Biosorption of Astrazone Blue basic dye from an aqueous solution using dried biomass of Baker's yeast

Abstract

In this study dried biomass of Baker's yeast, Saccharomyces cerevisiae, is used as a sorbent for Astrazone Blue basic dye aqueous solution.

Factors affecting the adsorption process: dye concentration, contact time, temperature and pH were investigated. The equilibrium concentration and the adsorption capacity at equilibrium were determined using three different sorption models namely: Langmuir, Freundlich and Temkin isotherms. It was found that increasing temperature and pH result in higher dye loadings per unit weight of the sorbent. The results gained from this study were described by Langmuir isotherm model better than Freundlich and Temkin isotherm models. The calculated heat of adsorption of the dye–yeast system indicates that the bio-sorption process is taking place by chemical adsorption and has an endothermic nature. The maximum adsorption capacity at 30 °C and pH 7 was calculated as 70 mg/g for dried biomass of Baker's yeast compared to 18.5 mg/g for commercial granular activated carbon, indicating that dried biomass of Baker's yeast can be considered as a good sorbent material for Astrazone Blue solution.

Introduction

Controlling pollution is the main concern of society today. Large amounts of dyes are annually produced and used in textile, cosmetics, paper, leather, pharmaceutical, food and other industries. The textile industry accounts for two-thirds of the total dyestuff market [1]. Even a very small amount of dye in water (10–50 mg/L) affects the aesthetic value, water transparency and gas solubility in water bodies [2]. Moreover, it may also affect photochemical activities in aquatic systems by reducing light penetration [3]. It has been also reported that several commonly used dyes are carcinogenic and mutagenic for aquatic organisms [4].

Removal of textile dyes from waste water is still of a major environmental concern because they are difficult to be removed by the conventional waste water treatment systems since they are designed to be resistant to degradation or fading by oxidizing agents and light. They must also be resistant to both high temperatures and enzyme degradation resulting from detergent washing. For these reasons, methods based on photo-degradation, aerobic and anaerobic biodegradation are slow and complete mineralization of most dyes is rather difficult. Degradation products are toxic to aquatic organisms [5]. The presence of such compounds in waste water is offensive and their removal is difficult.

Many physical and chemical methods including coagulation, flocculation, precipitation, filtration, adsorption, chemical degradation, ozonation and oxidation have been used for the treatment of dye-containing effluents [6]. Coagulation and flocculation using polyelectrolytes, lime, alum or ferrous salts produce huge amounts of toxic sludge that pose handling and disposal problems in addition to materials cost [7]. Alternatively, various adsorbents such as activated carbon and silica gel have been tested and used for the removal of dyes from polluted water. Activated carbon is the most widely used adsorbent for the removal of color and the treatment of textile effluents, but it is expensive [2]. This led many workers to search for the use of cheap and efficient alternative materials such as bagasse pith, carbonized bark, natural clay, peat, soil, wood chips, rice husk ash, fly ash, living or dead microbial biomass and algae, etc. [8], [9], [10].

Biologically based adsorption (biosorptions) uses low cost biological materials, namely living or dead microorganisms. Removal of organic colors using biosorption process stems from the work on the removal of metals in biological waste water treatment systems. The interactions between microorganisms (yeast, bacteria and/or fungi) and dyes depend on the chemical properties of all the reaction partners. Each dye has certain affinity to various microorganisms and on the other side one microorganism is able to bind or degrade more types of dyes [11].

Adsorption of solutes (adsorbates) from solutions or suspensions onto solid materials (adsorbents) occurs mainly through one of the following mechanisms: exchange of molecules from solution to the adsorbent, physical adsorption due to van der Waals forces and chemisorption [12].

Ability of Baker's yeast (Saccharomyces cerevisiae) as biosorbent for heavy metals has been recognized [13], [14], [15], [16]. However, there have been few researches on biosorption of textile dyes by S. cerevisiae which is inexpensive, safe, easily grown, readily available and produces high yields of biomass [1], [17], that is why it was selected as adsorbent material for the present study. Aim of this study is to investigate the sorption of a basic dye, Astrazone Blue, from an aqueous solution using dried biomass of Baker's yeast S. cerevisiae. Effect of some system variables including; dye concentration, contact time, temperature and pH were studied. Different published adsorption isotherm models were examined in order to choose the best fitting one to the obtained experimental data.