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Partial denitrification as nitrite provider for mainstream anammox

Wallin Holmin, Felix LU (2020) VVAM05 20201
Chemical Engineering (M.Sc.Eng.)
Abstract
In traditional wastewater treatment, nitrogen is removed through the biological process combination of nitrification and denitrification. Although it is a well-established method, the need for aeration and possible addition of an external carbon source results in it being an energy-negative and costly process, thus making alternative methods for nitrogen removal compelling to examine. Anaerobic ammonium oxidation (anammox) has been presented as such an alternative, providing a “short-cut” through the nitrogen cycle by anaerobically oxidizing ammonium (NH4+) to nitrogen gas (N2) using nitrite (NO2-) as elector acceptor. By coupling the anammox reaction to partial denitrification (PDA), where nitrate (NO3-) is reduced to nitrite,... (More)
In traditional wastewater treatment, nitrogen is removed through the biological process combination of nitrification and denitrification. Although it is a well-established method, the need for aeration and possible addition of an external carbon source results in it being an energy-negative and costly process, thus making alternative methods for nitrogen removal compelling to examine. Anaerobic ammonium oxidation (anammox) has been presented as such an alternative, providing a “short-cut” through the nitrogen cycle by anaerobically oxidizing ammonium (NH4+) to nitrogen gas (N2) using nitrite (NO2-) as elector acceptor. By coupling the anammox reaction to partial denitrification (PDA), where nitrate (NO3-) is reduced to nitrite, simultaneous nitrogen removal of ammonium and nitrate is possible under anoxic conditions and low concentrations of organic carbon.
To examine the start-up and operation of a PDA process treating synthetic mainstream wastewater, two continuous 2 L moving bed biofilm reactors (MBBRs) were operated in parallel for ten weeks. After being inoculated with K5 biofilm carriers (previously used for partial nitrification/anammox) provided by AnoxKaldnes, the reactors were fed with low concentration synthetic wastewater, with either acetate or propionate as carbon source at a chemical oxygen demand (COD) to NO3--N ratio of 2. Analysis of the influents and effluents were performed three times a week to determine the removal rates of the reactors. Furthermore, four ex-situ activity batch tests were performed during the ten weeks to determine the change of activity in the microbial populations on the biofilm carriers.
During the start-up period several modifications were made to the experimental setup, such as separating the carbon source influents, in order to achieve stable conditions and influent concentrations. Subsequently, the reactors displayed a general increase of PDA capabilities during the final five weeks, with total nitrogen removal rates increasing from 0.29 ± 0.01 to 0.47 ± 0.03 g N/(m2*d) in the acetate fed reactor and from 0.17 ± 0.03 to 0.23 ± 0.03 g N/(m2*d) in the propionate fed reactor. Additionally, the anammox contribution to nitrogen gas formation was calculated to approximately 91 % in the acetate fed reactor and 64 % in the propionate fed reactor in the final week of operation. The improved performance of the acetate fed reactor was mainly attributed to a higher denitrification rate achieved by less complex utilization of the carbon source, as well as a larger abundance of partial denitrifiers compared to complete denitrifiers on the biofilm carriers. Furthermore, the nitrate reducing activities, and thus the nitrogen removal rates, appeared to still be increasing during the final weeks, suggesting that the microorganisms had not yet reached a stable co-community of denitrifiers and anammox bacteria. Consequently, further operation is required to establish the full capacity of the process. (Less)
Popular Abstract (Swedish)
Anammox-processen erbjuder en hållbar och energieffektiv metod för biologisk kväve-avskiljning inom avloppsrening. Men bakterierna som utför arbetet kväver en källa till nitrit, och en möjlig lösning på detta är att kombinera metoden med partiell denitrifikation. Kan ett samarbete mellan dessa olika grupper av mikroorganismer upprättas, och vilken påverkan har typen av kolkälla som används i processen?
Biologisk kväveavskiljning är en viktig del av avloppsrening, då utsläpp av höga halter ammonium i miljön kan leda till både försurning och övergödning av mark och vatten. Metoden som ofta används idag för att behandla större delen av det inkommande avloppsvattnet, så kallad nitrifikation och denitrifikation, kräver dock mycket energi i... (More)
Anammox-processen erbjuder en hållbar och energieffektiv metod för biologisk kväve-avskiljning inom avloppsrening. Men bakterierna som utför arbetet kväver en källa till nitrit, och en möjlig lösning på detta är att kombinera metoden med partiell denitrifikation. Kan ett samarbete mellan dessa olika grupper av mikroorganismer upprättas, och vilken påverkan har typen av kolkälla som används i processen?
Biologisk kväveavskiljning är en viktig del av avloppsrening, då utsläpp av höga halter ammonium i miljön kan leda till både försurning och övergödning av mark och vatten. Metoden som ofta används idag för att behandla större delen av det inkommande avloppsvattnet, så kallad nitrifikation och denitrifikation, kräver dock mycket energi i form av luftning, och eventuella tillsatser av organiskt kol. Detta gör det till en kostsam process, som även bidrar till klimatförändring genom utsläpp av växthusgasen lustgas. I metoden omvandlas det inkommande kvävet, i form av ammonium, först till nitrat (nitrifikation) och sedan till kvävgas (denitrifikation) som kan släppas ut i atmosfären utan negativa konsekvenser.
Partiell denitrifikation och anammox (förkortat PDA) är en alternativ metod för biologisk kväveavskiljning som har potentialen att minska energikonsumtionen för avloppsreningsverk. Idén bygger på att endast hälften av det inkommande ammoniumet omvandlas till nitrat i nitrifikationssteget. I en PDA reaktor omvandlas sedan detta nitrat till nitrit (genom partiell denitrifikation), som sedan direkt används av anammoxbakterier för att bilda kvävgas av det återstående ammoniumet och nitriten. Svårigheterna i processen ligger främst i att ”stoppa” denitrifikation efter att nitriten bildats, och i att upprätthålla en samlevnad av rätt typer av mikroorganismer i reaktorn.
I detta examensarbete utforskades möjligheten att kombinera anammox med partiell denitrifikation för gemensam avskiljning av ammonium och nitrat i avloppsvatten. Efter tio veckors drift indikerade resultaten att de två grupperna av mikroorganismer som är nödvändiga kunde samexistera på bärarmaterialet i reaktorn, och därigenom arbeta tillsammans för att omvandla nitrat och ammonium till kvävgas. Avskiljningshasigheten visade även en generell trend av ökning mot slutet av experimentet, vilket tyder på att processen behöver en längre tid av drift för att uppnå maximal kapacitet. Utöver detta visade sig acetat vara en mer lämplig kolkälla för bakterierna jämfört med propionat, eftersom det resulterade både i högre avskiljningshastigheter och ett mer lämpligt mikrobiellt samhälle.
Genom att applicera PDA i behandling av huvudströms avloppsvatten kan behovet av luftning potentiellt minskas med 50 %, och behovet av organiskt kol med 80 %, i biologisk kväveav-skiljning. På grund av detta undersöker R&D (research and development) företaget Sweden Water Research möjligheterna för framtida tillämpningar av PDA i nästa generationens avloppsreningsverk, där detta examensarbete utgör början. Till följd av den påvisade potentialen av processen i detta arbete kan de två använda labbskalereaktorerna fortsättas hållas i drift under en längre tidsperiod, för att ytterligare utforska processens prestation när systemet nått en högre nivå av stabilitet. (Less)
Please use this url to cite or link to this publication:
author
Wallin Holmin, Felix LU
supervisor
organization
course
VVAM05 20201
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Water engineering, Environmental engineering, Mainstream anammox, Partial denitrification, PDA, MBBR, Nitrogen removal, Vattenförsörjningsteknik, Avloppsteknik
language
English
id
9022991
date added to LUP
2020-07-02 10:37:06
date last changed
2020-07-02 10:37:06
@misc{9022991,
  abstract     = {In traditional wastewater treatment, nitrogen is removed through the biological process combination of nitrification and denitrification. Although it is a well-established method, the need for aeration and possible addition of an external carbon source results in it being an energy-negative and costly process, thus making alternative methods for nitrogen removal compelling to examine. Anaerobic ammonium oxidation (anammox) has been presented as such an alternative, providing a “short-cut” through the nitrogen cycle by anaerobically oxidizing ammonium (NH4+) to nitrogen gas (N2) using nitrite (NO2-) as elector acceptor. By coupling the anammox reaction to partial denitrification (PDA), where nitrate (NO3-) is reduced to nitrite, simultaneous nitrogen removal of ammonium and nitrate is possible under anoxic conditions and low concentrations of organic carbon. 
To examine the start-up and operation of a PDA process treating synthetic mainstream wastewater, two continuous 2 L moving bed biofilm reactors (MBBRs) were operated in parallel for ten weeks. After being inoculated with K5 biofilm carriers (previously used for partial nitrification/anammox) provided by AnoxKaldnes, the reactors were fed with low concentration synthetic wastewater, with either acetate or propionate as carbon source at a chemical oxygen demand (COD) to NO3--N ratio of 2. Analysis of the influents and effluents were performed three times a week to determine the removal rates of the reactors. Furthermore, four ex-situ activity batch tests were performed during the ten weeks to determine the change of activity in the microbial populations on the biofilm carriers.
During the start-up period several modifications were made to the experimental setup, such as separating the carbon source influents, in order to achieve stable conditions and influent concentrations. Subsequently, the reactors displayed a general increase of PDA capabilities during the final five weeks, with total nitrogen removal rates increasing from 0.29 ± 0.01 to 0.47 ± 0.03 g N/(m2*d) in the acetate fed reactor and from 0.17 ± 0.03 to 0.23 ± 0.03 g N/(m2*d) in the propionate fed reactor. Additionally, the anammox contribution to nitrogen gas formation was calculated to approximately 91 % in the acetate fed reactor and 64 % in the propionate fed reactor in the final week of operation. The improved performance of the acetate fed reactor was mainly attributed to a higher denitrification rate achieved by less complex utilization of the carbon source, as well as a larger abundance of partial denitrifiers compared to complete denitrifiers on the biofilm carriers. Furthermore, the nitrate reducing activities, and thus the nitrogen removal rates, appeared to still be increasing during the final weeks, suggesting that the microorganisms had not yet reached a stable co-community of denitrifiers and anammox bacteria. Consequently, further operation is required to establish the full capacity of the process.},
  author       = {Wallin Holmin, Felix},
  keyword      = {Water engineering,Environmental engineering,Mainstream anammox,Partial denitrification,PDA,MBBR,Nitrogen removal,Vattenförsörjningsteknik,Avloppsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Partial denitrification as nitrite provider for mainstream anammox},
  year         = {2020},
}