The present investigation deals with the adsorption of chromium(III) from alkaline media using multi-walled carbon nanotubes. The adsorption of Cr(III) has been studied under various experimental conditions: stirring speed of the aqueous solution, initial metal and adsorbent concentrations, NaOH concentration in the aqueous solution, and temperature. The rate law indicated that chromium adsorption is well represented by the particle diffusion model, whereas the adsorption process fits to the pseudo-second order kinetic model within an exothermic character. Equilibrium data fit to the Langmuir type-2 equilibrium isotherm in an spontaneous process. Chromium(III) can be eluted from metal-loaded nanotubes using acidic solutions, from which fine chromium(III) oxide pigment can be ultimately yielded.

Even in the first quarter of XXI century, the presence of organic dyes in wastewaters is a normal occurrence in a series of countries, and being these compounds toxics, their removal from these waters is of a necessity. Among the separation technologies, adsorption processing appeared as one of the most widely used to reach this goal. The present work reviewed the most recent approaches (first half of 2021 year) about the use of a variety of adsorbents on the removal of, also, a variety of organic dyes of different nature.

A combination of straw filtration and nanofiltration was investigated for the first time as a sus-tainable approach aimed at valorizing olive mills wastewaters (OMWs) within a circular economy strategy. Ground straw filters with different granulometry (120, 250 and 500 m) were tested in the first step to clarify the raw wastewater. The 500m filter offered the best performance due to a lower exposed surface of the filtering fibers and a shorter filtering time allowing to reduce about 70% of the COD of the raw wastewater. Three different commercial membranes in flat-sheet con-figuration with molecular weight cut-off (MWCO) in the range 150-500 Da were tested to frac-tionate the clarified wastewater according to a dead-end configuration. Among the investigated membranes the NFA-12A membrane exhibited the highest productivity in selected operating conditions (steady-state values of 11.4 L/m2h at 20 bar and 24 ± 2 °C). In addition, flux decays for this membrane resulted lower than the other two tested membranes indicating a lower propensity to fouling phenomena. Higher rejections towards total polyphenols and TAA (76.6% and 73.2%, respectively) were also observed for this membrane. Flavanols and hydroxycinnamic acids were retained for more than 99%. The combination of straw filtration and NF with NFA-12A membrane allowed to reduce the COD of raw OMWs up to 97.6%. The retentate fraction of this membrane exhibited a TAA of 18.9 ± 0.7 mM Trolox supporting its propensity for the development of inno-vative formulations of interest in food and nutraceutical applications.

Intensive development of many industries, including textile, paper or plastic, which consume large amounts of water and generate huge amounts of wastewaters containing toxic dyes, contribute to pollution of the aquatic environment. Among many known methods of wastewater treatment, adsorption techniques are considered as the most effective. In the present study the weakly basic anion exchangers such as Amberlyst A21, Amberlyst A23 and Amberlyst A24 of the polystyrene, phenol-formaldehyde and polyacrylic matrices were used for C.I. Direct Yellow 50 removal from aqueous solutions. The equilibrium adsorption data were well fitted to the Langmuir adsorption isotherm. Kinetic studies were described by the pseudo-second order model. The pseudo-second order rate constants were in the range of 0.0609-0.0128 g/mg·min for Amberlyst A24, 0.0038-0.0015 g/mg·min for Amberlyst A21 and 1.1945-0.0032 g/mg·min for Amberlyst A23, and decreased with the increasing initial concentration of dye from 100-500 mg/L, respectively. There were observed auxiliaries (Na2CO3, Na2SO4, anionic and non-ionic surfactants) impact on the dye uptake. The polyacrylic resin Amberlyst A24 can be promising sorbent for C.I. Direct Yellow 50 removal as it is able to uptake 666.5 mg/g of the dye compared to the phenol-formaldehyde Amberlyst A23 of the 284.3 mg/g capacity.

The purpose of this work is to define optimal growth conditions for batch culture of the cyanobacterium Arthrospira maxima and the microalgae Chlorella vulgaris, Isochrysis galbana and Nannochloropsis gaditana. Thus, we study the effect of three variables on algae growth: i.e., inoculum:culture medium ratio, light:darkness photoperiod and type of culture medium, including both synthetic media and wastewaters. The results showed that the initial inoculum volume did not affect the amount of biomass at the end of the growth (14 days), whereas an excess (18 h) or defect (6 h) in the number of hours of light is determinant for its development. The contribution of nutrients from different culture media modified the growth of the different species. A. maxima was favoured in seawater enriched with Guillard's F/2 as well as C. vulgaris and N. gaditana but in fresh water medium. I. galbana had the greatest growth in the marine environment enriched with Walne’s media. Nitrate was the limiting growth reagent at the end of the exponential phase of growth for C. vulgaris and N. gaditana, while iron was for A. maxima and I. galbana. All species demonstrated their capability to grow in effluents from a wastewater treatment plant and they efficiently consume nitrogen, especially the three microalgae species.

Drug resistance has become an extremely serious problem worldwide. Antibiotic resistance genes (ARGs) entering the environment with wastewaters promote replenishment of the resistome of natural microbioms. Distribution of several clinically significant ARGs in wastewaters of Rostov-on-Don (Southern Russia), lower reaches of the Don River and natural waters of the neighboring region was investigated. Metagenomic DNA samples isolated from 250 ml of wastewaters or natural waters and 200 mg of surface sediments were used for the study. Identification of the ARGs was carried out with end-point detection PCR. Presence of NDM, OXA-48, CTX-M, VanA, VanB, ErmB, and TetM/TetO genes was detected in urban wastewaters. Samples of wastewater treatment plant (WWTP) sewage were enriched with ARGs in contrast to non-treated wastewaters from the sewage collector. NDM, VanA, ErmB, TetM/TetO genes were found only in wastewaters and were absent in samples of natural waters and surface sediments. Only OXA-48, VanB and CTXM genes were found in natural waters and surface sediments. The described ARGs are quite typical for urban and hospital wastewaters. The target ARGs were detected in the samples connected to the anthropogenous sources of pollution such as Rostov municipal WWTP or livestock enterprise effluents.