Coagulation and sedimentation performances of aluminum sulphate and ferric chloride were comparatively investigated in presence of Grewia spp. biopolymer for the treatment of concentrated laterite suspensions. Jar tests experiments were carried out at different laterite suspension concentrations (10, 20, and 30 g/L) and pH values (5 and 7). The performances of these coagulants were assessed in terms of interfacial settling velocities and sediment concentration factors. Results showed that after addition of Grewia spp. biopolymer, sedimentation velocities were greater when ferric chloride and aluminum sulphate were used alone. When hydrolyzing salts were used alone, the highest settling velocities were obtained with 10 g/L of laterite suspension at pH 5 and settling speeds were 0.22 and 0.28 cm/min for aluminum sulphate and ferric chloride, correspondingly. Addition of Grewia spp. biopolymer led to an increase of settling velocities to 0.56 and 0.57 cm/min, respectively. The sediment concentration factor was also found to be high when Grewia spp. was added. With 30 g/L of laterite suspension, sediment concentration factors at pH 5 were 1.47 and 2.12 for aluminum sulphate and ferric chloride separately. Addition of Grewia spp. biopolymer with aluminum sulphate and ferric chloride produced more compact sludge with sediment concentration factors of 4 and 3.13, respectively. Flocs structures could successfully explain the obtained results.

Diffusion coefficients of biopolymers extracted from Grewia spp. barks in water were studied under various physicochemical conditions. Extractions were carried out on barks of 3 cm in length at different pH (5-9), temperature (25-50°C) and ionic strength (10-3-10-2 M), using CaCl 2 and NaCl as background electrolytes. Factorial experimental plan design was used and diffusion coefficients were determined using second law of Fick equation, with linear and logarithmic approximation. Obtained results show that diffusion coefficients of Grewia spp. biopolymers are in the range of 9.78458E-06±1.6462E-08 cm 2 /min, and are not significantly influenced by the pH, the ionic strength and the temperature. Maximum diffusion was obtained with CaCl 2 at high ionic strength. Both linear and logarithmic approximations were found to be suitable for diffusion coefficients and were dependent on the background electrolyte used.

The growth of microorganisms is influenced by several physico-chemical parameters that need to be controlled before starting a biological treatment plant for better process efficiency. In this study, the influence of temperature (25-40 °C), pH (4-8), and ammonium formate concentration (1.59-7.94 mM) on the growth of two yeast strains (Y.lipolytica and P.guilliermondii ) examined in a batch process. Temperature has a direct impact on the kinetic growth parameters with an activation energy (Ea) of 14.3 kcal/mol and R2 0.95 for Y.lipolytica and 12.5 kcal/mol and R2 0.97 for P.guilliermondii, what indicating a dominant biological regime. The yeast strains are acidophilic with a maximum growth pH between pH 5 and 6.

Powdered Grewia species barks was extracted in water and one part of the extract was precipitated with absolute ethanol. Both the crude water extract and the ethanol precipitate were freeze dried, pulverized into powder and subjected to physicochemical analyses. Amongst others, proximate composition, morphology and metal contents by Scanning Electron Microscopy with Energy Dispersive X-Ray (SEM-EDX), functional group by Fourier-transform infrared spectroscopy (FTIR), crystallinity by X-ray powder diffraction (XRD), thermal behavior via Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The molecular mass of the ethanol precipitate was appraised through viscosity measurements and the Huggins plot. Results show that both the crude extract and the ethanol precipitate were rich in polysaccharide type polymers. However, precipitation led to a reduction in the metal contents confirmed by the ash contents and the EDX analysis as well as the absence of sharp peaks on the XRD plots as was the case of crude extracts. Precipitation led to a decrease in the lipid and protein contents initially present in the crude Grewia spp. extracts. XRD and SEM analyses revealed that Grewia spp. extract and the precipitate were both amorphous with a porous microstructure. Results also showed that Grewia spp. biopolymer has functional groups which can serve as active sites for the attachment of colloidal particles.