Research NoteImprovement of extraction method of coagulation active components from Moringa oleifera seed
Introduction
Many coagulants are widely used in conventional water treatment processes for tap water production. These coagulants can be either inorganic coagulants (e.g. aluminum sulfate and polyaluminum chloride), synthetic organic polymers (e.g. polyacrylamide derivatives and polyethylene imine) or naturally occurring coagulants (e.g. chitosan and microbial coagulants). These coagulants are used for various purposes depending on their chemical characteristics. An inorganic salt, alum (aluminum sulfate), is the most widely used coagulant in water treatment because of its proven capability and lower cost. Some synthetic organic polymers are also equally effective and relatively inexpensive. Recently, significant amounts of synthetic organic polymers are widely used for water treatment.
However, some studies Crapper et al., 1973, Martyn et al., 1989, have reported that aluminum which is the major component of alum and polyaluminum chloride, may induce Alzheimer's disease. It was also reported that monomers of some synthetic organic polymers such as acrylamide have neurotoxicity and strong carcinogenic properties (Mccollister et al., 1964). On the other hand, naturally occurring coagulants are biodegradable and are presumed safe for human health. Some studies on natural coagulants have been carried out and various natural coagulants were produced or extracted from microorganisms, animals or plants.
Moringa oleifera is known as a plant containing an active coagulating compound. Several studies have been done on the performance of M. oleifera seeds as an alternative coagulant or coagulant aid. M. oleifera, a tropical plant, belongs to the family Moringaceae that is a single genus family of shrubs. Earlier studies Schulz and Okun, 1983, Olsen, 1987, Jahn, 1988 recommended the use of M. oleifera seed extracts as coagulant for water treatment in African and South Asian countries where the plant is considered indigenous. If M. oleifera coagulant (MOC) is proven to be active, safe and inexpensive, it is possible to use MOC widely for drinking water and waste water treatment in other countries as well. M. oleifera may become one of the cash products bringing more economic benefits for the producing countries.
Turbidity removal by MOC as primary coagulant were up to 80–99%, both for raw waters and synthetic turbid waters Muyibi and Okuofu, 1995, Ndacigengesere et al., 1995, Muyibi and Evison, 1996. However, Muyibi and Evison (1995) found that the residual turbidity of samples increased with the decrease in initial turbidity at optimum dosage of MOC. This indicates that MOC may not be an efficient coagulant for low turbid water. MOC may be used for primitive treatment, whereas its use for drinking water treatment may not be appropriate since turbidity of raw water for drinking water is usually low. It is necessary to improve the coagulation efficiency, possibly by improving the extraction method for MOC, for its wide use not only in wastewater treatment but also in drinking water treatment. The active components in Moringa seeds were found to be soluble cationic proteins having molecular weight of about 13 kDa and isoelectric pH value of 10 and 11 (Ndacigengesere et al., 1995). The amino acid sequences of this protein had already been determined by Gassenschmidt et al., 1991, Gassenschmidt et al., 1995. It is well known that solubility of proteins increase with salt concentration at low salt ionic strength White et al., 1968, Voet and Voet, 1990. This salting-in phenomenon is due to the decrease in mutual association of protein molecules by shielding of salt. Since the active component for coagulation in MOC is protein, it is probable to increase its solubility by increasing salt concentration. The increase in solubility of the active component will improve coagulant ion efficiency.
The objectives of this study is to improve the extraction efficiency of the active component from M. oleifera seed by using salt solution. Aqueous solutions of sodium chloride, sodium nitrate, potassium chloride and potassium nitrate were individually tested for extraction of the active component from M. oleifera seed.
Section snippets
Preparation of M. oleifera seed extracts
The M. oleifera seeds used in this study were obtained from Los Baños, Laguna in the Philippines. Only seeds of dry pods were used. The seeds were removed from the pods, and stored at our laboratory at room temperature. The winged seed cover was shelled just before the extraction. The kernel was ground to a fine powder by using a mortar and pestle and 5.0 g of the seed powder was mixed with 500 ml of the extractant. The extractants tested were solutions of NaCl, KNO3, KCl and NaNO3 and distilled
Results and discussion
Figure 1 shows turbidity removal by coagulation with each MOC. The coagulant dosage is expressed in ml l−1 throughout this study. The residual turbidity using the coagulant extracted by ordinary solvent, distilled water (MOC–DW) was 11.8 NTU at its optimal dosage of 32 ml l−1. On the other hand, MOC extracted by 1.0 mol l−1 NaCl solution (MOC–SC), gave much lower residual turbidity. It was 1.6 NTU at the optimal dosage of 16 ml l−1. The efficiency of MOC–SC in terms of residual turbidity was 7.4 times
Conclusions
The purpose of this study was to develop an improved method for the extraction of the active coagulation component from M. oleifera seeds. The specific conclusions derived from this study are as follows:
- 1.
MOC–SC extracted by 1.0 mol l−1 NaCl solution showed better coagulation activity with dosages 7.4 times lower than that using MOC–DW extracted by distilled water for the removal of kaolinite turbidity. MOC–SC could effectively coagulate more than 95% of the 50 NTU initial kaolin turbidity using
Acknowledgements
The authors would like to thank Dr Eiji Shoto, head of the Institute of Wastewater Treatment, Hiroshima University where this study was conducted, for his reliable advice and assistance. The authors also appreciate the assistance of Dr Maxima Flavier of the Division of Analytical and Environmental Chemistry, UPLB during the preliminary experiments in the Philippines.
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