Over two thirds of Earth's surface is covered with water. However, water quality of the oceans, rivers, and other island is being reduced by human activities. In agro-ecosystems, a large proportion of nutrients, such as nitrogen (N) and phosphorus (P), are applied for crop production. The nutrients are also transported to aquatic ecosystems due to low fertilizer utilization efficiency, and caused serious pollution to aqueous environment.

A large number of methods (such as drainage ditches) were used to control nutrient loss from agricultural catchments. However, natural ditches and streams exhibit generally low nutrient removal capacities and high cost. The cost of building and operating an agricultural wastewater treatment system is an important factor in the selection of a treatment technique. 

A research team, led by Professor WU Jinshui in Institute of Subtropical Agriculture, Chinese Academy of Sciences(ISA), developed an innovative technology for effectively reducing nutrient transport with simulated drainage ditches using rice straw as an organic substrate. 

"We compared rice straw with three other substrates and found the rice straw organic channel barriers can reduce effectively nutrient export with low-cost maintenance" said researcher LIU Feng.

Fig. 1. Schematic diagram of the experimental set-up. (Image by ISA) 

Researchers then found rice straw organic channel barriers (OCBs) produced the highest mean removal rate of 73% for ammonium-N and 96% for nitrate-N. Release of carbon from the rice straw OCBs primarily occurred during the first three weeks, and total carbon loss accounted for less than 5% of the initial carbon mass. These findings indicated that rice straw OCBs can be used to construct a low-cost treatment system that requires minimal maintenance and can be easily integrated into drainage ditches to reduce nutrient export from agricultural areas. 

The study provided a new strategy and method to improve the nutrient removal capacity of constructed wetlands for other researchers and engineers. The study was supported by the key Chinese Academy of Sciences Programs (KZZD-EW-11 and 100-Talents), and the National Science and Technology Supporting Project (2014BAD14B00 and 2012BAD14B17), and the National Natural Science Foundation of China (41101478 and 41201260). 

The study entitled “Influence of substrates on nutrient removal performance of organic channel barriers in drainage ditches” has been published in Journal of Hydrology, details could be found at http://dx.doi.org/10.1016/j.jhydrol.2015.04.049.