Biomedical Engineering Reference
In-Depth Information
2. Materials and Methods
2.1. Nitrification Enrichment
Two identical laboratory-scale sequencing batch reactors (SBRs), each with an effective
volume of 2 litres, were used to investigate the short-term effects of glucose addition on
nitrification and settlement of activated sludge flocs. One reactor (the G-Reactor) was
operated with the addition of glucose, and the other reactor (the N-Reactor) without the
addition of glucose. The SBRs were operated as once-a-day feeding and drawing-off reactors
at temperatures ranging from 18 to 20°C. Each day, 1 litre of treated wastewater in both
reactors were exchanged, resulting in a HRT of 2 days. Pulse feeding and drawing-off were
applied, which occurred within approximately 2-minute durations. The period for aeration
was 23 hours and the settlement period was approximately 58 minutes. Air was supplied by
air pumps during the aerobic reaction phase and the concentration of dissolved oxygen (DO)
in the bulk water was maintained above 2 mg/l (usually around 8 mg/l). Mixed liquor (100
ml) was withdrawn from both reactors once a day just before the end of the aerobic react
phase. Both SBRs were seeded with activated sludge taken from Tuam Municipal Wastewater
Treatment Plant, Galway, Ireland.
The components of the synthetic wastewater were: 420 mg/l of NH
4
Cl, 200 mg/l of
Na
2
HPO
4
·12H
2
O, 12 mg/l of yeast extract, 500 mg/l of NaHCO
3
, 200 mg/l of KHCO
3
, 200
mg/l
of MgSO
4
·7H
2
O, 8 mg/l
of FeCl
3
·6H
2
O, 12 mg/l of CaCl
2
·6H
2
O and 8 mg/l
of
MnSO
4
·H
2
O. In addition, glucose was added to the G-Reactor at a concentration of 200 mg/l.
2.2. Analytical Methods
Suspended solids (SS), volatile suspended solids (VSS) and SVI were determined
according to standard methods (APHA, 1995). SVI was measured using a 100 ml graduated
cylinder. NH
4
-N, NO
2
-N and NO
3
-N were tested using a Konelab 20 analyzer (Thermo
Clinical Labsystems, Vantaa, Finland). DO and pH were measured using
WTW
portable
DO
and pH probes.
The free ammonia (NH
3
) and free nitrous acid (HNO
2
) concentrations were calculated
using (Anthonisen et al., 1976; Ford, 1980):
+
pH
NH
10
4
NH
=
(1)
3
10
pH
+
e
6344
/(
273
+
t
)
NO
−
HNO
=
2
(2)
2
pH
e
−
2300
/(
273
+
t
)
10
To examine extracellular polymeric substances (EPS), the activated sludge mixed liquor,
taken from the two reactors, was centrifuged at 3900 rpm for 10 minutes and then the biomass
was re-suspended in a 0.85% NaCl solution. EPS was extracted from the re-suspended
activated sludge mixed liquor using the formaldehyde-NaOH method (Liu and Fang, 2002).
After extraction, the mixed liquor was centrifuged at 4
o
C at 17,000 g for 20 minutes. The
