An Update on Agricultural Wastes Used as Natural Adsorbents or Coagulants in Single or Combined Systems for the Removal of Dyes from Wastewater

Abstract

Over a billion people in developing countries do not have access to clean water. Industries such as textiles, tanneries, and plastics release wastewater with toxic dyes that require treatment to remove the color. Adsorption and coagulation are known methods for removing dyes from wastewater. The production of natural adsorbents and coagulants involves the use of waste from agricultural products, which makes them cost-effective and environmentally friendly. They can be modified to achieve high dye removal rate. Natural adsorbents and coagulants are more eco-friendly than synthetic materials such as activated carbon and alum, because they can achieve similar levels of removal efficiency while being biodegradable and reusable. The combination of two methods can help to reduce the required dosage of adsorbent and coagulant and simultaneously improve the rate of dye removal. The purpose of this review is to evaluate and contrast the efficacy of recent natural agricultural adsorbents and coagulants, as they are environmentally friendly and abundant in nature. Additionally, it aims to introduce novelty by reviewing the combined coagulation/flocculation and adsorption systems in the treatment process for removing dyes, utilizing adsorbents and coagulants derived from agricultural wastes. As it turns out, the most examined dyes for removal were Methylene Blue and Congo Red and as adsorbents were used banana peels, orange peels, and nut. Furthermore, Moringa oleifera is used as a coagulant in both single and combined systems. Regarding adsorption, it was observed that banana peels could remove different dyes with high efficiency.