63
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 61-70
Chen
et al.
,
Reactivation of hypersaline aerobic granular sludge after low temperature storage
ISSN 2007-2422
•
(20-100 mg l
-1
as Ca basis) and 0.1 ml of trace
elements solution (Kishida, Kim, Tsuneda, &
Sudo, 2006).
Experiments
The granules, which had been stored under a
low temperature without DO and nutrients for
6 weeks, were taken out from the refrigerator to
thaw in a temperature controlled at 15±0.5 °C.
The microbes of the granular sludge were basi-
cally in a dormant state with low activity, and
therefore, it was inappropriate for the granules
to recover directly under a high loading. The
influent substrate concentration was raised
gradually by controlling COD/N ratio (20:1)
to slowly increase the organic loading, and
the DO level and temperature were improved
accordingly to control the reactor operating in
different phases. Detailed information about the
SBR operation is shown in table 2.
Analytical methods
Dehydrogenase activity (DHA) of granular
sludge was measured by 2, 3, 5-triphenyltetra-
zolium chloride (TTC) reduction method. The
particle size distribution was analyzed accord-
ing to Sauter formula as noted by Zhang
et al
.
(2006). DO concentration in the bulk liquor was
measured with a DO meter (HQ40d, HACH,
USA). pH was determined by a pH meter (SEN-
SION2, HACH, USA). MSV, SVI and NH
4
+
-N
were measured according to the standard meth-
ods (APHA, 2005).
Results and discussion
Appearance characteristics
Before low temperature storage, the average
diameter and dispersion of hypersaline aerobic
granules were 0.89 mm and 0.377 respectively.
The deep yellow granules with homogeneous
particles and smooth surface contained few
fragmentary sludge or small particles, as
showed in figure 1a. The apparent structure of
granules basically remained an initial shape af-
ter storage, while the colors had turned to gray
white or light yellow. Meanwhile, it was found
that the granules were becoming to be loose by
microscopy. When the reactor started up, the
loose granules broke up constantly, and the
break-up granules deteriorated into small pieces
Table 1. Characteristics of hypersaline aerobic granules before storage.
Parameters
Index
Appearance
Deep yellow, smooth
Salt stress content (%)
3.0
Average particle diameter (mm)
0.89
Sludge volume index (SVI) (ml g
-1
)
30.23
Minimum settling velocity (MSV) (m h
-1
)
4.79
Dehydrogenase activity (DHA) (ugTF g
-1
SS h
-1
)
39.27
Table 2. Operational parameters of the aerobic granular sludge reactor.
Phase
I
II
III
IV
V
Length of operation (cycles)
1-13
14-27
28-41
42-51
52-70
Organic loading (kg COD m
-3
d
-1
)
0.90
1.12
1.50
2.25
4.50
DO (mg l
-1
)
4-5
4-5
5-6
5-6
5-6
Temperature (°C)
20±0.5
20±0.5
20±0.5
25±0.5
25±0.5
