Waste Pineapple Peel (WPP) was tested as a low-cost adsorbent for Acid Yellow 42 dye removal from wastewater. Many factors were examined, including dye concentration (10–40 mg/L), contact period (10–90 min), adsorbent dosage (0.5–2.5 g/L), pH (3–11), and agitation speed (400–800 rpm). The modifying agent for WPP was employed as nitric acid (HNO3). Energy-dispersive X-ray (EDAX), Fourier transform infrared spectroscopy (FTIR), and a scanning electron microscope (SEM) were used to characterize the adsorbent. Results showed that Acid Yellow 42 dye was removed with 96% efficiency at 10 mg/L dye concentration, 2.0 g/L adsorbent dosage, 90 min, pH 3, and 800 rpm agitation speed. Isotherm analysis shows that the Langmuir isotherm model better describes the adsorption process. The most effective method for regenerating adsorbents involved reusing hydrochloric acid (HCl) for multiple cycles. The findings suggest that the utilization of modified waste pineapple peel (MWPP) as an adsorbent is a cost-effective and effective method for removing Acid Yellow 42 dye from wastewater.