Materials, Methods & Technologies ISSN 1314-7269, Volume 13, 2019 Journal of International Scientific Publications www.scientific-publications.net Page 230 EXTRACELLULAR BIOSYNTHESIS OF SILVER NANOPARTICLES BY TRICHODERMA REESEI AND THEIR APPLICATION TO REMOVE XANTHOGENATE FROM WASTEWATER O. Ts. Gemishev 1 *, M. I. Panayotova 2 , V. T. Panayotov 2 , E. S. Zaharieva 1 1 Department of Biotechnology, Faculty of Biology, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria 2 Department of Chemistry, University of Mining and Geology, Sofia, Bulgaria Abstract Application of fungi in the biosynthesis of silver nanoparticles is a green and feasible alternative to chemical and physical methods used for AgNPs synthesis. The fungus Trichoderma reesei is a non- pathogenic and environmentally friendly microorganism capable to produce extracellular enzymes and metabolites in high scale. An extracellular biosynthesis of silver nanoparticles (AgNPs) from AgNO 3 solution by using the cell-free extract of Trichoderma reesei biomass is presented in this study. Kinetics of the biotransformation is described by a second order reaction equation. Spherical or approximately spherical AgNPs that are well-dispersed and with a size between 3-4 and 15-17 nm have been produced at transformation degree of 30 % with respect to the initial silver ions concentration. The biosynthesized AgNPs show high stability against agglomeration even after storage for 60 days. Soluble xanthates, used in some industrial applications, are found toxic to aquatic biota even at low concentrations. The synthesized AgNPs are capable to immobilize potassium amyl xanthate from model wastewater. The pollutant adsorption is described by the Langmuir adsorption isotherm and the calculated maximum adsorption capacity is 4.67 mg/mg. The pollutant immobilization by AgNPs is much faster process and requires much less adsorbent (50 fold) in comparison with the activated carbon (chemical grade of purity). Keywords: silver nanoparticles, biosynthesis, Trichoderma reesei, potassium amyl xanthate removal 1. INTRODUCTION Nanosized particles have attracted the interest of scientific community due to their unique properties. Silver is one of metals often used for production of nanoparticles for different environmental applications, such as water disinfection, removal of pollutants from water, gas sensing etc. All those applications require stable, non-aggregable and in many cases non-hydrophobic nanoparticles. The Ag nanoparticles (AgNPs) can be synthesized by diverse physical (evaporation-condensation, laser ablation) and chemical (by use of organic and inorganic reducing agents) routes. In recent years the green synthesis of AgNPs is emphasized. It includes the use of plant extracts, and extracts from microbial sources like bacteria, fungi, algae and yeast. The biosynthesis method is considered to be “green”, i.e. clean, nontoxic and environmentally acceptable. The green synthesis of nanoparticles by fungi is thought as an important method due to the presence of a variety of enzymes in their cells and the simple handling. High rate of specific metabolite production, fast growth rate, easy, safe and efficient harvesting arrange the fungi among the most suitable candidates for metal nanoparticles synthesis. Seventy percent of fungi which have been studied as AgNPs biosynthesis agents are pathogenic for plant, human or animals [1]. Their use requires measures and costs to deal with their side negative effects on human society and the environment. Some Trichoderma species are a good example of nonpathogenic fungi for safe and environmentally friendly production of AgNPs. Extracellular biosynthesis of AgNPs has been realized by using T. asperellum [2], T. viride [3], T. atroviride [4], T. harizianum [5], T. koningii [6]. The fungus Trichoderma reesei is a non-pathogenic, environmentally friendly microorganism with high scale