The study area within the Stone Town Nature Reserve in Ciężkowice encloses a variety of occurrences of sandstone tors exposed within the Skała Hill (Rock Hill) from its top down into the Biała River Valley. The efflorescences of salt minerals on the walls of the sandstone tors represent end products of weathering. Several types of the efflorescences have been distinguished in relation to their distribution, the composition of the parent sandstones and local conditions of the natural environment. Laboratory methods have allowed identifying several sulphate minerals of various hydration (mainly pickeringite, hexahydrite, pentahydrite, alunogen, K-alum, gypsum, syngenite). They occur as two morphological varieties: as accumulations of a millimetre large flakes or as granules. The development, diversification and distribution of the efflorescences depend first of all on the rock moisture controlled by its capillary rise. The dampness of the lower tor parts is relatively the major factor; thus, such places are the sites favouring efflorescing phenomena. The presence of sulphur-bearing ions that are contained in salt minerals may be attributed to oxidation of pyrite occurring in the sandstone formations in the vicinity of Ciężkowice but may also be associated with local waters, more probably with mineral ones than with groundwater recharged by atmospheric precipitations. Air pollution, particularly with sulphur compounds, should also be considered in weathering of sandstone tors and the formation of the efflorescences.

An in situ wet chemical deposition method has been applied for the successful surface modification of Ce (IV)-incorporated hydrous Fe(III) oxide (CIHFO) with a hydrophilic graphene precursor, graphene oxide (GO). The surface area of as-prepared composite (GO-CIHFO) has enhanced (189.57 m² g⁻¹) compared with that of pristine CIHFO (140.711 m² g⁻¹) and has irregular surface morphology consisting of microcrystals (~ 2–3 nm) and mesoporous (3.5486 nm) structure. The GO-CIHFO composite shows enhanced fluoride scavenging capacity (136.24 mg F g⁻¹) than GO (3 mg F g⁻¹) and pristine CIHFO (32.62 mg F g⁻¹) at pH 7.0. Also, in acidic pH range and at 323 K temperature, the Langmuir capacity of as-prepared composite is 190.61 mg F g⁻¹. It has been observed that fluoride removal by GO–CIHFO occurs from solutions obeying pseudo-second-order kinetics and multilayer adsorption process. The film/boundary layer diffusion process is also the rate-determining step. The nature of the adsorption reaction is reasonably spontaneous and endothermic in thermodynamic sense. It was observed that 1.2 g.L⁻¹ of GO-CIHFO dosage can effectively optimise the fluoride level of natural groundwater samples (9.05 mg L⁻¹) to the desirable permissible limit. Reactivation of used material up to a level of 73.77% with a solution of alkaline pH has proposed reusability of nanocomposites ensuring sustainability of the proposed material as fluoride scavenger in future.

Aquaculture in many coastal estuaries is threatened by diffuse sources of runoff from different land use activities. The poor performance of septic tank systems (STS), as well as runoff from agriculture, may contribute to the movement of contaminants through ground and surface waters to estuaries resulting in oyster contamination, and following their consumption, impacts to human health. In monitoring individual STS in sensitive locations, it is possible to show that nutrients and faecal contaminants are transported through the subsurface in sandy soils off-site with little attenuation. At the catchment scale however, there are always difficulties in discerning direct linkages between failing STS and water contamination due to processes such as effluent dilution, adsorption, precipitation and vegetative uptake. There is often substantial complexity in detecting and tracing effluent pathways from diffuse sources to water bodies in field studies. While source tracking as well as monitoring using tracers may assist in identifying potential pathways from STS to surface waters and estuaries, there are difficulties in scaling up from monitored individual systems to identify their contribution to the cumulative impact which may be apparent at the catchment scale. The processes which may be obvious through monitoring and dominate at the individual scale may be masked and not readily discernible at the catchment scale due to impacts from other land use activities.

Sludge treatment beds (STBs) have been used widely in many countries due to low energy consumption, low operating and maintenance costs, and better environmental compatibility. Penetration, evaporation, and transpiration are the main processes for sludge dewatering in STBs. However, the leachate quality from STBs usually cannot meet discharge limits. Moreover, such leachate has very low COD/N ratio, which makes it difficult to treat. In the present study, two subsurface flow (SSF) constructed wetlands (CWs) were investigated for the treatment of leachate from STBs under three different hydraulic retention time (HRT) (3 days, 4 days, 6 days), aiming for evaluating the effects of plants and HRT on treatment performance, as well as the potential of SSF CWs to treat sludge leachate with low COD/N ration. The results showed that plants play an important role in leachate treatment. The best treatment performance was achieved with HRT of 4 days. In this condition, the mean removal efficiencies of COD (chemical oxygen demand), NH₄⁺-N, TN (total nitrogen), and TP (total phosphorus) in the planted and the unplanted CWs were 61.6% (unplanted − 3.7%), 76.6% (unplanted 43.5%), 70% (unplanted 41%), and 65.6% (unplanted 6%), respectively. Heavy metal concentrations were below the Chinese integrated wastewater discharge standard during the experimental period in the planted CW, and the removal efficiencies in the planted CW system were higher than in the unplanted CW system. In all, planted SSF CWs can be an effective approach in removing leachate from sludge treatment beds. Furthermore, considering to temperature and seasonal variation, the leachate from STBs needs to be further studied in pilot- and full-scale condition.

In this study, the properties of unstable and stable flocs were investigated under the steady operation of a membrane bioreactor (MBR). The extracellular polymeric substances (EPS) composition, surface charge, and hydrophobicity of unstable and stable flocs were examined and compared. Interfacial interactions of the membrane with unstable flocs, unstable flocs themselves, and unstable and stable flocs were assessed using the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) models. Cake layer resistance was found to contribute more than 80% of total resistance under steady operating conditions. Compared with stable flocs, unstable flocs possessed a higher level of EPS, more diverse protein, more negative charge, weaker hydrophobicity, and higher fouling potential. Thermodynamic analyses showed that unstable flocs had a higher adhesive strength (− 63.4 mJ/m²) with the membrane, lower self-cohesive strength (− 18.3 mJ/m²), and higher cohesive strength (− 54.3 mJ/m²) with stable flocs. Therefore, some unstable flocs remained on the membrane surface to form the cake layer due to their poor cohesion strength.

Efforts to improve sludge resource utilization have become increasingly important. In this study, humic acid (HA) was extracted from sludge samples collected from a sewage treatment plant, and then used for the adsorption of heavy metals. We used two-dimensional correlation spectroscopy (2D-COS) integrated with Fourier-transform infrared spectroscopy (FTIR) to explore the adsorption between sludge HA (HA) and three metal ions (Cu, Ni, and Pb). The resulting adsorbing data conformed to the isotherm of Langmuir adsorption. The maximum capacity values (qₘ) were 5.34, 1.49, and 26.29.8 mg/g for Cu, Ni, and Pb, respectively. The data from 2D-FTIR-COS analysis showed that the susceptibility of the functional group followed the order 2300 → 1130 → 1330 → 1480 → 1580 cm⁻¹ for Cu(II) and Ni(II), and 2300 → 1130 → 1330 → 1480 → 1200 → 1580 cm⁻¹ for Pb(II). The sludge HA with Pb(II) showed more adsorption sites than sludge HA with Cu(II) and Ni(II), and these adsorption sites could preferentially bond with Pb(II) at × 1 compared with Cu(II) and Ni(II). Our findings indicate that 2D-FTIR-COS technology has great potential for application as a useful tool for understanding the adsorption mechanism between adsorbents with heavy metals.

Bioconcentration factors (BCF) for regulatory purposes are usually determined by fish flow-through tests according to technical guidance document OECD 305. Fish bioconcentration studies are time consuming, expensive, and use many laboratory animals. The aim of this study was to investigate whether the freshwater amphipod Hyalella azteca can be used as an alternative test organism for bioconcentration studies. Fourteen substances of different hydrophobicity (log Kₒw 2.4–7.6) were tested under flow-through conditions to determine steady state and kinetic bioconcentration factors (BCFₛₛ and BCFₖ). The results were compared with fish BCF estimates for the same substances described in the literature to show the relationship between both values. Bioconcentration studies with the freshwater amphipod H. azteca resulted in BCF estimates which show a strong correlation with fish BCF values (r² = 0.69). Hyalella BCF values can be assessed in accordance with the regulatory B criterion (BCF > 2000, i.e., REACH) and thereby enable the prediction of B or non-B classification in the standard fish test. Therefore, H. azteca has a high potential to be used as alternative test organism to fish for bioconcentration studies.

The densely populated Greater Cairo (GC) region suffers from severe air quality issues caused by high levels of anthropogenic activities, such as motorized traffic, industries, and agricultural biomass burning events, along with natural sources of particulate matter, such as wind erosion of arid surfaces. Surface-measured concentrations of particulate matter (PM₁₀), sulfur dioxide (SO₂), and ozone (O₃) and its precursor’s gases (nitrogen dioxide, NO₂; carbon monoxide, CO) were obtained for the GC region. The PM₁₀ concentrations were found to exceed remarkably the Egyptian guidelines (150 μg/m³). These high levels of PM₁₀ were recorded throughout 68% of the period of measurement in some industrial areas (El-Kolaly). The measured data of pollutants were used for both the evaluation of environmental pollution levels and the validation of the online-integrated regional climate chemistry model “RegCM-CHEM4.” Calculation of the bias between the model results and the measured data was used to evaluate the model performance in order to assess its ability in reproducing the chemical species over the area. The model was found to reproduce the seasonal cycle of the pollutants successfully, but with a large underestimation of the PM₁₀ values. Validation of the RegCM-CHEM4 indicated that the emission inventories of mobile sources and anthropogenic activities need to be improved especially with respect to local and regional activities in order to enhance air quality simulations over the GC region.

In this work, it was analyzed the behavior of three commercial activated carbons with different textural and chemical properties to adsorb individually metronidazole and lead ions from aqueous solution. Afterwards, the activated carbons were modified with citric acid to remove both compounds simultaneously. Both sets of activated carbons were characterized chemically and texturally. XPS analysis was performed to corroborate the adsorption mechanism of lead on the surface of the carbons. Finally, the intraparticle diffusion of both adsorbates was elucidated by the application of diffusional model in three dimensions. The results evidenced that adsorption mechanism for MNZ and Pb(II) is independent, the adsorption for MNZ is governed by π–π dispersive interactions, whereas Pb(II) adsorption is mainly controlled by electrostatic interactions. The binary adsorption equilibrium shows that the adsorption of MNZ is independent from the concentration of Pb(II), whereas the adsorption of Pb(II) is affected by the presence of MNZ at low concentrations (0.1 mmol L⁻¹), but it remains almost constant at concentrations of MNZ between 0.1 and 1.5 mmol L⁻¹. Finally, the mass transport of MNZ was faster than Pb(II) from the solution to the external surface of activated carbon and the mass flux of MNZ inside the particle was superior to the mass flux of Pb(II). Lastly, there might be an obstruction phenomenon with MNZ impeding Pb(II) to reach the active sites placed into the carbon’s microporosity structure. Graphical abstract

This paper represents a new proposed trade model of “Intercountries Trade Force (ITF)” which is inspired by Intermolecular Interaction Forces in chemical sciences, and has potential to compensate for the deficiencies of the gravity trade model proposed by Jan Tinbergen in 1962. The main differences between our new model and the earlier gravity trade theory are (i) there is a time-variant variable called the gravity index (GI) which means that the earlier gravity theory was treated as only a variable in our new proposed model and (ii) our new proposed trade model has a higher chance of adoption in the real trade world rather than the earlier gravity trade model which always needs to be expanded by scholars. In order to empirically test our new proposed trade model, we applied it in an empirical econometric model to analyze the Russian gas export to the EU member states, not explored earlier. Results revealed that our new trade proposed model adjusts with the empirical energy trade pattern.