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BDOC in drinking water : Designing a recirculating batch reactor at Ringsjöverket

Sjöstedt, Hanna Elin LU (2012) VVRL01 20121
Division of Water Resources Engineering
Abstract
High levels of biodegradable dissolved organic carbon can affect odor, taste, color and chemical oxygen demand of distributed drinking water as a consequence of bacterial growth (Frias et al, 1995; Escobar, I.C. and Randall, A.A., 2001). The water industry would be able to improve the quality of distributed drinking water if spatial and temporal variations of BDOC could be mapped in the distribution system. The aim of this study is to design a method to measure the BDOC concentrations in the drinking water produced and distributed by the water treatment plant Ringsjöverket.
Two recirculating batch reactors were designed and packed with biologically active sand. Drinking water samples were collected at pump stations along the water... (More)
High levels of biodegradable dissolved organic carbon can affect odor, taste, color and chemical oxygen demand of distributed drinking water as a consequence of bacterial growth (Frias et al, 1995; Escobar, I.C. and Randall, A.A., 2001). The water industry would be able to improve the quality of distributed drinking water if spatial and temporal variations of BDOC could be mapped in the distribution system. The aim of this study is to design a method to measure the BDOC concentrations in the drinking water produced and distributed by the water treatment plant Ringsjöverket.
Two recirculating batch reactors were designed and packed with biologically active sand. Drinking water samples were collected at pump stations along the water distribution network that stretches from Stehag to Örby. The samples were recirculated in the bioreactors for approximately one week. COD and UV absorbance of the recirculated water was analyzed at different time intervals to be able to analyze the change in DOC concentrations and chemical composition. TOC concentrations in the water of the bioreactors were analyzed at VA SYD water laboratory. Before analysis all water samples were filtered to separate POC from the DOC pool (Kaplan and Newbold, 1995). The only available chemical analysis of dissolved organic carbon at Ringsjöverket was the CODMn method. To translate the COD values into DOC values a ratio (TOC/COD) was analyzed and determined to be 1.92.

The results show a general trend of higher outlet values of COD than inlet COD values. These results indicate that the fraction of biodegradable organic carbon dissolved in water could not be determined in the BDOC bioassay designed at Ringsjöverket since no or few reduced values of COD were observed. The probable reason for the increase of COD when the water samples were recirculated was that the bioactive sand was leaking organic matter. The biofilm probably needed more time to adapt to the organic loading and chemical composition of the water samples to reach a dynamic equilibrium with a net reduction of BDOC. Furthermore, it is possible that the BDOC concentrations in the distributed drinking water from Ringsjöverket are so low that changes in concentration cannot be measured with this method.
The results of the UV analysis show a general trend of increasing UV absorbance with time as the sampled water was recirculated in the bioreactor. One explanation for the increase in aromatic DOC is that the chemical composition in the water samples was altered by bacterial metabolism. Further studies are needed to establish such a correlation. Another possible explanation to the increase of aromatic DOC in the recirculated water is that the bioactive sand released aromatic organic matter.
As a conclusion, further studies are needed to provide Ringsjöverket with reliable and fast information about the BDOC concentrations in the water distribution system. (Less)
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author
Sjöstedt, Hanna Elin LU
supervisor
organization
course
VVRL01 20121
year
type
M2 - Bachelor Degree
subject
keywords
water treatment plant, drinking water, biodegradable dissolved organic carbon, COD, TOC, UV absorbance, bacterial growth, water distribution system, biofilm, bacth reactor
report number
TVVR 12/4004
ISSN
1101-9824
language
English
id
3159617
date added to LUP
2012-11-15 17:33:11
date last changed
2012-11-15 17:33:11
@misc{3159617,
  abstract     = {High levels of biodegradable dissolved organic carbon can affect odor, taste, color and chemical oxygen demand of distributed drinking water as a consequence of bacterial growth (Frias et al, 1995; Escobar, I.C. and Randall, A.A., 2001). The water industry would be able to improve the quality of distributed drinking water if spatial and temporal variations of BDOC could be mapped in the distribution system. The aim of this study is to design a method to measure the BDOC concentrations in the drinking water produced and distributed by the water treatment plant Ringsjöverket. 
Two recirculating batch reactors were designed and packed with biologically active sand. Drinking water samples were collected at pump stations along the water distribution network that stretches from Stehag to Örby. The samples were recirculated in the bioreactors for approximately one week. COD and UV absorbance of the recirculated water was analyzed at different time intervals to be able to analyze the change in DOC concentrations and chemical composition. TOC concentrations in the water of the bioreactors were analyzed at VA SYD water laboratory. Before analysis all water samples were filtered to separate POC from the DOC pool (Kaplan and Newbold, 1995). The only available chemical analysis of dissolved organic carbon at Ringsjöverket was the CODMn method. To translate the COD values into DOC values a ratio (TOC/COD) was analyzed and determined to be 1.92. 

The results show a general trend of higher outlet values of COD than inlet COD values. These results indicate that the fraction of biodegradable organic carbon dissolved in water could not be determined in the BDOC bioassay designed at Ringsjöverket since no or few reduced values of COD were observed. The probable reason for the increase of COD when the water samples were recirculated was that the bioactive sand was leaking organic matter. The biofilm probably needed more time to adapt to the organic loading and chemical composition of the water samples to reach a dynamic equilibrium with a net reduction of BDOC. Furthermore, it is possible that the BDOC concentrations in the distributed drinking water from Ringsjöverket are so low that changes in concentration cannot be measured with this method. 
The results of the UV analysis show a general trend of increasing UV absorbance with time as the sampled water was recirculated in the bioreactor. One explanation for the increase in aromatic DOC is that the chemical composition in the water samples was altered by bacterial metabolism. Further studies are needed to establish such a correlation. Another possible explanation to the increase of aromatic DOC in the recirculated water is that the bioactive sand released aromatic organic matter.
As a conclusion, further studies are needed to provide Ringsjöverket with reliable and fast information about the BDOC concentrations in the water distribution system.},
  author       = {Sjöstedt, Hanna Elin},
  issn         = {1101-9824},
  keyword      = {water treatment plant,drinking water,biodegradable dissolved organic carbon,COD,TOC,UV absorbance,bacterial growth,water distribution system,biofilm,bacth reactor},
  language     = {eng},
  note         = {Student Paper},
  title        = {BDOC in drinking water : Designing a recirculating batch reactor at Ringsjöverket},
  year         = {2012},
}