Performance Evaluation of Different Biological Filters for Treatment of Nutrients Agricultural Drainage

Due to the high consumption of water in agriculture, considerable drainage is produced annually. Currently, a significant volume of drainages (almost 3 BCM) is entered into the Khuzestan province environment without any beneficial use, resulting soil and water contamination. On the other hand, according to Iran's water problems, the quality conservation of water resources and the use of unconventional water resources are essential, especially drainage quality management, and applying them to agriculture and the environment.

This research is carried out to evaluate the efficiency of biological filters with different beds for the treatment of agricultural drainage in Mirza Kooch Khan and Amirkabir Agro-Industry fields in Khuzestan province of Iran during the spring and summer of 2019. The research aims to reduce drainage contamination when discharged into the environment and drainage reuse in agriculture. In this research, the effect of four different types of biological filter including wheat straw, rice husk, cotton stalk, and wood sawdust as the main factor and three retention time of 2, 5 and 10 days as the secondary factor are investigated. The quality factors monitored include turbidity, EC (as a salinity index), total nitrogen (TN), total phosphorus (TP), and BOD.

Analysis of variance demonstrates a significant difference between the mentioned treatments in terms of the studied parameters (at the level of 1%), except for pH. According to the results, the highest average refinement of qualitative factors based on filter type for turbidity equals 37.87% and relates to the treatment of cotton stalk. For EC, TN, TP, and BOD equal to 9.23%, 49.60%, 46.50%, and 97.59%, respectively, and relate to wood sawdust. Moreover, the average of the highest percentage of pollution reduction for the investigated factors is related to the retention time of 10 days, which for turbidity, EC, TN, TP, and BOD are equivalent to 56.79%, 12.97%, 66.51%, 53.49%, and 80.20%, respectively.

Observed results indicate that wood sawdust treatment has a relatively better performance than other treatments. This issue is important since the existence and abundance of this material in the country is high. In addition, due to the importance and effectiveness of hydraulic retention time in treating, it has a direct relationship with efficiency of treating. However, the increase in efficiency from the retention time of 2 days to 5 days is more significant than the increase of retention time from 5 days to 10 days, which can be considered an important factor in selecting the retention time based on pollutants concentration in the drainage. As a result, based on the concentration of input and output quality parameters, it is suggested to use a wood sawdust filter with a 5-day retention time due to its proper performance and being more economical in terms of volume and dimensions of the system.