Biosorption of reactive yellow 145 and direct blue 86 dye mixture by inactive ulocladium chartarum mold

Environmental pollution is still an important issue all over the world. The increased population and the rising demands have also accelerated industrialization. The textile industry is one of the important fields in our country. There are several textile factories in the Marmara region. It has the second-highest share in the economy after the automotive sector. The textile industry ranks first in using large amounts of water and dyestuffs. Due to stable structures, aromatic hydrocarbons such as benzene and naphthalene and their derivatives are used for low-cost synthesis of dyestuffs. The most important waste of textile factories is dyes. Dyes must be purified before being discharged. The textile industry's polluted wastewater negatively affects public health and the environment. Harmful chemical compounds negatively affect living biodiversity by creating complex structures and disrupting the metabolism of aquatic organisms. Dyes, generally of synthetic origin and complex, cause more difficult biodegradation due to their stable structure and toxic effects on aquatic creatures. Purification processes bring costs to companies and many factories not to operate these sections or to operate them partially. Innovative removal studies are needed to reduce costs. The currently used main dye treatment techniques are electrochemical methods, adsorption, and some types of physical filtration. Although electrochemical methods provide effective treatment, their cost is considerably higher than that of other methods due to electricity use. Filtering methods cannot always provide sufficient purification. Adsorption methods are practical and preferred due to the cheapness of the used adsorbents and their efficiency and ease of applicability. They can also be combined with filtering methods. The removal occurs when atoms, ions, or molecules adhere to the surface of the adsorbent in the adsorption process. There are different types of adsorption. The Van der Waals force is responsible for the removal in the physical adsorption process. The reversible adsorption occurs, and regeneration is easy due to weak forces. The adsorption percentages decrease as the temperature increases because of the leaving adsorbed molecules. In chemical adsorption, chemical bonding (usually covalent) occurs between the adsorbent and the adsorbate. Adsorption is monolayer. The removal stops when the active sites on the surface to bind molecules run out. The increasing temperature caused a stronger bond between the adsorbent and the solute in chemical adsorption. Ion exchange adsorption is the accumulation of ions on the adsorbate surface via electrostatic interaction. The adsorbate and adsorbent surfaces should have opposite charges to form an interaction. Ions with a higher charge are adsorbed better. Adsorption mainly depends on the chemical and physical properties of the adsorbent and adsorbate. The adsorption capacity of small-sized adsorbents is higher due to increased surface area. The other affecting factors are pH, shaking time, temperature, and shaking speed. The solution's pH value affects the adsorbent's charge and adsorbate. In the acidic solutions, the adsorbent surface becomes more positively charged. Thus, negatively charged ions can interact with the surface. Similarly, at basic pH, the adsorbent surface becomes more negatively charged, and positively charged ions can be adsorbed. Adsorption is generally exothermic, and adsorption capacity decreases with increasing temperature. The adsorption rate is controlled by film diffusion, which is determined by the shaking speed. The film diffusion rate is the limiting factor since the liquid film thickness around the particle will be high at low mixing speeds. The rate of film diffusion increases when adequate mixing is achieved. As the mixing time increases, the interaction change of the adsorbent and adsorbate increases. Thus, the adsorption increases and reaches equilibrium after a while. Some natural materials, such as clays, can be directly used as adsorbents, and some natural and unnatural substances can also be converted to adsorbents. The chosen adsorbents must be cheap, easily obtainable, efficient, and resistant to removal processes. The used material should not pollute the environment by dissolving and should be suitable for reusability. Microorganisms, such as bacteria, fungi, and algae, can biodegrade or bioaccumulate dyestuffs from wastewater. These approaches include dye removal with live and dead cells. Biodegradation is possible with living cells, but it has some limitations, such as the required nutrient medium, the toxic effect of higher concentrations of dyes, and the extended time necessary. Fungus are suitable for the mentioned adsorbent properties for adsorption. The fungus can be reproduced from spores over and over if stored under appropriate conditions after isolation. This property significantly reduces the process cost. Also, they can be obtained in large quantities in specific nutritional growth mediums. The fungi are a biological species that causes the adsorption process called biosorption. The fungi should be killed after the growth stages for use in the adsorption process. Functional groups on dead fungus cell walls are responsible for the adsorption process. These groups can ionize inappropriate pH environments and interact with the functional groups of the dyes. The used dyes are not of a single type in the textile industry. They belong to different classes: azo, anthraquinone, phthalocyanine, sulfur, nitro and nitroso, carbonyl, and indigo. The azo class dyes contain -N=N- groups in the structure and the highest number of dye types among the dye classes. The different forms of azo dyes are used in the cosmetics and food industry as well as the textile industry. Azo dyes may differ according to their structure, such as the number of azo bonds and aromatic side groups. Pyhtalocynines class are the synthetic complex dyes that contain metal ions to the phthalocyanine ring. It is formed by combining four isoindole rings and auxochrome groups. Different classes of dyes can be found as a mixture in wastewater. The individual analyses of dyes in such mixture solutions in textile wastewaters can be complicated. The dyes must be analyzed separately to analyze the removal efficiency. Although separation methods can be used for this purpose, the requirement of equipment or machinery and increased analysis time are the negative side of the processes. Single dyes can be analyzed by measuring the absorption of the dye with spectrophotometric analysis and related calculations. In the mixture, the analysis becomes impossible due to the overlapping absorption bands of dyes. Derivative spectrometry methods enable the analysis of overlapping absorption bands via the calculated derivatives of the absorption wavelengths. In the derivative spectrum, the signal of one of the two dyes should be zero or close to zero, and the other should be high at a wavelength point. If these zero crossing points can be created for both dyes, individual analyses can be made in the mixture via the created calibration curves at these wavelengths. If zero crossing points are not created in the first derivative spectrum, the second derivative spectrum can be plotted and examined. Thus, mixture analyses can be performed using an ultraviolet-visible spectrophotometer, the simplest and cheapest device. The adsorption isotherm is the relationship between the amount of adsorbed solute and the equilibrium concentration of the adsorbate in solution at constant temperature. The adsorption process continues until an equilibrium is reached between the amount of adsorbed solute on the adsorbent surface and the amount of adsorbate remaining in the solution. The most commonly used are Langmuir and Freundlich isotherms. The Langmuir isotherm describes monolayer homogeneous adsorption. It assumes that the adsorbent surface is in the same energy. Isotherm parameters are calculated with the graph drawn between the remaining equilibrium concentration (Ce, x-axis) and the remaining equilibrium concentration/amount of adsorbed solute (Ce/qe, y-axis). In the Freundlich isotherm, the graph is drawn between the logarithm of the remaining equilibrium concentration (log Ce, x-axis) and the adsorbed solute amount (log qe, y-axis). The Freundlich isotherm model describes multilayer heterogeneous adsorption. This model suggests that biosorption increases with raised concentration. On the other hand, kinetic models are equations used to determine the adsorption mechanism and adsorption time. The graph is drawn between time (t, x-axis) and the ln value of qe-qt (y-axis, removed dye amount at equilibrium - removed dye amount at any time) to calculate the pseudo-first-order kinetic model parameters. The graph between time (t, x-axis) and qt/t (y-axis) values is drawn to calculate the parameters in the pseudo-second-order kinetic model. In the thesis, Ulocladium chartarum MRC72584 fungus was used for the biosorption of Reactive Yellow 145 (RY145) and Direct Blue 86 (DB86) textile dye mixture. RY145 belongs to the azo dye class, and DB86 belongs to the phthalocyanine class. The absorption wavelengths of these two dyes overlap in the mixture solution. The first derivative method was used to calculate dye concentrations. In the first derivative spectrum, the signal of the DB86 was close to zero at 477.6 nm, and the signal of the RY145 was different from zero. Thus, the calibration curve was created at 477.6 nm to analyze the RY145. Similarly, for DB86, 602.0 nm, where the signal of RY145 is close to zero, was selected, and the calibration curve was created at this wavelength. The limit of detection (LOD) and limit of quantitation (LOQ) values of the developed method were calculated separately for the dyes. The method's accuracy was evaluated by the recovery percentage (R%) values of the 15 prepared mixtures. The method's precision was examined by calculating the relative standard deviation (RSD%) values. The fungus was grown in the nutritional medium for three days, and the obtained fungus was filtered and then killed in an autoclave. The dead fungus is dried in an oven before use. Biosorption experiments were performed by adding dead fungus to the dye mixture solution. After the process, the solution was centrifuged, and the upper solution was measured using a UV-Vis spectrophotometer. Different process parameters were examined to achieve maximum removal. The pH effect was examined between pH 2 – 12, and the best removal for both dyes was obtained at pH 4. The other performed parameters were the effect of time (15 - 120 min), stirring speed (50 - 200 rpm), and solution temperature (20 - 50 °C) using an orbital shaker. The increased amount of dead fungus increased removal efficiencies. Also, the raised dye concentrations decreased the removal percentages. As a result, 100% biosorption was achieved using 1.0 g of dead Ulocladium chartarum fungus at pH 4, 60 min, 125 rpm stirring speed, 25 °C, with a mixture of 50 mg/L dye concentration (from each dye). The biosorption better fits the pseudo-second-order kinetic model and Langmuir isotherm for both dyes.