Potential of Iron-Coated Jute Fabrics to Decrease Arsenic Concentration of Groundwater in Irrigation

Introduction:

Bangladesh is an agro-based developing country where agriculture is the centerpiece of Bangladesh economy. Mainly three varieties of rice are cultivated in Bangladesh which includes Aush, Aman and Boro. Among them Boro rice plays a potential role for intensifying rice yield which currently accounts for about 50 percent of total rice production in the country (BRRI, 2006). Being a dry season crop Boro rice requires higher amount of irrigation compared to the wet season crops. In Bangladesh, groundwater from shallow aquifer is widely used to irrigate dry season Boro rice. 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. It is increasing not only the elevated concentration of As in rice plants, but also human exposure to As. As such, rice yield is decreasing day by day.

Solution:

Since there are limited sources of water, As concentration can be reduced within the irrigation channel using natural or artificial structures. To solve this problem, many methods have been applied throughout the years and significant results have been observed from adsorption based technology. Adsorption of AS on mineral surfaces is found to be an effective solution for As removal from flowing irrigation water (Roberts et al., 2007). Studies also say that materials such as sand, cement, porous diatomite and activated carbon with iron oxide coating have high adsorption capacity and have potential of minimizing arsenic concentration (Jang et al., 2006; Kundu and Gupta, 2005; Benjamin et al., 1996; Edwards and Benjamin, 1989; Thirunavukkarasu et al., 2003). Sometimes these methods are not effective since they are too expensive to be adopted in agricultural field. Researches have been made to reduce As loading on rice fields by amending irrigation channels with jute-mesh structure which however did not achieve significant success. The objective of the previous study was to assess removal of Arsenite and Arsenate by “iron-oxide coated jute-mesh structure” through laboratory batch experiments. The objective of the present study is to assess the capacity of these iron coated jute-mesh structures in terms of removing As from water in flowing condition.

Experiment and results:

To coat the jute-mesh structures with iron, a definite procedure was adopted. Ferric Nitrate [Fe(NO3)3] solution and Sodium Hydroxide (NaOH) solution were used for providing iron coating. Locally available jute fabrics were collected (figure 1) and cut into pieces of approximately 5”x12” for the sake of coating them easily. Before coating the jute fabrics, they were washed carefully with deionized water and air dried to avoid interference of foreign materials adsorbed on the surface. In the present study, jute fabric was first soaked into 0.25 M ferric nitrate [Fe(NO3)3] solution (figure 2) and then iron was precipitated by neutralization with the addition of 10.0 M NaOH solution. The wet jute fabrics were subjected to dry for one week under room temperature. Afterwards, they were washed with deionized water to wash off the loose iron precipitation from the jute fabric and dried in room temperature again for one week. In laboratory, experimental channels have been fabricated using PVC pipes (cut through the middle), and the channels have been covered 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 at different flow rates (figure 3). Each set of experiment, with a particular flow rate, was continued for about 60 minutes. Experimental results showed appreciable removal of As within the irrigation channels but well below the removal achieved under equilibrium condition in batch experiments. With an initial As concentration of about 230 mg/l, As removal within the channel varied from a maximum of about 30% to a minimum of about 13%. Flow rate through the experimental channel and time have significant effect on As removal, and higher removal has been achieved at lower flow rates. These results suggest that iron-coated jute fabrics have significant potential of reducing As loading to rice fields in arsenic affected areas of Bangladesh.

Limitations and future opportunities:

Farther studies should be done to optimize the above described method to reduce As concentration within the irrigation channel. Field experiments have not yet been performed which might reveal new information about the potential of iron coated jute-mesh structures. The major limitation of this method is the cost of the procedure. Chemicals required for the experiment as well as arrangement of coating jute fabrics with iron are not cost efficient in large scale. Solving this problem, iron coated jute-mesh structures can be commercially supplied to the society.