Silica gel matrix immobilized Chlorophyta hydrodictyon africanum for the removal of methylene blue from aqueous solutions: Equilibrium and kinetic studies

Chlorophyta hydrodictyon africanum was immobilized on a silica gel matrix to improve its mechanical properties. The algae-silica gel adsorbent was used for batch sorption studies of a cationic dye, methylene blue (MB). Optimum adsorption was obtained with a dosage of 0.8 g bio sorbent. Results from sorption studies show that 124.11 mg·g-1 of MB could be adsorbed at an optimum pH of 8 and immobilization of 300 mg per gram silica. Maximum immobilization was 400 mg biomass per gram silica. Sorption capacity increased with an increase in initial dye concentration and reached equilibrium within 30 min. Three models were used to  simulate kinetic data and the pseudo–second order model gave a better fit with R2 greater than 0.98 in all cases. Equilibrium studies revealed that the adsorption of MB followed Freundlich isotherm (R2=1.00).Key words: Adsorbent, algae, Langmuir model, Freundlich isotherm

Extraction, growth and immobilization of Yarrowia lipolytica yeast cells for dye effluent treatment

The removal of organic dyes from industrial wastewater remains a problem, both technically and economically. In this study, Yarrowia lipolytica yeast cells were isolated from poultry meat and immobilized using alginate. The immobilized Yarrowia lipolytica yeast was used as biosorbent to remove methylene blue (MB) dye from synthetic effluent water. The results show that maximum adsorption capacity under optimum conditions was 66.67 mg∙g-1. The equilibrium adsorption data fitted well onto the Freundlich adsorption isotherms with R2>0.99. Adsorption kinetics was of pseudo-second order process suggesting that the adsorption was a chemisorption. FTIR spectra identified typical absorption bands of a biosorbent. Sorption of MB dye on Yarrowia lipolytica yeast cells was exothermic with weak sorption interaction

Preparation of rice hull activated carbon for the removal of selected pharmaceutical waste compounds in hospital effluent

The adsorbent (activated carbon) was prepared from rice hull obtained from communal farmers in Mutoko North (Zimbabwe) by chemical activation using phosphoric acid and was used in the adsorption of aspirin, paracetamol and ibuprofen from hospital effluent. Characterization of the rice hull activated carbon was carried out using the following methods: SEM, XRD, FT- IR. Physical properties such as iodine number, porosity, ash content, moisture content and volatile matter content were also determined. Iodine number was found to be 815.0 ± 2.52 mg/g. FT-IR analysis showed the presence of various functional groups such as C=O, C=C, –OH, and C-H on the surface of the adsorbent whereas SEM micrograph showed that the external surface of the rice hull activated carbon is full of regular cavities. XRD pattern showed broad peaks indicating that rice hull activated carbon produced has amorphous structure. The effect of adsorbent dose, contact time, initial concentration and pH was studied. Adsorption of aspirin fits the Freundlich isotherm, whereas ibuprofen and paracetamol fit the Langmuir isotherm. Kinetic studies showed that adsorption of ibuprofen, aspirin and paracetamol obey pseudo-second order kinetics. Aspirin, paracetamol and ibuprofen were detected in two hospital waste waters at the concentrations of 0.117 ±0.0058 mg/L, 0.100 mg/L and 0.010 ± 0.0006 mg/L respectively. The studies showed that pharmaceutical compounds studied can be removed from wastewater using rice hull derived activated carbon

Extraction of silica gel from Sorghum bicolour (L.) moench bagasse ash

Sweet sorghum (Sorghum bicolor (L.) moench), a crop that is grown by subsistence farmers in Zimbabwe was used to extract silica gel in order to assess its possible use as a raw material for the production of silica-based products. The gel was prepared from sodium silicate extracted from sweet sorghum bagasse ash by sodium hydroxide leaching. Results show that maximum yield can be obtained at pH 5 and with 3 M sodium concentration. The silica gel prepared at optimum pH 5 had a bulk density of 0.5626 g/cm3 and anestimated porosity of 71.87%. Silica gel aged over 10 h had improved moisture adsorption properties. X-ray fluorescence (XRF) determinations show that the silica content in the ash is 40.1%. Characterization of sweet sorghum ash and silica gels produced at pH 5, 7 and 8.5 by Fourier Transform Infrared spectroscopy gave absorption bands similar to those reported by other researchers.Transmission electron micrographs show that silica prepared under optimum conditions is amorphous and consisted of irregular particles. Sweet sorghum proved to be a potential low cost raw material for the production of silica gel