Utilisation of Nutmeg Seed Shell-Based Materials for Micropollutant Remediation

Abstract

Waste management of both solid and liquid fractions is gaining priority due to urbanisation, industrialisation, and increased resource demand. Agricultural waste, one of the components of solid waste, has huge potential to convert into several by-products. Nutmeg seed shell (NSS) is an agricultural waste obtained from the cultivation of nutmeg (Myristica Fragrans) spice that can convert into useful products due to its high calorific value and lignin content. NSS can find applications as in refuse-derived fuel (RDF) in the form of briquettes and adsorbents for wastewater treatment. An in-depth research and development in NSS waste valorisation can find its whole potential in wastewater treatment. Removal of micropollutants in wastewater is a significant challenge due to their diverse chemical properties. Even after numerous treatment processes, treated water still contains micropollutants, which include hazardous synthetic dyes; this shows the importance of including advanced treatment techniques in wastewater treatment. Thermally modified NSS can be used as an adsorbent for wastewater treatment. The higher phenolic and lignin content in NSS can be utilised to prepare biomass-based catalysts for wastewater treatment. The current research examines the removal of anionic dye: Remazol Brilliant Blue Reactive (RBBR), cationic: Methyl Violet 10B (MV), and zwitterionic dye: Rhodamine B (RhB), using NSS-based materials to evaluate the removal efficiency of textile wastewater treatment that contains dyes with various ionic states. Thermally modified NSS (NSS Biochar) was identified with micropores and nanopores, resulting in 93.41% RBBR dye removal, but it was less efficient in the case of other dyes. Due to the presence of reducing and capping agents in NSS aqueous extract, it is used to synthesise silver nanoparticles (AgNPs). The optimised synthesis process resulted in the formation of AgNPs with a size 10–60 nm and a surface area of 88.16 m2/g. The best radical scavenging activity was seen at 200 g/mL for AgNPs. The application of these AgNPs in antibacterial uses is supported by their bacterial inhibition against both gram-positive and gram-negative bacteria (IZD≥ 15 mm) when ii compared to ampicillin (IZD ≤ 13 mm) at a concentration of 50 μg/mL. Synthesised AgNPs were used to study their feasibility in dye removal, and the results showed a better photocatalytic degradation (>90%) of RhB (10 mg/L), RBBR (100 mg/L), and MV (100 mg/L) when exposed to UV light. According to the degradation process, AgNP's affinity towards dye and their radical action impacts how effectively the dye degrades. The degradation mechanism was found by analysing the degradation products using HRLC-MS. In the presence of AgNP, the fluorescent dye RhB could not degrade at higher concentrations. The NSS's higher lignin and phenolic content are also utilised to prepare the catalyst for dye degradation. Lignin was extracted from NSS using alkali; the optimal extraction was achieved with 12% sodium hydroxide, resulting in 33% of lignin yield. To separate the catalyst after the treatment process, a composite built on NSS lignin and silver with magnetic property (Ag/Fe/Lignin) is used for dye degradation. Ag/Fe/Lignin resulted in improved degradation for all category dyes, even at higher concentrations. The research was also done on a mixture of cationic, anionic, and zwitterionic dyes. Ag/Fe/Lignin accomplished 94% degradation for a dye mixture at 100 mg/L concentration under UV light. It degraded more quickly and efficiently at greater concentrations when H2O2 was added as an activator in the presence of UV light. The processes that degrade dyes into simple organic molecules include deamination, demethylation, dihydroxylation, and cleavage of the aromatic ring by radical action. The degradation efficiency for the reusability study was >95% even after five cycles of experiments. The dye degradation capacity NSS-based composite (Ag/Fe/Lignin) demonstrated an improved method of utilising lignocellulosic waste components, such as NSS with high lignin content, in wastewater treatment.