<p>Managing effluents released from composite industrial establishments is a significant challenge due to the high variability of effluent characteristics, making them difficult to treat using conventional methods. This study aims to assess the feasibility of phytoremediation using water caltrop (<i>Trapa natans</i> L.; WC) for treating composite industrial effluent (CIE) released from the SIDCUL industrial cluster in Haridwar, India. To achieve this, WC was grown under laboratory conditions for 40 days using five concentrations of CIE (0%, 25%, 50%, 75%, and 100%). The post-harvested plant biomass was then used for biogas production through anaerobic methanization. The results indicate that the WC plant effectively removed a significant amount (<i>p</i> &lt; 0.05) of physicochemical and heavy metal properties of CIE in the 75% concentration treatment. The study observed the maximum growth, proximate, and ultimate properties of the WC plant in the same treatment as the pollutant removal findings. The highest biomass was produced in the 75% concentration, which was used for biogas production. The biogas produced had a maximum volume of 6538 mL and a CH₄ content of 52.40%. After 20 days of anaerobic digestion, the properties of the biogas slurry were significantly reduced (<i>p</i> &lt; 0.05). This study presents a holistic solution for industrial wastewater treatment, along with resource recovery from produced biogas for sustainable green energy production.</p>