Wastewater Technology Fact Sheet: Trickling Filter ...

1 United States Office of Water EPA 832-F-00-015. Environmental Protection Washington, September 2000. Agency Wastewater Technology Fact Sheet Trickling Filter Nitrification DESCRIPTION domestic sewage is approximately 60 percent ammonia nitrogen, 40 percent organic nitrogen, and Nitrogen is one of the principal nutrients found in small quantities of nitrates. Wastewater . Discharges containing nitrogen can severely damage a water resource and it's Treated domestic sewage has varying levels of associated ecosystem. As a result, several nitrogen, depending on the method of treatment chemical, physical and biological processes have used.

2 Most treatment plants decrease the level of been used to promote the removal of nitrogen. total nitrogen via cell synthesis and solids removal. Nitrification and denitrification are two suggested However, unless there is a specific treatment processes that significantly reduce nitrogen levels in provision for nitrification, most ammonia nitrogen Wastewater . This fact sheet will primarily focus on passes through the system and is discharged as part the nitrification process using a Trickling Filter of the plant effluent. system. TFs are designed as aerobic attached growth reactors and have been proven to be suitable The presence of ammonia-nitrogen in discharges for the removal of ammonia nitrogen.

3 From Wastewater facilities can result in ammonia toxicity to aquatic life, additional oxygen demand Nitrogen Content in Wastewater on receiving waters, adverse public health effects, and decreased suitability for reuse. Nitrogen exists in many forms in the environment and can enter aquatic systems from either natural or Biological Nitrification human-generated sources. Some of the primary direct sources or transport mechanisms of nitrogen Nitrification is a process carried out by a series of from sewage include: bacterial populations that sequentially oxidize ammonium to nitrate with intermediate formation C Untreated sewage direct discharge.

4 Of nitrite carried out by nitrosomonas and nitrobacter. These organisms are considered C Publically owned treatment works (POTW) autotrophic because they obtain energy from the effluent direct discharge, land application. oxidation of inorganic nitrogen compounds. The two steps in the nitrification process and their C POTW waste solids direct discharge, land equations are as follows: application. 1) Ammonia is oxidized to nitrite (NO2-) by C Septic tanks and leaching Nitrosomonas bacteria. fields groundwater movement. 2 NH4+ + 3 O2 2 NO2- + 4 H+ + 2 H2O. Untreated sewage flowing into a municipal Wastewater facility has total nitrogen concentrations ranging from 20 to 85 mg/L.

5 The nitrogen in 2) The nitrite is converted to nitrate (NO3-) by extent by recirculation of the treated Nitrobacter bacteria. effluent. Recirculation also increases the instantaneous flow at points in the Filter and 2 NO2- + O2 2 NO3- reduces the resistance to mass transfer. This also increases the apparent substrate Once the nitrate is formed, the Wastewater can concentration and the growth and removal either flow to a clarifier or continue on through a rate. The third major benefit of denitrification process to reduce the nitrate to recirculation in nitrifying Trickling filters is nitrogen gas that is released into the atmosphere.

6 The reduction of the influent BOD. The process is dependent on the desired percent of concentration which makes the nitrifiers nitrification. Since complete nitrification is a more competitive. This in turn increases sequential reaction treatment process, systems must the nitrification efficiency and increases the be designed to provide an environment suitable for dissolved oxygen concentration. the growth of both groups of nitrifying bacteria. These two reactions essentially supply the energy TABLE 1 TYPICAL LOADING RATES. needed by nitrifying bacteria for growth. FOR SINGLE-STAGE NITRIFICATION.

7 There are several major factors that influence the Loading Rate lb kinetics of nitrification. These are organic loading, %. TF Media BOD/1,000 ft3/d (g hydraulic loading, temperature, pH, dissolved Nitrification BOD/m3/d). oxygen concentration, and Filter Rock 75-85 10-6 (160-96). 1. Organic loading: The efficiency of the 85-95 6-3 (96-48). nitrification process is affected by the Plastic 75-85 181-12 (288-192). organic loadings. Although the Tower TF 85-95 12-6 (192-96). heterotrophic biomass is not essential for Source : Metcalf & Eddy, Inc. with permission from The nitrifier attachment, the heterotrophs McGraw-Hill Companies, 1991.

8 (organisms that use organic carbon for the formation of cell tissue) form biogrowth to 3. Temperature: The nitrification process is which the nitrifiers adhere. The very dependent on temperature and occurs heterotrophic bacteria grow much faster over a range of approximately 4E to 45E C. than nitriifers at high BOD concentrations. (39E to 113 E F). Quantifying the effects of As a result, the nitrifiers can be over grown temperature on the nitrification process has by heterotrophic bacteria and eventually been very difficult and as a result the effects cause the nitrification process to cease.

9 In are variable. Higher nitrification rates are order to achieve a high level of nitrification expected to be more affected by temperature efficiency, the organic loadings listed in than lower rates of nitrification. Figure 1. Table 1 should be maintained. shows how temperature can effect nitrification rates in a TF system. 2. Hydraulic loading: Wastewater is normally introduced at the top of the attached growth 4. pH: According to EPA findings (EPA, reactor and trickles down through a 1993), pH levels in the more acidic range medium. The value chosen for the have been reported to decrease the rate of minimum hydraulic loading should ensure ammonium oxidation.

10 As a result, complete media wetting under all influent nitrification rates may drop significantly as conditions. Hydraulic and organic loading pH is lowered below neutral range. For are not independent parameters because the Wastewater concentration entering the plant cannot be controlled. The total hydraulic flow to the Filter can be controlled to some performance stability it is best to maintain a nitrification while very effective pH between and The effect of nitrification can be achieved in an aeration lower pH conditions, if anticipated, should ditch where the hydraulic retention time is not be ignored when sizing nitrification 24 hours.