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 12oC. 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.