Effectiveness of iron coated jute fabrics to decrease arsenic loading to rice fields in Bangladesh

Abstract

ABSTRACT In Bangladesh, groundwater from shallow aquifer is the principal source of both drinking water and irrigation water. Ddry season boro rice accounts for more than half of the total rice production in Bangladesh. However, it requires groundwater irrigation. But shallow aquifers in many regions of Bangladesh are highly contaminated with arsenic (As). Irrigation with As contaminated groundwater is therefore increasing As concentration in top soil, resulting in elevated concentration of As in rice plants, decreased rice yield and increased human exposure to As. Reduction of As concentration of groundwater within irrigation channel could be an effective way to reduce arsenic loading in rice fields. Efforts have been made to reduce As loading to rice fields by amending irrigation channels with jute-mesh structure, which however achieved limited success. The objective of the present study was to assess removal of arsenic by “iron-oxide-coated jute-fabrics” through laboratory batch experiments and channel experiments, which could be used in amending irrigation channels for more efficient removal of As. Two different types of locally available jute fabrics have been coated with iron oxide following two different coating methods and two drying methods. The iron-coated jute fabrics were subsequently used to assess their effectiveness in removing arsenic from groundwater in laboratory batch experiments. Results from batch experiments suggest that iron oxide coated jute fabrics have significant capacity to remove arsenic from groundwater. The method of coat¬ing and drying have been found to have a significant influence on arsenic removal efficiency of the iron-coated jute fabrics. Iron-coated jute fabrics prepared by drying at room temperature are more efficient in removing As (III), while the iron-coated jute fabrics prepared by heating the fabrics at 45 ± 2oC are more efficient in removing As (V). The variation of As (III) and As (V) adsorption onto the jute fabrics prepared by different dry¬ing conditions is most likely due to differences in the pre¬cipitated forms of iron under different heating/drying conditions. Under the experimental conditions, the highest As (III) uptake of 36.0 mg/m2 of jute fabric was achieved for an aqueous arsenic concentration of 749 µg/l; compared to an uptake of about 4.93 mg/m2 by uncoated jute fabrics. Ability of the iron-coated jute fabrics from flowing water was assessed in experimental channels (made of PVC pipes) that were lined with the iron-coated jute fabrics. Then, this study focuses on assessment of removal of arsenic from groundwater under flowing conditions. In laboratory, experimental channels have been fabricated using PVC pipes (cut through the middle), and the channels have been lined with iron oxide coated jute fabrics. Arrangements have been made for flow of arsenic bearing groundwater from one end of the channel to the other end at different flow rates. Experimental results showed appreciable removal of As within the irrigation channels lined with iron-coated jute fabrics (compared to uncoated fabrics). However, the arsenic removal capacity of iron coated jute fabrics decreases with time. With repeated use, arsenic uptake capacity of iron-coated jute fabrics approaches and exceeds those obtained under similar conditions (i.e. similar aqueous arsenic concentration) in batch experiments. Arsenic removal under flowing condition appears to decrease with increasing flow velocity (i.e., with decreasing contact time) through the channel. Arsenic removal efficiency in channel increased by increasing contact with jute fabrics, which was achieved by using jute fabrics as vertical barriers (in addition to channel lining). The ability of iron coated jute fabrics in removing arsenic suggests that these could potentially be used for amending irrigation channel in order to remove arsenic from irrigation water. However, efforts should be made in rdevise ways to improve effective contact between irrigation water and iron-coated jute fabric in order to maximize arsenic removal.

; but well below the removal achieved under equilibrium condition in batch experiments. With an initial As concentration of about 230 g/l, As uptake by coated jute fabrics within the channel varied from a maximum of about 6.2 mg/m2 to a minimum of about 2.3 mg/m2. Flow rate through the experimental channel and contact time have significant effect on As removal, and higher removal has been achieved at lower flow rates. Arsenic removal capacity of coated jute fabrics in batch experiments is much higher than in channel experiments. However, installation of coated jute barriers into the channel perpendicular to initial flow path increases the percentage of arsenic removal from flowing groundwater by increasing trapping of arsenic-bearing particles and water residence time. Arsenic uptake capacity of coated jute fabrics from arsenic bearing groundwater varied 2.3mg/m2 to 6.2 mg/m2 in channel lined with iron-coated jute fabrics without barriers while it varied 10.2 mg/m2 to 5.2 mg/m2 with barriers. Efforts should be made in devised ways to improve effective contact between irrigation water and iron-coated jute fabric in order to maximize arsenic removal in irrigation channel.