Moringa oleifera: a natural coagulant, adsorbent and filter aid

摘要

Most of the processes in water and wastewater treatment use chemicals which could be expensive and could have negative impacts on consumer health and the environment. In the last decades the search for alternative natural materials has increased. In Europe there is a renewed interest in chitosan (a natural material from animal origin) for water treatment use. This study is, however, looking at Moringa oleifera seed (a tropical tree) as a coagulant, adsorbent and filter aid. The plant is draught resistant and most of its parts are useful for various applications. Extracts from the seed were investigated for coagulation, filter aid and adsorption. The coagulation potential of M. oleifera was compared against alum and iron salts and it was used as a filter aid to enhance the ripening of slow sand filter. Activated carbon prepared from the seed shell and solid residues after coagulant extraction were used for the adsorption of chromium. With respect to coagulation of turbid natural and synthetic waters, M. oleifera showed similar performance as the metal salts and it was effective in a wider range of pH. The M. oleifera coagulant was found to be effective as a coagulants aid in combination with metal salts better organic removal was observed. Slow sand filtration (SSF) studies in combination with M. oleifera as a filter aid indicated that during the start up use of filter aid significantly reduced the ripening period compared to SSF without filter aid. It was observed that intermittent and short period dosing of M. oleifera was sufficient to enhance ripening as continuous dosage resulted in excessive headloss development. Adsorption studies for the removal of chromium were carried out in batch experiments and the effects of adsorbent dose, contact time, initial metal concentrations, metal speciation and pH were analysed. Adsorption studies indicated that the seed (after coagulant extraction) achieved more than 94% and 43% removal of Cr (III) and Cr (VI), respectively. The activated carbon from the seed shell removed 99.9% and 83% Cr (III) and Cr (VI), respectively. The studies demonstrated that the different applications of the biomaterial can be integrated to achieve optimum utilization of the resource both in water and wastewater treatment.