Environmental Engineering Reference
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Fig. 6.11 Results of the interference tests by the phosphate MEA sensors in various concentra-
tions of KH 2 PO 4 at pH 7.5. No meaningful differences were found, indicating no interference
susceptibility to the tested ions [59]
6.3.1
DO and ORP Microprofile Measurements in Biofilms
A multi-species biofilm was developed for the DO and ORP microprofile measure-
ments using activated sludge from a municipal wastewater treatment plant aeration
tank (Mill Creek WWTP, Cincinnati, OH) [58]. Activated sludge was decanted,
washed with DI water several times, and transferred to Petri dishes. Frosted glass
slides (12-544-5CY, Fisher Scientific) were placed inside of the Petri dishes for
biofilm formation and growth. After 24 h, biofilm containing glass slides were sus-
pended from the top of a closed reactor, schematically illustrated in Fig. 6.12a. A
two ring polycyclic aromatic hydrocarbon, naphthalene, was used as the sole car-
bon source. In order to obtain a stable influent concentration of naphthalene (around
18 ~ 20 mg/L), a 20 L glass jar was used as a feed solution tank, containing an
excess amount of crystal naphthalene (4 g/L) mixed with mineral salt solution.
The mineral salt solution was prepared by mixing 32 mg/L of NaNO 3 ,10mg/Lof
NH 4 Cl, 40 mg/L of Na 2 HPO 4 ,10mg/LofKH 2 PO 4 , 1.4 mg/L of CaCl 2 , 3.8 mg/L
of MgSO 4 , 0.65 mg/L of FeCl 3 , 11.2
μ
g/L of MnSO 4 ,0.7
μ
g/L of CuSO 4 ,0.4
μ
g/L of ZnSO 4 . To remove naphthalene particles from
the influent, a fabric filter was attached to the outlet line of the naphthalene tank
and the flow was cycled through the closed biofilm reactor with a peristaltic pump
(Cole-Parmer Instrument Co., Chicago, IL). Feed solution with naphthalene was
prepared in advance; naphthalene was allowed to dissolve for three days before
it was used. The feed solution was changed every three days. Hydrogen peroxide
g/L of NaMoO 4 , and 12
μ
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