How does the SBR reduce total nitrogen?

Posted by on March 29, 2012 in Clear Rex Bubbler, SBR, Wastewater Treatment | 0 comments

Nitrogen reduction in wastewater is a two-step process that requires an aerobic step followed by an anaerobic step. Since the aeration step comes first, this makes the process more complicated, since the primary settling portion of treatment plants is anaerobic.

If left alone in wastewater, nitrogen causes the following problems:

  1. Depletion of oxygen in the water.
  2. Causes algae blooms and eutrophication.
  3. Pollutes drinking water and can cause blue baby syndrome.

Nitrogen enters wastewater in some organic form, but once it hits the water, it quickly becomes ammonia or ammonium, depending on the pH of the water.

The Process of Nitrogen Reduction

Nitrogen enters wastewater in organic form and, through hydrolysis, quickly changes to ammonia or ammonium, depending on pH.
During aeration, Nitrosomonas convert ammonia and ammonium to nitrate. Almost immediately, Nitrobacter convert nitrate to nitrite. 4.6 lbs of oxygen are required to convert 1 lb of ammonia to nitrate.

2NH3 + 3O2 –> 2NO2 + 2H2O

2NO3- + O2 –> 2NO3- + 2H2O

In the absence of oxygen, microorganisms undergo anaerobic respiration where they use nitrate as the electron acceptor. The microbes break about nitrite to free the oxygen, freeing the nitrogen to escape as nitrogen gas or nitrous oxide.

2NO3- + 2CH2O + 2H+ –> N2O + 2CO2 + 3H2O

 

In order to promote nitrogen removal, a wastewater treatment plant has to create the environment that allows each step to take place. SBR’s create the conditions for these processes in a sequence of time throughout a cycle in a single reactor chamber, ergo the name Sequencing Batch Reactor.

 

The following chemicals are especially toxic to nitrifiers:  cyanide, phenol, thiourea and heavy metals such as silver, copper, mercury, nickel, chromium and zinc