Valorization of food waste as adsorbents for toxic dye removal from contaminated waters: A review.

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability.

Extraction and detection methods of microplastics in food and marine systems: A critical review.

The ubiquitous presence of microplastics as contaminants in the ecosystem has become a matter of environmental concern gaining considerable attention in the research community as well as public arena. Lack of efficient collection and improper management of plastic have resulted in the enormous amounts of plastic wastes landing into the marine systems with oceans being the ultimate sink. Due to non-biodegradability, these plastics break down into smaller fragments over a period of time leading to consumption by aquatic species, threatening marine life. In the recent years, a wide range of food products has also been contaminated with microplastics directly affecting human health. This review focuses on the separation and identification technologies for extraction and detection of microplastics in food and marine ecosystems. Efficient technologies like floatation, membrane separation, chemical treatment, enzymatic treatment, and other miscellaneous techniques have been discussed considering their merits and demerits. Additionally, identification technologies like optical detection, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, thermo-analytical methods, and hyperspectral imaging have been emphasized for the detection of microplastic particles. The emerging techniques like enzymatic digestion combined with hyperspectral imaging could be a possible way for obtaining higher separation efficiency and characterization with minimal harm to food sample. This article narrows the gap for choosing a standard separation technology for microplastic detection in food matrices keeping in mind the composition, particle size, shape, data visualization techniques and cost.

Eco-friendly pH detecting paper-based analytical device: Towards process intensification.

This work describes the development of a miniaturized paper-based pH detection platform using natural dye extracted from red cabbage (Brassica oleracea). The easily available paper was used as a substrate and the requisite patterned zone was created with the aid of a punching machine. Experimental parameters were optimized to obtain the best signal readout. The performance of the device at different pH values was quantitatively assessed using digital image analysis with various color space models. Regression analysis suggested that a∗ parameter in CIEL∗a∗b∗ color space model, which captures the variations on the red-green scale, exhibited the best fit with experimental data (R2 = 0.9754). This parameter was used for the quantitative estimation of pH variations in a wide range of pH (1-12). A series of real test samples were examined using the paper-based device and results validated with a standard pH meter. The use of paper and natural dye makes the device eco-friendly. The simplicity of fabrication, ease of usage and low reagent and sample volume requirements render the methodology suitable for in situ measurements of pH. The approach demonstrated here would pave the way for the development of clean, sustainable and intensified chemical sensor technologies.

Techniques and modeling of polyphenol extraction from food: a review.

There is a growing demand for vegetal food having health benefits such as improving the immune system. This is due in particular to the presence of polyphenols present in small amounts in many fruits, vegetables and functional foods. Extracting polyphenols is challenging because extraction techniques should not alter food quality. Here, we review technologies for extracting polyphenolic compounds from foods. Conventional techniques include percolation, decoction, heat reflux extraction, Soxhlet extraction and maceration, whereas advanced techniques are ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, high-voltage electric discharge, pulse electric field extraction and enzyme-assisted extraction. Advanced techniques are 32-36% more efficient with approximately 15 times less energy consumption and producing higher-quality extracts. Membrane separation and encapsulation appear promising to improve the sustainability of separating polyphenolic compounds. We present kinetic models and their influence on process parameters such as solvent type, solid and solvent ratio, temperature and particle size.

Optimization of process using carboxymethyl chitosan for the removal of mixed heavy metals from aqueous streams.

This paper highlights the efficacy of carboxymethyl chitosan (CMCh), a bio-degradable water-soluble derivative of chitosan for the separation of a mixture of heavy metal ions such as copper, nickel, zinc and lead from aqueous streams, as they constitute, the major industrial pollutants present in wastewater. The experimental studies are conducted using commercially available ultrafiltration module using synthetic solutions of the contaminants. The design of experiments was performed by Response Surface Methodology (RSM) with split-plot D-optimal design. Parametric studies were carried out using initial pH of the feed solution, loading ratio (P/M) and initial metal ion concentration to assess the percentage rejection and recovery of metal ions. The maximum percentage rejection of Cu(II), Ni(II), Zn(II) and Pb(II) with CMCh were found to be 100%, 100%, 95%, and 98% respectively under optimum conditions. Subsequently the metal ions were recovered collectively by reversing the pH to 2. The results show that CMCh could be an effective size enhancing species for the removal and recovery of mixture of metals by SEUF.

Removal and recovery of heavy metals through size enhanced ultrafiltration using chitosan derivatives and optimization with response surface modeling.

N­N­N­triethylammonium chitosan (TEAC) and carboxymethyl chitosan (CMCh), the two water-soluble chitosan derivatives were utilized for the removal and recovery of heavy metals by size enhanced ultrafiltration (SEUF). The strong positive quaternary ammonium [-N+(C2H5)3] cation in TEAC interacts with Cr(VI), which exists as a strong chromate anion thereby enabling the efficient removal of chromate through ultrafiltration. CMCh consists of COOH and NH2 moieties, which facilitate interactions with heavy metals such as Cu(II) and Ni(II). FTIR, SEM, and EDAX were used to characterize the chitosan derivatives before and after the removal of metals. The experiments were designed with the central composite design (CCD) of response surface methodology (RSM). The metal ion removal experiments were conducted as per the statistical design to determine the optimum process conditions; initial pH of the feed solution, polymer to metal loading ratio (P/M), and initial concentration of the feed solution. The optimization study was conducted to maximize the heavy metal rejection and binding capacity of the chitosan derivatives. The analysis of variance (ANOVA) was performed to validate the developed regression models.

Nitrate decontamination through functionalized chitosan in brackish water.

N, N, N-Triethyl ammonium functionalized cross-linked chitosan beads (TEACCB) was prepared by alkylation of glutaraldehyde cross-linked chitosan beads to remove nitrate from brackish water. Physico-chemical characteristics of TEACCB were analyzed using FTIR, SEM, EDAX, TGA, DTA, BET surface area, swelling ratio and pHzpc. The maximum nitrate removal capacity of TEACCB was 2.26meq/g and is higher than other reported chitosan based adsorbents. Nitrate removal ratio in the presence and absence of common anions like chloride and sulphate demonstrated the selectively of TEACCB towards nitrate. The kinetic data of nitrate removal fitted well with the pseudo-second-order kinetic model. The thermodynamic parameters indicated that nitrate removal could be spontaneous and exothermic in nature. TEACCB was reused with 100% efficiency after regenerating with 0.05N HCl. Column study was carried out to remove nitrate from brackish water. These results are very significant to develop TEACCB based nitrate removal technology with great efficiency.