This study is devoted to the Fenton reaction, which, despite hundreds of reports in a number of scientific journals, provides opportunities for further investigation of its use as a method of advanced oxidation of organic macro- and micropollutants in its diverse variations and hybrid systems. It transpires that, for example, the choice of the concentrations and ratios of basic chemical substances, i.e., hydrogen peroxide and catalysts based on the Fe²⁺ ion or other transition metals in homogeneous and heterogeneous arrangements for reactions with various pollutants, is for now the result of the experimental determination of rather randomly selected quantities, requiring further optimizations. The research to date also shows the indispensability of the Fenton reaction related to environmental issues, as it represents the pillar of all advanced oxidation processes, regarding the idea of oxidative hydroxide radicals. This study tries to summarize not only the current knowledge of the Fenton process and identify its advantages, but also the problems that need to be solved. Based on these findings, we identified the necessary steps affecting its further development that need to be resolved and should be the focus of further research related to the Fenton process.

The freshwater green microalgae, Dictyosphaerium chlorelloides (CCALA 330), has the ability to produce extracellular polysaccharides (EPS). Conditions for optimum growth and EPS overproduction were determined in laboratory-scale tubular photobioreactors (PBR) with a working volume of 300 mL. Multiple limitations in nutrient supply were proven to be an effective method for EPS overproduction. Salinity stress was also applied to the culture, but no significant increase in EPS production was observed. The effects of different nitrogen sources were examined and the microalgae exhibited the fastest growth and EPS production in medium containing ammonium nitrate. Under determined optimal conditions, EPS concentration reached 10 g/L (71% of the total biomass) and a total biomass of 14 g/L at the end of 17 days cultivation. Pilot-scale cultivation was also carried out in a column type airlift photobioreactor (PBR) with a working volume of 60 L. A new and efficient methodology was developed for separating cells from the EPS-containing culture broth. Due to the strong attachment between cells and EPS, high-pressure homogenization was carried out before a centrifugation process. The EPS in the supernatant was subsequently purified using ultrafiltration. The green microalgae Dictyosphaerium chlorelloides may therefore be appropriate for the commercial production of EPS.

The method of decomposition of chlorinated organic substances in contaminated water based upon successive steps of chemical pretreatment of organic compound with a) active radicals (Fenton reaction) and/or with b) reductive dehalogenation on metallic Pd in the presence of zero‐valent iron, followed by aerobic biodegradation using bacteria strain Pandoraea sp. was studied. 4‐chlorophenol was chosen as a model compound. Generally, chlorophenols show limited biodegradability. The average efficiency of biodegradability of 4‐chlorophenol with both free and immobilized cells does not exceed 70% after 42 days of biodegradation, but their intermediates obtained by partial oxidation (products of hydrolytic‐hydroxylation) and/or a product of their partial reductive dechlorination (phenol) show increased biodegradability. To test the efficiency of the method, water exposed to this contaminant was treated in the laboratory in batch conditions. Because the products of partial oxidation and partial reductive dehalogenation of 4‐chlorophenol essentially differ, the main factor studied was the efficiency of biodegradation of 4‐chlorophenol after oxidative or reductive pre‐treatment steps. In comparison with the rate of biodegradation using free cells without application of the pre‐treatment step, the rate of degradation of 4‐chlorophenol by the application of consecutive combination of Fenton reagent and biotreatment was two‐fold. As for the combination of reductive dechlorination pre‐treatment step with consecutive biodegradation, the rate of decontamination of the 4‐chlorophenol was a little bit higher here in comparison with the rate of biotreatment after the pre‐oxidizing step: the remaining concentration of 4‐chlorophenol corresponding to the sampling in 7, 28, and 56 days after the inoculation were 70 mg/L, 12 mg/L, and 1.1 mg/L, respectively, in samples containing the average initial concentration of 126 mg/L of 4‐chlorophenol. Positive results may probably be due to the co‐substrate effect of phenol presented in the samples after the pre‐traetment reductive step. We have shown that both procedures followed with aerobic biodegradation can be considered suitable for removing hazardous chlorinated compounds from contaminated waters. The rate of biodegradation after the application of pre‐treatment procedures was slightly enhanced in comparison with the rate of biodegradation without the application of the pre‐treatment steps. It is evident that the choice of the decontamination pre‐treatment procedure cannot be generalized and will essentially depend upon the type and concentration of target contaminants and on process costs.

Municipal waste water treatment plants have a fundamental task, which is to rid waste water of toxic and health-threatening organic and inorganic substances, including unwanted microorganisms and other pollutants, with the highest possible efficiency so that the discharged water does not contaminate the natural environment, which happens in the case of imperfect cleaning. Current WWTPs usually have a preliminary, primary, and secondary stage, and in very few cases even a tertiary stage, which no longer guarantees the sufficient removal of pollutants from waste water. This research presents the current situation in different parts of the world concerning the possibility of solving the current situation regarding the tertiary and quaternary stages of this process, especially in small and rural WWTPs serving up to approx. 10,000 equivalent inhabitants, which could ensure the removal of so-called emerging pollutants, including microplastics, and would stop WWTPs being point sources of environmental contamination.

This review summarizes the current knowledge in the field of preparing new and/or innovative materials that can be advantageously used for the sorption of emerging pollutants from water. This paper highlights new innovative materials such as transition metal-modified biochar, zeolites, clays, carbon fibers, graphene, metal organic frameworks, and aerogels. These materials have great potential for the removal of heavy metals from water, particularly due to their large surface area, nanoscale size, and availability of various functionalities; moreover, they can easily be chemically modified and recycled. This paper not only highlights the advantages and ever-improving physicochemical properties of these new types of materials but also critically points out their shortcomings and suggests possible future directions.