Removal of turbidity from drinking water using natural coagulants
Graphical abstract
Introduction
A great problem in many developing countries is to get clean drinking water at low price. This can be normally solved by adding chemical coagulants such as aluminum sulfate which is generally at a high cost. The application of a coagulation/flocculation process is applied in water, wastewater treatment to remove turbidity, color and natural organic matter [1], [2]. Inorganic coagulants such as aluminum sulfate, ferric chloride and calcium carbonate and synthetic organic polymer (polyaluminium chloride (PACl) polyethylene imine) are common coagulant used in this treatment. However the sludge obtained from treatments using aluminum salts leads to disposal problems such as aluminum accumulation in the environment [3]. Moreover, some studies have reported that residual aluminum sulfate (alum) and polyaluminium chloride may induce Alzhemier's disease [4], [5]. Whereas the synthetic organic polymers, such as acrylamide, have neurotoxic and carcinogenic effects [6]. One possible solution to these problems may be natural coagulants which are preferably alternative excellent method for removal of turbidity from drinking water. These coagulants must be safe for human health and biodegradable.
In recent years, numerous studies on a variety of plant materials which can be used as source of natural coagulants have been reported. For example natural coagulants from Moringa oleifera (drumstick) [7], common bean (Phaseolus vulgaris) [8] and Nirmali seed (Strychnos potatorum) [9], [10] have been investigated. The material that has received the greatest degree of attention is the seed of M. oleifera [11], [12], [13]. M. oleifera seeds contain between 30% and 35% (w/w) of vegetable oil known as Behen (or) Ben oil. M. oleifera (drumstick) treatment due to the presence of water soluble cationic coagulant protein is able to reduce the turbidity of the water treated [14]. The seed extracts of S. potatorum (Nirmali) contain the anionic polyelectrolyte [15]. The crude extracts of common bean (P. vulgaris) seed showed ability to act as a natural coagulant [16].
The common bean seed has a food grade nature and contains no oil [17]. The three agro based seeds M. oleifera (drumstick), S. potatorum (Nirmali), and P. vulgaris (common bean) are non-toxic and effective coagulant aids useful for removing turbidity and bacteria from water. In this study the aim is to improve the coagulant agent from M. oleifera, P. vulgaris and S. potatorum. Since the active coagulant agent in the M. oleifera seed is believed to be a soluble cationic protein [18], [19], [20], it is of interest to investigate coagulant agent extraction using the different type of solvent, such as NaCl, NaOH and water. In addition previous research has also made use of ultrasound treatment in order to improve the extraction method [21]. The advantage of selectivity of natural coagulants used is having antimicrobial properties [22], [23]. The natural coagulants is the low cost method for removal of turbidity from drinking water. In the present study we collected pond water and used various naturally available seeds for removal of turbidity.
Section snippets
Materials
Sulfuric acid (98%), glycerol (95%), hydrochloric acid (35.4%), ethyl alcohol (95%), and silver nitrate (99.5%) were obtained from Merck (India).
Apparatus and measurements
Turbidity was measured using a turbidity meter (ELICO CL 52D NEPHELOMETER) and it was expressed in nephelometric turbidity units (NTU). pH is measured using a pH meter (ELICO LI 120 pH metre). Analytical instrument (ELICO PE 135 DO Analyser) was used to determine the dissolved oxygen. Conductivity meter (ELICO CM 180) was used to measure the water
Physicochemical characteristics of turbidity water given in Table 1
The physicochemical characteristics such as turbidity, alkalinity, hardness, sulfate, chloride and other ions concentration was measured for pond water and given in Table 1.
Effects of using different solvents as the extracting agent of the coagulant from natural seeds
In the determination of best solvent to be used for the extraction of the active coagulant agent from M.O seeds, the effects of M.O 0.5 NaCl and 0.5 M NaOH were compared with M.O distilled water. Fig. 1 shows the turbidity removal of synthetic wastewater using these three types of solvents. At 500 NTU M.O 0.5 M NaCl could
Conclusion
M. oleifera, P. vulgaris and the seeds of S. potatorum significant improvement in removing turbidity from synthetic raw water was found. Maximum turbidity reduction was attained in high turbid water. After dosing NaCl soluble extract of M. oleifera, S. potatorum and P. vulgaris reduced turbidity to 5, 10, 1 NTU respectively from 500 NTU. The natural coagulant NaCl extract is the greatest removal of turbidity compared to NaOH and distilled water.
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