NITRIFICATION - DENITRIFICATION (N-DN): Consists in separating fractions at 250 or 80 microns depending on the type of slurry and physiological state of the animals. The solid fraction, with a high nitrogen load, we will use it for composting. And the liquid fraction will be used to the bacterial nitrification-denitrification cultivation, which will be located in a bioreactor of about 20 days of TRH. This reactor will have mechanical aeration and homogenization controled by a timer. We will meet the following stages in each “batch” of the SBR type process (“Sequencing Batch Reactor”):
  • a. Liquid fraction input: The effluent dose from the separator comes to the reactor. The aeration will be stopped and the homogenization agitation in operation.
  • b. Denitrification: The anoxic microbial activity degrades organic matter using nitrates (NO3-). They were previously generated for anaerobic respiration. It generates N2 (denitrifies) that is released into the atmosphere.
  NOTE: At this first stage of microbiological activity, immediately after the entry of the liquid fraction, in order to optimize the greatest transformation of organic matter, that occurs in these anoxic conditions, without air supply. And therefore, with the minimum energy consumption.
At the same time, good bacterial activity of denitrifiers produce a high denitrification index.
  • c. Nitrification: Aerobic microbial activity that oxidizes the ammonium (NH4+) generated in the previous stage, in addition to that which already directly involves the liquid fraction of the slurry, to NO3-. These bacteria do not require organic matter, as they are autotrophic.
 NOTE: In this first stage of aerobic microbiological activity, is interesting for it to be carried out with little organic matter, so the energy consumption for its degradation is minimal. This maximizes the nitrification process.
  • d. Decantation or sedimentation: Rest stage in the homogenization agitation and in the air supply, in which the formation of large bacterial flocs for sedimentation is desired.
  • e. Sludge purge and effluent outlet: At this moment the sludge and biological muds are separeted from the purified liquid, we can purged of excess sludge. The bacterial populations have multiplied in favor of the purification of the effluent that is obtains, and the effluent can leave as leftover from the decanted system.
 FUNDAMENTAL NOTE: The process works with the repetition of stages b, c and d within each “batch” period, with a liquid fraction input and a single effluent output. The first DN-N comes to be the intensive performance of the microbiological process. And the second, or repeat run, is based on the refinement of the results. And the most important, the accommodation of the cultivation in the variability of the input slurry. The duration of each “batch” period is usually 6 hours (4 daily entries of liquid fraction, in which the daily entry to be treated is distributed), but this duration is conditioned to the characteristics of the slurry of the farm and , as a consequence, to those of the liquid fraction to be treated.
This technology provides us with the reduction of the organic nitrogen and ammonia content of the system in favor of the emission of nitrogen gas (N2) into the atmosphere (from 50 to 70% of the total N introduced into the reactor); considering here an average reduction of 58% (Bonmatí et al., 2018) compared to the input slurry.
Sludge thickener: The sludge obtained from the bioreactor purges and in the settling channels usually represent very high volumes to manage, since they are very little concentrated. Consequently, a deposit is required for the thickening of the sludge. The volume of this tank can be from 34 to 57 m3
according to the TRH of 3-5 days.
The “Sequencing Batch Reactor” or “SBR” (Aparna Dutta & Sudipta Sarkar) These are discontinuously operating reactors, that have a history of about 100 years since Sir Thomas Wardle published his experiences. Arden and Lockett published some SBR results at the pilot level. But it was not until Irvine (1971) reinvented the SBR that they were very successful. Since 1971, SBR has been extensively researched and built in different countries such as Australia, the northern United States, or Japan. At the begining, SBRs aim to remove organic matter, but now their use has spread. Nutrients such as phosphorous and nitrogen can also be removed with the Nitrification-Denitrification process. Improvements in some aeration and control systems have allowed SBRs to successfully compete with conventional active sludge reactors against classic reactor plus settling tank.