Cyanobacterial water blooms represent toxicological, ecological and technological problems around the globe. When present in raw water used for drinking water production, one of the best strategies is to remove the cyanobacterial biomass gently before treatment, avoiding cell destruction and cyanotoxins release. This paper presents a new method for the removal of cyanobacterial biomass during drinking water pre-treatment that combines hydrodynamic cavitation with cold plasma discharge. Cavitation produces press stress that causes Microcystis gas vesicles to collapse. The cyanobacteria then sink, allowing for removal by sedimentation. The cyanobacteria showed no signs of revitalisation, even after seven days under optimal conditions with nutrient enrichment, as photosynthetic activity is negatively affected by hydrogen peroxide produced by plasma burnt in the cavitation cloud. Using this method, cyanobacteria can be removed in a single treatment, with no increase in microcystin concentration. This novel technology appears to be highly promising for continual treatment of raw water inflow in drinking water treatment plants and will also be of interest to those wishing to treat surface waters without the use of algaecides.

Solid particles (SP) suspended in water represent a common contamination that degrades the water quality, not only in drinking water sources. Particles differ in size, nature, and related features like surface charge. Thus, various methods can be utilized for their removal—physical approaches including settling or filtration, chemical coagulation/flocculation, biological microbial degradation, and others. This paper aims to summarize currently available methods for SP removal with special attention devoted to alternative, cost-effective, sustainable, and eco-friendly approaches with low energetic demands where the power of renewable energy sources can be utilized. Besides SP properties, the selection of the proper method (or a sequence of methods) for their separation also depends on the purpose of water treatment. Drinking water production demands technologies with immediate effect and high throughputs, like conventional filtration and coagulation/flocculation (electro- or chemical with alternative coagulant/flocculant agents) or some hybrid approaches to ensure quick and cost-effective decontamination. Such technologies usually imply heavy machinery with high electricity consumption, but current progress allows the construction of smaller facilities powered by solar or wind power plant systems. On the other hand, water decontamination in rivers or ponds can include slower processes based on phytoremediation, being long-term sustainable with minimal energy and cost investments.

We investigated the production of highly reactive oxygen species (ROS) in solutions undergoing treatment using CaviPlasma (CP) technology. This technology combines plasma discharge with hydrodynamic cavitation. This study focused on factors such as pH, conductivity, presence of salts and organic matter affecting ROS formation and their stability in solutions. Depending on the used matrix, CP produces 450–580 µg L⁻¹ s⁻¹ of hydrogen peroxide and 1.9 µg L⁻¹ s⁻¹ of hydroxyl radicals dissolved in liquid. Using cyanobacteria and cyanotoxins as example, we proved that CP technology is a highly efficient method for destroying microorganisms and persistent toxins. The biocidal effect of the CP treatment was confirmed on two species of cyanobacteria, Synechococcus elongatus and Merismopedia minutissima. The effectiveness of the technology in degrading microcystins was also demonstrated. The potential of this technology is based on its high energy efficiency, G(H₂O₂) ≈ 10 g kWh⁻¹ and G(O₃) ≈ 0.03 g kWh⁻¹ (in deionised water), realistic applicability with throughput rates (> 1 m³ h⁻¹), and comparatively easy scalability system.

The present paper investigated the potential of hydrodynamic cavitation (HC) as an effective tool for activating sodium percarbonate (SPC). The method's efficiency was demonstrated by effectively removing estrogens, which are pollutants that have adverse impacts on aquatic ecosystems. The effects of the SPC concentration, temperature of solution, and cavitation time were evaluated. After SPC/HC treatment, the removal of estrogens was monitored by liquid chromatography-tandem mass spectrometry (LC -MS/MS). Already after 4 s of treatment and 24 h of reaction time, more than 97% of estrogens (initial concentration of 300 ng/L) were removed. The effect of post-treatment time is not considered in several papers, even though it seems to be crucial and is discussed here. The results were supported by the values of degradation rate constants, which fit the pseudo-first-order kinetic model. We also verified that HC alone was not effective for estrogen removal under the selected conditions. The sustainability of the SPC/HC system was evaluated based on electric energy per order calculation. The combination of SPC and HC is a promising approach for rapidly degrading micropollutants such as estrogenic compounds without the need for additional technological steps, such as pH or temperature adjustment.

The production and use of manufactured chemicals have risen significantly in the last few decades. With interest in preserving and improving the state of the environment, there is also growing interested in new technologies for water purification and wastewater treatment. One frequently discussed technological group is advanced oxidation processes (AOPs). AOPs using sulphur-based radicals appear to reduce the volume of organic contaminants in wastewater significantly. The use of persulfate has excellent potential to successfully eliminate the number of emerging contaminants released into the environment. The main disadvantage of sulphur-based AOPs is the need for activation. We investigated an economically and environmentally friendly solution based on hydrodynamic cavitation, which does not require heating or additional activation of chemical substances. The method was evaluated for emerging contaminant removal research, specifically for the group of steroid estrogens. The mixture of estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2) was effectively eliminated and completely removed during a treatment that lasted just a few seconds. This novel method can be used in a broad spectrum of water treatment processes or as the intensification of reactions in chemical engineering technologies.

The fate of pharmaceuticals in the human body, from their absorption to excretion is well studied. However, medication often leaves the patient’s body in an unchanged or metabolised, yet still active, form. Diazepam and its metabolites, ranging up to 100 µg/L, have been detected in surface waters worldwide; therefore, the question of its influence on model aquatic plants, such as duckweed (Lemna minor), needs to be addressed. Lemna was cultivated in a Steinberg medium containing diazepam in three concentrations—0.2, 20, and 2000 µg/L. The activity of superoxide dismutase (SOD) and catalase (CAT), leaf count, mass, and the fluorescence quantum yield of photosynthesis were assessed. The medium was also analysed by LC-MS/MS to determine the concentration of diazepam metabolites. Our results show no negative impact of diazepam on Lemna minor, even in concentrations significantly higher than those that are ecotoxicologically relevant. On the contrary, the influence of diazepam on Lemna suggests growth stimulation and a similarity to the effect diazepam has on the human body. The comparison to the human body may be accurate because γ-Aminobutyric acid-like (GABA-like) receptors responsible for the effect in humans have also been recently described in plants. Therefore, our results can open an interesting scientific area, indicating that GABA receptors and interference with benzodiazepines are evolutionarily much older than previously anticipated. This could help to answer more questions related to the reaction of aquatic organisms to micropollutants such as psychopharmaceuticals.