Beef Cattle Effluent Treatment in a Denitrifying Bioreactor.

Excess nutrient runoff, especially nitrate and phosphate, has led to degradation of the Chesapeake Bay from the development of algal blooms and hypoxic zones. Nearly half of all nutrient runoff sources originate from agricultural production with a quarter resulting solely from improper treatment and management of animal manures. Denitrifying bioreactors show promise in the removal of these nutrients from runoff waters before they reach sensitive waterways. Denitrifying bioreactors provide a substrate, usually wood-based, that acts as a carbon source and that supports denitrifying bacteria which systematically convert nitrate to nitrogen gas via microbial denitrification. Recently, biochar products have been shown to minimize soil nutrient leaching. As a result, biochar additions could supplement these bioreactors by capturing unconverted nitrate. For this study, locally sourced wood chips were selected as the carbon substrate with five biochar additions of 0, 1, 2.5, 5, and 10% by mass. A pre-made manure slurry was introduced to the system and allowed to incubate under anaerobic conditions for 1, 2, 4, 8, 16, and 24 hours after an initial 72-hour hold. Samples were evaluated for total and inorganic phosphorus, total nitrogen, nitrate, and total organic carbon. Nutrient reductions were calculated by difference and expressed as a total percentage of nutrient reduced.