Water is a prime requisite among all natural resources. It is a fundamental need for the sustenance of every living organism [1]. Water covers about two-thirds of the earth’s surface. The freshwater only contributes about 3 percent which supports all forms of life on earth and the remaining 97 percent of water is saline. Amongst water resources, groundwater is the major source and is widely dispersed in India. It is utilized for all purposes including domestic, agricultural and industrial purposes. The quality of ground water is degraded with increasing population[2].

Irrigation water quality plays a vital role in sustaining crop productivity and feeding a growing world population [3]. Indian agriculture mainly depends on groundwater for irrigation and it plays a foremost role in increasing the yield and productivity of crops. The over use of groundwater and quality deterioration led India towards a serious crisis, in spite of having 30 million groundwater structures. Groundwater is threatened by several factors related to the mismanagement.

Groundwater was polluted mostly by sea water intrusion in coastal areas and it has an adverse effect on crop growth and productivity. Soil salinity is directly related to groundwater salinity of the coastal region. The increase of salinity level in water affects the plants in numerous ways like drought and oxidative stress, toxicity of ions, nutritional disorders, alteration of metabolic processes and reduction of cell division and expansion. All these factors will ultimately leads to reduction in plant growth, development and yield [4].

Due to the global increase in water demand, the scarcity of water is a major issue in most of countries. One of the feasible solutions for reducing water scarcity is desalination [5]. Desalination refers to the removal of salts and minerals. The ions responsible for salinity include the major cations (Ca²⁺, Na⁺, Mg²⁺, K⁺) and anions (Cl^–, SO₄^2-, HCO₃^–, CO₃^2-). Removing salts from groundwater through the desalination process is beneficial in point of human health, natural resource conservation and betterment of socioeconomic conditions.

Adsorption is one of the significant techniques in which salts and minerals are adsorbed onto a membrane, or a fixed bed packed with resin or other materials [6]. The synthetic materials such as alum and calcium hypochlorite are efficient, because these material are expensive and is not affordable for most rural population. Hence this study describes the low cost and locally available materials as effective adsorbent for the removal of salts and minerals from water under laboratory conditions, which may be economical and an eco-friendly approach.

MATERIALS AND METHODS

An experiment was conducted with moringa seed, papaya seed, neem leaf, tulasi leaf, lemon peel and amla bark. These bio adsorbents were taken as powder form @ 0.5 per cent concentration and tested against salt reduction. The water used in this study was collected from the coastal areas of Thoothukudi district. The EC of water was tested once in every 24 hours using a Multiparameter analyser kit to know the salt reduction potential of each bio adsorbents.  The bio adsorbents which exhibit good salt reduction potential were identified for optimization of dosage.

To optimize the dosage of these bio adsorbents, the experiment was conducted with different concentrations of moringa seed and amla bark powder (0.1, 0.3, 0.4, 0.5, 0.6 and 0.7 per cent). The changes in the EC were recorded once in every 24 hours up to 168 hours. Although the moringa seed powder reduced the salt load of water but caused foul odour on the fourth day of treatment. Amla bark powder produced no odour even up to one week and performed better salt reduction. Hence, Amla bark powder was used for further study.

Adsorption study at different levels of salinity

            The salt reduction potential of Amla bark powder was good @ 0.5 per cent concentration. Further, a confirmation study was conducted. In this study, water containing different EC’s was taken in which Amla bark powder was added @ 0.5 per cent concentration. The changes in EC were recorded upto 168 hours.

Characterization of chemical constituents of organic amendments

Moringa seed and amla bark was collected, dried and powdered. One gram of the powdered samples were taken in 95 per cent ethanol and kept in shaker for 24 hrs. Then the samples were centrifuged at 3000 rpm for 15 min and the supernatant was collected and stored at 4⁰ C for further analysis.

GC-MS analysis

The analysis was done on a GC-MS QP. The following conditions were employed:

Column R_xi– 5 MS silica column with 30 m length, 0.25 mm diameter and 0.25 µm thicknesses. Helium was used as a carrier gas with a flow rate of 1 ml min^-1 and an injection volume of 0.5 µl was employed with split ratio of 1:10, interface temperature 270⁰ C, ion source temperature 200⁰C. The oven temperature was set at 70⁰ C with an increase of 5⁰ C min^-1 to 120⁰ C ending with a 5 min isothermal at 280⁰ C. In Gas chromatography, the total running time was 40 min. The compounds were identified by comparing with the spectra library.

RESULTS AND DISCUSSION

Among all the bio adsorbents, Moringa seed powder (T₁) and Amla bark powder (T₅) @ 0.5 per cent concentration showed a better reduction of EC in the water samples from 4.57 dS m^-1 to 4.12 and 4.06 dS m^-1, respectively at 144 hours of incubation (Table 1). Moringa oleifera reduced the conductivity of ground water up to 53 per cent @ 100 mg L^-1. The addition of coagulant M. oleifera may result in the dispersion of some mineral ions and inorganic compounds into a floc which will then be precipitated and separated from the solution. This caused the reduction of EC. The salinity removal efficiency of Phyllanthusemblica was found to be 55 per cent for a dosage of 1g and at a time period of 240 minutes [7][8][9].