Nano-biomaterial treatment of noxious microbial pollutant in water

Abstract

The development of biomaterial industries in South Africa, action plan and implementation strategy are currently being discussed. Applying natural products like plant materials in water treatment is a vital effort in line with global sustainable development initiatives. This initiative will reduce or eradicate the cost, undesirable by-products, high metal concentrations and sludge development that is typical of conventional water treatment procedures. Addressing the critical gap in the area of water treatment through nano-bioformulations and product development in South Africa is therefore of great necessity. This work aimed at the preparation of effective nano-biomaterials for treatment and purification of noxious contaminants in water. The formulations of biomaterials for use in the remediation of contaminated waters were accomplished by using polymeric extract, cellulose fibres of wild Sesame and composites of silver-doped ferrite metal particles. The performance and efficiency of the active nano-bioformulations were investigated by batch experiments for dual activities of disinfection (against several ATCC bacteria strains including B. cereus 14579, P. mirabilis 12453, E. coli 25922, S. typhimurium 14028, E. cloacae 13047, S. choleraesuis 10708, P. vulgaris 33420, K. pneumonia 13883 and B. subtilis 11774) and physico-chemical activities in polluted water. The structural, adsorptive and bioactive properties of the different parts of a wild Sesame obtained from Thohoyandou, Limpopo, South Africa were investigated during bioprospecting for material with water treatment application. The morphometric properties of the different plant parts were investigated to establish eco-physiological contributions to sorption. Nano-biomaterials were formulated from leaf extract, stem and root fibres, as well as silver-doped ferrite metallic particles and were subsequently used in water treatment. Morphometric property of the studied materials was investigated using light microscopy. The structural and surface characteristics of the pulverised biomass were studied by thermogravimetric analysis (TGA), Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis and scanning electron microscopy. Functional and bioactive properties were studied by fourier transform infrared (FTIR) spectroscopy, thin-layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS). The minimum inhibitory antimicrobial assay and therapeutic indices were used to ascertain the disinfection potential of the prepared nano-biomaterial. The synthesised nano-biomaterials were characterised by scanning electron microscopy and energy dispersive x-ray spectroscopy. Preliminary synthetic liquid and solid culture antimicrobial assays were used to assess the potentials of the atomised nano-bioparticles for water purification and disinfection during a target-based antimicrobial study. Application of the synthesised materials for environmental water sample treatment was conducted by assessing coliform and total heterotrophic bacteria disinfection and physico-chemical parameter improvement in a jar test. Turbidity, electrical conductivity and pH of treated water were measured using a multimeter. A central composite design was utilised to model the effects of important water treatment process in order to establish optimized parameters for water treatment when using the developed material. Phytochemical signatures of plant extract indicated the presence of polysaccharides, aliphatic esters and aromatic compounds, amines, protein, water, fatty acids, phospholipids, and triglycerides that could aid nanomaterial stabilisation. The main volatile compounds found included Phenol, 2,4-bis(1,1-dimethylethyl)- (12,36), 7,9-Di-tert-butyl-1-oxaspiro(4,5) deca-6,9-diene-2,8-dione (12,27), Phenol, 2,5-bis(1,1-dimethylethyl) (11,52), Hexadecanoic acid, methyl ester (10,00%), Octacosane (4,62) and Hexadecane (4,40%). A plant extract stabilised nanomaterial (AgNP-PE) developed resulted in 0.45 NTU; 99.6 % turbidity removal at 5 μg/mL of nanomaterial concentration in water but with no recovery prospect. The Fe3O4@TiO2@Ag core/shell composite material performed optimally for water disinfection and physico-chemical parameter improvement among all formulations made. The material possessed notable antimicrobial activity against noxious microbial pathogens and water contaminants at concentrations of 3.0-4.5 μg. Maximum disinfection activity of 98.1% and over 90 % turbidity removal was achieved after polluted environmental water sample was treated with this material. Electrical conductivity, pH, and microbial counts of treated polluted water falls within acceptable limit recommended by the South African National Standard for potable water. The composite particle could be recovered without a substantial loss while optimised water treatment process of 35oC, 75 mins, 100 rpm, 2.5 μg and 24oC, 30 mins, 149 rpm, 7.3 μg of nanocomposites was established as the best conditions for water treatment considering treatment dosage and time. The time for treatment drastically reduced from 120 and 90 mins obtained with un-optimised treatment studies to 30 mins during the implementation of treatment process with the developed material. The optimum treatment dose also reduced to 2.5 μg as against 5 μg reported for other treatment materials. The developed recyclable silver doped ferrite particle has been formulated with nanocellulose from the stem and root of a selected wild Sesame for the very first time. The quality of raw wetland water treated with developed material was improved to acceptable SANS/WHO limits of microbial quality of 0 cfu per 100 mL) and turbidity (<5 NTU) standards for drinking water. Fungal isolates from water and multidrug resistant strain of E. coli were effectively inhibited by the eco-friendly polymer-metal and composite nanomaterials synthesised. During a comparative study, the combined activities of sodium hypochlorite and alum treatment resulted in final turbidity of 0.90 NTU and 99.7% turbidity removal at optimum time of 6 hours using a 100 μg/mL treatment material. Therefore, the nano-biomaterial seemed to perform comparatively with commercial chlorine and aluminium sulphate for disinfection and coagulation processes. The optimum time and amount of the developed treatment material was, however, greatly optimised for water treatment when compared to the commercial water treatment counterparts; a 100% pathogen removal from water was also achieved. This observation showed that established protocol in this study leads to the development of effective nano-biocomposites from plant material to meet the challenges of water purification and sustainable development goal.