Using Unique Carbon Source Combinations to Increase Nitrate and Phosphate Removal Rates in Bioreactors.

Nitrogen (N) and phosphorus (P) losses from croplands contribute to impairment of water bodies. This study was conducted to test candidate denitrifying bioreactor media for nitrate-N and dissolved reactive P (DRP) removal from agricultural tile drainage effluent. The nitrate-N and DRP removal performance of candidate media treatments – woodchips (WC), corn cobs (CC), woodchips with biochar (WC+BC), woodchips with continuous sodium acetate injection (WC+A), corn cobs with modified coconut coir (CC+MC), and corn cobs with modified coconut coir and biochar (CC+MC+MBC) – were tested by pumping water with 20 mg/L nitrate and 0.3 mg/L phosphate through PVC columns packed with media. The flow rate was adjusted to match the rise and decay of a typical drainage hydrograph. Effluent was sampled after hydraulic residence times (HRT) of 1.5, 8, 12, and 24 h. The experiments were conducted at 15°C for 14 weeks, 5°C for 13 weeks, and 15°C again for 7 weeks in a temperature controlled chamber. Nitrate-N load reduction performance at all temperatures was: WC+A > CC+MC > CC > CC+MC+MBC > WC > WC+BC. Nitrate-N load reductions ranged from 24% to 96% in warm temperatures and 4% to 80% in the colder temperature. DRP load reductions in warm temperatures were the best for the CC, CC+MC, and CC+MC+MBC treatments, with DRP load reductions of 74%, 81%, and 67%, respectively.  The WC+A treatment performed the best at the colder temperature with a 45% DRP load reduction.