21 research outputs found
Enhanced Methane Production from Food Waste Using Cysteine To Increase Biotransformation of l‑Monosaccharide, Volatile Fatty Acids, and Biohydrogen
The
enhancement of two-stage anaerobic digestion of polysaccharide-enriched
food waste by the addition of cysteineî—¸an oxygen scavenger,
electron mediator, and nitrogen sourceî—¸to the acidification
stage was reported. It was found that in the acidification stage the
accumulation of volatile fatty acids (VFA), which mainly consisted
of acetate, butyrate, and propionate, was increased by 49.3% at a
cysteine dosage of 50 mg/L. Although some cysteine was biodegraded
in the acidification stage, the VFA derived from cysteine was negligible.
In the methanogenesis stage, the biotransformations of both VFA and
biohydrogen to methane were enhanced, and the methane yield was improved
by 43.9%. The mechanisms study showed that both d-glucose
and l-glucose (the model monosaccharides) were detectable
in the hydrolysis product, and the addition of cysteine remarkably
increased the acidification of l-glucose, especially acetic
acid and hydrogen generation, due to key enzymes involved in l-glucose metabolism being enhanced. Cysteine also improved the activity
of homoacetogens by 34.8% and hydrogenotrophic methanogens by 54%,
which might be due to the electron transfer process being accelerated.
This study provided an alternative method to improve anaerobic digestion
performance and energy recovery from food waste
Acute and Chronic Responses of Activated Sludge Viability and Performance to Silica Nanoparticles
Recently, the potential health and environmental risks
of silica
nanoparticles (SiO<sub>2</sub> NPs) are attracting great interest.
However, little is known about their possible impacts on wastewater
biological nitrogen and phosphorus removal. In this study, the acute
and chronic effects of SiO<sub>2</sub> NPs on activated sludge viability
and biological nutrient removal performance were investigated. It
was found that the presence of environmentally relevant concentration
(1 mg/L) of SiO<sub>2</sub> NPs caused no adverse acute and chronic
effects on sludge viability and wastewater nitrogen and phosphorus
removal. However, chronic exposure to 50 mg/L SiO<sub>2</sub> NPs
induced the increase of effluent nitrate concentration, and thus depressed
the total nitrogen (TN) removal efficiency from 79.6% to 51.6% after
70 days of exposure, which was due to the declined activities of denitrifying
enzymes, nitrate reductase and nitrite reductase. Wastewater phosphorus
removal was insensitive to 1 and 50 mg/L SiO<sub>2</sub> NPs after
either the acute or chronic exposure, because the critical factors
closely related to biological phosphorus removal were not significantly
changed, such as the activities of exopolyphosphatase and polyphosphate
kinase and the intracellular transformations of polyhydroxyalkanoates
and glycogen. Denaturing gradient gel electrophoresis (DGGE) analysis
revealed that the bacterial community structure was changed after
long-term exposure to 50 mg/L SiO<sub>2</sub> NPs, and the quantitative
PCR assays indicated that the abundance of denitrifying bacteria was
decreased, which was consistent with the declined wastewater nitrogen
removal
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
Response of Anaerobic Granular Sludge to a Shock Load of Zinc Oxide Nanoparticles during Biological Wastewater Treatment
The increasing use of zinc oxide nanoparticles (ZnO NPs)
in consumer and industrial products highlights a need to understand
their potential environmental impacts. In this study, the response
of anaerobic granular sludge (AGS) to a shock load of ZnO NPs during
anaerobic biological wastewater treatment was reported. It was observed
that the extracellular polymeric substances (EPS) of AGS and the methane
production were not significantly influenced at ZnO NPs of 10 and
50 mg per gram of total suspended solids (mg/g-TSS), but they were
decreased when the dosage of ZnO NPs was greater than 100 mg/g-TSS.
The visualization of EPS structure with multiple fluorescence labeling
and confocal laser scanning microscope revealed that ZnO NPs mainly
caused the decrease of proteins by 69.6%. The Fourier transform infrared
spectroscopy analysis further indicated that the C–O–C
group of polysaccharides and carboxyl group of proteins in EPS were
also changed in the presence of ZnO NPs. The decline of EPS induced
by ZnO NPs resulted in their deteriorating protective role on the
inner microorganisms of AGS, which was in correspondence with the
observed lower general physiological activity of AGS and the death
of microorganisms. Further investigation showed that the negative
influence of ZnO NPs on methane production was due to their severe
inhibition on the methanization step
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
Effect of CO<sub>2</sub> on Microbial Denitrification via Inhibiting Electron Transport and Consumption
Increasing
anthropogenic CO<sub>2</sub> emissions have been reported
to influence global biogeochemical processes; however, in the literature
the effects of CO<sub>2</sub> on denitrification have mainly been
attributed to the changes it causes in environmental factors, while
the direct effects of CO<sub>2</sub> on denitrification remain unknown.
In this study, increasing CO<sub>2</sub> from 0 to 30 000 ppm
under constant environmental conditions decreased total nitrogen removal
efficiency from 97% to 54%, but increased N<sub>2</sub>O generation
by 240 fold. A subsequent mechanistic study revealed that CO<sub>2</sub> damaged the bacterial membrane and directly inhibited the transport
and consumption of intracellular electrons by causing intracellular
reactive nitrogen species (RNS) accumulation, suppressing the expression
of key electron transfer proteins (flavoprotein, succinate dehydrogenase,
and cytochrome c) and the synthesis and activity of key denitrifying
enzymes. Further study indicated that the inhibitory effects of CO<sub>2</sub> on the transport and consumption of electrons were caused
by the decrease of intracellular iron due to key iron transporters
(AfuA, FhuC, and FhuD) being down-regulated. Overall, this study suggests
that the direct effect of CO<sub>2</sub> on denitrifying microbes
via inhibition of intracellular electron transport and consumption
is an important reason for its negative influence on denitrification
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
Effects of CuNPs on phosphorus anaerobic release and aerobic uptake during one cycle of EBPR process.
<p>Error bars represent the standard deviations of triplication tests.</p
The effect of CuNPs on the flocculating ability of activated sludge.
<p>Error bars represent standard deviations of triplicate measurements.</p
Influence of Copper Nanoparticles on the Physical-Chemical Properties of Activated Sludge
<div><p>The physical-chemical properties of activated sludge, such as flocculating ability, hydrophobicity, surface charge, settleability, dewaterability and bacteria extracellular polymer substances (EPS), play vital roles in the normal operation of wastewater treatment plants (WWTPs). The nanoparticles released from commercial products will enter WWTPs and can induce potential adverse effects on activated sludge. This paper focused on the effects of copper nanoparticles (CuNPs) on these specific physical-chemical properties of activated sludge. It was found that most of these properties were unaffected by the exposure to lower CuNPs concentration (5 ppm), but different observation were made at higher CuNPs concentrations (30 and 50 ppm). At the higher CuNPs concentrations, the sludge surface charge increased and the hydrophobicity decreased, which were attributed to more Cu<sup>2+</sup> ions released from the CuNPs. The carbohydrate content of EPS was enhanced to defense the toxicity of CuNPs. The flocculating ability was found to be deteriorated due to the increased cell surface charge, the decreased hydrophobicity, and the damaged cell membrane. The worsened flocculating ability made the sludge flocs more dispersed, which further increased the toxicity of the CuNPs by increasing the availability of the CuNPs to the bacteria present in the sludge. Further investigation indicated that the phosphorus removal efficiency decreased at higher CuNPs concentrations, which was consistent with the deteriorated physical-chemical properties of activated sludge. It seems that the physical-chemical properties can be used as an indicator for determining CuNPs toxicity to the bacteria in activated sludge. This work is important because bacteria toxicity effects to the activated sludge caused by nanoparticles may lead to the deteriorated treatment efficiency of wastewater treatment, and it is therefore necessary to find an easy way to indicate this toxicity.</p></div