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Wastewater from a biodiesel plant: characterization of streams and suggestions for treatment options

Andersson, Linnea LU (2017) VVA820 20171
Chemical Engineering (M.Sc.Eng.)
Abstract
Biodiesel is an important alternative to ordinary diesel when limiting the effects on the climate. However, the production path of biodiesel produces a wastewater with a high chemical oxygen demand (COD) and it needs to be cleaned. The aim of this study was to characterise biodiesel wastewater as well as to suggest treatment options.

The biodiesel wastewater studied came from a biodiesel plant in the south of Sweden. The wastewater is generated when the biodiesel is washed to remove the by-product glycerol, the reactant methanol and a catalyst. Streams from different processing steps were investigated as well as the final mixed stream that today is sent for treatment to at plant in Kristianstad about 56 kilometers away.

The... (More)
Biodiesel is an important alternative to ordinary diesel when limiting the effects on the climate. However, the production path of biodiesel produces a wastewater with a high chemical oxygen demand (COD) and it needs to be cleaned. The aim of this study was to characterise biodiesel wastewater as well as to suggest treatment options.

The biodiesel wastewater studied came from a biodiesel plant in the south of Sweden. The wastewater is generated when the biodiesel is washed to remove the by-product glycerol, the reactant methanol and a catalyst. Streams from different processing steps were investigated as well as the final mixed stream that today is sent for treatment to at plant in Kristianstad about 56 kilometers away.

The wastewater was characterised by measuring general parameters such as total bound nitrogen, total phosphorus, COD, pH and density. The results varied between the streams but the results of the final mixed stream will be presented here. The mixed water was found to have a high COD of 241 g/L, higher than many compared studies. It also had a high total phosphorus content of 1480 mg/L and a nitrogen content of 57 mg/L. The pH was neutral around 6 and the density was 996 g/L, which is somewhat lower than the density of water.

When the samples were visually examined it was found that the mixed streams were most cloudy whereas some of the non-mixed streams were clear. This was supported by analysing the turbidity of the samples, which also indicated that there were many particles in the water. To find out if the COD was dissolved or particulate the samples were microfiltrated. Prior to the microfiltration the particle size distribution was determined to decide the pore size of the membrane, which was chosen to 0.2 µm. The analyses of the permeate showed that the turbidity decreased but the COD remained virtually unchanged. This meant that the COD was mainly dissolved.

To evaluate the origin of the COD the streams were characterised further with HPLC and gas chromatography (GC). From the HPLC it was found that the final mixed stream had high concentration of glycerol of 41.7 g/L. This is higher than the compared studies. The results from the GC showed that the streams contain residues of biodiesel and some other unidentified components.

Anaerobic digestion was evaluated as a treatment method by testing the biochemical methane potential (BMP) for the wastewater. The BMP of the mixed stream was 185.5 NmL CH4/g COD. It was found that codigestion of the wastewater with the glycerol by-product would have a higher BMP of 263.8 NmL CH4/g COD. This means that not only would the addition of glycerol to the stream generate a larger volume for anaerobic digestion but the potential of that stream would be higher.

The results from the BMP tests were used to estimate the biogas production. The biogas production was then compared to the mean yearly energy consumption of a Swedish house. Using only the mixed stream the yearly production could cover the consumption of 8 houses per year. With the codigestion of the streams the yearly production could cover the yearly consumption of 67 houses. (Less)
Popular Abstract (Swedish)
AVLOPPSVATTEN FRÅN EN BIODIESELANLÄGGNING: VAD INNEHÅLLER DET OCH HUR BEHANDLAR MAN DET?

Avloppsvatten från biodieselproduktion innehåller b.la. höga halter av organiskt material. Det betyder att vattnet måste behandlas för att få släppas ut. Innehållet i avloppsvattnet från en biodieselanläggning i Blekinge och förslag till behandling diskuteras i detta arbete.

Biodiesel är ett viktigt alternativ till vanlig diesel eftersom användandet av biodiesel kan bidra till att minska klimatpåverkan från fordonstrafik. Biodiesel kan tillverkas av olika råmaterial så som tallolja, animaliskt fett och rapsolja. I det undersökta fallet är råvaran rapsolja och ger s.k. rapsmetylester (RME).

Vid tillverkningen av biodiesel bildas glycerol som... (More)
AVLOPPSVATTEN FRÅN EN BIODIESELANLÄGGNING: VAD INNEHÅLLER DET OCH HUR BEHANDLAR MAN DET?

Avloppsvatten från biodieselproduktion innehåller b.la. höga halter av organiskt material. Det betyder att vattnet måste behandlas för att få släppas ut. Innehållet i avloppsvattnet från en biodieselanläggning i Blekinge och förslag till behandling diskuteras i detta arbete.

Biodiesel är ett viktigt alternativ till vanlig diesel eftersom användandet av biodiesel kan bidra till att minska klimatpåverkan från fordonstrafik. Biodiesel kan tillverkas av olika råmaterial så som tallolja, animaliskt fett och rapsolja. I det undersökta fallet är råvaran rapsolja och ger s.k. rapsmetylester (RME).

Vid tillverkningen av biodiesel bildas glycerol som en biprodukt. En annan biprodukt från den vanligaste tillverkningsprocessen är förorenat vatten. Detta vatten innehåller vanligtvis höga halter av organiskt material som kan leda till övergödning och syrebrist, om det når vattendrag och sjöar obehandlat. Alltså behöver vattnet behandlas innan det kan släppas ut igen.

Idag skickar företaget som tillverkar RMEn sitt vatten för behandling i Kristianstad. Problemet är att det är ganska långt att transportera avloppsvatten på en lastbil 5,6 mil och det är inte heller särskilt miljövänligt. Därför har möjligheten till att behandla vattnet på plats undersökts i detta arbete. En stor del av arbetet har även handlat om att undersöka vad som finns i vattnet för att komma fram till den bäst lämpade behandlingen.

Genom analyser av vattnet har det konstaterats att det innehåller höga halter av organiskt material. Detta var förväntat men det är intressant att värdena var högre än i de studier som jämförts (Phukingngam et al., 2011, Srirangsan et al., 2009). Biprodukten glycerol identifierades som en del av det organiska materialet. Genom ytterligare analyser har det konstaterats att vattnet innehåller höga halter av fosfor. Fosfor är viktigt att ta hänsyn till då det också bidrar till övergödning.

Ett sätt att behandla vattnet är att röta det för att få fram biogas. För att analysera hur mycket biogas som kan produceras så gjordes försök där mikroorganismer från en fungerande rötkammare användes. Mikroorganismerna matades med det förorenade vattnet och det mättes hur mycket biogas som producerades. Resultaten visade att med dagens produktion skulle företaget kunna producera 66 950 normaliserade kubikmeter metan per år (Nm3metan/år). Det, lågt räknat, skulle kunna täcka energibehovet för 8 villor per år (Eon, 2017a, Myfuelcell, 2017, Petersson, 2011). Försök gjordes även på en blandning av den tillverkade glycerolen och det förorenade vattnet. Genom att blanda dessa skulle produktionen kunna bli 563 900 Nm3metan/år och kunna täcka behovet för 67 villor.

Att röta vattnet är ett miljövänligt alternativ för behandling, eftersom processen ger ett mervärde genom biogasen som ett extra energitillskott. En del av fosforn i vattnet kan dessutom tas upp av mikroorganismerna och gör det då möjligt att potentiellt använda överskottet av slam som gödsel (Jarvis, 2012, Jonstrup et al., 2011). Dock är rening genom rötning inte det enda alternativet och det behövs mer studier för att fastställa vilket reningsalternativ som passar bäst. (Less)
Please use this url to cite or link to this publication:
author
Andersson, Linnea LU
supervisor
organization
alternative title
Rejektvatten från en biodieselanläggning: karakterisering av strömmar och förslag till reningsalternativ
course
VVA820 20171
year
type
H2 - Master's Degree (Two Years)
subject
keywords
water engineering, environmental engineering, avloppsteknik, vattenförsörjningsteknik
language
English
id
8904993
date added to LUP
2017-04-19 10:54:02
date last changed
2017-04-19 10:54:02
@misc{8904993,
  abstract     = {Biodiesel is an important alternative to ordinary diesel when limiting the effects on the climate. However, the production path of biodiesel produces a wastewater with a high chemical oxygen demand (COD) and it needs to be cleaned. The aim of this study was to characterise biodiesel wastewater as well as to suggest treatment options. 

The biodiesel wastewater studied came from a biodiesel plant in the south of Sweden. The wastewater is generated when the biodiesel is washed to remove the by-product glycerol, the reactant methanol and a catalyst. Streams from different processing steps were investigated as well as the final mixed stream that today is sent for treatment to at plant in Kristianstad about 56 kilometers away.
 
The wastewater was characterised by measuring general parameters such as total bound nitrogen, total phosphorus, COD, pH and density. The results varied between the streams but the results of the final mixed stream will be presented here. The mixed water was found to have a high COD of 241 g/L, higher than many compared studies. It also had a high total phosphorus content of 1480 mg/L and a nitrogen content of 57 mg/L. The pH was neutral around 6 and the density was 996 g/L, which is somewhat lower than the density of water. 

When the samples were visually examined it was found that the mixed streams were most cloudy whereas some of the non-mixed streams were clear. This was supported by analysing the turbidity of the samples, which also indicated that there were many particles in the water. To find out if the COD was dissolved or particulate the samples were microfiltrated. Prior to the microfiltration the particle size distribution was determined to decide the pore size of the membrane, which was chosen to 0.2 µm. The analyses of the permeate showed that the turbidity decreased but the COD remained virtually unchanged. This meant that the COD was mainly dissolved. 

To evaluate the origin of the COD the streams were characterised further with HPLC and gas chromatography (GC). From the HPLC it was found that the final mixed stream had high concentration of glycerol of 41.7 g/L. This is higher than the compared studies. The results from the GC showed that the streams contain residues of biodiesel and some other unidentified components. 

Anaerobic digestion was evaluated as a treatment method by testing the biochemical methane potential (BMP) for the wastewater. The BMP of the mixed stream was 185.5 NmL CH4/g COD. It was found that codigestion of the wastewater with the glycerol by-product would have a higher BMP of 263.8 NmL CH4/g COD. This means that not only would the addition of glycerol to the stream generate a larger volume for anaerobic digestion but the potential of that stream would be higher. 

The results from the BMP tests were used to estimate the biogas production. The biogas production was then compared to the mean yearly energy consumption of a Swedish house. Using only the mixed stream the yearly production could cover the consumption of 8 houses per year. With the codigestion of the streams the yearly production could cover the yearly consumption of 67 houses.},
  author       = {Andersson, Linnea},
  keyword      = {water engineering,environmental engineering,avloppsteknik,vattenförsörjningsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Wastewater from a biodiesel plant: characterization of streams and suggestions for treatment options},
  year         = {2017},
}