Sustainable Management of Sewage Sludge Using Dhaincha (<i>Sesbania bispinosa</i> (Jacq.) W.Wight) Cultivation: Studies on Heavy Metal Uptake and Characterization of Fibers

In this study, the potential use of sewage sludge (SS) as a fertilizer source for cultivated Dhaincha (<i>Sesbania bispinosa</i> (Jacq.) W.Wight) crops was investigated. Field experiments were conducted using different doses of SS such as 0% (T0), 5% (T1), 10% (T2), and 15% (T3) to amend the soil (<i>w</i>/<i>w</i>). The findings showed that soil amended with SS significantly (<i>p</i> < 0.05) improved the response parameters of <i>S. bispinosa</i> with an increase in the dose of SS from 0% to 15%. In particular, the T3 treatment gave the best results (mean values) for plant growth and yield parameters such as plant height (380.59 cm), fresh weight (1.47 kg/plant), dry weight (0.27 kg/plant), base diameter (3.19 cm), seed yield (44.71 g/plant), total chlorophyll (3.15 mg/g fwt), carotenoids (0.88 mg/g fwt), carbohydrates (9.40 mg/g), and phenol (0.13 mg/g) contents. Moreover, the selected proximate and fiber characteristics of the <i>S. bispinosa</i> crop were significantly (<i>p</i> < 0.05) improved by the same treatment (T3); such as ash (7.25%), crude fiber (32.70%), crude protein (15.94%), lignin (24.60%), cellulose (37.25%), fiber weight (3.06 g/plant), stick weight (32.08 g/plant), fiber: stick ratio (0.10), fiber diameter (26.97 µm), ultimate tensile strength (855.98 MPa), strength (58.92 g/tex), density (1.54 g/cm³), and luster (45.65%) compared with the control treatment (T0). The bioaccumulation factor (BAF) studies showed that the <i>S. bispinosa</i> plant was capable of accumulating selected heavy metals from the soil following the order: Fe > Mn > Zn > Cu > Cd > Cr. The study suggested a sustainable approach for efficient soil fertilization and high-quality <i>S. bispinosa</i> fiber production that could minimize the environmental pollution caused by the unsafe disposal of SS.