Journey to develop process for the nitrification of Ammonia rich effluents for a Petro Chemicals Industry
It was the second week of April 1977, a week after I had joined the Department for Pollution Control at Bayer AG, Germany , when my boss informed me that I should read something on nitrification process. The reason was that in the coming week we were called at a petrochemical site for their nitrogen removal problem. I quickly rush to my desk and spent whole week in searching for useful information about nitrification and it seemed to me that available technical literature offered quite a poor and weak information related to nitrification (folks that was 1977 and a lot was to be discovered for nitrification!!!). But I had been successful in joting down few useful and most important statement like:
- Nitrification is slow and sensitive reaction
- Nitrification occurs at low BOD loading rates and high sludge ages
- Nitrifying bacteria become inhibited by organic carbon and the two steps should be carried out in separate bioreactors.
The manager responsible for the wastewater treatment had shocked us with the statement about the situation. The wastewater from the petrochemical production contained ca. 300 mg/L phenols, 800 mg/L COD and ca. 600 to 750 mg/L NH4N ! So far all engineering companies said goodbye after having received the above information. As innovative company we couldn´t say no and my boss suggested to run at first lab scale tests to find out whether is nitrification feasible with this effluent or not.
Again at home(Leverkusen , Bayer HQ) a big meeting with 8 – 10 people had been set, to discuss the problem, among them two microbiologists, engineers and of course chemists as omniscient authorities.
The committee concluded that biological nitrogen from the mentioned effluents was nowhere described and will never work, but we should show that we will try it and then confirm our theory.
In the lab of the wastewater treatment plant (WWTP) a two step lab scale plant was constructed for the biological BOD removal (org. carbon) and a subsequent nitrification. The reactors were seeded with sludge from the full scale plant. The “BOD-free” effluent was introduced into the second nitrification reactor at very low loading rates, in order to adapt the biomass for nitrification. Within few weeks stable nitrification had been established, despite to the negative judgement of the “experts”!!!
Everything was OK, but in the follow up meeting my boss insisted on pilot tests, in order to confirm the results of lab tests.
A 30 m³ pilot plant was built and operated at first as BOD oxidizer, while the treated effluent was collected in a >1200 m³ basin for the coming nitrification tests, which have been started again with activated sludge of the full scale plant.
Pilot Plant at Petro Refinery for Two Step Nitrification process 1977
The nitrification of the effluent with 700 mg/L NH4N and 30 mg/L BOD had started and run successful, however after a week MLSS content began to decrease daily, while the NH4N in the outlet increased and after two weeks the MLSS dropped to 0,5 g/L and nitrification crashed. The plant was checked, there was no leaking in the plant, so we started again with fresh biomass.
After a week it happened the same again, both MLSS and nitrification performance decreased and stopped at least.!!!!
EMERGENCY CONFERENCE at home ! Give up ! -were most of the comments.
I had suggested to check why the existing full scale plant is nitrifying partially during our pilot tests, maybe is organic carbon not so danger, but the microbiologist showed me a publication of a famous professor with the conclusion of the BOD toxicity.
Due to the agreement we concluded to operate the pilot plant further two months and than stop the tests without success !!!!
But then came summer holidays, when the complete committee was not present.
In a secret action with the pilot plant manager we had decided to operate the pilot plant with untreated, COD and NH4N containing raw wastewater.
The nitrification had started successfully , we succeeded to maintain an efficient nitrification over the summer holidays and have also optimized the process during this period, which results served as basis for the design of a five step process for the nitrogen removal. The plant was built, started in July 1981 and is still removing NH4N.
The conclusions from this tests:
- Nitrifying bacteria require the presence of organic carbon in order to build flocs, which was essential for the entrapment of non flocculating nitrifies.
- The evaluation of all results showed that there was no correlation between BOD vol. loading rate and nitrification, but between N-food: mass ratio (g NH4N/gMLSS*d). This N- Food : mass ratio was decisive factor for the successful and stable nitrification.
- The results of own tests are more reliable than relying on the basis of publications.!
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