Smartphone microscopic method for imaging and quantification of microplastics in drinking water.

Analysis of microplastics in drinking water is often challenging due to smaller particle size and low particle count. In this study, we used a low cost and an easy to assemble smartphone microscopic system for imaging and quantitating microplastic particles as small as 20 µm. The system consisted of a spherical sapphire ball lens of 4 mm diameter attached to a smartphone camera as a major imaging component. It also involved pre-concentration of the sample using ZnCl2 solution. The spike recovery and limit of detection of the method in filtered distilled and deionized water samples (n = 9) were 55.6% ± 9.7% and 34 particles/L, respectively. Imaging performance of the microscopic system was similar to a commercial bright field microscopic system. The method was further implemented to examine microplastic particles in commercial bottled and jar water samples (n = 20). The particles count in bottled and jar water samples ranged from 0-91 particles/L to 0-130 particles/L, respectively. In both sample types, particles of diverse shape and size were observed. The particles collected from water samples were further confirmed by FTIR spectra (n = 36), which found 97% of the particles tested were made of plastic material. These findings suggested that the smartphone microscopic system can be implemented as a low-cost alternative for preliminary screening of microplastic in drinking water samples. RESEARCH HIGHLIGHTS: Ball lens based smartphone microscopic method was used for microplastic analysis. Particles of diverse shape and size were found in bottle and jar water samples.

Acid-treated pomegranate peel; An efficient biosorbent for the excision of hexavalent chromium from wastewater.

We studied the sequestration of hexavalent chromium Cr(VI) from an aqueous solution using chemically modified pomegranate peel (CPP) as an efficient bio-adsorbent. The synthesized material was characterized by X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). The impacts of parameters like solution pH, Cr(VI) concentration, contact time, and adsorbent dosage were investigated. Experimental results of the isotherm studies and adsorption kinetics were found agreeing to the Langmuir isotherm model and pseudo-second-order kinetics, respectively. The CPP showed appreciable Cr(VI) remediation capacity with a maximal loading capacity of 82.99 mg/g at pH 2.0, which was obtained in 180 min at room temperature. Thermodynamic studies revealed the biosorption process as spontaneous, feasible, and thermodynamically favorable. The spent adsorbent was eventually regenerated and reused, and the safe disposal of Cr(VI) was ensured. The study revealed that the CPP can be effectively employed as an affordable sorbent for the excision of Cr(VI) from water.

Adsorption of nitrate and nitrite anion by modified maize stalks from aqueous solutions.

The newly developed aminated maize stalk (AMS) was prepared by a chemical process using charred maize stalk (CMS). The AMS was used for the removal of nitrate and nitrite ions from aqueous media. The effects of initial anion concentration, contact time, and pH were studied by the batch method. The prepared adsorbent was characterized by FT-IR, XRD, FE-SEM , and elemental analysis. The concentration of the nitrate and nitrite solution before and after was determined with the help of a UV-Vis spectrophotometer. The maximum adsorption capacities were found to be 294.11 mg/g for nitrate and 232.55 mg/g for nitrite, respectively, at pH 5 for both ions attaining equilibrium within 60 min. The BET surface area of AMS was found to be 25.3 m2/g with a pore volume of 0.02cc/g. The pseudo-second-order kinetics model fit well, and the adsorption data supported the Langmuir isotherm. The findings revealed that AMS has a high capability for removing nitrate (NO3-) and nitrite (NO2-) ions from their aqueous solutions.

Effective biosorption of As(V) from polluted water using Fe(III)-modified Pomelo (Citrus maxima) peel: A batch, column, and thermodynamic study.

Pomelo, Citrus maxima, peel was chemically modified with lime water and then loaded with Fe(III) to develop anion exchange sites for effective sequestration of As(V) from water. Biosorbent characterizations were done by using FTIR, SEM, XRD, EDX, and Boehm's titration. The batch biosorption studies were carried out at various pHs using modified and non-modified biosorbents and optimum biosorption of As(V) occurred at acidic pH (3.0-5.0) for both the biosorbents. A kinetic study showed a fast biosorption rate and obtained results fitted well with the pseudo-second-order (PSO) model. When isotherm data were modeled using the Langmuir and Freundlich isotherm models, the Langmuir isotherm model fit the data better and produced maximal As(V) biosorption capacities of 0.72 ± 03, 0.86 ± 06, and 0.95 ± 05 mmol/g at temperatures 293± 1K, 298± 1K and 303± 1K, respectively. Desorptionof As(V) was effective using 0.1 M NaOH in batch mode. Negative values of ΔG° for all temperatures with positive ΔH° confirmed the spontaneous and endothermic nature of As(V) biosorption. The existence of co-existing chloride (Cl-), nitrate (NO3 -), sodium (Na+), and calcium (Ca2+) showed insignificant interference whereas a high concentration of sulphate (SO4 2-) and phosphate (PO4 3-) significantly lowered As(V) biosorption percentage. Arsenic concentrations in actual arsenic polluted groundwater could be reduced to the WHO drinking water standard (10 µg/L) by using only 1 g/L of investigated Fe(III)-SPP. The dynamic biosorption of As(V) in a fixed bed system showed that Fe(III)-SPP was effective also in continuous mode and different design parameters for fixed bed system were determined using Thomas, Adams-Bohart, BDST, and Yoon-Nelson models. Therefore, from all of these results it is suggested that Fe(III)-SPP investigated in this study can be a potential, low cost and environmentally benign biosorbent material for an effective removal of trace amounts of arsenic from polluted water.

Comparative study of Hg(ii) biosorption performance of xanthated and charred sugarcane bagasse from aqueous solutions.

The main target of this study was to evaluate the efficiency of charred xanthated sugarcane bagasse (CXSB) and charred sugarcane bagasse (CSB) in the removal of Hg(ii) ions from aqueous media. Batch experiments were performed to study the experimental parameters such as effects of pH, concentration, contact time and temperature. The adsorption velocity of Hg(ii) onto CSB and CXSB was fast and reached equilibrium within 60 minutes. Isotherm and kinetic studies showed that Hg(ii) uptake using both the biosorbents followed Langmuir isotherm and pseudo second order kinetics. The maximum adsorption capacity of Hg(ii) at optimum pH 4.5 onto CSB and CXSB was found to be 125 mg g-1 and 333.34 mg g-1, respectively. A negative value of ΔG° and positive ΔS° value (0.24 kJ mol-1 for CSB and 0.18 kJ mol-1 for CXSB) for both the biosorbents confirm the spontaneous nature of Hg(ii) adsorption. A positive value of ΔH° (52.06 kJ mol-1 for CSB and 30.82 kJ mol-1 for CXSB) suggests the endothermic nature of biosorption. The investigated results shows that CXSB compared to CSB can be used as a low cost and environmentally benign bio-adsorbent for the removal of Hg(ii) ions from aqueous solutions.

Thermochemical study of Cr(VI) sequestration onto chemically modified Areca catechu and its recovery by desorptive precipitation method.

A new biosorbent for Cr(VI) sequestration was investigated from betel nut waste (BNW), Areca catechu, by H2SO4 charring. Aqueous insolubility and Cr(VI) uptake capacity of native BNW were potentially improved after H2SO4 modification due to cross-linking reaction of betel nut cellulose, thereby creating suitable complexation sites for Cr(VI) ion removal. Langmuir isotherm and pseudo second order (PSO) kinetic models described well with the experimental data. A trace amount of Cr(VI) was effectively removed below the safe drinking water standard (WHO, 0.05 mg/L) using charred BNW (CBNW). The negative value of ΔG° evaluated for all the temperatures suggested the spontaneous nature of Cr(VI) sequestration and positive value of ΔH° (42.43±0.13 kJ/mol) confirmed an endothermic reaction. Co-existing NO 3 - , Cl-, Na+ and Zn2+ ions showed negligible interferences, whereas SO 4 2 - and PO 4 3 - notably reduced Cr(VI) uptake capacity of CBNW. More than 98% of adsorbed Cr(VI) was desorbed using 1M NaOH solution. A light yellow precipitate of BaCrO4 was recovered from the desorbed solution after precipitation with BaCl2 solution. Therefore, the CBNW biosorbent investigated in this work is expected to be a promising material for Cr(VI) sequestration and its recovery from polluted water.

Assessing volatile organic compound level in selected workplaces of Kathmandu Valley.

Volatile organic compounds (VOCs) are one of the major contributors to poor indoor air quality. Due to advancements in sensor technologies, continuous if not regular monitoring total VOC (TVOC) and or some specific VOC in potential high risk workplaces is possible even in resource limited settings. In this study, we implemented a portable VOC sensor to measure concentration of TVOC and formaldehyde (HCHO) in six types of potential high risk workplaces (n = 56 sites) of Katmandu Valley. For comparison, concentration was also measured in immediate surroundings (n = 56) of all the sites. To get preliminary information on safety practices, a survey study was also conducted. The mean TVOC and HCHO concentration in the sites ranged from 1.5‒8 mg/m3 and <0.01-5.5 mg/m3, respectively. The indoor: outdoor TVOC and HCHO ratio (I/O) was found to be significantly higher (I/O > 1.5 and p < 0.05) in 34 (~61%) and 47 sites (∼84%), respectively. A strong positive correlation between HCHO and TVOC concentration was observed in furniture industry (R = 0.91) and metal workshops (R = 0.98). Interestingly, we found TVOC and HCHO concentration higher than WHO safe limit in ∼64% and ∼32% sites, respectively. A rough estimate of chronic daily intake (CDI) of formaldehyde showed that CDI is higher than WHO limit in four sites. These findings suggested that indoor air quality in the significant number of the workplaces is poor and possible measures should be taken to minimize the exposure.

Unusual Pressure-Induced Periodic Lattice Distortion in SnSe_{2}.

We performed high-pressure x-ray diffraction (XRD), Raman, and transport measurements combined with first-principles calculations to investigate the behavior of tin diselenide (SnSe_{2}) under compression. The obtained single-crystal XRD data indicate the formation of a (1/3,1/3,0)-type superlattice above 17 GPa. According to our density functional theory results, the pressure-induced transition to the commensurate periodic lattice distortion (PLD) phase is due to the combined effect of strong Fermi surface nesting and electron-phonon coupling at a momentum wave vector q=(1/3,1/3,0). In contrast, similar PLD transitions associated with charge density wave (CDW) orderings in transition metal dichalcogenides (TMDs) do not involve significant Fermi surface nesting. The discovered pressure-induced PLD is quite remarkable, as pressure usually suppresses CDW phases in related materials. Our findings, therefore, provide new playgrounds to study the intricate mechanisms governing the emergence of PLD in TMD-related materials.

Preparation of novel alginate based anion exchanger from Ulva japonica and its application for the removal of trace concentrations of fluoride from water.

A green seaweed, Ulva japonica, was modified by loading multivalent metal ions such as Zr(IV) and La(III) after CaCl2 cross-linking to produce metal loaded cross-linked seaweed (M-CSW) adsorbents, which were characterized by elemental analysis, functional groups identification, and metal content determination. Maximum sorption potential for fluoride was drastically increased after La(III) and Zr(IV) loading, which were evaluated as 0.58 and 0.95 mmol/g, respectively. Loaded fluoride was quantitatively desorbed by using dilute alkaline solution for its regeneration. Mechanism of fluoride adsorption was inferred in terms of ligand exchange reaction between hydroxyl ion on co-ordination sphere of the loaded metal ions of M-CSW and fluoride ion in aqueous solution. Application of M-CSW for the treatment of actual waste plating solution exhibited successful removal of fluoride to clear the effluent and environmental standards in Japan, suggesting high possibility of its application for the treatment of fluoride rich waste water.

Adsorptive removal of fluoride from aqueous medium using a fixed bed column packed with Zr(IV) loaded dried orange juice residue.

The potential of the adsorbent prepared from DOJR marketed as cattle food in Japan was identified as an efficient and low cost adsorbent for fluoride using fixed bed column. DOJR was loaded with Zr(IV) ions to develop active adsorption sites for fluoride. Fluoride adsorption performance of column packed with Zr(IV) loaded DOJR was assessed under variable operating conditions such as Zr(IV) loading temperature, initial fluoride concentration, bed depth, initial pH, and flow rate. Breakthrough curve modeling showed that Thomas and bed depth service time (BDST) models were in good agreement with the experimental data. Application of adsorbent investigated in this study to the treatment of actual waste plating solution containing fluoride ion showed successful removal below acceptable standard in Japan using a fixed bed column, hence, Zr(IV)-DOJR can be expected to be a promising candidate for the treatment waste water containing trace amount of fluoride ion in fixed bed column.

Optimization of an adsorption process for tetrafluoroborate removal by zirconium (IV)-loaded orange waste gel from aqueous solution.

This investigation provides new insights into the effective removal of tetrafluoroborate (BF4-) by means of bio-sorption on waste generated in the orange juice industry. It was undertaken to evaluate the feasibility of zirconium (IV)-loaded saponified orange waste gel for BF4- removal from an aqueous solution. Batch adsorption experiments were carried out to study the influence of various factors such as pH, presence of competing anions, contact time, initial BF4- concentration and temperature on the adsorption of BF4-. The optimum BF4- removal was observed in the equilibrium pH region 2-3. The presence of coexisting anions showed no adverse effect on BF4- removal except SO4(2-). The equilibrium data at different temperatures were reasonably interpreted by the Langmuir adsorption isotherm and the maximum adsorption capacities were evaluated as 2.65, 3.28, 3.87 and 4.77 mmol g(-1) at 293, 298, 303 and 313 K, respectively. Thermodynamic parameters such as deltaGo, deltaHo and deltaSo indicated that the nature of BF4- adsorption is spontaneous and endothermic. The results obtained from this study demonstrate the potential usability of orange waste after juicing as a good BF4- selective adsorbent.

Adsorptive removal of fluoride from aqueous solution using orange waste loaded with multi-valent metal ions.

Adsorption gels for fluoride ion were prepared from orange waste by saponification followed by metal loading. The pectin compounds contained in orange waste creates ligand exchange sites once it is loaded with multi-valent metal ions such as Al(3+), La(3+), Ce(3+), Ti(4+), Sn(4+), and V(4+) to be used for fluoride removal from aqueous solution. The optimum pH for fluoride removal depends on the type of loaded metal ions. The isotherm experiments showed the Langmuir type monolayer adsorption. Among all kinds of metal loaded gels tested, Al loaded gel appeared to exhibit the most favorable adsorption behavior. The adsorption kinetics of fluoride on loaded gel demonstrated fast adsorption process. The presence of NO(3)(-), Cl(-) and Na(+) ions has negligible effect on fluoride removal whereas SO(4)(2-) and HCO(3)(-) retarded the fluoride removal capacity in some extent. Fluoride removal at different adsorbent doses showed that fluoride concentration can be successfully lowered down to the acceptable level of environmental standard. The fluoride adsorption mechanism was interpreted in terms of ligand exchange mechanism. The complete elution of adsorbed fluoride from the gel was successfully achieved using NaOH solution.