AW in the postmonsoon period and ∼2.06 m ha in premonsoon time (Seenivasan, 2013). Monitoring AW is a complex and costly procedure. In India, the overall yearly charge for manually controlling AW is ∼$490/ha/year, and that of power-driven is ∼$910/ha/year (Jayan & Sathyanathan, 2012). Numerous control procedures such as machine-driven, chemical, and biological are investigated to eliminate them. Still, these efforts are not effective due to their high reproduction frequency; furthermore, all the eliminated AW are discarded in landfills, which is a significant reason for GHG release. Henceforth, the employment of AW as bioenergy feedstock appears to be a more feasible and inexpensive approach.

Water hyacinth (WH) is a free-floating, perennial aquatic plant. Initially, it was discovered in the Amazon River basin and later has dispersed globally. It has displayed enormously extreme growth rates, and WH covers the channels, which has generated numerous difficulties, such as ecosystem destruction, irrigation complications, and a place for mosquito breeding (Sindhu et al., 2017). It is known as the most prolific plant on Earth and now becoming a severe menace to biodiversity. WH adverse effects initiated numerous research and developmental actions for controlling this aquatic weed. Numerous physical, chemical, and biological approaches have been utilized for controlling and eliminating WH. Still, none of these approaches showed a perpetual result for weed control. WH comprises cellulose (20%), hemicelluloses (48%), and lignin (3.5%). The presence of a high content of cellulose and hemicellulose in WH can be a prospect for several valuable products and bioenergy. Since the yield is significantly high, it could be exploited as a biomass for biofuel generation. It has numerous benefits as it can be cultivated in aquatic regions without challenging with cultivable land to produce crops and vegetables. Various research studies have been carried to convert WH to biofuel (Okewale et al., 2016).

The release of industrial effluents into the milieu causes various environmental and health problems (Begum et al., 2022; Devi et al., 2022; Ojaswini et al., 2022). Water plants are well-acknowledged for water cleansing and removing pollutants and nutrients. In contrast to other water plants, WH is the utmost appropriate for phytoremediation (Borah et al., 2021; Kushwaha, Goswami, Lee, et al., 2021). WH potential for elimination of contaminants is a well-known ecological fortification method. WH biosorption capability has been investigated to eliminate numerous pigments and heavy metals from several industrial discharges (Devi et al., 2021; Gupt et al., 2021; Yadav, Dwivedi, et al., 2021; Yadav, Goswami, et al., 2021). WH cultivation in industrial effluents results in the reduction of total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD). It is an economical and eco-friendly approach, and the mechanism comprises biosorption by extracellular accumulation/precipitation, cell surface sorption/precipitation, and intracellular accretion (Kushwaha, Goswami, Hans, et al., 2022).

The present review discusses the current bioenergy potency of WHs due to their copious accessibility, high yield, and exceptional composition. Furthermore, the study discusses the various approaches for bioenergy production and other value-added production from WH for energy and environmental application, emphasizing the importance of circular economy (CE). Furthermore, a comprehensive techno-economic and ecological analysis is led by a mathematical model, techno-economic analysis (TEA), life cycle assessment (LCA), and CE application. The CE approach is proposed to improve energy production. Therefore, the present chapter delivers a viable strategy to converting and managing aquatic biowaste and resources.

2: Potential of water hyacinth as a biofuel feedstock

WH are invasive florae that cause severe fiscal and environmental mutilation once familiarized in marine ecology. Their fast growth frequency, numerous means of proliferation, and worldwide dispersal can have severe financial and ecological consequences. They severely disturb all water channels utilized for irrigation, hydropower production, and frivolous activities. They also impend water biodiversity by substituting natural plants and animals, thus instigating permanent vicissitudes to environments. Their extreme development reduces the oxygen content in water, generating anoxic environments promising for methanogenesis, causing global warming.

Eutrophication is the leading reason for their incursive growth, i.e., the steady surge in nutrient concentrations in an aquatic environment. Natural eutrophication, a slow progression, encompasses the nutrients and sediment accretion resulting from rocks and soil weathering (Bhan et al., 2022). But, human actions have significantly amplified the eutrophication frequency by enhancing the nutrient flow in an aquatic system from farmed and municipal runoff, sewage releases, and industrial effluents with dreadful influence on piscaries, frivolous, and drinking water bodies (Mohan et al., 2010).

These WH forms an impenetrable layer on the water surface, limiting the diffusion of sunlight, thereby decreasing the DO level, causing the destruction of the native aquatic flora. Furthermore, the death of these WH leads to the growth of microbes, which further reduces the DO, resulting in an anoxic milieu that is insufficient in supporting the growth of other organisms. The formation of anerobic environments in aquatic ecology also causes an increase in methane gas release, resulting in 21 times more global warming than carbon dioxide.

2.1: WH as an efficient source of bioenergy

2.1.1: Rapid growth rate

WH are naturally growing flora with a hasty reproduction frequency, and they deliver an enormous source of inexpensive bioenergy raw material. The main reason to employ these harmful weeds and monitor their redundant growth is that they display suggestively higher yields than terrestrial biomass for bioenergy (Miranda et al., 2016). For example, the yearly production of WH is 100 dry tons/ha in lakes naturally, whereas the 25 dry tons/ha was obtained from switchgrass in the U.S (Wullschleger et al., 2010).

2.1.2: Biochemical configuration

They contain a considerable amount of cellulose, hemicellulose, and starch with less content of lignin. The fermentable carbohydrates can be hydrolyzed easily, making WH an economical and efficient biofuel feedstock in contrast to other lignocellulosic sources. The presence of a high amount of fat and proteins in WH than in grass, lignocellulosic feedstock, and wood that can be efficiently and effortlessly digested to gaseous fuels such as biomethane and biohydrogen.

2.1.3: More efficient feedstock

WH can curb the restraints of another lignocellulosic biomass. Contrasting to crops utilized for energy production, WH does not need fertile land, other agricultural inputs, or freshwater.

2.1.4: Adaptableness to extreme environments

WH can grow well in an extreme environment, which can be unfavorable for plant growth. They can also survive in the seasonal restraints owing to their capability to produce in varied temperature regions. Therefore, biofuels can be attained throughout the year (Sindhu et al., 2017).

2.1.5: Bioremediation capability

WH is used to treat wastewater on-site since they deliver dual advantage, i.e., for wastewater treatment and biofuel generation (Rezania et al., 2015). WH can clean up severely polluted water (Smolyakov, 2012). The waste Stabilization Pond (WSP) has gained attention for treating swine effluents. Both laboratory and pilot investigations displayed that WH can decrease various contaminants existing in the swine wastewater (Valero et al., 2009). Several investigators have studied E. crassipes, Salvinia rotundifolia, and Lemna minor and observed that E. crassipes have maximum nitrogen and phosphorus removal capacity (Mergaert et al., 1992; Seghezzo et al., 1998).

2.1.6: Cost-effective

WH are reproduced via vegetation or spore proliferation, thus removing the kernel cost. Also, they grow very fast in wastewater, therefore reducing the cost of biofuel generation. They can be harvested easily via machine-driven reapers or by skimming (Kaur et al., 2018).

2.1.7: Effective application

Exploiting WH as a bioenergy raw material would offer a further cost-effective advantage of RE production in addition to decreasing the environmental and financial harm. Their implementation for bioenergy production offers the dual advantage of nutrient retrieval from wastewater and transforming nutrients into organic fertilizers via anerobic fermentation (Gupta et al., 2020; Kaur et al., 2018). Thus, their use is favored over their control as WH is an energy-intensive method where nonrenewable resources are used for the production of herbicide, paraphernalia manufacturing, and machinery process. It displays negative effects on the well-being of the aquatic life as they do not display the complete WH elimination and lead to accretion of plant residues. This causes nutrients to release from the plant residues, a significant reason for algal blooms that cause fish death. Moreover, dumping harvested WH in landfills only deteriorates the condition by instigating methane gas emissions (Kaur et al., 2018).

2.1.8: Value-added co-products

Addition to bioenergy generation, WH biomass has other energy-associated alternate uses. WH contains a high amount of N, P, and K; thus, its final product after anerobic digestion (AD) can be utilized as an organic fertilizer (Kaur et al., 2018).

3: Methods for bioenergy generation from WH

WH is one of the promising bioenergy feedstocks. They contain high cellulose, starch, and lipids, which can easily be transformed into various types of energy, such as bioethanol, biodiesel, biohydrogen, and biomethane. Bioprocessing of aquatic biomass for converting it into bioenergy requires appropriate technologies. Some of the significant technologies are implemented to convert WHs into bioenergy which are categorized as follows: biochemical conversion, AD, dark fermentation, and ethanol fermentation. Fig. 1 gives an overview of appropriate processing technologies for generating bioenergy and other value-added products.

Fig. 1

Fig. 1 WH biomass conversion processes into bioenergy and other value-added products. Reprinted with permission from Li, F., He, X., Srishti, A., Song, S., Tan, H. T. W., Sweeney, D. J., Ghosh, S., & Wang, C. H. (2021). Water hyacinth for energy and environmental applications: A review. Bioresource Technology, 124809.

3.1: Biochemical conversion

AD, alcoholic fermentation, and dark fermentation are three primary technologies used to convert WH biomass into liquid and gaseous fuels. These techniques are broadly implemented to produce different biofuels, including biohydrogen, bioethanol, and biomethane.

3.1.1: Anerobic digestion

AD is a technology in which microorganisms break down organic biomass without oxygen to generate biogas. This process involves four steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Goswami, Kushwaha, Goswami, Gupta, et al., 2022; Patra et al., 2022). First, complex molecules in biomass such as carbohydrates, lipids, or proteins break down into simple monomers through hydrolysis. These monomers are converted into volatile fatty acids such as acetic acid, propionic acid, butyric acid, alcohol, CO2, H2, or ammonia by the acidogenesis process. Then, in the acetogenesis process, volatile fatty acids are further converted into acetic acid, CO2, and H2 by acetogenic bacteria. In the final step, methanogenic bacteria convert acetic acid into biogas, majorly consisting of CH4 and CO2. This method is widely used to produce biogas as it is economically feasible compared to other biomass conversion techniques due to its fewer capital expenditures (Rao et al., 2010). Therefore, WHs rich in carbohydrate content and optimum C/N ratio are effectively used to produce biogas.

3.1.2: Acidogenic fermentation

It is a process in which organic molecules from biomass are transformed to volatile fatty acids (VFAs) together with hydrogen with the help of hydrogen-producing culture (Kushwaha, Mishra, et al., 2022). These volatile fatty acids are further converted into hydrogen by the photo-fermentation process. The most commonly used microorganisms for biohydrogen production include Clostridium and Enterobacter. This method for biohydrogen production is considered the simplest and economically feasible method. Also, it yields a high hydrogen rate at mild operation conditions and requires low energy compared with the photo-fermentation process.

3.1.3: Ethanol fermentation

Aquatic biomasses contain a large number of sugars in soluble and insoluble forms. These sugars are hydrolyzed into simple monomeric sugars, further fermented to produce bioethanol. The most commonly used method for producing bioethanol from biomass is enzymatic hydrolysis or saccharification. After hydrolysis, fermentation is mostly carried out by yeast (mainly Saccharomyces cerevisiae) or bacteria. Nowadays, WHs are preferred for production of bioethanol over lignocellulosic crops because aquatic biomass contains very low lignin; hence, it requires mild pretreatment processing in ethanol production. Thereby, WH is considered cost-effective to produce cellulosic ethanol. Magdum et al. (2012) investigated WH for ethanol generation by Pichia stipitis NCIM 3497 and observed 19.2 g/L yield. The hydrolysates of Pichia stipitis (10.44 g/L), Candida shehatae (8.24 g/L), and S. cerevisiae (6.76 g/L) were used for ethanol production (Das et al., 2015). WH dry biomass (9.62 metric tons) produced 2020.2 kg of sugar with an experimental yield of 1131 ethanol/day.

3.2: Thermochemical conversion

During the thermochemical composition process, biomass is decomposed thermally and is converted into solid, liquid, or gaseous fuel products. This method is classified into three subgroups: pyrolysis, liquefaction, and supercritical water gasification.

3.2.1: Pyrolysis

It is a thermochemical conversion technique in feedstock exposed to elevated temperatures between 300°C and 1000°C in oxygen-free and pressurized environmental conditions. The pyrolysis produces a liquid known as bio-oil or tar and solid products called biochar. Synthetic fuel, i.e., bio-oil can be upgraded to fuel gas range and used as a substitute for petroleum. While biochar has lower ash content, making it a more efficient fuel than fossil fuel, it can also be used for various applications like combustion, carbon sequestration, soil amendment, and adsorption of pollutants from water (A. Singh et al., 2022). Various studies have reported that WH yields high bio-oil and can be possibly transformed into renewable fuels, which include green gasoline and diesel using different technologies (Sarkar et al., 2015). Masto et al. (2013) found that pyrolysis at 300°C for 30 min yielded the desired biochar from E. crassipes. Similarly, pyrolysis at 900°C resulted in the production of cost-effective, eco-friendly WH biochar (Allam et al., 2020).

3.2.2: Hydrothermal liquefaction (HTL)

It is a biothermal conversion process in which wet feedstock can be directly converted into bio-oil at low-to-moderate temperature and high-pressure conditions. The bio-oil generated using this process comprises much higher energy density than pyrolysis oil, approximately two times higher. Therefore, bio-oil can be used for heavy engines or can be enhanced for conveyance fuels such as gasoline, diesel, or jet fuels (Goswami et al., 2019). The HTL process is also used to convert wet biomass into valuable products, including biofuels and biochemicals. This method is an energy-efficient process in contrast to other conversion processes such as pyrolysis or gasification; it avoids the step of dewatering or drying of feedstock, thereby making it more economically feasible by reducing energy cost (Duan & Savage, 2011). Therefore, WHs after harvesting are used directly for the HTL process to produce bio-oil. It has been reported that different species of WH yield 20%–30% of bio-oil using the HTL process with a high heating value in the range of 32–36 MJ kg−1 (R. Singh et al., 2015).

3.2.3: Supercritical water gasification

It is a modern technology used to convert wet feedstock with moisture content higher than 90% into products at excessively higher temperatures and pressure (greater than the critical conditions). This technique is widely used to produce a higher percentage of biohydrogen from wet biomass. It is the most energy-efficient conversion technology as it is used to enhance the hydrogen yield at suitable process conditions, which is usually higher than that of other conventional processes such as gasification, pyrolysis, AD, or liquefaction process. Therefore, WH with 70%–80% of moisture content are perfectly suitable for supercritical water gasification for producing bioenergy products from them (Matsumura, 2002).

3.3: Chemical reaction

Some of the WHs constitute high lipid content and are utilized to produce biodiesel. Crude oil or lipids extracted using organic nonpolar solvents undergo fatty acid methyl ester (FAME) synthesis via the transesterification process. After the formation of FAME, fatty acids are analyzed using gas chromatography. Analysis of FAME of lipids from WHs confirmed the presence of many fatty acids with the highest composition of palmitic acid (C16:0), linoleic acid (C18:2), and γ-linolenic acid (C18:3). These fatty acids with good biodiesel properties make WHs suitable for biodiesel production (Miranda et al., 2016).

3.4: WH-microbial electrolysis cell

It is a hybrid technology in which electrochemical reactions happen in the presence of microorganisms, which facilitates the production of biohydrogen or biogas. The electric voltage used in this process is much lower than the voltage required for the electrolysis of water (Pasupuleti et al., 2015). WH are utilized for the bio-catalyzed microbial electrolysis cell (MEC) process for biohydrogen production, which can be obtained in three ways. The plant exudates rich in carbohydrates and carbon-containing primary and secondary metabolites are released into the phytosphere (Bais et al., 2006). Therefore, these exudates can be used by the plant-MEC process for converting them into hydrogen. Second, aquatic plants with high carbohydrate content can undergo some mild pretreatment by electrogenic microbes via the MEC process, which facilitates their conversion into biohydrogen (H. Liu et al., 2010). Finally, the MEC process can be co-integrated with the traditional dark fermentation process to produce hydrogen. This can upsurge the overall energy efficacy of the technology. As we know, conventional dark fermentation limits hydrogen production to approximately 15% due to thermodynamic restraints. It also forms end products such as acetates and VFAs like propionic acid and butyric acid, which can be utilized by bacteria to produce hydrogen. Therefore, the dark fermentation process inhibits biohydrogen production by lowering the pH of the entire system. But according to recent reports, the MEC process can be employed to covert the un-processable end products of the dark fermentation process into biohydrogen by implementing a small voltage of electric energy (L. Goswami et al., 2020). Henceforth, the MEC system for the production of biohydrogen is much more energy-efficient and yields a higher amount of hydrogen from biomass than any other type of process (Borole & Mielenz, 2011).

It is known that 1 mol of glucose can produce a maximum stoichiometric yield of 12 mol hydrogen. Although, by different fermentative processes, a maximum of only 4 mol of hydrogen yield can be attained. Therefore, instead of fermentation, the MEC process is employed to enhance the biohydrogen production from the waste effluent of WH produced after anerobic fermentation. This makes MEC a sustainable process that increases the viability and feasibility of the biofuel industry, especially for amalgamated biorefineries and bioenergy complexes (Lu & Ren, 2016). Also, waste streams generated during the fermentation process contain a high amount of organics converted into biofuel using the MEC process. Therefore, integrating the biorefinery process with MEC results in an augmented recovery of energy from feedstock. This process led to the treatment of waste produced in fermentation with improved efficiency of energy (Gil-Carrera et al., 2013).

3.5: WH-based CWs as bioenergy pools

3.5.1: WH-CW for biofuel generation

WH-based CWs are a man-made system that imitate the characteristics of natural wetlands. These constructed wetlands treat various types of wastewater streams naturally by exploiting plants and microorganisms to uptake and break down nutrients present in wastewater (Mohan et al., 2010). This system helps eradicate pollutants from wastewater streams by utilizing physicochemical and biological techniques (D. Liu et al., 2009). Therefore, these CWs became a substitute to the wastewater treatment plant, providing numerous benefits, such as water quality, reusability, and security of water and reduction of carbon dioxide gases. Currently, wastewater from different sources such as industrial effluent, agriculture runoff, landfill leachate, or sewage discharge is being treated by wetlands constructed and operated in large numbers worldwide. Rai et al. have developed a subsurface flow constructed wetland at Ganga River, India. They carried out an on-site study to treat sewage water by adding AWs such as Phragmites australis, Polygonum hydropiper, Alternanthera sessilis, and Pistia stratiotes into CWs. Their study revealed that approximately 90% of biochemical oxygen demand (BOD) was removed efficiently, significantly reducing HM content (Rai et al., 2013). This shows that WH plants in CWs play an important role in adsorbing pollutants from wastewater and, thus, inducing the suspended particulate matter sedimentation, which reduces BOD effectively (Mohan et al., 2010). Compared with other conventional wastewater treatment technologies, CWs consume extremely less energy and emit a negligible amount of greenhouse gases (GHGs). This suggests that the CW system is a more economically feasible and eco-friendly approach for treating various wastewaters.

Besides taking and storing nutrients, the roots of WH plants also facilitate the growth of microorganisms by providing a broad surface area. Although aquatic plants should be regularly removed from the wetlands, if not, then contaminates taken up by them will be discharged back to the water from the dead parts of the plants. Hence, the management of plentiful aquatic biomass in CWs is a major challenge. Recently, some studies show that WH waste biomass coupled with CWs is utilized for bioenergy production. This benefits the environment in the recovery of nutrients and simultaneously removing excess biomass, making aquatic weed-based CWs an environment-friendly and feasible choice for both wastewater treatment and biofuel generation. But, the application of aquatic weed-based CWs is still in the early stage of research for biofuel production. However, Tilak et al. (2016) reports the use of AWs such as Eichhornia crassipes in CWs for the application of phytoremediation. Liu et al. have investigated that invasive AWs growing on the wastewater supplemented with nutrients in CW resulted in cellulosic bioenergy production. They have also analyzed the life cycle assessment (LCA) of energy balance to convert biomass to biofuel and emissions of greenhouse gases (GHGs) during the process (D. Liu et al., 2012). They reported that aquatic weed-based constructed wetlands produced maximum biofuel annually, i.e., 1836.5 GJ ha−1 yr−1. However, this yield was lower than the biofuel produced by algae (4178.4 GJ ha−1 yr−1) but more significant than other commonly used biomass such as grassland, switchgrass, corn, and soybean which produces biofuel 88.8, 199.1, 158.1, and 45.8 GJ ha−1 yr−1, respectively. They have also concluded that CW systems sequester more carbon dioxide than they release, which reduces net GHGs. Similarly, Soda et al. (2013) have reported that AWs, WH, and water lettuce in CWs yield 0.14–0.17 g/g of ethanol. They have also observed that aquatic weed-based CWs efficiently removed total nitrogen and total phosphorus up to 45% and 66%, respectively, from the secondary treated effluent.

3.5.2: WH-CW-microbial fuel cell

A new and unique design of CWs has been developed, composed of cathode and anode zones in which the cathode zone is for the aerobic area on the surface of the water, and the anode zone is the anerobic area in the depth of the water body. This newly designed system is coupled with microbial fuel cells (MFCs) fabricated inside the CWs. CW-MFC is considered a new technical approach to produce electricity and the treatment of wastewater (Oon et al., 2015; Venkata Mohan et al., 2014). It has been reported that chemical oxygen demand (COD) from wastewater is effectively removed from 27%–49% by using MFC-based CWs. Also, CW-MFCs produced a maximum power density of 320.8 mW m−3 and a current density of 422.2 mA m−3 (Srivastava et al., 2015). The CW-MFC system with the WHs plays an essential role during photosynthesis; in the rhizosphere, it releases oxygen and organic matter such as organic acids, sugars, carbohydrates, and enzymes. The organic matter released is utilized as substrates for the growth of a broad range of microorganisms, and aquatic weeds provide a surface for their attachment. During photosynthesis, nitrifying bacteria gets activated and produces electrons at the anode by converting the ammonia (NH3) from the wastewater into nitrate (NO³−). Oxygen released during photosynthesis and NO³− produced acts as electron acceptors at the cathode zone, supporting the MFC in generating electricity. Hence, electroactive microorganisms in this MFC-based CW system and WH generate electricity by transforming solar energy directly into electrical power (J. Wang et al., 2017). Lu et al. (2015) have studied the role of microorganisms in the MFC-based CWs. They have reported that aquatic weed Canna indica planted in MFC-CWs supports diversities of microorganisms compared to control without aquatic weeds. They have also observed that these microbes utilize the organic matter released by aquatic plants and act as an electron donor to generate a maximum current of 105 mA m−2. The mechanism of conversion of these organic matter into the current was investigated by pyrosequencing and clone library of microorganisms present in the rhizosphere. They found that Anaerolineaceae (fermentative bacteria) and Geobacter (electrochemically active bacteria) carry out a syntrophic interaction with each other. Simultaneously, hydrogenotrophic methanogens and thermophilic archaea act as the primary electron donor to produce current. In another study by J. Wang et al. (2017), the large substrate size in MFC-based constructed wetlands results in more electrochemically bacteria such as β-Proteobacteria at the anode zone, which led to generation of high bioelectricity up to 8.91 mW m−2. Fang et al. (2013) has reported the generation of 610 mV voltage in MFC-based CWs in the presence of the aquatic weed Ipomoea. They have also concluded that aquatic plant in MFC-CWs is 92.24% effective in decolorizing the azo dye. Also, the MFC coupled with continuous flow constructed wetlands and aquatic plant Cattails led to the generation of a maximum 6.12 mW m−2 power density and showed 100% efficiency in COD removal (Oon et al., 2015).

Hence, microbial diversity in the rhizosphere and power density in the anode and cathode zone are affected by WH plants’ presence in CWs. Aquatic plants support the growth of several electrogenic bacteria, such as Geobacter sulfurreducens and β-Proteobacteria, for the generation of electricity (Lu et al., 2015). Therefore, this advanced MFC-based CW technology provides remarkable results in bioenergy recovery along with the treatment of wastewater streams, although the influence of MFC-based CWs on the rhizospheric milieu or physiology of aquatic plant or microbial diversity should be studied further at different operating conditions.

Aquatic weed-based constructed wetlands have many other applications for the production of bioenergy. Aquatic weeds such as Azolla can be used in the constructed wetland as it is reported to sequester CO2 at a rate of 32.5 metric tons CO2 ha−1 yr−1 and hence reduce GHG emissions. As a feedstock of bioenergy in constructed wetlands, aquatic weeds reduce the need for nutrients and water requirements for their cultivation, making this system cost-effective to produce bioenergy. This system also solves the problem of land use efficiency as it can easily be sustained on marginal lands, not like other systems of biofuel production. Therefore, aquatic weed-based constructed wetlands are considered the most promising and economically feasible system for biofuel production. This system simultaneously solves the problem of wastewater management by treating various types of wastewater streams along with bioenergy production (Mohan et al., 2011).

Traditional systems for bioenergy production were less efficient, required intensive energy in processing, and increased production costs by excessive fertilizers. An integrated model of CWs with WHs is a closed-loop of nutrients that provides the fertilizers for WH production and therefore reduces the energy input in the production of the biofuel. At the same time, WHs grown in constructed wetlands facilitate bioremediation or treatment of wastewater. Hence, this modern approach of biomass production, bioenergy generation, and wastewater treatment by WH-based constructed wetlands make it a more eco-friendly, sustainable, and promising technology for biofuel production than the conventional systems (Mohan et al., 2016).

4: WH for carbonaceous materials

The WH-derived carbonaceous materials (CMs) have been employed for heavy metals, organic chemicals, toxic gas adsorption, wastewater treatment (Kushwaha et al., 2016; Kushwaha, Goswami, Hans, et al., 2021; Kumar et al., 2022; Saha et al., 2022), and air purification (Salas-Ruiz & del Mar Barbero-Barrera, 2019). Table 1 depicts the utilization of WH-derived CMs for contaminant removal and other applications. The technical approaches comprise pyrolysis and Fe impregnation to generate adsorbents for removal of Cd, chemical reactions to remove Cu and Ni, and the preparation of superior magnetic carbon composite adsorbents via hydrothermal carbonization, chemical activation, and pyrolysis (Tarapitakcheevin et al., 2013). The maximum adsorption capacity for Pb (II), Co(II), and Cr(VI) removal was 1199 mg/g (Huang et al., 2014), 1411 mg/g (Riyanto & Prabalaras, 2019), and 200 mg/g (Santhosh & Dhandapani, 2013), respectively. The adsorption of Cu by WH-based CMs was investigated by C. Liu et al. (2020), and they observed a maximum surface area (95 m²/g) and pore size (33.7 nm) of CM. CMs with Fe were more efficient for Cd removal, and the high adsorption capacity was 45.8 mg/g. The highest removal capacity for Cr (97 mg/g), Cu (78 mg/g), and Ni (60 mg/g) was observed by WH-based CM adsorbent (W. Qu et al., 2019). WH-based superior magnetic carbon composite adsorbents were explored to remove numerous organic contaminants (Saning et al., 2019). CMs were found to be effective for removal of methylene blue (524.2 mg/g), methyl orange (425.2 mg/g), and tetracycline (294.2 mg/g). In short, CMs have been extensively used for the adsorption of phenolic compounds (Barbosa et al., 2014), organic pollutants (Rashwan & Girgis, 2004), and Rhodamine-B (Lalitha & Sangeetha, 2008).

Table 1

Moreover, the influence of various pretreatment approaches on the chemical constituent and structure of CMs is crucial in pollutant removal (Kushwaha, Mishra, et al., 2022; Rizvi et al., 2020). The amalgamation of pretreatment processes can be investigated to produce CMs with maximum adsorption capacity, for instance, microwave-heated alkali pretreatment and acid-combined microbial pretreatment (Zhang et al., 2018). The performance of catalytic pyrolysis is influenced by the pretreatment process, and the results showed that pyrolysis kinetics and WH biomass behavior are influenced by microwave pretreatment. Also, hydrothermal carbonization is an alternate for the enhanced moisture content biomass processing, for instance, WH, algae, and food waste. It is an effective method to produce valuable CMs economically (Khoshbouy et al., 2019).

5: WH for other applications

WH is also a propitious source in cosmetics, medical, and science, particularly in cooling and decontamination, eliminating humidity, and implanting for exterior heat sores (Kushwaha, Goswami, & Kim, 2022). Also, WH is a viable source for MFC production (Widharyanti et al., 2020), can be utilized for the generation of concrete (Okwadha & Makomele, 2018), and the generation of furfural (Poomsawat et al., 2019).

Scientists have explored fiber composites derived from WH via alkaline treatment (Tan & Supri, 2016). After alkaline treatment, the fiber composites showed improved tensile strength and thermal stability and rough surface. WH is also applied in seawater desalination as a sustainable method. WH is also used to create handicrafts, a budding WH development approach (Rakotoarisoa et al., 2016).

WH's other parts are also helpful; for instance, the complete WH (excluding stolon) can be utilized as sustenance, animal fodder, and well-being products. WH flowers and leaves (grown in clean freshwater) are consumable. The flower can be used in cosmetics such as nutrients in the facial mask because of the occurrence of lipophilic and polar extracts and antioxidants abundantly. Owing to the WH leafstalk thermo-physical and microstructural properties, it can be used as a feedstock for thermal insulation particleboard production (Salas-Ruiz et al., 2019). The leaf and leafstalk can be transformed into water-resistant material, electrodes in fuel cells, and dehumidification and purification for air conditioners (Pakutsah & Aht-Ong, 2020). Furthermore, the stolon is used to produce carbon nanofibers and biomembranes in life science (Ávila et al., 2019).

6: Environmental and techno-economic analysis

The ecological and financial analysis plays a vital part in assessing the feasibility of environmental solutions for industrial applications (Borgaonkar et al., 2022; Goswami, Kayalvizhi, et al., 2022). Controlling the proliferation of WH has been assessed by comparing the AD and discarding it in landfills. The AD was found to be more economical and aid in water quality enhancement. The projected net present value (NPV) for 11,000 tons WH annually is 2.0 million USD. AD also aids in reducing greenhouse gas (GHG) due to lower methane generation from landfills. Z. Wang et al. (2019) examined the WH techno-economic analysis for bioethanol production. The reduction of GHG release is valued depending on the shadow cost of 19 USD per ton. Depending on the 15-year life cycle, the NPV value for 25,000 tons WH is 183 million USD. Likewise, Bentzen et al. (2018) analyzed the co-digestion of WH and rice-straw economic feasibility and found 433 USD cost (1009 USD benefit) on a 15-year lifespan. Fig. 2 illustrates the LCA analysis framework for environmental sustainability.

Fig. 2

Fig. 2 Assessment of the environmental sustainability of the projected strategies. Reprinted with permission from Li, F., He, X., Srishti, A., Song, S., Tan, H. T. W., Sweeney, D. J., Ghosh, S., & Wang, C. H. (2021). Water hyacinth for energy and environmental applications: A review. Bioresource Technology, 124809.

The ecological influence and economic feasibility of wastewater treatment plants combined with WH-CW were assessed by Laitinen et al. (2017). In contrast to the activated sludge process (ASP), LCA displayed a 69% reduction in GHG emissions. The price of remaining treated wastewater was decreased from 0.4 USD/m³ to 0.2 USD/m³. The financial feasibility of generating biochar and bio-oil from WH via fast pyrolysis was evaluated by Buller et al. (2015). The financial study of a 10 year displayed a 62% profit margin ratio and a 37% return of asset ratio. Güereña et al. (2015) estimated WH's financial and ecological benefits. They compared three diverse technologies: combustion, AD, and gasification/pyrolysis. The pyrolysis and gasification process exhibited a net value of 89–226 USD/ton (together with energy and by-products), similar to AD (65–233 USD/ton), and combustion showed 43.1–43.4 USD/ton net value. The result showed an improved carbon sequestration potential (146–264 kg C/ton) via gasification in contrast to the combustion (−87 kg C/ton) and AD (146 kg C/ton).

WH is a valuable biomass for energy production and environmental remediation depending on the ecological and techno-economic evaluation. AD and gasification/pyrolysis are cost-effective processes. The advantage of AD depends on its capability to utilize high-moisture-containing biomass; however, the constraint is less extraction efficacy and biogas production. The benefit of gasification and pyrolysis produces several energy products, such as syngas, bio-oil, and biochar, but restraint is the high operational cost.

6.1: Mathematical model

For the development of an economical process for WH-derived biochar, a mathematical model has to be developed to forecast and improve the thermochemical conversion depending on the energy performance. A model is designed to simulate experimental run and then focus on numerical experiment simulation. Depending on the model's result, the rate of generation and quality of biochar, syngas, and bio-oil can be projected (Ephraim et al., 2016). It is essential to design a model on the thermochemical reactor to generate biochar effectively and inexpensively. The laboratory-scale and pilot-scale reactors Discrete Phase Model and Representative Particle Model are of interest, respectively (You et al., 2016). Furthermore, the influence of biomass, processing agents, drying method, and operational parameters can be examined to improve the conversion of energy (Yao et al., 2020). Still, it is problematic to establish a methodical structure of diverse mathematical models due to complex aspects which have a comparatively more rational amalgamation with difficult situations.

6.2: Techno-economic analysis

To evaluate the eco-solution feasibility commercially, mathematical simulation is used for reactor improvement to meso- or macro scale for implementation in industries (Kumar et al., 2022; Kushwaha, Hans, Giri, et al., 2022). Since pilot-level experimentations for the thermochemical process are expensive and laborious, mathematical methods are valuable for forecasting the attainable performance and controlling the process constituents. Both small and pilot levels should be measured for the multi-level modeling process. During small scale, the biochar and bioenergy generation are corroborated by WH thermo-conversion experimentations. The lab-scale techno-economic analysis (TEA) is based on the feedstock cost, energy utilization, syngas and biochar generation. The model can be advanced to the pilot level after the corroboration at the laboratory level. The reactor size, investment and operational cost, and production of heat, electricity, and cooling should be examined at the pilot-level TEA (Yao et al., 2018). The economic study can be investigated to inspect the best approach for WH utilization. The outcome is equated with the existing biomass waste recycling approaches to identify the potential for large-scale industry adoption.

6.3: Life cycle assessment (LCA)

Substantial research has been carried out to use sustainable approaches as a circular economy (CE) principle. One of the most prevalent approaches is eco-design directed by the LCA (Kushwaha, Yadav, et al., 2022). In Singapore, the carbon tax is set at $5 per ton of GHG release from 2019 to 2023. The biochar generation in the eco-solutions embodies a method for CO2 sequestration, and the ecological profits are projected via LCA based on ISO 14040 standard. The statistics from the model system and mathematical models estimate the produced or eradicated ecological influence.

6.4: Analysis of circular economy (CE)

Circular economy (CE) has gained attention due to the combined growth of the milieu, economy, and society. Fig. 3 gives a schematic overview of the impact of WH on environment, society, and economy. It boosts nations, organizations, and clients to decrease the damage to the milieu and ‘close the loop’ of the product lifespan via three major methods, i.e., reduction, reuse, and recycling for raw material, energy, and waste. It also plays a vital role in decreasing the emission of GHG and leading to a sustainable economy (Z. Liu et al., 2018). The possibility of implementation of CE indorses target resources, products, and divisions. The theoretic methods can help understand the CE concept and the development of novel CE. In Europe, the eco-design, waste inhibition, and reuse lead to a net savings of EUR 600 billion with a substantial decrease of GHG release (Milios, 2018). Administration, government, and NGOs are the major characters contributing to CE growth. Studies examined the WH biomass eco-design and LCA. The results displayed WH is an extremely inexpensive feedstock for the production of the liquid fuel at $40/ton depending on LCA for a subsequent conversion method of growth, harvesting, and digestion. Overall, it is essential to carry out complete and rigorous research concentrating on CE in WH conversion and supervision.

Fig. 3

Fig. 3 Impact of water hyacinth impact on environmental, social, and economical ( Ezzariai et al., 2021).

7: Research needs and future directions

WH's biochar production has gained significant attention owing to its high biomass yield, enhanced carbon concentration, and environmental application such as carbon sequestration and contaminants elimination. The thermochemical process has been utilized for biochar generation from WH to remove and immobilize pollutants, energy production, and multi-faceted materials. The milieu, economy, and society are interconnected to emphasize the novel understanding of biochar application and reverberating with the phytoremediation approach. It is indispensable to conduct further studies in implementing CE for a virtuous and sustainable method for managing WH. In addition, the WH applications in CMs, renewable energy, and chemicals should be studied broadly for a greater apprehension of the biowaste feedstock usage.

The biochar-derived CMs have been utilized as adsorbents to remove aquatic contaminants and noxious gases, as a geopolymer for in situ edifices, or as the conductor in fuel batteries. The influence of different pretreatment processes on WH's constituents and structure is vital in heavy metal removal. Innovative collective pretreatment processes can be discovered for high-quality CM generation with less or no HM content. The application of WH shows a propitious research area through HM recovery. The CM residue can be utilized in the green industry as a catalyst, synthetic biology as catalytic carriers, and fuel cells as electrode materials. The particle shape, chemical composition, size, and additives are essential features in the CM production and application. The WH-based products are also utilized for dehumidification, detoxification, and biomass to produce wearable devices and paper constituents. The WH application varies depending on morphologic parts due to their physicochemical composition variances and unusual edifice. An effective approach should be fortified via WH sustainable development and appropriate strategies for controlling and managing these invasive species.

8: Conclusions

Biowaste leads to an adverse effect on the ecosystems, causing health problems and ecological catastrophe. WH utilization to produce bioenergy and valuable products will substantially decrease the socio-economic crisis linked with the expansive growth of the weed. The advancement in the development of better strains via genetic engineering to produce value-added products and process amalgamation to improve product yield will establish an economically sustainable approach, thus making the method commercially feasible. Various R&D activities are working in this path worldwide to convert WH to wealth, moving toward sustainable control of this weed. This chapter delivers a viable method to convert WH into biofuels, CMs, and chemicals for bioenergy and ecological implementation. It is essential to syndicate process modeling, risk evaluation, and machine learning to improve energy conversion efficacy, reutilization of the waste stream, and phytoremediation. Multifarious skills, guidelines, and diversity policies are needed to increase innovation and ecological fortification for a zero-waste society.

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