66
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
that low diffusion of DO in aerobic granule is
unfavorable to formation and stability of aero-
bic granules. In addition, rise of influent am-
monium nitrogen (NH
4
+
-N) concentration can
also lead loose morphology and overgrowth of
filamentous bacteria located on the outer layer
of the granules (Liu & Liu, 2006; Liu, Yang, Pu,
Liu, & Lan, 2009). When filamentous bacteria
in/on granules became as dominant microbes in
SBR, particles had presented in a decentralized
growth pattern, dominated by filamentous in-
ter-twine mode (Liu, Liu, & Tay, 2004; Wang, Li,
& Wang, 2008). Unfortunately, there were short
of sufficient extracellular polymeric substances
(EPS), metabolic products accumulating on the
surface of bacterial cells and bridging bacterial
cells and other particulate matter into an ag-
gregate (Adav, Lee, Show, & Tay, 2008; Liu, Liu,
& Tay, 2004), to strengthen microbial structure,
which can lead to granules disintegrated easily
and then induced filamentous bulking (Chen,
Yang, & Yu, 2013). Therefore, overcoming the
occurrence of filamentous growth induced by a
low DO level and increasing influent ammonia,
some effective strategies had been adopted in
this study, such as properly adding influent
water alkalinity with NaHCO
3
to adapt initial
pH value of 8.0±0.5, increasing aeration rate,
shortening settling time and others, and then
decentralized growth pattern of granules was
availably controlled in the following operation
phase. It was explained that increasing alka-
linity of reaction system can contribute to the
growth of non-filamentous bacteria on pH value
of 8.0±0.5, and the propagation of zoogloea
bacteria on a high DO level condition resulted
in a competitive relationship with filamentous,
which can inhibit the growth of filamentous.
Moreover, filamentous bacteria breeding on
granules was gradually cut off with the high
upflow liquid stream, and then washed out on
a short settling time of reactor. Furthermore,
enhancing shear force of reaction system and
shortening settling time can also improve cel-
lular surface hydrophobicity of zoogloea bac-
teria and microbial activity, and promote cell to
secrete more EPS content, which can facilitate
cell-to-cell adhesion and strengthen microbial
structure through polymeric matrices (Lee,
Chen, Show, Whiteley, & Tay, 2010; Tay, Liu, &
Liu, 2001; Liu & Tay, 2004). Whereas residuary
filamentous in granules would enter inside to
bind and connect with zoogloea bacteria, high
density and good settling property granular
sludge was thus formed.
DHA
Figure 3 shows the variation of DHA of gra-
nules during the whole reactivation process.
The thawed granules had low activity after
experiencing a low temperature idle phase,
and DHA was low to 5.42 ugTF g
-1
SS h
-1
, only
1/8 of activity before storage. Heterotrophs in
granules were prone to endogenous respiration
and intracellular hydrolysis being short of DO
and nutrients at cryogenic temperatures, which
can explain why microbes in granular sludge
lost growth activity during storing. With the
running of reactor, zoogloea and filamentous
bacteria in granules were in the condition of
adequate nutrients and DO, and then activity of
aerobic granules restored gradually. On cycle 27,
DHA reached up to the maximum of 48.9 ugTF
g
-1
SS h
-1
, exceeding the initial level, whereas sett-
ling property of granules dropped to the lowest
level and dehydrogenase activity reached to the
maximum, causing by overgrowth of massive
filamentous bacteria on granules as dominant
microbes. When some related measures were
adopted to control overgrowth of filamentous,
granular activity gradually decreased and stabi-
lized at about 38 ugTF g
-1
SS h
-1
. Result indicates
that activity of hypersaline granular sludge had
recovered basically after more than one-month
re-cultivated.
Nitrification characteristic
Hypersaline aerobic granules before storage
have good nitrification property, and removal
efficiency of NH
4
+
-N is up to 81.8% at 225 mg l
-1
of influent concentration. Change in the removal
efficiency for NH
4
+
-N by re-cultured thawed
granules after cryogenic storage during reacti-
vation is showed in figure 4.
