**6. Opportunities: valorization and value-added resource recovery**

Although it has a significant negative impact on aquatic ecosystems, the valorization of WH offers a variety of potential economic benefits. The plant is known for many potential industrial applications reviewed in the following sections. The summary of the selected articles on valuable material recovery from WH is presented in **Tables 3** and **4**.

#### **6.1 Animal fodder: nonconventional source of protein**

The need for food security without exerting pressure on the global land use for agricultural purposes has necessitated the search for cost-effective, accessible, and healthy supplements. Studies have shown that WH is a decent source of creature feed because of its proven protein and mineral substance accessible to ruminants [63, 64]. WH leaf protein concentrate was shown to contain valuable amounts of nutrients including 56.38% crude protein, 33% carbohydrates, and 17 amino acids [63]. Researchers have promoted the use of WH as animal feed as it has high water and mineral content, which suggests that the nutritional value may be appropriate for certain animals, it can be used to supplement protein feed and roughage [65, 66]. Its utilization for creature feed is urged in developing countries to help tackle a portion of the dietary issues [67]. Fresh WH cooked with rice grain and fish feast and blended with vegetable waste, rice bran, copra cake, and salt and copra meal is utilized as feed for pigs, ducks, and lake fish in nations like Thailand, Malaysia, China, and the Philippines [57]. Other researchers also showed the utilization of WH as dairy cattle feed [56]. Akinwande et al. [68] also, with their study conducted on three water bodies in Nigeria, demonstrated that biomass yield, synthetic arrangement, and nutritive capability of WH to be used as feed for creatures, particularly ruminants.


#### **Table 3.**

*Summary of selected literature reviewed on animal feed, phytoremediation, biosorbent, insulation board, and biopolymers recovery technologies of WH.*

Protein digestibility is a significant factor to evaluate the dietary quality of food; a high digestibility rate signifies high nutrients use. However, histology assessment revealed that the kidneys of the fish had degeneration of renal tubules, necrotic damage in tubular epithelial cells, and tubular lysis. There was no report of toxicity in the study of de Vasconcelos et al. [20], which was aimed at substituting Tifton-85 hay used in sheep diet with WH as the globulin concentrations were suitable. It is evident that WH is used as animal feed, however, it calls for suitable precautious procedures such as pretreatment before use to reduce its toxicity and seed viability.

**Valorization Aim Investigations Ref.** Briquette Evaluating the fuel features of briquettes produced from the mixture of WH and empty fruit bunch (EFB) The combination of WH and EFB showed a high perspective as the combustion properties: moisture content, ash content, fixed carbon content, and average calorific value is within a suitable range [24] Development and characterization of charcoal briquettes from WH-molasses blend The highest calorific value (16.6 MJ/kg) and compressive strength (19.1 kg/cm<sup>2</sup> ) with 30:70 charcoal/molasses ratio briquet was produced. Charcoal briquettes were tested for their flammable characteristics through their burning rates and ignition time [23] Bioethanol Enhancing bioethanol yield from WH by integrated pretreatment method 1.40 g/L of bioethanol produced from the pretreatment of WH with microbial + dilute acid pretreatment. This was achieved without any additional cellulase. [24] Evaluating the best method and the optimal conditions for fermentable sugar production from WH; these sugars were then fermented to bioethanol. 14 g/l bioethanol produced from C. tropical is Y-26 in the fermentation of fungal- and acid-treated hydrolysate was higher than the 6 g/l bioethanol produced from the fermentation of acid-only-treated hydrolysate. [26] Biogas The potential bioenergy recovery from anaerobic digestion of WH and its codigestion with fruit and vegetable waste (FVW) The biogas potential of WH-FVW (0.141 m<sup>3</sup> /kg VS) co-digestion was 23% higher than that of WH alone (0.114 m<sup>3</sup> /kg VS). [29] Investigation of the effects of chemical pretreatment (H2SO4) on biogas production from WH Cellulose was degraded during pretreatment. The optimum biogas yield of 424.30 mL resulted from the 5% v/v H2SO4 pretreatment at a residence time of 60 min [30] Comparative investigation on biogas yield and quality from anaerobic digestion of WH and Salvinia Biogas production from WH (552 L/kg VS) was considerably greater (p < 0.05) than Salvinia (221 L/kg VS). The biogas yield is estimated to generate 1.18 kWh and 0.47 kWh energy from WH and Salvinia (per kg VS), respectively. [61] Bio-fertilizer Investigation of the viability of utilizing WH composted with pig manure and without pig manure as a peat substitute. For tomato seedling germination, substrates 1–3 performed well (92.0– 95.3%), while Figure substrate 4 was poor (76.0%). However, substrate1 (72.5%) performed better than others in cabbage growth, with substrate4 being the lowest. [62] WH as green manure for organic farming. WH can be used as a biofertilizer when incorporated into soil increasing the performance of the wheat plant. It is revealed that both physical and chemical parameters of the wheat plant treated with WH compost had higher values as compared to control. [17]

*Invasive Water Hyacinth Challenges, Opportunities, Mitigation, and Policy Implications… DOI: http://dx.doi.org/10.5772/intechopen.106779*

#### **Table 4.**

*Summary of selected literature review on renewable energy, biofuel, biogas, and agricultural fertilizer recovery technologies of WH.*

## **6.2 Phytoremediation: scavenging toxic elements and heavy metals**

Despite the negative impacts of the expansion of water bodies, WH can adsorb pollutants due to its polyfunctional meta-binding sites and chemical functional groups. In the use of WH for the adsorption of dye, most studies investigated the effects on cationic dyes [21, 60] with limited studies on anionic dyes [69]. In this respect, WH is an excellent choice for remediating contaminated sites because of its propensity to absorb heavy metals from wastewater [70]. WH was able to absorb and transport Ag, Cd, Cu, Pb, Sb, Sn, and Zn from an effluent waste recycling plant, demonstrating its ability to remove heavy metals from water. Nash et al. [71] tested the efficiency of WH in remediating sago mill effluent for a month at different concentrations of 20%, 15%, and 10%. Ammonia, phosphorus, and chemical oxygen demand (COD) concentrations were lowered approximately by 91–97%, 80–97%, and 86–97%, respectively. Other studies proved WH can be used to remediate heavy metals [22, 58, 71].

Because the interaction of numerous metals has yet to be defined, there have been significant differences in the degree of adsorption of heavy metals by WH; it is hypothesized that WH contains lignocellulose, which can result in the tethering of metal ions [21]. The use of WH as a biological agent for phytoremediation has been challenged because the plant has the potential to evade the chosen site and become a disturbance [69]. Along with phytoremediation, a sustainable mechanism to transform WH biomass into value-added products is required. For example, Sayago [72] designed a sustainability system in which WH is used to treat chromium-infested water, then its biomass was used to produce bioethanol. Therefore, when WH is used for phytoremediation, adequate precautions need to be accompanied as it has a terrible effect on the environment.
