Measurements of assimilable organic carbon (AOC) in high
saline conditions using P17
Eunjeong Mun, Sangyoup Lee, Inhyuk Kim, Boksoon Kwon,
Heedueng Park and Seungkwan Hong
ABSTRACT
Biofouling caused by the deposition or growth of microorganisms on the membrane surface is one of
the major concerns in nanofiltration (NF) and reverse osmosis (RO) processes. Assimilable organic
carbon (AOC) has been a useful index to assess the growth potential of bacteria. In the case of
drinking water, the AOC assay method has been widely applied to estimate growth or regrowth
potential of bacteria in distribution and storage systems. However, studies on AOC measurement for
high salinity water samples such as brackish water and seawater are rather scarce. The objective of
this research is to investigate the influence of water salinity on the conventional AOC assay method.
AOC samples with different salt concentrations were prepared by varying NaCl concentration from 0
to 35,000 mg/L, while the acetate concentration was held at 100 μg/L. The number of cells produced
in water samples was measured by the heterotrophic plate count (HPC) method using R2A agar. The
result showed that the cell production of Pseudomonas fluorescens strain P17 and Spirillum strain
NOX decreased with increasing salinity. Especially, the growth of Spirillum strain NOX was noticeably
influenced by water salinity. To further observe the relation between acetate concentration and cell
production in high salinity water, organic-free saline water samples were prepared by spiking NaCl in
deionized (DI) water. The organic-free saline water samples were enriched with acetate of which
concentration was varied to be 0–1,000 μg/L (as acetate). Also, P. fluorescens strain P17 was
adjusted to high total dissolved solids (TDS) condition prior to being injected into the saline water
samples. The result demonstrated that the amount of microorganisms increased with increasing
acetate concentration. Although AOC measurement of saline water using Spirillum strain NOX
seemed unacceptable, it was suggested that P. fluorescens strain P17 has the possibility to be used in
measuring AOC in saline water. Moreover, the yield factor was altered as a result of reflecting salinity
impact as the growth number of P. fluorescens strain P17 was unstable with high saline condition.
Eunjeong Mun
Sangyoup Lee
Inhyuk Kim
Heedueng Park
Seungkwan Hong (corresponding author)
School of Civil, Environmental & Architectural
Engineering,
Korea University,
1, 5-ga, Anam-Dong,
Sungbuk-Gu,
Seoul, 136-713,
Korea
E-mail: skhong21@korea.ac.kr
Boksoon Kwon
Environment G. Emerging Tech,
Center/SAIT Samsung Electronics,
Korea
Key words | assimilable organic carbon (AOC), biofouling, nanofiltration (NF), Pseudomonas
fluorescens strain P17, reverse osmosis (RO), saline water, seawater desalination
INTRODUCTION
The use of reverse osmosis (RO) and nanofiltration (NF) is
increasing in seawater desalination and brackish water treat-
ments (Ebrahim & Abdel-Jawad ; Almulla et al. ;
Mohammad et al. ). One of the major concerns in the
efficient application of RO and NF is membrane fouling
which leads to the deterioration of both quantity and quality
of product water. Membrane fouling is usually caused by
the deposition of feed water components rejected by the
membrane (e.g. sparingly soluble inorganic compounds, col-
loidal or particulate matter, and dissolved organics) or the
attachment and growth of microorganisms on the mem-
brane surface (i.e. biofouling) (Al-Ahmad et al. ).
265 © IWA Publishing 2013 Water Science & Technology: Water Supply | 13.2 | 2013
doi: 10.2166/ws.2013.019