Abstract
M.Tech. (Chemical Engineering)
Milled Moringa Oleifera (M.O) seeds were characterised and used as a bio-sorbent in the
removal of metals from acidic mineral effluents, coagulant/flocculent and antimicrobial agent
in water and wastewater treatment. Biosorption experiments were conducted by means of
agitation in a thermostatic shaker using synthetic acidic mineral wastewater consisting of
20 ppm Ni, 20 ppm Cu, 100 ppm Mn and 500 ppm Fe. The effects of solid loading, pH, contact
time and temperature were investigated. Adsorption isotherms, kinetics and thermodynamics
parameters were calculated from the experimental data obtained. The ability of milled spent
Moringa seeds to be re-used (without recycling) and to be recycled was also investigated. Jar
test experiments were conducted in order to evaluate the coagulation/flocculation process using
synthetic turbid water. Optimum M.O dosage and TSS removal efficiency were determined
from the experimental data obtained. The antimicrobial activity of M.O seeds was determined
through experiments investigating the effect of raw seed extract and aqueous seed extract on
coliforms and Heterotrophic Plate Count (HPC) bacteria.
Metal removal followed the order: Ni > Cu > Fe > Mn. Metal removal efficiency increased
with pH, time, % solid loading and temperature until sorption equilibrium was achieved.
Optimum operating conditions achieved were pH = 3, Temperature = 308K, % solid loading =
10% and residence time of 60, 90, 90 and 120 minutes for Ni, Cu, Fe and Mn respectively. The
bio-sorption process was feasible and spontaneous for Cu and Ni only as shown by the negative
ΔG◦ values. These values increased on the negative scale with temperature (-80.3 to -2926.9
J/mol for Cu and -782.9 to -2647.3 J/mol for Ni) implying increased probability of the sorption
process at higher temperatures. For all metals, ΔH◦ and ΔS◦ values were positive signifying the
endothermic nature of the adsorption process and the increase in the degrees of freedom on the
surface of the sorbent and disorderness of the system. For the adsorption reaction to proceed
spontaneously, ΔG◦< 0, ΔS◦ > 0 and ΔH◦ > 0. The Langmuir model and second order kinetics
best described the adsorption process for Ni, Cu and Fe. Ion exchange or chemisorption was
the possible mechanism of adsorption as suggested by the Temkin model. FTIR spectrum
suggested -C=O- to be the predominant functional group that binds and reacts with Me2+ ions.
The spent milled seeds could be effectively re-used for metal removal for two cycles without
desorption and could possibly be recycled for further use as bio sorbents for metal removal
from AMD...