Researchers from the Frank Laboratory of Neutron Physics, JINR, have explored the possibility of using brewer's yeast to remove heavy metals from wastewater. Using the example of real electroplating effluent containing zinc and other metals, as well as model wastewater solutions of different compositions, they studied optimal conditions for its use and mechanisms of heavy metal adsorption by the biosorbent.

Heavy metal water pollution

Since ancient times, man has strived to purify water from contaminants. If thousands of years ago people used settling ponds, sand, charcoal and plants for this purpose, nowadays they apply a variety of physicochemical methods and biotechnological processes. Today, the level of water pollution has a serious impact on people's lives and the development of the world economy. The shortage of fresh water continues to grow in the world, while industrial and domestic water consumption has risen by almost an order of magnitude over the past century. One of the sources of water pollution is the discharge of untreated or insufficiently treated industrial wastewater containing heavy metal ions (copper, zinc, nickel, strontium and others), which affects the pH, color, transparency and other properties of water and pollutes the environment, harming living organisms and posing a threat to humans as it can lead to various diseases.

Ions of one of these metals, for example, zinc, are found in high concentrations in wastewater from electroplating, metalworking, mining and petrochemical facilities. In water, they accumulate in bottom sediments in the form of hydroxides, carbonates, sulfides or phosphates. On the other hand, zinc is an essential trace element and a component of several hundred enzymes involved in various metabolic processes in the human body. Intake of excessive amounts of zinc, however, leads to severe poisoning, and its removal is problematic due to the fact that heavy metals bind tightly to proteins and other components of cell structures.

Therefore, the task of wastewater treatment and heavy metal removal is of particular importance. Various conventional physical and chemical methods (flocculation, precipitation, ion exchange, membrane separation and solvent extraction) are not always sufficiently effective, environmentally friendly or economically justified in contrast to innovative biotechnological methods of treatment. In biosorption, for example, non-living microorganisms such as algae and bacteria, fungi and yeast are used, which efficiently remove metals from wastewater.

Yeast and kinetics of biosorption

Over the last few years, scientists at FLNP have been conducting research in the field of environmental chemistry, studying various composite sorbents and biosorbents for heavy metal removal from wastewater using advanced, state-of-the-art laboratory equipment. This time, their studies focused on an inexpensive, safe and effective biosorbent - yeast cells of Saccharomyces cerevisiae (brewer’s yeast). These microorganisms are extensively used in beverage and food production and are therefore available in large quantities at a low cost as a by-product of fermentation processes.

To assess the efficiency of adsorption of zinc, nickel, strontium and barium in model effluents, the scientists performed neutron activation analysis (NAA), which is a sensitive method for qualitative and quantitative analysis of elements, using an NAA facility at the IBR-2 pulsed reactor. The concentration of copper was determined by means of atomic absorption spectrometry, and high-resolution inductively coupled plasma mass spectrometry was used to measure concentrations of metals in real effluents before and after sorption experiments.

The study of sorption kinetics in wastewater treatment, that is, the mechanism and rate of the processes, allows the nature of biosorption (chemical or physical) to be determined. Surface adsorption, chemisorption, and ion exchange were found to be the main mechanisms of metal removal from solution. In addition, the scientists evaluated the effect of contact time, initial zinc concentration, temperature, and pH on the sorption process in model effluents. According to their results, at a pH range of 3.0-6.0, which is optimal for metal removal, model effluents can be purified by 45-100% (depending on the metal) in 15-45 minutes. With an increase in the concentration of zinc ions, the biosorbent more actively removes zinc from solutions, without affecting the sorption of other metal ions.

Treatment of wastewater from electroplating plant in Dubna

“We have studied the effect of pH and sorbent dosage on the removal of heavy metals from electrotechnical effluents. At a biosorbent concentration of 10 g/L, by varying pH, we managed to reduce the concentration of copper, barium, strontium and nickel ions below the maximum permissible concentration values. In our experiments, the maximum efficiency for removal of Zn ions was achieved in two stages (first, by adding the biosorbent at a dosage of 20 g/L, and then adding 10 g/L of yeast biomass to the effluent obtained after the first stage of purification) at pH 6.0 and contact time of 60 min. The additional treatment to remove zinc ions was necessitated by a higher concentration of this metal compared to other pollutants,” explained the study leader Dr. Inga Zinicovscaia, a researcher at FLNP.

Thus, the scientists have shown that yeast cells of Saccharomyces cerevisiae proved to be an excellent candidate for treatment of complex industrial effluents containing zinc and other heavy metal ions, and the sorption efficiency is determined by the pH values and the dosage of the sorbent.

As noted in the study*, biological sorbents that cannot be regenerated after several cycles of industrial wastewater treatment can be used as additives for road construction materials.

* Inga Zinicovscaia, Nikita Yushin, Daler Abdusamadzoda, Dmitrii Grozdov and Margarita Shvetsova. Efficient Removal of Metals from Synthetic and Real Galvanic Zinc–Containing Effluents by Brewer’s Yeast Saccharomyces cerevisiae. Materials 2020, 13(16), 3624; https://doi.org/10.3390/ma13163624

Olga Baklitskaya-Kameneva