Pollution of the aquatic environment with microplastics has recently been recognised as a new environmental threat considering their negative impact on the ecosystem. Due to the low density and small particle size of microplastics, they are easily discharged into sewage systems and wastewater treatment plants. Thus, wastewater treatment plants are considered major sources of microplastic pollution in aquatic and terrestrial environments. Therefore, there is an urgent need for an in-depth understanding of the occurrence, behaviour, and fate of microplastics in wastewater treatment plants before they are discharged into natural water bodies. This paper comprehensively reviews the current state of knowledge on the characteristics and removal of microplastics in a series of wastewater treatment plants by comparing their removal efficiency in different unit processes, both during pretreatment, biological treatment, and tertiary treatment. The study found varying efficiencies in wastewater treatment technologies, with the first stage of treatment removing between 16.5 and 98.4% of microplastics, while during biological treatment the overall efficiency of microplastics removal ranges from 78.1 to 99.9% (membrane bioreactor). Nevertheless, given the large volumes of wastewater continuously discharged to receiving bodies, even tertiary treatment plants can be a significant source of microplastics in surface waters. The largest fraction of MPs removed in conventional wastewater treatment plants is trapped in the sludge. Among the critical treatment technologies, microplastic quantitative analysis showed that membrane bioreactors and filter-based treatment technologies have the highest microplastic removal efficiency. Based on a review of the existing literature, it was concluded that existing wastewater treatment plants are ineffective in removing microplastics completely, and there is a risk that they could be discharged into surrounding water sources.

Boron is emitted into the environment in a natural (weathering of rocks) and anthropogenic (wastewaters coming from industry, agriculture) way. It is a micronutrient for plants and animals, as well as a useful component in many branches of commercial activities. However, an excess of boron is toxic for both plants and animals. Extremely narrow is the range between permissible and harmful doses both to people and plants. It is often necessary to remove it from water and wastewater. The acceptable content of boron in drinking water and wastewater discharge into the environment is 1 mg/L. Removal of boron from the aquatic environment can be carried out in the following ways: ion exchange and adsorption onto boron-selective resins; reverse osmosis, in multistage configurations with RO and sorption; hybrid systems combining sorption onto fine resins with membrane filtration and polymer-enhanced ultrafiltration; processes with application of ion exchange membranes. The work presents a comprehensive review of the literature on boron removal with above-mentioned methods. The fundamentals of each process and the effect of experimental parameters are discussed.

The aim of the study was to compare the two reference methods for the determination of boron in water samples and further assess the impact of the method of preparation of samples for analysis on the results obtained. Samples were collected during different desalination processes, ultrafiltration and the double reverse osmosis system, connected in series. From each point, samples were prepared in four different ways: the first was filtered (through a membrane filter of 0.45 μm) and acidified (using 1 mL ultrapure nitric acid for each 100 mL of samples) (FA), the second was unfiltered and not acidified (UFNA), the third was filtered but not acidified (FNA), and finally, the fourth was unfiltered but acidified (UFA). All samples were analysed using two analytical methods: inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The results obtained were compared and correlated, and the differences between them were studied. The results show that there are statistically significant differences between the concentrations obtained using the ICP-MS and ICP-OES techniques regardless of the methods of sampling preparation (sample filtration and preservation). Finally, both the ICP-MS and ICP-OES methods can be used for determination of the boron concentration in water. The differences in the boron concentrations obtained using these two methods can be caused by several high-level concentrations in selected whole-water digestates and some matrix effects. Higher concentrations of iron (from 1 to 20 mg/L) than chromium (0.02–1 mg/L) in the samples analysed can influence boron determination. When iron concentrations are high, we can observe the emission spectrum as a double joined and overlapping peak.