In this study, two biomass-based adsorbents were used as new precursors for optimizing synthesis conditions of a cost-effective powdered activated carbon (PAC). The PAC removed dyes from an aqueous solution using carbonization and activation by KOH, NaOH, and H2SO4. The optimum synthesis, activation temperature, time and impregnation ratio, removal rate, and uptake capacity were determined. The optimum PAC was analyzed and characterized using Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), Zeta potential, and Raman spectroscopy. Morphological studies showed single-layered planes with highly porous surfaces, especially PAC activated by NaOH and H2SO4. The results showed that the experimental data were well-fitted with a pseudo-second-order model. Based on Langmuir isotherm, the maximum adsorption capacity for removing methylene blue (MB) was 769.23 mg g−1 and 458.43 mg g−1 for congo red (CR). Based on the isotherm models, more than one mechanism was involved in the adsorption process, monolayer for the anionic dye and multilayer for the cationic dye. Elovich and intraparticle diffusion kinetic models showed that rubber seed shells (RSS) has higher α values with a greater tendency to adsorb dyes compared to rubber seed (RS). A thermodynamic study showed that both dyes’ adsorption process was spontaneous and exothermic due to the negative values of the enthalpy (ΔH) and Gibbs free energy (ΔG). The change in removal efficiency of adsorbent for regeneration study was observed in the seventh cycles, with a 3% decline in the CR and 2% decline in MB removal performance. This study showed that the presence of functional groups and active sites on the produced adsorbent (hydroxyl, alkoxy, carboxyl, and π − π) contributed to its considerable affinity for adsorption in dye removal. Therefore, the optimum PAC can serve as efficient and cost-effective adsorbents to remove dyes from industrial wastewater.

This paper provides a comprehensive review of 71 previous studies on the life cycle assessment (LCA) of nanomaterials (NMs) from 2001 to 2020 (19 years). Although various studies have been carried out to assess the efficiency and potential of wastes for nanotechnology, little attention has been paid to conducting a comprehensive analysis related to the environmental performance and hotspot of NMs, based on LCA methodology. Therefore, this paper highlights and discusses LCA methodology’s basis (goal and scope definition, system boundary, life cycle inventory, life cycle impact assessment, and interpretation) to insights into current practices, limitations, progress, and challenges of LCA application NMs. We found that there is still a lack of comprehensive LCA study on the environmental impacts of NMs until end-of-life stages, thereby potentially supporting misleading conclusions, in most of the previous studies reviewed. For a comprehensive evaluation of LCA of NMs, we recommend that future studies should: (1) report more detailed and transparent LCI data within NMs LCA studies; (2) consider the environmental impacts and potential risks of NMs within their whole life cycle; (3) adopt a transparent and prudent characterization model; and (4) include toxicity, uncertainty, and sensitivity assessments to analyze the exposure pathways of NMs further. Future recommendations towards improvement and harmonization of methodological for future research directions were discussed and provided. This study’s findings redound to future research in the field of LCA NMs specifically, considering that the release of NMs into the environment is yet to be explored due to limited understanding of the mechanisms and pathways involved.

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The lack of clean water sources, due to the presence of pollutants in water, is a major issue in many countries, including Malaysia. To overcome this problem, various methods have been introduced, including phytoremediation treatment. Therefore, this phytoremediation study examined the ability of five aquatic plants—Centella asiatica, Ipomoea aquatica, Salvinia molesta, Eichhornia crassipes, and Pistia stratiotes—to remove three pollutants—total suspended solids (TSS), ammoniacal nitrogen (NH3-N), and phosphate—from aquaculture wastewater. Using wastewater samples, each containing 50 g of one of the plants, the pollutant levels were measured every two days for 14 days. The results showed a drastic decline in the concentration of pollutants, where C. asiatica was able to remove 98% of NH3-N, 90% of TSS, and 64% of phosphate, while I. aquatica showed the potential to eliminate up to 73% of TSS and NH3-N, and 50% of phosphate. E. crassipes drastically removed 98% of phosphate, 96% of TSS, and 74% of NH3-N, while P. stratiotes was able to eliminate 98% of TSS, 78% of NH3-N, and 89% of phosphate. S. molesta was efficient in removing 89.3% of TSS and 88.6% of phosphate, but only removed 63.9% of NH3-N.

Leachate is a complex liquid that is often produced from landfills, and it contains hazardous substances that may endanger the surrounding environment if ineffectively treated. In this work, four leachate treatment applications were examined: combined leachate/palm oil mill effluent (POME) (LP), leachate/tannin (LT), pre-(leachate/tannin) followed by post-(leachate/POME) (LT/LP), and pre-(leachate/POME) followed by post-(leachate/tannin) (LP/LT). The aim of this work is to evaluate and compare the performance of these treatment applications in terms of optimizing the physicochemical parameters and removing heavy metals from the leachate. The highest efficiency for the optimization of the most targeted physicochemical parameters and the removal of heavy metals was with the LP/LT process. The results are indicative of three clusters. The first cluster involves raw leachate (cluster 1), the second contains LP and LP/LT (cluster 2), and the third also consists of two treatment applications, namely, LT and LT/LP (cluster 3). The results demonstrate that LP/LT is the most appropriate method for leachate treatment using low-cost agro-industrial materials.