Enhancement of nitrogen and phosphorus removal from eutrophic water by annual ryegrass bombarded with low energy ions

Authors: LI, M - University Of Science And Technology Of China; JIANG, F - University Of Science And Technology Of China; SHENG, G-P. - Chinese Academy Of Sciences; WU, Y-J. - Chinese Academy Of Sciences; YU, Z-L. - Chinese Academy Of Sciences; Banuelos, Gary; YU, H-Q. - University Of Science And Technology Of China

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2013
Publication Date: 1/1/2014
Citation: Li, M., Jiang, F.J., Sheng, G., Wu, Y., Yu, Z., Banuelos, G.S., Yu, H. 2014. Enhancement of nitrogen and phosphorus removal from eutrophic water by annual ryegrass bombarded with low energy ions. Chemosphere. 21(16):9617-25

Interpretive Summary: Eutrophication of water resources is a problem of global concern. In recent years, many of the rivers and lakes in China have become enriched with nutrients, e.g., nitrogen and phosphorus, resulting in eutrophication and harmful algal blooms. New efforts using phytoremediation are underway in an attempt to remove excessive nutrients by growing and harvesting terrestrial plants, e.g., perennial ryegrass. The ryegrass grows quickly, produces great biomass, and is a high-quality palatable forage. Moreover, it is one of the plants of choice for using in a floating raft terrestrial plant-based treatment system (FRTTS). Previous research has found that bombarding plants with low energy ions can improve the nutrient removal efficiency of terrestrial plants in the FRTTS system. In the large hydroponic study described in this paper with the FRTTS system, we bombarded ryegrass seeds with ions to eventually stimulate ryegrass’s ability to remove nitrogen and phosphorus from eutrophic water. After 84 days in the FRTTS system, growth rate was increased and more nitrogen and phosphorus were removed compared to the FRTTS system with ryegrass not exposed to the ion bombardment. These results imply that the use of ion-beam biotechnology may enhance the ability of ryegrass as part of the FRTTS system to remove nitrogen and phosphorus from contaminated waters.

Technical Abstract: Water eutrophication and subsequent growth of harmful algal blooms is often the result of the influx of point and non-point sources of excessive nutrients into water bodies. Excessive growth of algae can slowly remove the oxygen from the water and destroy the biological viability of the water source. Phytoremediation of such waters with the cultivation of terrestrial plant species, e.g., perennial rye grass (Lolium perenne) implanted within a floating raft system (FRTTS), uses the plants' ability to remove excessive nitrogen (N) and phosphorus (P) by plant uptake. Methods are currently in progress to optimize and improve the plant's ability to extract excessive nutrients from the eutrophic waters using a floating raft terrestrial plant-based treatment system (FRTTS). One technique showing promising results involves the use of exposing seeds to low-energy ion bombardment, which indiscriminately induces physiological changes in the seed and in subsequent growth of the plant. In our hydroponic study, perennial ryegrass seeds were exposed to N+ ions at low energy of 25 keV and at a current of 20 mA. The pulse time was 10 s with an interval of 50 s. In each pulse, the applied dose D0 (1500 or 3000) was 2.6 x 1013 ions/cm2. The floating rafts within the FRTTS had a size 33 x 32 x 3 cm and were planted with irradiated seeds, as well as with unradiated seeds (controls) in replicates of three. The artificial eutrophic water contained total N and P at concentrations of 4.6 and 0.55 mg/L, respectively. After 84 days of floating on the eutrophic water as part of the FRTTS, the greatest biomass occurred on ryegrass exposed to 3000 x 2.6 x 1013 N+ ions/cm2. Plants were larger with increased root length and number of tillers. Importantly, N and P accumulation and consequent removal of each nutrient was significantly greater in the ion-bombarded plants compared to controls (un-radiated). Preliminary evaluation of plant material indicated that the plants’ defense-related peroxidase activities (enzymes) within the cells were affected by the ion bombardment, which allowed the plant cells of the ryegrass to adapt and thrive in the unfavorable water environment. As a result, floating rafts planted with L. perenne exposed to ion bombardment showed a promising potential for enhancing N and P removal under these tested conditions. Future research needs to evaluate other physiological effects resulting from ion bombardment, including eutrophic genetic stability, before this ion beam technology can be safely used on plants grown for large scale phytoremediation of eutrophic waters.