3 research outputs found
Polycyclic Aromatic Hydrocarbon Affects Acetic Acid Production during Anaerobic Fermentation of Waste Activated Sludge by Altering Activity and Viability of Acetogen
Till
now, almost all the studies on anaerobic fermentation of waste
activated sludge (WAS) for bioproducts generation focused on the influences
of operating conditions, pretreatment methods and sludge characteristics,
and few considered those of widespread persistent organic pollutants
(POPs) in sludge, for example, polycyclic aromatic hydrocarbons (PAHs).
Herein, phenanthrene, which was a typical PAH and widespread in WAS,
was selected as a model compound to investigate its effect on WAS
anaerobic fermentation for short-chain fatty acids (SCFAs) accumulation.
Experimental results showed that the concentration of SCFAs derived
from WAS was increased in the presence of phenanthrene during anaerobic
fermentation. The yield of acetic acid which was the predominant SCFA
in the fermentation reactor with the concentration of 100 mg/kg dry
sludge was 1.8 fold of that in the control. Mechanism exploration
revealed that the present phenanthrene mainly affected the acidification
process of anaerobic fermentation and caused the shift of the microbial
community to benefit the accumulation of acetic acid. Further investigation
showed that both the activities of key enzymes (phosphotransacetylase
and acetate kinase) involved in acetic acid production and the quantities
of their corresponding encoding genes were enhanced in the presence
of phenanthrene. Viability tests by determining the adenosine 5′-triphosphate
content and membrane potential confirmed that the acetogens were more
viable in anaerobic fermentation systems with phenanthrene, which
resulted in the increased production of acetic acid
Long-Term Effects of Copper Nanoparticles on Wastewater Biological Nutrient Removal and N<sub>2</sub>O Generation in the Activated Sludge Process
The increasing use of copper nanoparticles (Cu NPs) raises
concerns about their potential toxic effects on the environment. However,
their influences on wastewater biological nutrient removal (BNR) and
nitrous oxide (N<sub>2</sub>O) generation in the activated sludge
process have never been documented. In this study the long-term effects
of Cu NPs (0.1–10 mg/L) on BNR and N<sub>2</sub>O generation
were investigated. The total nitrogen (TN) removal was enhanced and
N<sub>2</sub>O generation was reduced at any Cu NPs levels investigated,
but both ammonia and phosphorus removals were not affected. The mechanism
studies showed although most of the Cu NPs were absorbed to activated
sludge, the activated sludge surface was not damaged, and the released
copper ion from Cu NPs dissolution was the main reason for TN removal
improvement and N<sub>2</sub>O reduction. It was also found that the
transformation of polyhydroxyalkanoates and the activities of ammonia
monooxygenase, nitrite oxidoreductase, exopolyphosphatase, and polyphosphate
kinase were not affected by Cu NPs, whereas the decreased metabolism
of glycogen and the increased activities of denitrification enzymes
were observed. Further investigation revealed that Cu NPs increased
the number of denitrifiers (especially N<sub>2</sub>O reducing denitrifiers)
but decreased nitrite accumulation. All these observations were in
correspondence with the enhancement of TN removal and reduction of
N<sub>2</sub>O generation
Short-Chain Fatty Acid Production from Different Biological Phosphorus Removal Sludges: The Influences of PHA and Gram-Staining Bacteria
Recently,
the reuse of waste activated sludge to produce short-chain fatty acids
(SCFA) has attracted much attention. However, the influences of sludge
characteristics, especially polyhydroxyalkanoates (PHA) and Gram-staining
bacteria, on SCFA production have seldom been investigated. It was
found in this study that during sludge anaerobic fermentation not
only the fermentation time but also the SCFA production were different
between two sludges, which had different PHA contents and Gram-negative
bacteria to Gram-positive bacteria (GNB/GPB) ratios and were generated
respectively from the anaerobic/oxic (AO) and aerobic/extended-idle
(AEI) biological phosphorus removal processes. The optimal fermentation
time for the AEI and AO sludges was respectively 4 and 8 d, and the
corresponding SCFA production was 304.6 and 231.0 mg COD/g VSS (volatile
suspended solids) in the batch test and 143.4 and 103.9 mg COD/g VSS
in the semicontinuous experiment. The mechanism investigation showed
that the AEI sludge had greater PHA content and GNB/GPB ratio, and
the increased PHA content accelerated cell lysis and soluble substrate
hydrolysis while the increased GNB/GPB ratio benefited cell lysis.
Denaturing gradient gel electrophoresis profiles revealed that the
microbial community in the AEI sludge fermentation reactor was dominated
by <i>Clostridium sp.</i>, which was reported to be SCFA-producing
microbes. Further enzyme analyses indicated that the activities of
key hydrolytic and acids-forming enzymes in the AEI sludge fermentation
reactor were higher than those in the AO one. Thus, less fermentation
time was required, but higher SCFA was produced in the AEI sludge
fermentation system