THESIS
2014
xxii, 171 pages : illustrations (some color) ; 30 cm
Abstract
Numerous sulfate conversion biotechnologies (SCBs) have been developed for
treating various sulfate-laden domestic and industrial wastewater generated from
natural and anthropogenic activities. Different ambient conditions and fluctuant
characteristics of sulfate-laden wastewater such as temperature, pH and salinity
constrain the application of current SCBs. Compact and resilient sulfate-converting
granular sludge systems may offer a promising solution to overcome these constraints
in implementation of SCBs. No study on granulation of SCB sludge in saline
wastewater treatment was reported; rather many researches were focused on activity
suppression of sulfate reducing bacteria (SRB) in anaerobic treatment processes. The
present research, therefore, aimed at developing SRB granu...[
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Numerous sulfate conversion biotechnologies (SCBs) have been developed for
treating various sulfate-laden domestic and industrial wastewater generated from
natural and anthropogenic activities. Different ambient conditions and fluctuant
characteristics of sulfate-laden wastewater such as temperature, pH and salinity
constrain the application of current SCBs. Compact and resilient sulfate-converting
granular sludge systems may offer a promising solution to overcome these constraints
in implementation of SCBs. No study on granulation of SCB sludge in saline
wastewater treatment was reported; rather many researches were focused on activity
suppression of sulfate reducing bacteria (SRB) in anaerobic treatment processes. The
present research, therefore, aimed at developing SRB granular sludge in a lab-scale
sulfate reducing up-flow bed reactor (SRUSB), with synthetic saline sewage as the
feed and anaerobic digestion sludge as the inoculum. The SRUSB is applied in sulfate
reduction, autotrophic denitrification and nitrification integrated process (SANI) as
the major reactor to realize organic removal and nitrogen removal in the subsequent
anoxic reactor.
Granulation successfully appeared at around 30 days and became well established
within 60 days after the SRUSB start-up. The physiochemical and biological
characteristics of the granules were extensively investigated at this formation stage to
the steady state operation stage throughout this 655-day research. The well-developed
SRB granules or named mature SRB granules in this study possessed an average diameter of 400-500 μm and stably stayed in the compact (gravity= 1.068-1.074) and
porous (pore volume= 0.022 mL/g) structures. The SRB population in the granular
sludge reached 44% of the total population, predominately present over the inner
granules with other bacteria constituted a thin outer shell on the surface of the granule.
The bacteria on the surface are believed to be the acidogens based on molecular
microbiological analyses of pyrosequencing and fluorescence in situ hybridization
(FISH). Such granule characteristics enabled the SRUSB to sustain 22 g/L biomass
concentration effectively and thus achieve 90% of COD removal even under a very
short hydraulic retention time (HRT), i.e. 1 h, indicating a very compact and stable
SRUSB. Three-dimensional investigation was conducted to optimize operation and
design of the SRUSB for performance improvement and scale up. The organics and
sulfur conversion profiles along the height of the SRUSB were examined; moreover,
the SRUSB internal hydrodynamics and microbial community were analyzed
correspondingly. Based on these investigations, a further modification of SRUSB was
conducted achieving better organics degradation profile along the reactor. Evaluation
of the inhibitions against the activity of SRB granules by temperature, pH, oxygen,
nitrite and free nitrous acid (FNA) as well as the reactor resilience was finally carried
out. SRB granules had good resilience against dissolved oxygen, high nitrite, low
temperature, pH (>5) and FNA (2.3 mgN/L) showed minimal impact on the granular
sludge. In conclusion, SRB granulation is proved to be a promising technology for
exploring SCB application with respect to enhancement in sludge retention, active
bio-volume and substrate loading rate, and reactor resilience.
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