More than 40% of the crystalline silicon has been wasted as silicon cutting waste (SCW) during the wafer production process. This waste not only leads to resource wastage but also causes environmental burden. In this paper, SCW produced by the diamond-wire sawing process was recycled by Al-Si alloying process. Cryolite was introduced to the reaction system to dissolve the SiO₂ layer existed on the surface of the Si particles in SCW. Alloys with 12.02 wt% of Si were prepared and the mechanism of the alloying process was investigated in detail. The Si-Al-cryolite system and SiO₂-Al-cryolite system were studied individually to analyze the reaction process and transferring behavior of Si and SiO₂ in SCW. The SiO₂ shell was firstly transformed into Si-O-F ions. Then the Si-O-F ions diffused to the reaction interface by the effect of the concentration gradient and were reduced to Si by the aluminothermic reduction reaction: 4Al (l) + 3SiO₂ (dissolved in the melt) = 3Si (Al)+ 2Al₂O₃ (dissolved in the melt). Then the internal Si particles were released into cryolite after the dissolution of SiO₂ and transferred to the reaction interface by the effect of gravity. The influences of the mass ratio of Al/SCW and agitation modes on the Si content of the alloys and the Si recovery ratio in SCW were investigated. With the increase of the mass ratio of Al/SCW from 2.2 to 6.5, the Si recovery ratio in SCW increased from 44.08% to 69.05%, but the silicon content of the alloys decreased from 16.06 wt% to 8.83 wt%. Agitation can effectively improve the smelting effect during smelting by which the silicon content of the alloys and the Si recovery ratio in SCW increased from 12.02 wt% and 64.25% to 13.17 wt% and 69.46%, respectively.

In this study, methodological factors influencing the dissolution of metal(loid)s in simulated lung fluid (SLF) was assessed in order to develop a standardised method for the assessment of inhalation bioaccessibility in PM2.5. To achieve this aim, the effects of solid to liquid (S/L) ratio (1:100 to 1:5000), agitation (magnetic agitation, occasional shaking, orbital and end-over-end rotation), composition of SLF (artificial lysosomal fluid: ALF; phagolysosomal simulant fluid: PSF) and extraction time (1–120 h) on metal(loid) bioaccessibility were investigated using PM2.5 from three Australian mining/smelting impacted soils and a certified reference material. The results highlighted that SLF composition significantly (p < 0.001) influenced metal(loid) bioaccessibility and that when a S/L ratio of 1:5000 and end-over-end rotation was used, metal(loid) solubility plateaued after approximately 24 h. Additionally, in order to assess the exposure of metal(loid)s via incidental ingestion of surface dust, PM2.5 was subjected to simulated gastro-intestinal tract (GIT) solutions and the results were compared to extraction using SLF. Although As bioaccessibility in SLF (24 h) was significantly lower than in simulated GIT solutions (p < 0.05), Pb bioaccessibility was equal to or significantly higher than that extracted using simulated GIT solutions (p < 0.05).

Benzene, toluene and xylene (BTX) belong to an important group of aromatic volatile organic compounds (VOCs) that are usually emitted from various sources. BTX play a vital role in the tropospheric chemistry as well as pose health hazard to human beings. Thus, an investigation of ambient benzene, toluene and xylene (BTX) was conducted at urban and rural sites of Gorakhpur for a span of one year in order to ascertain the contamination levels. The sampling of BTX was performed by using a low-flow SKC Model 220 sampling pump equipped with activated coconut shell charcoal tubes with a flow rate of 250 ml/min for 20–24 h. The analysis was in accordance with NIOSH method 1501. The efficiency of pump was checked weekly using regulated rotameters with an accuracy of ±1%. The samples were extracted with CS₂ with occasional agitation and analyzed by GC-FID. The total BTX concentration ranged from 3.4 μg m⁻³ to 45.4 μg m⁻³ with mean value 30.95 μg m⁻³ and median 24.8 μg m⁻³. The mean concentration of total BTX was maximum during winter (39.3 μg m⁻³), followed by summer (28.4 μg m⁻³) and monsoon season (25.1 μg m⁻³). The mean concentration of BTX at urban site (11.8 μg m⁻³) was higher than that at rural site (8.8 μg m⁻³). At both the sites, T/B and X/B ratios were highest in monsoon and lowest in winters. Toluene against benzene plot shows R² value of 0.96 and 0.49 at urban and rural sites respectively. Higher R² value at urban site clearly indicates similar sources of emission for benzene and toluene. At both the sites, the estimated integrated lifetime cancer risk (ILTCR) for benzene exceeded the threshold value of 1E-06 whereas the individual hazard quotients (HQ) for BTX did not exceed unity at any of the sites.

The genus Artemia sp. has been accepted as a reliable model organism for aquatic toxicity and nanotoxicity experiments, as far as the ISO TS 20787 has recently been published to standardize nanotoxicity test with this organism. Experimental and environmental conditions may affect the toxicity of nanomaterials on aquatic organisms including Artemia sp. nauplii. In this study, acute toxicity effects of silver nanoparticles (AgNPs) on the nauplii of Artemia salina was investigated under various conditions (e.g. different lights, salinities, temperatures, volume and agitation of exposure media and instar stages of nauplii). The EC values were calculated using Probit program and all data were analyzed statistically by SPSS software. At all test conditions, the immobilization rate of Artemia nauplii increased in a concentration-dependent manner (P < 0.05). The sensitivity of instar stage II to different concentrations of AgNPs was significantly higher than instar I (P < 0.05). The toxicity effect of AgNPs was affected by alteration of environmental conditions, so that the effective concentration (EC) values for instar I of A. salina decreased with increasing water temperature, decreasing water salinity and in continuous darkness condition. The EC50 value of AgNPs was significantly lower in 100 mL beakers (21.35 ± 5.67 mg L−1) than 10 mL well plates (42.44 ± 11.30 mg L−1). Agitation of exposure media did not affect the toxicity of AgNPs. The results indicated that the experimental and environmental conditions influence on the toxicity of AgNPs in the nauplii of A. salina.

A fast (16min) procedure to assess the bioaccessible metallic fraction of Cd, Cr, Cu, Ni, Pb and Zn simultaneously extracted (SEM) from marine sediments plus an indirect approach to determine acid volatile sulfides (AVS) are presented. For the extraction process magnetic agitation was compared with ultrasonic stirring (using a bath and a probe), and several stirring times were assayed. The proposed SEM procedure uses an ultrasonic probe and 1mL of HCl. It dramatically minimizes the turnaround time and the residues. AVS were evaluated as the difference between the amounts of sulphur in the solid residue after the extraction and total sulphur in the original sample. These procedures are fast, easy to implement and cost-effective to assess the potential risk posed by metals in marine sediments. They were tested using several CRMs and applied to sediments from two Galician Rias (NW Spain); their SEM-AVS differences indicated no biological risk.

Microplastics are gaining worldwide attention due to their omnipresence. The marine environment is one of the most affected systems; especially the sediment compartment. Microplastic separation from the sediment matrix is the first step to evaluate its abundance and availability. Nevertheless, a lack of consistency in extraction protocols is a fact. This paper describes the optimization of the microplastic extraction procedure from marine sediments. The Plackett-Burman saturated factorial design was used to identify the significant factors and to select optimum working conditions. With this purpose, the following variables were studied: the number of extractions; the amount of sediment; the settling time; the density separation solution volume; the agitation time and the suitability of using wet or freeze-dried sediment. The Plackett-Burman design has revealed that the most statistically significant variables were sediment mass and agitation time. The optimized method was applied for two marine sediments collected in the Mar Menor Lagoon.

Heavy metal contamination plays a major role in water pollution. It needs remediation without raising the issues of secondary waste generation and their related issues. Heavy metal residues adversely affect soil and water quality. Their leachate would disturb the whole ecological system. It needs remediation to avoid the effect on soil and water. Azospirillium biofertilizer has the ability to reduce hazardous components without disturbing the growth of the plant. Hence, the use of low-cost biosorbent was proposed for heavy metal removal. The investigations showed excellent removal of heavy metals like copper (Cu) and chromium (Cr) using Azospirillium biofertilizer. These materials showed efficient removal of Cu and Cr at 94% and 70%, respectively. Separation was dependent upon the interaction between sorbent and sorbate, which makes separation tunable for the removal of the desired material from effluent or other streams. Parameter optimization like temperature, adsorbent dose, time, pH, and agitation speed was studied for both metals. At optimum parameters, Langmuir capacity was found to be 35.71 mg/g and 5.58 mg/g of copper and chromium. Experimental data was best fitted to Langmuir isotherm, and the pseudo-second-order kinetic model was suitable for the study of both metals.

Most methods that promote carbohydrate production negatively affect cell growth and microalgal biomass production. This study explores, in a two-stage cultivation strategy, in Chlamydomonas debaryana the optimization of certain culture conditions for high carbohydrate production without loss of biomass. In the first stage, the interaction between sodium bicarbonate supplementation, aeration, and different growth periods was optimized using the response surface methodology (RMS). The 3-factor Box-Behnken design (BBD) was applied, and a second-order polynomial regression analysis was used to analyze the experimental data. The results showed that 0.45 g L⁻¹ of sodium bicarbonate combined with a good aerated agitation (0.6 L min⁻¹) and a cultivation period of 18 days are optimal to produce 5.02 g L⁻¹ of biomass containing 43% of carbohydrates.Under these optimized growth conditions, accumulation of carbohydrates was studied using different modes of nutritional stress. The results indicated that carbohydrate content was improved and the maximum accumulation (about 60% of the dry weight) was recorded under sulfur starvation with only a 14% reduction in biomass as compared to control. This study showed promising results as to biomass production and carbohydrate yield by the microalgae C. debaryana in view of production of third-generation biofuels.

Pharmaceuticals and personal care products (PPCPs) do not have standard regulations for discharge in the environment and are categorized as contaminants of emerging concern as they pose potential threats to ecology as well as humans even at low concentrations. Conventional treatment processes generally employed in the wastewater treatment plants are not adequately engineered for effective removal of PPCPs. Identifying cost-effective tertiary treatment is therefore, important for complete removal of PPCPs from wastewater prior to discharge or reuse. Present study demonstrates adsorption using granular-activated carbon (GAC) as a possible tertiary treatment for simultaneous removal of five PPCPs from aqueous media. Adsorbent was characterized in terms of morphology, surface area, surface charge distribution, and presence of functional groups. Performance of GAC was investigated for sorption of three hydrophilic (ciprofloxacin, acetaminophen, and caffeine) and two hydrophobic (benzophenone and irgasan) PPCPs from aqueous solution varying the process parameters (initial concentration, adsorbent dose, pH, agitation time). Langmuir isotherm model (correlation coefficients (R²): 0.993 to 0.998) appeared to fit the isotherm data better than Temkin isotherm model for these adsorbates. Adsorption efficiencies of these compounds (8.26 to 20.40 mg g⁻¹) were in accordance with their log Kₒw values. While the adsorption kinetics was best explained in terms of a pseudo-second-order kinetic model, the data suggested that adsorption mechanism was mainly governed by the intraparticle diffusion. The role of physical factors like molecular volume, molecular size, and area of targeted PPCPs were investigated through computational studies which in turn can help predicting their uptake onto GAC.

This study demonstrated the dye removal potential of a lesser studied Actinobacteria, Nocardiopsis sp., on triphenylmethane (TPM) dyes. The actinobacterium was sampled from forest soil and identified as Nocardiopsis alba (99.24% similarity) via partial 16S rRNA sequencing. Both live and dead cells were used to decolorize TPM dyes (i.e., malachite green (MG), methyl violet (MV), crystal violet (CV), and cotton blue (CB)). The influence of pH, agitation speed, biomass, initial dye concentration, and oxygen was determined via one-factor-at-a-time (OFAT) approach. Results revealed that live cells showed higher dye removal potential following treatment under optimized conditions, i.e., pH 7, 100 rpm agitation, 0.75 g cell biomass, 100 mg L⁻¹ initial dye concentration (50 mg L⁻¹ for CB), and oxygen availability, with 96.8 (MG), 95.9 (MV), 48.8 (CV), and 80.6% (CB) of decolorization efficacy (DE). On the contrary, dead cells were less effective in decolorizing MG (91.1%), MV (68.9%), CV (46.6%), and CB (63.7%), although decolorization was performed at optimum conditions (pH 9 for MG, MV, CV; pH 3 for CB, 100 rpm agitation, 0.75 g cell biomass, and 100 mg L⁻¹ initial dye concentration (50 mg L⁻¹ for CB)). UV–Vis analysis revealed that the removal of TPM dyes occurred primarily via biodegradation (live cells) and biosorption (dead cells). The sorption data complied with Langmuir model (R² = 0.984–0.999), confirming the monolayer sorption of TPM dyes by cells of Nocardiopsis. This study established Nocardiopsis sp., particularly live cells, as an effective biological agent for the remediation of TPM dyes.