Determination of potential use of chitosan for the removal of Pb, Fe and Mn in the water samples collected from different areas of Sri Lanka

Abstract

Water contamination is one of the major concerns in the world. From the beginning of the 21 century, the drinking water sources in the main agricultural regions under reservoir based irrigation of Sri Lanka have been polluted from heavy metals in considerable amounts and exposure to heavy metals can cause a number of health problems, ranging from nausea and stomach discomfort to development of cancers and kidney diseases (Bandara et al.,2008). Although a wide range of physical and chemical processes are available for the removal of heavy metals from natural water bodies, most of these methods are not practicable to developing country like Sri Lanka as they are extremely expensive. In recent years, biosorption has been recognized

as an effective method of removal of heavy metal contaminants in surface water as low cost bio-

adsorbents are readily available, environmentally friendly, and biodegradable. The bioadsorbent

chitosan; deacetylated product of chitin (Gamage et al.,2007) has been used as a bioadsorbent for the removal of toxic/heavy metals from waste water. Depending on the pH of the medium the interaction of metals with chitosan are possibly dominated by adsorption, ion-exchange and chelation. Chitosan has been used to remove heavy metals mainly from industrial wastewater and as a non-toxic flocculent in the treatment of organic polluted wastewater (Shanmugapriya et al., 2011); but little attempt has been made to understand the ability of chitosan to uptake heavy metals in polluted drinking water containing trace amounts (ppb levels) of heavy metals (De Silva et al.,2014).

The current study focuses on potential of using chitosan as a low cost, environmentally friendly

biosorbent for purification of drinking water contaminated by the low levels of heavy metal

pollutants; Pb, Fe and Mn.

Methodology

Drinking water samples were collected from different areas of the country including Anuradhapura, Nikkawewa, Vavuniya, Trincomalee, Badulla and Kantale. First the basic parameters such as colour, pH and total hardness of the collected water samples were measured and recorded. Then the initial metal ion concentration of Pb, Fe and Mn of acid digested water samples were measured using AAS. Next, all the water samples with initial metal ion concentrations above the permissible limits for

drinking water defined by the World Health Organization (WHO) were treated with chitosan as

follows. A finely crushed chitosan (0.0250 g) was taken separately into clean dry polypropylene

containers. A volume (50.00 mL) of digested water sample was introduced into polypropylene

container having chitosan sample. pH of the sample was adjusted to pH 7 using NaOH (0.1 M)

and the sample container was stirred at room temperature (29.0 ± 0.5 C) for 2 hours. Control

sample was prepared simultaneously with chitosan (0.0250 g) and deionized water (50.00 mL)

and pH was adjusted to pH 7. Control sample was also stirred at room temperature (29.0 ± 0.5 C)

for 2 hours. After 2 hours stirring period, both sample and control were filtered using filter papers.

Filtrates of sample and control were analyzed by AAS to determine the amount of Pb, Fe, and Mn

remaining in the solutions after treatment with chitosan. The procedure was carried out in

duplicate for each digested drinking water sample.

Result and Discussion

The pH values of the collected water samples range from 6.53 – 7.31 which were in the range of accepted pH value range (6.5 – 8.5) for drinking water defined by WHO. But hardness in some of the collected water samples had exceeded 250 ppm, the maximum permissible level defined by the Sri Lanka Standards Institution (SLSI) for the drinking water.

The Initial metal concentrations in collected water samples, metal concentrations after treatment with chitosan, and percentage metal removal (%) of Pb Fe and Mn are shown in table 1, table 2 and table 3 respectively. The maximum permissible levels for drinking water given by WHO for corresponding metals are shown in table 4.