The removal of arsenic was investigated by four types of thin-film polyamide nanofiltration (NF) (NF270, NF90) and reverse osmosis (RO) (XLE, BW30) membranes in a flat-sheet module. The influence of membrane types, pressure, pH, and pre-oxidation step on the removal of arsenic (As(III)) was investigated. Initial As(III) concentration was 100 μg/l for all of the experiments. Flux was determined over a pressure range of 3.5–10 bar for both NF and RO membranes. Experiments were conducted at pH 3.5, 5, 7.5, and 10 to evaluate the effect of pH on As(III) removal. The impact of pre-oxidation and oxidant concentrations on As(III) removal were also evaluated. It was found that the percentage of As(III) removal of RO membranes were in the range of 97–99 for all transmembrane pressure applied. In the range of operating conditions, As(III) and As(V) rejection were found almost equally good by RO membranes. RO permeate met the WHO and Turkish standard for arsenic. Pre-oxidation step improved the rejection performance of NF. Nevertheless, NF permeate did not meet the standards in the range of operating conditions.

Compacted clay soils are widely used as a barrier to protect environment from leachate migration. The suitability of clay soil for liner material, depends on resistibility to increase in hydraulic conductivity and contaminant transport. In this article, the influence of compaction energy and permeated leachate properties on the hydraulic conductivity were investigated. Natural attenuation capacities of clays compacted both standard and modified compaction methods were also evaluated. With this purpose, a series of laboratory tests were conducted with soil and real leachate samples obtained from Şile-Kömürcüoda Organized Landfill Site. DI and real leachate samples were percolated through the laboratory-scale column reactors that were filled with compacted clay samples prepared according to Standard and Modified Proctor method. During percolation, the hydraulic conductivity and natural attenuation capacity of the clay liner were determined by hydraulic conductivity calculation and chemical oxygen demand (COD), suspenden solids (SS), total Kjeldahl nitrogen (TKN), total phosphorus (TP) monitoring, respectively. According to the hydraulic conductivity measurements using leachate, it is shown that hydraulic conductivity decreased in both compacted clay prepared by Standard and Modified Proctor methods, possibly associated with biological and chemical clogging mechanisms. It is thought that clogging formed due to biofilm growth and/or suspended solids accumulation between the particles of the clay soil. When the variations of the COD, SS, TKN, and TP were examined, it was observed that the removal efficiency of the clay compacted by the modified compaction method was greater than the one compacted by the standard compaction method, especially for SS.

Many treatment methods are used to remove iron and manganese from water. Aeration and membrane filtration are two of these methods. In this study, Fe²⁺ and Mn²⁺ removal by aeration with different catalysts and instead of simple membrane filtration applied in other studies, the aerated-submerged membrane systems were evaluated separately. When Fe(OH)₃ was applied in the aeration step and complete oxidation of Fe²⁺ was obtained after 27 min, while complete Mn²⁺ oxidation was obtained in 76 min. However, when MnO₂ was applied in the aeration step, complete oxidation of Fe²⁺ and Mn²⁺ was relatively slow (36 and 110 min, respectively). According to the results obtained from the aerated membrane system, Fe²⁺ and Mn²⁺ removal were extended by Fe(OH)₃ via adsorption/surface oxidation. It is clearly shown from the flux, resistance results, scanning electron microscope (SEM) and Fourier transform infrared (FT/IR) spectroscopy observation that manganese oxides were deposited mainly in membrane pores forming membrane fouling by small flocs, while iron oxide particles were deposited on the membrane surface. Although the flux performance of PT PES membrane was higher than HF PP membrane, fouling resistance of HF PP membrane was higher than PT PES.

Since the COVID-19 pandemic, a huge number of face masks have been used to prevent the spread of the coronavirus on a global scale. Unfortunately, several studies have reported the presence of used face masks in marine litter in different countries around the world. Face masks produced from synthetic polymers can increase the environmental burden and contradict sustainability. This study aimed to investigate the environmental behavior of face masks when exposed to natural environmental conditions following improper disposal. New and naturally aged surgical and FFP2 masks were exposed to deionized water (DI) and sea water conditions to understand the environmental behavior of face masks when exposed to different environmental conditions. Following natural aging and DI and sea water exposure, face masks were characterized with Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), and compared with new masks. According to the results, the middle layers of both mask types were exposed to more severe degradation. Aging resulted in higher microplastic (MP) release than new masks in DI and seawater for both types of face masks. Compared to new ones, aging and seawater exposure caused 11 to 13 and 14 to 22 times higher MP release from surgical and FFP2 face masks, respectively. Following seawater exposure, aged FFP2 mask released higher amounts of MP (4.36–6.20 × 10⁶) than aged surgical masks (4.03–5.45 × 10⁶). According to the results, a significant portion of the released MPs were <10 µm for both types of masks. However, when aged FFP2 masks were exposed to seawater, a remarkable increase was found in the fraction of 10–50 µm and 50–100 µm, suggesting that aged FFP2 masks also became fragmented in seawater conditions. FTIR and SEM analyses confirmed the transformation in the structure and chemical composition of the materials. A significant change was observed in chemical and physical structure of the masks after being exposed to weathering conditions in a relatively short period of time (one month).

Lab-scale continuous operation of self-forming microfiltration (MF) or ultrafiltration (UF) dynamic membranes were investigated simultaneously by applying iron oxide as an alternative treatment option in those waters having natural organic matter (NOM), iron and manganese. Both dynamic membranes gave high removal rates and effluent concentrations of pollutants were below the limit values in synthetic water. 60 and 62% (of DOC) and 75 and 78% (of UV254) were removed in low dissolved organic carbon (DOC) synthetic (LS) water by MF and UF dynamic membranes, respectively. Although only 42 and 49% (of DOC) and 48 and 53% (of UV254) could be removed by MF and UF dynamic membranes, respectively, a remarkable effect on fouling alleviation was observed in high DOC synthetic (HS) water. Iron oxide did not enhance the removal of organic matter in low DOC natural (LN) water as much as it did in synthetic water. Iron oxide led to the removal of high molecular weight organics, thus reversible fouling was reduced almost 2 orders of magnitude through both types of dynamic membranes in high DOC natural (HN) water. Reversible and irreversible resistances were reduced by iron oxide to some extent in LN water. Nevertheless the effect of iron oxide on fouling alleviation was much higher in HN rather than in LN water.