PubMed Health⌕ Search

Biomedical subjects

Q S Liu

Publications and source records attributed to Q S Liu.

At least 19 recordsLinked to original sources
PubMed2005

Startup of pilot-scale aerobic granular sludge reactor by stored granules.

The startup of a pilot-scale aerobic granular sludge reactor was investigated by seeding with 4-month stored aerobic granules. Two liters of granules were inoculated into the reactor (5.9% of reactor volume), which gave a biomass concentration of 1.03 g l(-1). Experimental results showed that seeding granules could be successfully maintained in the reactor. The microbial activity of seeding granules could be fully recovered to that of fresh granules after 2 days of operation, and new granules started to grow after day 5. Newly developed aerobic granules at stable period had similar size and morphology as seeding granules, and a biomass concentration of 6.0 g l(-1) was achieved in the reactor. The experiment demonstrated for the first time that stored aerobic granules could be used for easy and quick startup of aerobic granular sludge reactor.

Aerobiosis↗
PubMed2004

The effect of upflow air velocity on the structure of aerobic granules cultivated in a sequencing batch reactor.

The effect of upflow air velocity on the formation and structure of aerobic granules was studied in three column sequencing batch reactors. Upflow aeration would be the major cause of hydrodynamic shear force in the column reactor. Results showed that high upflow air velocity resulted in more compact, denser, rounder, stronger and smaller aerobic granules, while high biomass retention in the reactor was achieved. It was found that high upflow air velocity could induce granular sludge to secrete more cell polysaccharides which in turn contributed to the compact and strong structure. It appears from this study that the structure of aerobic granules could be controlled by manipulating the upflow air velocity.

Air Movements↗
PubMed2003

Substrate concentration-independent aerobic granulation in sequential aerobic sludge blanket reactor.

The development of aerobic granules was studied in four column-type sequential aerobic sludge blanket reactors fed with different substrate concentrations ranging from 500 to 3000 mg l(-1) COD. Results showed that aerobic granules successfully formed in all reactors fed with different substrate concentrations, indicating that the formation of aerobic granules is independent of the substrate concentration. The granule size, roundness, compactness, physical strength, as well as cell surface hydrophobicity and cell polysaccharides contents of the cultivated aerobic granules were investigated. It was shown that aerobic granules formed with different substrate concentrations had similar roundness and compactness. However, the size of aerobic granules slightly increased with an increase in substrate concentration, while granule strength decreased with substrate concentration. It was found that there was a significant increase in cell surface hydrophobicity and cell polysaccharides of the aerobic granules compared to that of seed sludge. The high cell surface hydrophobicity and high cell polysaccharides contents were believed to play an important role in the formation of aerobic granules. However, substrate concentration seems not to be a governing factor for the formation of aerobic granules. The results of this study would be useful for developing aerobic granules-based bioreactor and for better understanding of the mechanism of aerobic granulation. It was also clearly demonstrated that aerobic granules-based bioreactor would have great potential in the treatment of high-strength wastewater.

Bacteria, Aerobic↗
PubMed2002

Characteristics of aerobic granules grown on glucose and acetate in sequential aerobic sludge blanket reactors.

Aerobic granules were cultivated in two column-type sequential aerobic sludge blanket reactors fed with glucose and acetate, respectively. The characteristics of aerobic granules were investigated. Results indicated that the glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density, hydrophobicity, physical strength, microbial activity and storage stability. Substrate component does not seem to be a key factor on the formation of aerobic granules. However, microbial diversity of the granules is closely associated with the carbon sources supplied to the reactors. Compared with the conventional activated sludge flocs, aerobic granules exhibit excellent physical characteristics that would be essential for industrial application. This research provides a complete set of characteristics data of aerobic granules grown on glucose and acetate, which would be useful for further development of aerobic granules-based compact bioreactor for handling high strength organic wastewater.

Aerobiosis↗
PubMed2002

Aerobic granulation in sequential sludge blanket reactor.

Aerobic granulation was studied in a column-type of sequential sludge blanket reactor. Reactor was operated 4 hours per cycle under a chemical oxygen demand (COD) loading rate of 6.0 kg/m3/d by using acetate as substrate. Results showed that aerobic granules with a mean diameter of 0.35 mm were observed at cycle 42. With granulation proceeding, the sludge volume index (SVI) value gradually decreased, and to an average value of 50 mL/g at stable granulation period. Observation of granules' microstructure by scanning electron microscopy (SEM) showed that rod bacteria were dominant in granules with lots of cavities presented. An increase in cell hydrophobicity was observed after the appearance of aerobic granules. The cell hydrophobicity of sludge was found to be about 50% higher after granulation. It appears that high hydrophobicity could induce cell attachment and further strengthen cell-cell interaction; cell hydrophobicity might therefore play a major role in the formation of aerobic granules.

Bacteria, Aerobic↗
PubMed2001

The effects of shear force on the formation, structure and metabolism of aerobic granules.

The effect of shear force on aerobic granulation was studied in four column-type, sequential aerobic sludge blanket reactors. Hydrodynamic turbulence caused by upflow aeration served as the main shear force in the systems. Results showed that aerobic granulation was closely associated with the strength of shear force. Compact and regular aerobic granules were formed in the reactors with a superficial upflow air velocity higher than 1.2 cm s(-1). However, only typical bioflocs were observed in the reactor with a superficial upflow air velocity of 0.3 cm s(-1) during the whole experimental period. The characteristics of the aerobic granules in terms of settling ability, specific gravity, hydrophobicity, polysaccharide and protein content and specific oxygen utilization rate (SOUR) were examined. It was found that the shear force has a positive effect on the production of polysaccharide, SOUR, hydrophobicity of cell surface and specific gravity of granules. The hydrophobicity of granular sludge is much higher than that of bioflocs. Therefore, it appears that hydrophobicity could induce and further strengthen cell-cell interaction and might be the main force for the initiation of granulation. The shear-stimulated production of polysaccharides favors the formation of a stable granular structure. This research provides experimental evidence to show that shear force plays a crucial role in aerobic granulation and further influences the structure and metabolism of granules.

Aerobiosis↗
PubMed2001

Microscopic observation of aerobic granulation in sequential aerobic sludge blanket reactor.

AIMS: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors. METHODS AND RESULTS: A series of experiments were conducted in two column-type sequential aerobic sludge reactors fed with glucose and acetate as sole carbon source, respectively. The evolution of aerobic granulation was monitored using image analysis and optical and scanning electron microscopy. The results indicated that the formation of aerobic granules was a gradual process from seed sludge to compact aggregates, further to granular sludge and finally to mature granules with the sequential operation proceeding. Glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density and microbial activity. However, the microbial diversity of the granules was associated with the carbon source supplied. In this work, an important aerobic starvation phase was identified during sequential operation cycles. It was found that periodical aerobic starvation was an effective trigger for microbial aggregation in the reactor and further strengthened cell-cell interaction to form dense aggregates, which was an essential step of granulation. The periodical starvation-induced aggregates would finally be shaped to granules by hydrodynamic shear and flow. CONCLUSION: Aerobic granules can be formed within 3 weeks in the systems. The periodical starvation and hydrodynamic conditions would play a crucial role in the granulation process. SIGNIFICANCE AND IMPACT OF THE STUDY: Aerobic granules have excellent physical characteristics as compared with conventional activated sludge flocs. This research could be helpful for the development of an aerobic granule-based novel type of reactor for handling high strength organic wastewater.

Aerobiosis↗
PubMed2001

The role of cellular polysaccharides in the formation and stability of aerobic granules.

AIMS: This paper attempts to investigate the role of cellular polysaccharides in the formation and stability of aerobic granules. METHODS AND RESULTS: Three column sequential aerobic sludge blanket reactors (R1, R2 and R3) were operated at a superficial air upflow velocity of 0.3 cm s(-1), 1.2 cm s(-1) and 2.4 cm s(-1), respectively. Aerobic granules appeared at cycle 42 in R2 and R3 with a mean size of 0.37 mm in R2 and 0.35 mm in R3, however, aerobic granulation was not observed in R1. After the formation of aerobic granules, the sludge volume index (SVI) decreased to 55 ml g(-1) in R2 and 46 ml g(-1) in R3. Aerobic granulation was concurrent with a sharp increase of cellular polysaccharides normalized to cellular proteins, which increased from 5.7 to 13.0 mg per mg proteins in R2, and 7.5-13.9 mg per mg protein in R3. The content of polysaccharides in aerobic granules was 2-3 times higher than that in the bioflocci cultivated in R1. The disappearance of aerobic granules in R2 was tightly coupled to a drop in cellular polysaccharides. After the reappearance of bioflocci in R2, the content of cellular polysaccharides were found to be restored to the level observed in R1. CONCLUSION: It appears that the production of cellular polysaccharides could be stimulated by hydrodynamic shear force and contributes to the formation and stability of aerobic granules. SIGNIFICANCE AND IMPACT OF THE STUDY: It is expected that this study would provide useful information for better understanding the mechanisms of aerobic granulation.

Aerobiosis↗
PubMed1999

Kainate acts at presynaptic receptors to increase GABA release from hypothalamic neurons.

Recent reports suggest that kainate acting at presynaptic receptors reduces the release of the inhibitory transmitter GABA from hippocampal neurons. In contrast, in the hypothalamus in the presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor antagonists [1-(4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466) and D,L-2-amino-5-phosphonopentanoic acid (AP5)], kainate increased GABA release. In the presence of tetrodotoxin, the frequency, but not the amplitude, of GABA-mediated miniature inhibitory postsynaptic currents (IPSCs) was enhanced by kainate, consistent with a presynaptic site of action. Postsynaptic activation of kainate receptors on cell bodies/dendrites was also found. In contrast to the hippocampus where kainate increases excitability by reducing GABA release, in the hypothalamus where a much higher number of GABAergic cells exist, kainate-mediated activation of transmitter release from inhibitory neurons may reduce the level of neuronal activity in the postsynaptic cell.

Animals↗
PubMed1999

Extracellular calcium regulates responses of both alpha3- and alpha7-containing nicotinic receptors on chick ciliary ganglion neurons.

Neuronal nicotinic receptors are generally both permeable to calcium and potentiated by it. We have examined acute calcium regulation of both native alpha7-containing and the less abundant alpha3-containing nicotinic receptors on chick ciliary ganglion neurons. Most of the receptors are concentrated on somatic spines tightly overlaid in situ by a large presynaptic calyx. Whole cell patch-clamp recording from dissociated neurons using perforated patch-clamp techniques indicates that the rapidly desensitizing nicotinic response of alpha7-containing receptors achieves maximum amplitude in 2 mM calcium; both lower and higher concentrations of calcium are less effective. Barium and strontium but not magnesium can substitute for calcium in potentiating the response. Neither calcium current through the receptors nor calcium action at intracellular sites is necessary. These latter conclusions are supported by current-voltage analysis of the nicotine-induced response, ion substitution experiments, and internal perfusion of the cells with 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) via a conventional patch pipette. Varying the agonist concentration indicates that some of the calcium-dependent enhancement may involve a shift in the dose-response curve for agonist binding, but much of the effect is also likely to involve increased receptor responsiveness. Blockade of alpha7-containing receptors with alpha-bungarotoxin showed that the heteromeric alpha3-containing nicotinic receptors also undergo calcium-dependent potentiation. Calcium did not have a major effect on the desensitization rate of either receptor class but did have a selective effect on the rise time of alpha7-containing receptors. Analysis of stably transfected cells expressing an alpha7 gene construct showed that the calcium potentiation observed for native receptors did not require neuron-specific modifications or components and that it could be seen with the natural agonist acetylcholine. Receptor dependence on extracellular calcium may provide a regulatory mechanism for constraining synaptic signaling, avoiding local depletion of external calcium, and limiting calcium buildup in postsynaptic compartments.

Animals↗
PubMed1999

Selective modulation of excitatory transmission by mu-opioid receptor activation in rat supraoptic neurons.

Opioid peptides have profound inhibitory effects on the production of oxytocin and vasopressin, but their direct effects on magnocellular neuroendocrine neurons appear to be relatively weak. We tested whether a presynaptic mechanism is involved in this inhibition. The effects of mu-opioid receptor agonist D-Ala(2), N-CH(3)-Phe(4), Gly(5)-ol-enkephalin (DAGO) on excitatory and inhibitory transmission were studied in supraoptic nucleus (SON) neurons from rat hypothalamic slices using whole cell recording. DAGO reduced the amplitude of evoked glutamatergic excitatory postsynaptic currents (EPSCs) in a dose-dependent manner. In the presence of tetrodotoxin (TTX) to block spike activity, DAGO also reduced the frequency of spontaneous miniature EPSCs without altering their amplitude distribution, rising time, or decaying time constant. The above effects of DAGO were reversed by wash out, or by addition of opioid receptor antagonist naloxone or selective mu-antagonist Cys(2)-Tyr(3)-Orn(5)-Pen(7)-NH(2) (CTOP). In contrast, DAGO had no significant effect on the evoked and spontaneous miniature GABAergic inhibitory postsynaptic currents (IPSCs) in most SON neurons. A direct membrane hyperpolarization of SON neurons was not detected in the presence of DAGO. These results indicate that mu-opioid receptor activation selectively inhibits excitatory activity in SON neurons via a presynaptic mechanism.

Animals↗
PubMed1997

Nitric oxide inhibits neuronal activity in the supraoptic nucleus of the rat hypothalamic slices.

The presence of abundant nitric oxide synthase (NOS) in magnocellular neurons of the rat hypothalamus suggests that nitric oxide (NO) may be involved in controlling the release of oxytocin and vasopressin. To test this possibility, we examined the effect of NO-related drugs on extracellular discharges of 124 supraoptic nucleus (SON) neurons from slices of rat hypothalamus in vitro. Twenty-three (43%) of 53 neurons were inhibited by sodium nitroprusside (SNP), a spontaneous releaser of NO, at 1-3 mM. This inhibition was prevented by preincubation of the slices with 1 microM hemoglobin, an inactivator of NO (n = 14), whereas hemoglobin alone enhanced neuronal activity in seven (35%) of 20 neurons. L-Arginine (1 mM), a precursor of NO, inhibited neuronal activity in five (36%) of 14 neurons, while D-arginine (1 mM), the inactive counterpart of L-arginine, was ineffective (n = 12). N-omega-nitro-L-arginine methyl ester (L-NAME, 10 microM), an inhibitor of NOS, also enhanced neuronal activity in five (29%) of 17 neurons, while N-omega-nitro-D-arginine methyl ester (DNAME, 10 microM), the inactive enantiomer of L-NAME, was without effect (n = 11). Together, our data show that NO exerts predominantly an inhibitory effect on SON neurons and may serve as a negative feedback loop in controlling release of oxytocin and vasopressin.

Animals↗
PubMed1997

[Whole-cell recordings of the supraoptic nucleus neurons from rat hypothalamic slices in vitro].

Fifty-two supraoptic nucleus neurons in rat slice preparations were studied using whole cell patch-clamp technique. The mean passive and active membrane properties were measured as follows: resting membrane potential, 59 +/- 8 mV; input resistance, 535 +/- 129 M omega; time constant, 32 +/- 9 ms; amplitude of the action potentials, 99 +/- 11 mV; overshoot, 37 +/- 13 mV (n = 39). Most of these neurons showed a prominent slow after-hyperpolarization potential or current in response to depolarizing pulse. In votage-clamp condition, it was found that virtually all supraoptic neurons (n = 13) were invaded by spontaneous synaptic inputs. Pharmacological experiments showed that the excitatory postsynaptic currents (EPSCs) were mediated by non-NMDA glutamate receptors, whereas inhibitory postsynaptic currents (IPSCs) by GABAA receptors.

Animals↗
PubMed1996

[Opposite actions of ACh on excitatory and inhibitory synaptic transmission in cultured rat cortical neurons].

Effect of ACh on spontaneous EPSC and IPSC in cultured postnatal rat cortical neurons was studied using whole-cell voltage-clamp technique. EPSC was blocked by a non-NMDA glutamate receptor antagonist DNQX, while IPSC was blocked by a GABAA receptor antagonist bicuculline. When ACh (10-100 mumol/L) was applied by puff pipettes to the cells recorded, the frequency of EPSC was enhanced greatly, but the amplitude distribution was not changed significantly. However, the frequency of IPSC was attenuated by ACh even at a quite low concentration (1 mumol/L). The effect of ACh on EPSC and IPSC could be blocked by M type ACh receptor antagonist atropine (1 mumol/L). ACh had no significant effect on whole-cell currents activated by glutamate and GABA. The above results provide evidence that ACh has opposite effects on excitatory and inhibitory synaptic transmission in rat cortex by acting at presynaptic sites. It is also suggested that ACh plays an important role in the maintenance of excitability of cortical neurons.

Acetylcholine↗
PubMed1995

[Whole cell recording of sodium, potassium and calcium currents of cultured neonatal rat sympathetic neurons].

Na, K and Ca currents and other electrophysiological characteristics of cultured neonatal rat superior cervical sympathetic neurons were studied using whole cell clamp technique. The mean passive and active membrane properties measured are as follows: resting membrane potential, -51 +/- 6 mV; input resistance, 1432 +/- 389 M omega; time constant, 130 +/- 32 ms; amplitude of action potential, 96 +/- 10 mV; overshoot, 42 +/- 6 mV. Na, K and Ca currents were isolated upon pharmacological manipulations. The predominant type of K current was a noninactivating delayed rectifier. Voltage-clamp studies also showed the presence of a high voltage-activated sustained inward Ca current, while low voltage could not elicit any transient Ca current.

Animals↗
PubMed1995

[Nicotinic currents of cultured rat superior cervical ganglion neurons and use-dependent block by mecamylamine].

AIM: Comparison of action of nicotinic agonists and antagonists on nicotinic acetylcholine receptor (nAChR) in superior cervical ganglion (SCG) neurons. METHODS: Whole-cell recordings were made from cultured neonatal rat SCG neurons. Cholinergic drugs were applied by local pressure perfusion. RESULTS: The neurons were activated by nicotinic agonists and peak current were acetylcholine (ACh), 443 +/- 183 pA; nicotine, 1175 +/- 377 pA; dimethylphenylpiperazinium (DMPP), 2946 +/- 358 pA, respectively. The nicotinic responses were blocked by mecamylamine (Mec), hexamethonium and curare, the efficacies were 435 +/- 154 pA, 725 +/- 320 pA, 887 +/- 214 pA, but not by alpha-bungarotoxin. The block by Mec was use-dependent, i.e., it was dependent on repeated presentation of the agonists. The first 6 peak currents were expressed as percentage of the first response as following: 100, 64 +/- 3, 50 +/- 3, 41 +/- 4, 32 +/- 3%. CONCLUSION: The present data suggest that nAChR of SCG neurons have different pharmacological characteristics from that of muscle or central neurons.

Animals↗
PubMed1994

[The use of laser ignited mini-explosive technique in treating 100 cases of gastric bezoars].

The experience of breaking gastric bezoars endoscopically with a laser ignited mini-explosive head was reported. After successful application of this technique in vitro and in experimental animals, we began to use it clinically in January 1988. In a period of more than four years, we treated 100 cases of gastric bezoars, 80 cases being male and 20 female, aged from 5 to 65 years. 70 cases were cured after one treatment, 24 after two and the remaining 6 cases after three times of treatment. The cure rate was 100%. Except one case complicated with gastric perforation, no other complications were observed. The etiology and prevention of gastric bezoars, as well as the new method and experience in treating this disease were discussed.

Adolescent↗