Possibility evaluation of treating agricultural drainage water byusing bio-filters, in Sepidrud irrigation and drainage network

Considerable amount of water in irrigation practices drain out due to it uses much more than crop water requirement. Agricultural wastewaters are the most important reuse sources because of extremely high amount. Therefore, using of these resources is crucial in Iran because of shortage water resources. One of the drainage water reuse strategies is treating by biological filters. The cheap adsorbents materials, especially agronomical waste matters, can have good potential for treating and building suitable condition in environmental asspect (Niknam et al., 2014). These materials are such as rice bran, wood sawdust, wood charcoal, pressed tea, walnut shell, peanut skin and others, based on availability in the experimental area. These natural adsorbents have the ability to adsorb metal ions due to different functional groups present on their macromolecules (Tarley et al., 2004). The first research was conducted on metal absorption by using of different organic waste and xylem vessels by examining the removal of mercury (Friedman and Waiss, 1972). The other researches were done by (Bina et al., 2003) in removing heavy metal and (Abdel-Ghani et al., 2007) in removing Pb. Masri et al. (1974) used Yew skin for absorbing of the soluble ions like mercury, Pb and cadmium. Based on results, the most absorption was considered in mercury. Nowadays, there is much attention to use of natural materials with ability of absorbing contamination such as heavy metals. The use of rice husks as a natural solid adsorbent of trace metal for Cd and Pb was studied by (Tarley et al., 2004). The results showed that modified rice husks with 0.75 mol l-1 NaOH solution had more adsorption rate than natural rice husks. In last years, the amount of water supply in Guilan province has decreased due to constructing dams in upstream of Sepidrud River, so it is important and necessary to find new resources. On the other hand, due to low efficiency of irrigation in this area, the high amount of water is discharged as runoff and drain water. Therefore, reusing of drainage water is the best solution for overcoming the water scarcity. The purpose of this study was to investigate the effect of four types of bio-filters including wood sawdust, rice bran, wood charcoal and pressed tea on treating of Nitrate, Magnesium, Sodium, pH and EC in agricultural drain water.
Experiments were conducted on paddy fields drainage water in Astaneh town, Guilan province, Iran. First, four basins were dug in side of main drain by using of trenchers with 1 m×2.5 m×20 m sizes and 2% gradually slope. After that, the bottom and sidewall of basins were covered with thick plastics to prevent water seepage. At the end of each basin, drain tubes in shape of T were used to control drainage water. The thickness of applied bio-filter materials in each basin (including wood sawdust, rice bran, wood charcoal and pressed tea) was 80 cm, and mineral envelop was applied above the bio-filters to fix them and prevent of damage. Then, the pump was installed next to the basinsfor irrigating. The schedule of pump was 22 hrs working in a day night and 2 hrs resting, and the amount of pumpage was determined by saturated hydraulic conductivity of materials. During summer, rice growing season, 8 times and during autumn, 11 times was sampled of outlet water of bio-filters, so overall these were 19 samples. The parameters such as N, Mg, Na, pH and EC in the samples were determined in laboratory of Guilan regional water company. The statistical analysis of T paired in SPSS software was used to determine significance differences among samples.
The results demonstrated that all bio-filters had significant effect on filtering of some parameters in the drain water investigated in this study. This was due to the concentration of pollutants. All bio-filters decreased the pH of water. The pressed tea was not good in decreasing the pollutants, although rice bran and wood charcoal were a little effective in that. This result can be due to the low amount of contamination in drainage water, in some experiences. Also, the wood charcoal decreased the amount of N, significantly. However, sawdust bio-filter had positive effect in decreasing of EC, pH, N and Na, and had better results than the other filters. In addition, this bio-filter decreased N in outlet water by 0.7 mg lit-1. Therefore, the role of sawdust bio-filter in biological processes of drain water should deserve more attention.