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Stabilization of urine by nitrification in a Moving Bed Biofilm Reactor

Olofsson, Marianne LU (2016) VVA820 20161
Chemical Engineering (M.Sc.Eng.)
Abstract
Municipal wastewater contains a lot of compounds that could be seen as resources. Nitrogen, phosphorus and potassium are common ingredients in fertilizers and can all be found in wastewater. Nowadays only a small part of the nutrients found in wastewater are used on arable land. Urine contains the most of the nitrogen, phosphorus and potassium secreted by humans. Source separation of urine is a way to facilitate recovery of nutrients in wastewater and to lower the load on existing wastewater treatment plants.
Fresh urine contains urea which may undergo ureolysis and form ammonia during storage. In order to prevent ammonia volatilization during further treatment such as volume reduction, urine needs to be stabilized. One method for... (More)
Municipal wastewater contains a lot of compounds that could be seen as resources. Nitrogen, phosphorus and potassium are common ingredients in fertilizers and can all be found in wastewater. Nowadays only a small part of the nutrients found in wastewater are used on arable land. Urine contains the most of the nitrogen, phosphorus and potassium secreted by humans. Source separation of urine is a way to facilitate recovery of nutrients in wastewater and to lower the load on existing wastewater treatment plants.
Fresh urine contains urea which may undergo ureolysis and form ammonia during storage. In order to prevent ammonia volatilization during further treatment such as volume reduction, urine needs to be stabilized. One method for stabilization of urine is nitrification. Nitrification is a biological process performed in two steps. In the first step, ammonia is oxidized to nitrous acid by ammonia oxidizing bacteria. This oxidation lowers the pH, which prevents ammonia from vaporizing. The second step is performed by nitrite oxidizing bacteria which oxidize nitrite to nitrate. Since ammonia and not ammonium is the substrate for the ammonia oxidizing bacteria only a part of the ammonia will be oxidized as pH drops. Ammonia and nitrate are common compounds in fertilizers.
In 2025, the housing area Sege Park in the city of Malmö should function as an example for sustainable city development. One goal is that the area should accommodate at least one test facility for source separation of urine. Before the construction of the facility can begin VA SYD, the regional water and sewer organisation, wants to investigate different volume reduction methods. Because ammonia may vaporize during volume reduction, they also want to investigate different stabilization methods.
The purpose of this work was to study the start-up process of a nitrification reactor for stabilization of urine. A bench-scale moving bed biofilm reactor was run for 57 days. The highest nitrification rate measured was 0.97 g N m-2 d-1. Nitrite accumulation, which is very problematic for a nitrification reactor, occurred two times. The first nitrite accumulation was handled by increased air flow and decreased load. To get rid of the second nitrite accumulation the solution in the reactor was diluted until the nitrite concentration was not measurable (< 0.6 mg L-1). The dilution resulted in a second start-up of the reactor. The two nitrite accumulations occurred at inlet nitrogen concentrations of 1,220 mg N L-1 and 1,320 mg N L-1 respectively. The load was 2.10 g N m-2 d-1 before the first nitrite accumulation and 1.54 g N m-2 d-1 before the second nitrite accumulation. After the second start-up the reactor ran stably and the inlet nitrogen concentration was increased to a maximum of 1,450 mg N L-1.
In order to find signs of process instabilities early and to prevent nitrite accumulations it is important to measure pH and dissolved oxygen in the reactor. Both parameters may indicate if something happens with the process. If any or both of the parameters are regulated, flow changes can probably be studied instead. It may also help to regularly measure the nitrite concentration in the reactor in order to be able to prevent nitrite accumulation from inhibiting the nitrification process. (Less)
Popular Abstract (Swedish)
Stabilisering av urin för återanvändning av näringsämnen

I naturen finns kretslopp för näringsämnen. När människan via avloppsvattenreningsverk släpper ut näringsämnen i vattendrag eller i luften bryts kretsloppen. För att bli en del av de naturliga kretsloppen behöver näringsämnena som människan avger återföras till jorden.

Av: Marianne Olofsson
Populärvetenskaplig sammanfattning av masteruppsatsen:
Stabilization of Urine by Nitrification in a Moving Bed Biofilm Reactor

Dagens avloppsvattenreningsverk kan inte avskilja alla näringsämnen i avloppsvatten fullständigt, och en del av dem släpps ut i vattendrag eller i luften. För att minska belastningen på avloppsvattenreningsverk och återföra en stor del av näringsämnena till... (More)
Stabilisering av urin för återanvändning av näringsämnen

I naturen finns kretslopp för näringsämnen. När människan via avloppsvattenreningsverk släpper ut näringsämnen i vattendrag eller i luften bryts kretsloppen. För att bli en del av de naturliga kretsloppen behöver näringsämnena som människan avger återföras till jorden.

Av: Marianne Olofsson
Populärvetenskaplig sammanfattning av masteruppsatsen:
Stabilization of Urine by Nitrification in a Moving Bed Biofilm Reactor

Dagens avloppsvattenreningsverk kan inte avskilja alla näringsämnen i avloppsvatten fullständigt, och en del av dem släpps ut i vattendrag eller i luften. För att minska belastningen på avloppsvattenreningsverk och återföra en stor del av näringsämnena till jordbruket kan urin separeras och behandlas separat. Separeringen kan ske med en toalett med två avlopp, i vilken urinen aldrig blandas med resten av avföringen.
Urin innehåller en kväveförening som kallas urea. När urea kommer i kontakt med ett naturligt förekommande enzym som kan bryta ner urea omvandlas urean till ammoniak. Ammoniak är en flyktig förening som luktar fränt. För att undvika att ammoniak avges från urinen behöver urinen stabiliseras. I jord finns bakterier som kan omvandla ammoniak till nitrat, genom att byta ut väteatomerna i ammoniak mot syreatomer. Samma typ av bakterier har man kunnat få att växa på specialutformade plastbitar, kallade rörligt bärarmaterial. Dessa bärare kan användas vid avloppsvattenrening.
Koncentrationen av kväveföreningar i urin är mycket högre än den i vanligt avloppsvatten. Bakterier på plastbärare som tidigare behandlat vanligt avloppsvatten kan därför behöva tid på sig att vänja sig vid de höga kvävekoncentrationerna i urin. Syftet med det här arbetet var att studera uppstarten av en reaktor för stabilisering av urin.
Uppstarten skedde genom att utspädd urin pumpades in till en reaktor med plastbärare. Allt eftersom tiden gick ökades andelen urin i inflödet och kvävekoncentrationen blev högre. Två gånger ackumulerades nitrit i reaktorn. Nitrit är mellanprodukten då ammoniak omvandlas till nitrat och ska helst inte ackumuleras i för stora mängder. Vid höga nitritkoncentrationer kan nämligen bakteriernas aktivitet minska, vilket gör att stabiliseringsprocessen försämras.
För att kunna upptäcka en nitritackumulering på ett tidigt stadium bör nitritkoncentrationen i reaktorn mätas kontinuerligt. Om en ökning av nitritkoncentrationen upptäcks tidigt kan eventuellt en nitritackumulering förebyggas. Genom att kontinuerligt studera pH och syrekoncentrationen i reaktorn kan processavvikelser upptäckas och åtgärdas.
Att kunna köra en sådan här processen stabilt är en förutsättning för att anläggningar ska byggas. Just nu planerar Malmö stad att bygga en sådan här anläggning, men mer information om hur en sådan här process fungerar behöver införskaffas innan bygget kan påbörjas och en reaktor kan köras på ett tillfredsställande sätt.
Nästa gång du möts av en toalett med två hål, bli glad, din urin kan komma till nytta! (Less)
Please use this url to cite or link to this publication:
author
Olofsson, Marianne LU
supervisor
organization
course
VVA820 20161
year
type
H2 - Master's Degree (Two Years)
subject
keywords
urine stabilization, urine, source separation, nitrogen recovery, nitrification, MBBR, city development, moving bed biofilm reactor, water engineering, environmental engineering, vattenförsörjningsteknik, avloppsteknik
language
English
id
8883081
date added to LUP
2016-06-20 15:53:46
date last changed
2016-06-20 15:53:46
@misc{8883081,
  abstract     = {Municipal wastewater contains a lot of compounds that could be seen as resources. Nitrogen, phosphorus and potassium are common ingredients in fertilizers and can all be found in wastewater. Nowadays only a small part of the nutrients found in wastewater are used on arable land. Urine contains the most of the nitrogen, phosphorus and potassium secreted by humans. Source separation of urine is a way to facilitate recovery of nutrients in wastewater and to lower the load on existing wastewater treatment plants. 
Fresh urine contains urea which may undergo ureolysis and form ammonia during storage. In order to prevent ammonia volatilization during further treatment such as volume reduction, urine needs to be stabilized. One method for stabilization of urine is nitrification. Nitrification is a biological process performed in two steps. In the first step, ammonia is oxidized to nitrous acid by ammonia oxidizing bacteria. This oxidation lowers the pH, which prevents ammonia from vaporizing. The second step is performed by nitrite oxidizing bacteria which oxidize nitrite to nitrate. Since ammonia and not ammonium is the substrate for the ammonia oxidizing bacteria only a part of the ammonia will be oxidized as pH drops. Ammonia and nitrate are common compounds in fertilizers. 
In 2025, the housing area Sege Park in the city of Malmö should function as an example for sustainable city development. One goal is that the area should accommodate at least one test facility for source separation of urine. Before the construction of the facility can begin VA SYD, the regional water and sewer organisation, wants to investigate different volume reduction methods. Because ammonia may vaporize during volume reduction, they also want to investigate different stabilization methods. 
The purpose of this work was to study the start-up process of a nitrification reactor for stabilization of urine. A bench-scale moving bed biofilm reactor was run for 57 days. The highest nitrification rate measured was 0.97 g N m-2 d-1. Nitrite accumulation, which is very problematic for a nitrification reactor, occurred two times. The first nitrite accumulation was handled by increased air flow and decreased load. To get rid of the second nitrite accumulation the solution in the reactor was diluted until the nitrite concentration was not measurable (< 0.6 mg L-1). The dilution resulted in a second start-up of the reactor. The two nitrite accumulations occurred at inlet nitrogen concentrations of 1,220 mg N L-1 and 1,320 mg N L-1 respectively. The load was 2.10 g N m-2 d-1 before the first nitrite accumulation and 1.54 g N m-2 d-1 before the second nitrite accumulation. After the second start-up the reactor ran stably and the inlet nitrogen concentration was increased to a maximum of 1,450 mg N L-1. 
In order to find signs of process instabilities early and to prevent nitrite accumulations it is important to measure pH and dissolved oxygen in the reactor. Both parameters may indicate if something happens with the process. If any or both of the parameters are regulated, flow changes can probably be studied instead. It may also help to regularly measure the nitrite concentration in the reactor in order to be able to prevent nitrite accumulation from inhibiting the nitrification process.},
  author       = {Olofsson, Marianne},
  keyword      = {urine stabilization,urine,source separation,nitrogen recovery,nitrification,MBBR,city development,moving bed biofilm reactor,water engineering,environmental engineering,vattenförsörjningsteknik,avloppsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Stabilization of urine by nitrification in a Moving Bed Biofilm Reactor},
  year         = {2016},
}