Environmental Engineering Reference
In-Depth Information
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