Although dilution of lake water has been used for improvement of water quality and algal blooms control, it has not necessarily succeeded to suppress the blooms. We hypothesized that the disappearance of algal blooms by dilution could be explained by flow regime, nutrient concentrations, and their interaction. This study investigated the effects of daily renewal rate (d), nitrogen (N) and phosphorus (P) concentration, and their interaction on the domination between Microcystis aeruginosa and Cyclotella sp. through a monoxenic culture experiment. The simulation model as functions of the N:P mass ratio and dilution rate (D) (calculated from d) was constructed, and the dominant characteristics of both species were predicted based on the model using parameters obtained in a monoculture experiment and our previous study. Results of monoxenic culture experiment revealed that M. aeruginosa dominated in all conditions (d = 5 or 15%; N = 1.0 or 2.5 or 5.0 mg-N L⁻¹; P = 0.1 or 0.5 mg-P L⁻¹) and the predicted cell densities were substantially correspondent to experimental data. Under various N:P ratios and D values, characteristics of domination for each species were predicted, indicating that Cyclotella sp. tended to be dominant under high P concentrations (P ≥ 0.36 mg-P L⁻¹) when the N:P ratio was less than 7.0, and M. aeruginosa could not form algal blooms at the N:P ratio ≤ 7.0 (N ≤ 0.7 mg-N L⁻¹). It was also suggested that the dilution rate leading to the Cyclotella sp. domination required 0.20 day⁻¹ or higher regardless of the N:P ratios. Graphical Abstract • M. aeruginosa and Cyclotella sp. could be a superior competitor in nutrient-limited and nutrient-rich conditions, respectively. • The simulation model in this study indicated that the predicted cell density and nutrient concentration were substantially correspondent to experimental data. • The model predicted that Cyclotella sp. tended to be dominant at the P ≥ 0.36 mg-P L⁻¹ when the N:P ratio was less than 7.0, and M. aeruginosa could not form algal blooms at the N:P ratio ≤ 7.0 (N ≤ 0.7 mg-N L⁻¹).

Hexavalent chromium is a type of toxic chemical, it may cause allergies, hereditary genetic defects and cancer in humans by inhalation, and it is also a persistent danger to the environment. However, chromium metal, trivalent chromium and tetravalent chromium have low toxicities. In this study, semiconductor materials (quartz fibre and TiO₂) were added to a hexavalent chromium solution and the removal efficiency of hexavalent chromium as a function of the γ-ray irradiation dose, as well as the catalytic mechanism, was investigated. It was observed that the reduction of hexavalent chromium by γ-ray irradiation was largely promoted in the presence of semiconductor materials; the semiconductor materials act as catalysts under the gamma-ray irradiation. The hexavalent chromium in the solution can be converted to an insoluble precipitate by gamma-ray irradiation. These results are highly beneficial to apply semiconductor materials as catalysts for the removal of contaminants by radiation.

The operation variables and electro-kinetic field (EKF) were investigated to enhance the remediation of arsenic (As)- and cesium (Cs)-contaminated soils with soil washing. Extractant types, concentrations, liquid/solid (L/S) ratios, solution pH values, washing temperatures, and agitation modes were important criteria to determine the efficiency of soil washing. The KH₂PO₄ was proved to be a suitable alternative to Na₂EDTA in extracting As and Cs from contaminated soils. A 2-h washing with KH₂PO₄ at concentration of 0.01 M and L/S ratio of 20 mL g⁻¹ showed the most efficient washing performance. In addition, the lower solution pH, higher temperature, and ultrasound also favored soil washing of As and Cs with KH₂PO₄. The EKF greatly enhanced metals extraction with soil washing. It offered acidic soil environment around the anode areas for the release of soluble Cs from its soil solid-phase components before soil washing. Moreover, the alkalization around the cathode areas also benefited the desorption of stable As since labile As were mainly presented in anionic forms. The effect of CA for neutralizing OH⁻ was proved to be limited, while the reversed subsequent EKF process effectively alleviated Cs precipitation generated during the initial EKF process. It also effectively restored soil pH altered by the initial EKF. The overall EKF (4 V cm⁻¹) enhanced removal efficiency of As and Cs with soil washing from the anode area was 37 and 31%, respectively. Higher removal of As (52%) was obtained in the cathode area. Moreover, the reversed EKF resulted in another 28% removal of Cs in the initial cathode area which showed the capacity of EKF on continuous soil metal remediation.

The purpose of this research was to evaluate the biodegradation extent of petroleum hydrocarbons by Phormidium ambiguum strain TISTR 8296 in the presence of inorganic nutrients and heavy metals as co-contaminants. In this context, waste motor oil served as a source of petroleum hydrocarbons. Strain TISTR 8296 grew actively with waste motor oil at 0.5–2.0% (v/v) concentrations and also exhibited good biodegradation potential at this concentration range. Meanwhile, its growth and biodegradation capacity fell down with increasing oil concentration to 3.0 and 4.0%. Strain TISTR 8296 adapted quickly to pH changes, showing good growth ability and biodegradation capability at a pH range of 4.0–9.0 with an acidic pH of 4.0 and 5.0 appearing to decelerate its biodegradation efficiency. The addition of PO₄ ³⁻ and NO₃ ⁻ exerted a strong stimulatory effect on growth and biodegradation efficiency, while a slight promoting effect was observed for NO₂ ⁻. By contrast, amendment of NH₄ ⁺ as well as heavy metals caused a substantial inhibitory effect on growth and biodegradation efficiency with NH₄ ⁺ and Mn(II) appearing to show a weak suppressing effect. GC-MS analyses indicated that strain TISTR 8296 could transform and degrade both aliphatic and aromatic compounds.

The mechanisms involved in immobilization of soil Cu and the role of extracellular polymeric substances (EPS) in Cu(II) adsorption by Bacillus subtilis DBM were investigated in this study. Adsorption and desorption experiments with intact DBM cells revealed that complexation with surface functional groups and intracellular accumulation were involved in the immobilization of soil Cu. The removal of EPS using cation exchange resin resulted in a 26.6% decrease in the Cu(II) adsorption capacity relative to untreated cells. Compared to intact cells, EPS-free cells showed a 9.9% decrease in the proportion of complexed Cu(II), while the intracellular fraction increased by 8.0%. Surface complexation modeling indicated that the total concentration of complexation sites on the intact DBM cell surface was 1.11 mmol/g dry biomass, which was decreased by 17% to 0.92 mmol/g after EPS removal. Infrared analysis revealed that the pKa values of the carboxyl and phosphate groups in the DBM cell wall differed from those in the EPS. Carboxyl, carbonyl, hydroxyl, amino, and phosphate groups were involved in binding Cu(II) by both intact and EPS-free cells, and Cu(II) was more likely to combine with organic rather than inorganic phosphates. The presence of the EPS increased the binding potential of surface functional groups and may help to prevent heavy metals from entering the cells.

The efficiency of the following systems: photolysis (UV-C only), photocatalysis with titanium-dioxide (UV-C/TiO₂), photocatalysis with granular-activated carbon (UV-C/GAC), and by adsorption on GAC, was assessed under different initial contaminant concentrations, i.e., 0.1–100 mg L⁻¹. The experiments were conducted in a batch photocatalytic reactor (1.9 L and 32 W UV power). It was found that UV-C/TiO₂ and UV-C/GAC systems showed fairly equal removal efficiencies under lower MNZ concentrations (0.1–5 mg L⁻¹) compared to higher concentrations at similar catalyst loading of 2.5 g L⁻¹. A decline in removal rate (based on first-order reaction) was observed with respect to increase in initial MNZ concentration in all systems. MNZ removal by adsorption on GAC was much lesser compared to UV-C only, UV-C/TiO₂, and UV-C/GAC systems. The adsorption data well correlated with the Freundlich model indicated that the adsorption was on the heterogeneous surface of the catalyst. The effectiveness of the systems were evaluated by calculating electrical energy consumed per order (E EO). The lowest E EO value was found to be for UV-C/TiO₂ (0.03 kWh m⁻³ order⁻¹) for the degradation of 0.1 mg L⁻¹ of MNZ compared to UV-C/GAC (0.06 kWh m⁻³ order⁻¹), UV-C only (0.15 kWh m⁻³ order⁻¹), and adsorption (0.44 kWh m⁻³ order⁻¹). The total organic carbon and nitrogen ion analyses have confirmed the mineralization of MNZ via aliphatic carboxylic acid compounds in the photocatalytic system. Overall, the photocatalytic system seems to be an energy-efficient treatment option for the removal of MNZ and similar other micropollutants.

This study aimed to investigate the potency of soil reflectance spectroscopy in the visible and near infrared (Vis-NIR) spectral regions in estimating soil heavy metal pollution in the western coastal front of Thessaloniki (N. Greece) and how the protocol used for chemical analyses can affect the models’ performance. For this purpose, 49 topsoil samples were collected and the concentrations of Cd, Cr, Cu, and Pb were determined by two different analytical methods, i.e., ISO 11466 based on the technique of atomic absorbance spectrometry (AAS) and ISO 14869-1 using the technique of inductively coupled plasma-atomic emission spectrometry (ICP-AES). The spectral signatures were applied for modeling the metal concentrations by using the partial least squares regression (PLSR) method. To eliminate the “noise” of data and enhance the models’ accuracy, four spectral pre-treatment methods were used. The overall results showed that there is heavy metal pollution in the soils of specific areas in the studied region and that the use of different chemical analytical methods can affect the performance of examined prediction models. Better prediction models were created for the cases of Pb, Cu, and Cr concentrations, which were estimated by the application of ISO 14869-1, while for the case of Cd better prediction models were obtained, by the application of ISO 11466. These results may indicate that soil reflectance spectroscopy can measure the total heavy metal content in soil samples.

Decomposition of aquatic plant might generate a significant influence on the receiving water body. In this study, decomposition of emergent aquatic plant (cattail) litter was investigated under different conditions to determine the influencing level of the decomposition process on the water quality. Different litter addition rates (0.1, 0.5, 1.0 g L⁻¹), temperature changes, sediment additions, and kinestates (static and dynamic conditions) were selected as the influencing factors for the decomposition process. The results suggested that the decomposition process could be all accelerated when conducted at a higher litter addition rate, under a cold condition, with sediment addition or on dynamic condition, respectively. Additionally, the maximum ratio of releasing carbon to nitrogen (C/N) was increased when the decomposition process was conducted with a higher litter addition rate, under a cold condition (31.0), with sediment addition (24.6) and on a dynamic condition (28.0), respectively, and the C/N ratios were all higher than that with only 0.5 g L⁻¹ litter addition (24.5), suggesting that lowering of water temperature, sediment addition, and increasing of oxygen might also enhance the C/N. The high C/N released during the decomposition process implied that the cattail litter might be utilized as the potential organic carbon source for nitrogen removal in the CW system.

Nonlinear sorption of substituted phenols (degradation products of several pesticides) onto soils was often observed. This sorption nonlinearity at low solute concentration ranges could result in higher soil organic carbon-water distribution coefficient (K ₒc) values than those predicted by their hydrophobicity (K ₒw). In this study, nonlinear sorption characteristic of four substituted phenols (2,6-dimethylphenol, 2-chlorophenol, 2-nitrophenol, and 2,4-dichlorophenol) onto two agricultural soils was investigated. The sorption nonlinearity gradually approached apparent saturation at low solute activity ranges (e.g., a ᵢ < 0.01). At high a ᵢ ranges, linear sorption was observed. Thus, partition and adsorption of solutes were successfully evaluated by a dual-mode sorption model. The concentrations of substituted phenols in the environment are pretty low (e.g., usually lower than 1 mg/L). According to our results, nonlinear adsorption is dominant in such low concentration ranges in the environment. To predict varied log K ₒc values resulted from nonlinear adsorption, especially for low a ᵢ range, an expanded polyparameter linear free energy relationship (pp-LFER) is established: log K ₒc = [(1.829 ± 0.488) + (3.481 ± 0.462) log a ᵢ)]E+ [(− 4.307 ± 0.466) log a ᵢ]S+ [(− 0.876 ± 0.138) log a ᵢ]A+ [(− 0.086 ± 0.529) + (1.209 ± 0.218) log a ᵢ]B+ (6.280 ± 0.649)V – (6.814 ± 0.917) (E, the excess molar refraction; S, the dipolarity/polarizability parameter; A, the solute H-bond acidity; B, the solute H-bond basicity; and V, the molar volume). This model can provide a better prediction (within 0.3 log unit) than previous models. This study provides essential parameters for predicting and understanding the environmental behavior of substituted phenols in agricultural soils. Graphical Abstract ᅟ

Samples of roots and spatial soils of native Rubus fruticosus L. were collected from the spots positioned at different distances from the copper smelter and city heating plants in the industrial zone of the town of Bor (Serbia) and subjected to chemical analyses in order to determine the content of several heavy metals, and 15 priority polycyclic aromatic hydrocarbons (PAHs). In this study, the results for 9 low and medium molecular weight PAHs (LMW and MMW PAHs) are represented and processed using the calculation of bio-concentration factors and statistical methods such as hierarchical cluster analysis and Pearson’s correlation study with the aim of investigating the plant capabilities for their uptake from the soil and later accumulation into the root tissue, under the hostile circumstances of multiple contamination. The obtained data revealed different accumulation rates for the investigated PAHs and showed that in several cases, the contents of root PAHs were under the strong influence of present contaminants such as soil copper and some soil PAHs, indicating at the same time that R. fruticosus can regulate the processes of LMW and MMW PAHs extraction/accumulation using different mechanisms, depending on the existing environmental circumstances. The used mechanisms could be exploited in phytoremediation methods based not only on the extraction and concentration of PAHs in plant roots but also on PAH degradation or stabilization in the soil. Also, the results of this study confirmed that, except in the case of naphthalene and fluoranthene, there was no PAH pollution, which originated solely from the industrial zone.