Nanomembranes - Nanotechnologies for Water Environment Applications - page 382

literature data about rejection values are available, but as a hydrophilic molecule with a
relatively high molar mass, a relatively higher rejection than primidone is expected. The
anti-epileptic carbamazepine is quite hydrophobic and has a relatively high molar mass,
but is uncharged, so a high initial rejection and a moderate to high equilibrium rejection
are expected. Xu et al. (2005) found a rejection of 93% after 10 min of nanofiltration. It
is difficult to assess whether this is the equilibrium rejection value. Rejection of the
analgesic ibuprofen is very well documented in the literature. Since at neutral pH
ibuprofen is charged, a high rejection is expected. At lower pH, under the pKa, the
compound is hydrophobic and is expected to demonstrate the same rejection behavior as
the hormones. Bellona and Drewes (2005) and Park and Cho (2005) described a constant
rejection value for ibuprofen of 70% at neutral pH by NF, which is lower than expected.
At lower pH-values, Bellona and Drewes (2005) described an initial rejection of 95%
(due to adsorption), decreasing in time to a value of about 30%.
The elimination of these chemicals during drinking water and wastewater
treatment processes at full- and pilot-scale also was investigated (Kim et al., 2007).
Conventional drinking water treatment methods were relatively inefficient for
contaminant removal, while efficient removal ( 99%) was achieved by granular
activated carbon (GAC). In wastewater treatment processes, membrane bioreactors
(MBR) showed limited removal for target compounds, but were effective at eliminating
hormones and some pharmaceuticals (e.g., acetaminophen, ibuprofen, and caffeine).
Membrane filtration processes using RO and NF showed excellent removal (> 95%) for
all target analytes.
12.2.4 Biostability Improvement
Biostability of product water has been receiving considerable attention in the
field of water engineering. This interest stems from the recognition that biodegradable
organic matter in product water, indicated by biological degradable organic carbon
(BDOC) and assimilable organic carbon (AOC), can serve as a food source for the
growth of microorganisms in a distribution system. Water that is classified as
biologically unstable promotes the growth of microorganisms, known as bacteria
regrowth. The term bacteria regrowth is commonly used to describe the phenomenon of
bacterial growth in treated water, typically in the distribution system (Huck, 1990). The
negative effects of bacteria regrowth on water quality depend on numbers and identity of
the bacteria present. The negative effects in various applications of the water, have been
reported as the deterioration of water quality, reducing hydraulic capacity, pipe
corrosion, and an increased incidence of coliform bacteria, which may pose a threat to
public health.
The organic carbon in water supplies is mainly composed of humic and fulvic
acids, carbohydrates, proteins, and carboxylic acids. In many distribution systems, it is