Treatment of As(III)-contaminated food waste using alkali treatment and its potential application for methylene blue removal from aqueous solutions

Abstract

Conventional methods for managing food waste become ineffective when the waste is contaminated with toxic chemicals due to the risk of further contamination. To address this issue, this study proposes an alkali pre-treatment approach to decontaminate processed food waste containing As(III) and repurpose it as an adsorbent for treating wastewater. The study investigates the effects of different alkali treatment conditions, (concentration, treatment time, and temperature), on the decontamination of As(III) and its impact on the adsorption behavior of methylene blue. Experimental results demonstrate that treating the material with 0.8 M NaOH at 60 °C for 4 h effectively eliminates As(III), achieving a remarkable removal rate of 99.8 %. Characterization results revealed that the alkali-treated material exhibits desirable properties, including increased carboxylation, improved thermal stability, reduced crystallinity, and a significantly enlarged specific surface area (66.03 %) compared to the original contaminated food waste. The alkali-treated waste demonstrates good adsorption capacity towards methylene blue, with a maximum adsorption capacity of 534.6 mg/g achieved at pH 8.0, 40 g/L adsorbent dose, 10 h shaking time, and 20 °C. The Temkin (R2 = 0.978) and intraparticle diffusion models effectively describe the adsorption data. Notably, the adsorbent demonstrates excellent reusability, as it can be utilized for at least 4 cycles of adsorption-desorption without a significant reduction in methylene blue removal efficiency (only a 5.2 % decrease), highlighting its practical potential. The results strongly indicate that alkali pre-treatment represents a simple and efficient method for eliminating As contamination from food waste while concurrently producing an effective adsorbent for removing dyes from aqueous solutions.