Nutrient Removal from Agricultural Subsurface Drainage Using Denitrification Bioreactors and Phosphate Adsorbents

摘要

Agricultural subsurface drainage is widely used to remove excess water from the soil. Nitrate and phosphate contained in subsurface drainage can negatively affect water quality. The objective of this project is to develop a new woodchip bioreactor system using iron media as post-treatment to simultaneously remove nitrate and phosphate from subsurface drainage. Batch testing was conducted to determine removal capacity of selected steel by-products. Maximum adsorption capacities for A500 steel shavings, 1018 carbon steel chips, 1018 carbon steel small turnings and 1018 carbon steel large turnings were 5.81, 2.00, 1.47, and 1.30 mg phosphate/g steel, respectively. Two column reactors were built to simulate a woodchip bioreactor followed by the steel media as post-treatment. The design hydraulic retention times for the woodchips and steel media are 24hr and 6hr, respectively. The results of the column experiments show that woodchips completely remove nitrate in the influent (20 mgJL ad N) at design conditions. A 55% reduction of phosphate from the initial 1 mgA. was observed through the woodchip reactor after 100 days of operation. The steel media completely removed any phosphate from the woodchip reactor effluent. Doubling and quadrupling the flow from the design HRT lead to a nitrate reduction of 92% and 54% respectively from the influent of 20 mg N/L. A wet and dry cycle test was performed indicating that complete denitrification is achieved within 24hr of start-up. This new technology has great potential to reduce the nutrient loading from agricultural subsurface drainage to surface water bodies.