Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae (Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides) and one cyanobacteria (Microcystis aeruginosa) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO2 for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe2+ and Fe3+ cations in ammonia at room temperature. Subsequently, the prepared Fe3O4 nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe3O4. The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

Synthetic dyes widely used in many kinds of industry affect the colour of wastewater when released to environment due to insufficient treatment in typical sewage treatment plants. Only a small dose of those dyes may significantly affect colour of water and, according to the chemical composition, may pose risks to wildlife and humans. In the research described in this study, decolorization of three various dyes was investigated. Since colour removal of Congo Red such as Methylene blue using ozone have been reported by several authors, and the literature on Naphthol Green B is rather limited, in the present study we compare the decolorization rate of CR, MB and NGB. The colour removal occurred quickly and more than 90% of colour reduction was achieved within 3-6 minutes throughout all tested pH of the solution.

Nowadays, we can hardly imagine our life without the achievements of modern technology, such as refrigerators, televisions, computers, or smartphones. Producers are pushing consumers to buy newer, more modern appliances instead of repairing the original ones. However, all the devices represent a huge amount of waste. E-waste is one of the fastest growing types of waste, and only less than a half of it is recycled. Its disposal poses a great challenge for the population and constitutes a huge burden for the environment. In the research described in this article, we focused on individual techniques for metals recovery from e-waste. In the experimental part, we deal with the recycling of electronic waste by bioleaching, using microorganisms Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Compared to conventional techniques, bioleaching is a more environmentally friendly and economical alternative of metals recovery from e-waste.

Over the last few decades, nanotechnologies have gained a great deal of attention, and various nanomaterials and techniques have been developed for water remediation. This study deals with the adsorption of Naphthol green B onto the magnetite nanoparticles synthetized by the coprecipitation method at the laboratory temperature. According to the obtained results, the sorption process is obvious only at the acidic condition when the pH of solution decreases to pH level 3. According to nonlinear fit of experimental data, the sorption of the Naphthol green B onto magnetite nanoparticles is assumed as multilayer, while the Freundlich model fits better (96.158 %) than the Langmuir model does (55.941 %).