# Yeast-Based Magnetic Biocomposite for Efficient Sorption of Organic Pollutants
## 1 Introduction  
Recently, there has been a significant increase in the number of discharges of synthetic dyes into water reservoirs. Different dyes are removed from industries such as textiles, cosmetics, paper, pharmaceuticals, food, and tanning, generating a wide range of colors [1]. They can be used individually or in combination with other ingredients. Recent estimates indicate that about 280 thousand tons of undegraded synthetic dyes accumulate globally in water bodies [2]. Dyes limit light penetration into the water because they can intensely color it. This is a big problem for both households and the water environment. Lack of light transmittance through water may harm the photosynthesis process, as well as animals living in water, e.g., fish. Aquatic microorganisms may have problems adapting to the changed water composition, and, as a result, aquatic animals may run out of food. For humans, the presence of dyes in water can also lead to health problems by causing skin irritation or allergies [3]. Methylthionine chloride is a compound known as methylene blue. It is in the group of cationic dyes and is used in many areas, including the production of medicines, the dye industry, and the paper industry. Typically, the content of dyes, for example MB, is between 10 and 250 mg/dm\({}^{3}\), but in the case of wastewater from textile industry it may reach even 1500 mg/dm\({}^{3}\). Common international standards set limits for chemical substances hazardous to the environment at approximately 125 mg/dm\({}^{3}\) in the case ofdirect discharge of wastewater containing dyes [4]. However, in developing countries in which there is no adequate regulation of the amounts of these dyes in wastewater, or where regulations exist but are insufficient, the content of those dyes in discharged sewage is often very high [5]. Methylene blue can lead to various negative side effects when consumed by humans, including vomiting, jaundice, cyanosis, increased heart palpitations, limb paresis and tissue necrosis, high blood pressure, abdominal pain, and even mental disorders [6]. Methylene blue is indicated in the treatment of methemoglobin, where it accelerates the conversion of methemoglobin to hemoglobin. When higher doses are administered, methylene blue accumulates, making it an oxidizing agent [7]. Additionally, dyes released into the environment cause water turbidity, limit the photosynthetic abilities of aquatic plants, and disturb the ecosystem [8]. Many methods are used to eliminate dyes from the environment. These include different methods. Combined techniques are widely due to the variety of contaminants. These can be specific and a combination of methods will be more effective when trying to remove contaminants. Coagulation, oxidation, and flocculation are examples of chemical methods used [9; 10]. Physical methods effective in removing dyes include membrane filtration, reverse osmosis, and adsorption techniques. However, these techniques are energy-intensive and require complex and expensive procedures, and the production of undesirable byproducts (e.g., sludge) is inevitable [2]. Amongst the most popular methods of removing dyes is adsorption on activated carbon. Carbon materials have a porous structure (produced by a system of diffusion channels and pores) and this influences their good adsorption properties. The porous structure of these materials causes diffusion and colored compounds from contaminated water to enter the material. The adsorption space is filled starting from the macropores and moving on to the deeper pores of activated carbon. The disadvantage of adsorption with the use of activated carbon-based methods is the price of the material, which affects the cost of the process. Nowadays, research aims for the use of available, cheap, and efficient substrates for activated carbon. For this purpose, the possibility of using agricultural by-products as a cheap alternative adsorbent, such as malt pomace, cashew nut shells, banana peels, or coconut shells, was investigated [11].