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Challenges during start-up of urine nitrification in an MBBR

Ascard Edefell, Ellen LU (2017) VVA820 20162
Chemical Engineering (M.Sc.Eng.)
Abstract
Nitrogen and phosphorous compounds are secreted by humans and treated in wastewater treatments plants. These substances are also found in agricultural fertilisers and needed for plant growth. Nutrient recycling is limited in conventional treatment systems and valuable products are lost. Urine contains most of the nutrients from humans and by separating it from wastewater it is possible to close the cycle and use as fertiliser. The overall load to existing treatment plants is simultaneously decreased which is beneficial in growing urban areas.
Urea in urine is hydrolysed to ammonia during storage. To prevent nitrogen loss due to ammonia volatilisation, separated urine needs stabilisation. One method is biological nitrification. Ammonia... (More)
Nitrogen and phosphorous compounds are secreted by humans and treated in wastewater treatments plants. These substances are also found in agricultural fertilisers and needed for plant growth. Nutrient recycling is limited in conventional treatment systems and valuable products are lost. Urine contains most of the nutrients from humans and by separating it from wastewater it is possible to close the cycle and use as fertiliser. The overall load to existing treatment plants is simultaneously decreased which is beneficial in growing urban areas.
Urea in urine is hydrolysed to ammonia during storage. To prevent nitrogen loss due to ammonia volatilisation, separated urine needs stabilisation. One method is biological nitrification. Ammonia oxidising bacteria convert ammonia to nitrite while pH drops. Nitrite is then further oxidised to nitrate by nitrite oxidising bacteria. Limitations in alkalinity allow half of the ammonia to oxidise. The remaining half is stabilised in non-volatile ammonium when pH decrease. The treated solution contains equal parts ammonium and nitrate which are widely used in nitrogen fertilisers. However, the treated urine needs further processing to concentrate the solution to compete with existing products.
Sege Park in Malmö, Sweden, is a housing area which aims to be an example of sustainable city development by 2025. The idea is to have one house with source separation of urine and facilities for further processing. The regional water and sewage organisation, VA SYD, therefore needs to investigate and determine an appropriate method for urine treatment.
This project aimed to provide knowledge of nitrification as a stabilisation method. The start-up of a nitrification reactor for source-separated urine was studied in a bench-scale moving bed biofilm reactor, operated for two periods of 103 and 100 days respectively. The first part experienced continuous instabilities with fluctuating pH and repeated nitrite accumulations. Another start-up was initiated in the second half of the project with overall successful results. A shorter period of instabilities caused accumulation of nitrite twice at an influent nitrogen concentration of 1,390 mgN L-1. The problems were overcome by lowering the load and then by exchanging the influent pump from a fixed-flow pump to pH-regulation at pH 6.2. The urine concentration could be further increased to 4,680 mgN L-1 nitrogen in the reactor by the end of the experimental period. The corresponding nitrification rate was 0.3 gN m-2d-1
(60 gN m-3d-1). The rate decreased while the nitrogen concentration increased. Maximum rate was 0.9 gN m-2d-1 (160 gN m-3d-1) when the reactor concentration was 2,230 mgN L-1.
It seems crucial to observe and counteract process instabilities early for successful long-term operation of highly concentrated nitrification reactors. Continuous monitoring of pH and dissolved oxygen in combination with nitrite samples facilitate detection of instabilities. Reactor regulation with pH controlled influent ensure ideal conditions for well-balanced bacterial interplay and thus enhanced reactor stability. (Less)
Popular Abstract (Swedish)
Avloppets gula guld kan sluta naturens kretslopp

Dagens jordbruk kräver tillskott av växtnäringsämnen genom gödsling. Många av dessa ämnen återfinns i avloppsvatten. Med dagens avloppshantering är möjligheterna ganska små att återanvända näringen på åkrarna. Urinsortering skapar nya vägar att sluta naturens kretslopp.

Populärvetenskaplig sammanfattning av masteruppsatsen:
Challenges during start-up of urine nitrification in an MBBR

Urbana områden växer och med det höjs belastningen på kommunala avloppsreningsverk. På sikt måste många verk byggas ut för att matcha behovet och möta kraven på rening. I avloppsvatten är det urinen som står för den största delen av näringsämnena. Genom att separera urinen från resterade avlopp i... (More)
Avloppets gula guld kan sluta naturens kretslopp

Dagens jordbruk kräver tillskott av växtnäringsämnen genom gödsling. Många av dessa ämnen återfinns i avloppsvatten. Med dagens avloppshantering är möjligheterna ganska små att återanvända näringen på åkrarna. Urinsortering skapar nya vägar att sluta naturens kretslopp.

Populärvetenskaplig sammanfattning av masteruppsatsen:
Challenges during start-up of urine nitrification in an MBBR

Urbana områden växer och med det höjs belastningen på kommunala avloppsreningsverk. På sikt måste många verk byggas ut för att matcha behovet och möta kraven på rening. I avloppsvatten är det urinen som står för den största delen av näringsämnena. Genom att separera urinen från resterade avlopp i urinseparerande toaletter kan belastningen minska på de befintliga anläggningarna. Dessutom skapas möjligheter för vidare behandling av urinen för att kunna sluta naturens kretslopp av växtnäring.
Urin innehåller kväveföreningen urea som snabbt bryts ner till ammoniak då den lämnar kroppen. Ammoniak luktar fränt och avdunstar lätt, vilket minskar möjligheterna för en optimal kväverecirkulering. Men genom behandling kan kvävet i urinen stabiliseras så att den inte avdunstar och istället kan återföras till åkermark. I denna studien har nitrifikation studerats som en stabiliseringsmetod. Biologisk nitrifikation utnyttjar bakterier för att omvandla ammoniak till nitrat. Organismerna finns naturligt i jord och används i konventionell avloppsrening, då koncentrerade i slam eller på plastbärare.
Denna studien har undersökt uppstarten av en nitrifikationsreaktor i labbskala, med mikroorganismer på bärare från ett avloppsreningsverk. Koncentrationerna av näringsämnen är betydligt högre i urin än i kommunalt avloppsvatten. Urinen var därför kraftigt utspädd med vatten i början av uppstarten och koncentrationen höjdes långsamt för att vänja bakterierna vid de nya förhållandena.
Försöken visade att det är möjligt att behandla ganska koncentrerad urin. Men uppstarten tar tid och processen är långsam. Urinen skapar en ganska extrem miljö för mikroorganismerna. Dessutom är systemet känsligt för variationer, vid flertalet tillfällen varierade pH kraftigt och mellanprodukten nitrit ackumulerades i reaktorn. Höga nitritkoncentrationer kan ha förödande konsekvenser i processen. Genom att göra en del ändringar i regleringen av reaktorn kunde processtabiliteten öka.
I framtiden är planen att ett system för urinsortering och efterföljande behandling ska installeras i området Sege Park i Malmö. Området ska visa förslag på hur hållbar stadsutveckling kan se ut. Innan dess måste processen undersökas mer för att klargöra att nitrifikation är vägen att gå. På sikt kan det finnas möjligheter att installera liknande system i nybyggda områden eller i samband med stambyte. På det sättet minskar belastningen på de kommunala avloppsreningsverken.
En del förändringar i livsstil och infrastruktur krävs för att skapa en hållbar stadsutveckling. Genom att ta tillvara avloppets gula guld ökar möjligheterna att sluta naturens kretslopp. (Less)
Please use this url to cite or link to this publication:
author
Ascard Edefell, Ellen LU
supervisor
organization
course
VVA820 20162
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Urine, source-separation, urine stabilisation, nitrogen recovery, nitrification, moving bed biofilm reactor, MBBR, water engineering, environmental engineering, vattenförsörjningsteknik, avloppsteknik
report number
2017-01
language
English
id
8903473
date added to LUP
2017-02-21 12:11:27
date last changed
2017-02-21 12:11:27
@misc{8903473,
  abstract     = {Nitrogen and phosphorous compounds are secreted by humans and treated in wastewater treatments plants. These substances are also found in agricultural fertilisers and needed for plant growth. Nutrient recycling is limited in conventional treatment systems and valuable products are lost. Urine contains most of the nutrients from humans and by separating it from wastewater it is possible to close the cycle and use as fertiliser. The overall load to existing treatment plants is simultaneously decreased which is beneficial in growing urban areas.
Urea in urine is hydrolysed to ammonia during storage. To prevent nitrogen loss due to ammonia volatilisation, separated urine needs stabilisation. One method is biological nitrification. Ammonia oxidising bacteria convert ammonia to nitrite while pH drops. Nitrite is then further oxidised to nitrate by nitrite oxidising bacteria. Limitations in alkalinity allow half of the ammonia to oxidise. The remaining half is stabilised in non-volatile ammonium when pH decrease. The treated solution contains equal parts ammonium and nitrate which are widely used in nitrogen fertilisers. However, the treated urine needs further processing to concentrate the solution to compete with existing products.
Sege Park in Malmö, Sweden, is a housing area which aims to be an example of sustainable city development by 2025. The idea is to have one house with source separation of urine and facilities for further processing. The regional water and sewage organisation, VA SYD, therefore needs to investigate and determine an appropriate method for urine treatment.
This project aimed to provide knowledge of nitrification as a stabilisation method. The start-up of a nitrification reactor for source-separated urine was studied in a bench-scale moving bed biofilm reactor, operated for two periods of 103 and 100 days respectively. The first part experienced continuous instabilities with fluctuating pH and repeated nitrite accumulations. Another start-up was initiated in the second half of the project with overall successful results. A shorter period of instabilities caused accumulation of nitrite twice at an influent nitrogen concentration of 1,390 mgN L-1. The problems were overcome by lowering the load and then by exchanging the influent pump from a fixed-flow pump to pH-regulation at pH 6.2. The urine concentration could be further increased to 4,680 mgN L-1 nitrogen in the reactor by the end of the experimental period. The corresponding nitrification rate was 0.3 gN m-2d-1 
(60 gN m-3d-1). The rate decreased while the nitrogen concentration increased. Maximum rate was 0.9 gN m-2d-1 (160 gN m-3d-1) when the reactor concentration was 2,230 mgN L-1.
It seems crucial to observe and counteract process instabilities early for successful long-term operation of highly concentrated nitrification reactors. Continuous monitoring of pH and dissolved oxygen in combination with nitrite samples facilitate detection of instabilities. Reactor regulation with pH controlled influent ensure ideal conditions for well-balanced bacterial interplay and thus enhanced reactor stability.},
  author       = {Ascard Edefell, Ellen},
  keyword      = {Urine,source-separation,urine stabilisation,nitrogen recovery,nitrification,moving bed biofilm reactor,MBBR,water engineering,environmental engineering,vattenförsörjningsteknik,avloppsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Challenges during start-up of urine nitrification in an MBBR},
  year         = {2017},
}