Nitrifying Trickling Filter Provides Reliable, Low-Energy and Cost- Effective Tertiary Municipal Wastewater Treatment of a Lagoon Effluent

The case study described in this paper demonstrates that the nitrifying trickling filter (NTF) is a reliable and robust bioreactor. The studied NTF was designed to oxidize ammonia-nitrogen (NH3-N) remaining in the effluent stream of an aerated lagoon that is located in Newton, Mississippi, USA. NTF performance data was collected during a period beginning in June 2007 and ending in January 2010. An analysis of the data demonstrated that the NTF consistently met, amongst other permitted criteria, a moderately stringent permit limit requiring an annual average NH3-N concentration less than 2.0-mg/L remaining in the effluent stream. Comparison of operating costs revealed that the NTF evaluated in this study required approximately one-third of the power required to meet the same treatment objective with a moving bed biofilm reactor (MBBR). However, the NTF required a slightly more foot print than the MBBR (e.g. 90 vs. 80 m2) to meet the treatment objective. The studied NTF was designed using generally accepted criteria defined throughout this paper. The NTF used medium-density modular plastic trickling filter media comprised of corrugated plastic sheets. The required biofilm surface area, and therefore bioreactor volume, was defined based on a 0.65-g NH3-N/m2/d zero-order nitrification rate and a 0.1-kg/m3/d five-day biochemical oxygen demand (BOD5) load at 12°C. The method for calculating NTF ventilation is demonstrated. Implementation of the NTF design and construction included some unique features: (1) the NTF influent pumps were located to provide NTF effluent recirculation (which provides proper media wetting, controls biofilm thickness and minimizes macro fauna accumulation), (2) use of influent pump(s) speed control to optimize the NTF superficial hydraulic application rate (or Spülkraft), (3) the ventilating area was conservatively designed to maximize airflow, and therefore process oxygen, for the nitrification process (i.e., 0.1-m2 (1.0-ft2) open area per 2.4-m (8.0-ft) of NTF periphery), and (4) the application of a column and pier support system to facilitate simple installation and increased air flow.