Abstract
Ulva lactuca has been used to remove many toxic substances from industrial wastewater. In the present study we tried to optimize the efficiency of U. lactuca as an adsorbent of methylene blue (MB) in aqueous solution. U. lactuca was chemically treated with sulfuric acid (UL-H) and sodium hydroxide (UL-OH) and by a slow pyrolysis process (carbonization process) at high temperature T = 600 °C (UL-T) and compared to the nonactive Ulva (UL-NA) and the water insoluble substance (UL-WIS). Several spectroscopic analyses were carried out to detect the biosorption mechanisms of Ulva to remove MB in solution. The effects of different parameters on the adsorption process were studied, i.e., pH (2–10), mass concentration (1–10 g L−1), and contact time (0–120 min). The results showed that the best adsorption of MB by Ulva was at pH = 8, with 5 g L−1 of biomass at 75 min; the best adsorption capacity was 625.0 mg g−1 for UL-OH, which was able to remove more than 89% of MB compared to UL-T, whose removal rate did not exceed 5%. Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) indicated the presence of oxygenated functional groups with a highly porous surface. The kinetic studies confirmed that the majority of treatments follow the pseudo-second-order type. The mathematical models showed that Langmuir model is favorable to UL-OH, UL-WIS, and UL-NA. According to the experimental results, the primary treatment for U. lactuca is a promising environmentally friendly method and an economical strategy for removing MB from aqueous solution. This method can help address the growing demand for adsorbents used in environmental protection processes and the resultant increase in their price.
Highlights
The daily use of dyes has caused both environmental and nutritional complications.Environmental pollution is caused by the discharge of industrial wastewater due to the manufacture of plastic, paper, textiles, rubber, cosmetics, leather, food, pharmaceuticals, etc., which creates a large amount of toxic dyes, mutagens, and carcinogens
The results suggest that the most suitable mechanism in the biosorption process of the adsorbents UL-NA and UL-OH on methylene blue (MB) is by chemical bonds rather than by ion exchange [53,59]; in UL-WIS, UL-H, and UL-T, the mechanism in the biosorption process was probably the ion exchange type
In this study, activated carbon was obtained from dry U. lactuca (UL-NA) by chemical treated with different reagents and by carbonization to obtain UL-H, UL-OH, and UL-T
Summary
Environmental pollution is caused by the discharge of industrial wastewater due to the manufacture of plastic, paper, textiles, rubber, cosmetics, leather, food, pharmaceuticals, etc., which creates a large amount of toxic dyes, mutagens, and carcinogens. Biosorption is the most practical technique for recycling industrial wastewater rich in dyes due to its simplicity and economy [1,2]. Algae have become one of the most used sources as a disinfectant for wastewater rich in dyes and heavy metals [12,13]. In the current study, Red sea Ulva lactuca was selected to be an adsorbent of methylene blue (MB) dye due to its low-cost availability over the season and its fast blooming, which causes green tide worldwide and is hard to control [14]. U. lactuca is well known for its efficiency in the defense process through its release of an efficient amount of polyunsaturated aldehyde [15] as well as its ability as an adsorbent of heavy metals [16,17,18]
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