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1.
Nitrite accumulates during biological denitrification processes when carbon sources are insufficient. Acetate, methanol, and
ethanol were investigated as supplementary carbon sources in the nitrite denitrification process using biogranules. Without
supplementary external electron donors (control), the biogranules degraded 200 mg l−1 nitrite at a rate of 0.27 mg NO2–N g−1 VSS h−1. Notably, 1,500 mg l−1 acetate and 700 mg l−1 methanol or ethanol enhanced denitrification rates for 200 mg l−1 nitrite at 2.07, 1.20, and 1.60 mg NO2–N g−1 VSS h−1, respectively; these rates were significantly higher than that of the control. The sodium dodecyl sulfate polyacrylamide
gel electrophoresis of the nitrite reductase (NiR) enzyme identified three prominent bands with molecular weights of 37–41 kDa.
A linear correlation existed between incremental denitrification rates and incremental activity of the NiR enzyme. The NiR
enzyme activity was enhanced by the supplementary carbon sources, thereby increasing the nitrite denitrification rate. The
capacity of supplementary carbon source on enhancing NiR enzyme activity follows: methanol > acetate > ethanol on molar basis
or acetate > ethanol > methanol on an added weight basis. 相似文献
2.
Removal of nitrate and phosphate ions from water, by using the thermophilic cyanobacterium Phormidium laminosum, immobilized on cellulose hollow fibres in the tubular photobioreactor at 43 °C, was studied by continuously supplying dilute
growth medium for 7 days and then secondarily treated sewage (STS) for 12 days. The concentrations of NO−
3 and PO3−
4 in the effluent from the dilute growth medium decreased from 5.0 mg N/l to 3.1 mg N/l, and from 0.75 mg P/l to 0.05 mg P/l
respectively, after a residence time of 12 h. The concentrations of NO−
3 and PO3−
4 in the effluent from STS decreased from 11.7 mg N/l to 2.0 mg N/l, and from 6.62 mg P/l to 0.02 mg P/l respectively, after
a residence time of 48 h. The removal rates of nitrogenous␣and phosphate ions from STS were 0.24 and 0.11 mmol day−1 l reactor−1 respectively, under the same conditions. Although, among nitrogenous ions, nitrate and ammonium ions were efficiently removed
by P.␣laminosum, the nitrite ion was released into the effluent when STS was used as influent. Treatment of water with thermophilic P. laminosum immobilized on hollow fibres thus appears to be an appropriate means for the removal of inorganic nitrogen and phosphorus
from treated wastewater.
Received: 15 August 1997 / Received last revision: 18 November 1997 / Accepted: 29 November 1997 相似文献
3.
Low-temperature bioremediation of a waste water contaminated with anionic surfactants and fuel oil 总被引:7,自引:0,他引:7
We conducted a laboratory study at 10 °C on the biological decontamination of the waste water from a garage and car-wash
that was contaminated with anionic surfactants (57 mg l−1) and fuel oil (184 mg hydrocarbons l−1). The indigenous microorganisms degraded both contaminants efficiently after biostimu- lation by an inorganic nutrient supply.
After 7 days at 10 °C, the residual contaminations were 11 mg anionic surfactants l−1 and 26 mg hydrocarbons l−1. After 35 days, only the anionic surfactants had been further reduced to 3 mg l−1. Bioaugmentation of the unfertilized waste water with a cold-adapted inoculum, able to degrade both hydrocarbons (diesel
oil) and anionic surfactants (sodium dodecyl sulphate), resulted in a significant increase of the hydrocarbon biodegradation
during the first 3 days of decontamination, whereas biodegradation of anionic surfactants was inhibited during the first 21 days
following inoculation. Bioaugmentation of the nutrient-amended waste water was without any effect.
Received: 14 November 1997 / Accepted: 29 November 1997 相似文献
4.
4-Chlorophenol degradation by a bacterial consortium: development of a granular activated carbon biofilm reactor 总被引:5,自引:0,他引:5
Caldeira M Heald SC Carvalho MF Vasconcelos I Bull AT Castro PM 《Applied microbiology and biotechnology》1999,52(5):722-729
A bacterial consortium that can degrade chloro- and nitrophenols has been isolated from the rhizosphere of Phragmitis communis. Degradation of 4-chlorophenol (4-CP) by a consortium attached to granular activated carbon (GAC) in a biofilm reactor was
evaluated during both open and closed modes of operation. During the operation of the biofilm reactor, 4-CP was not detected
in the column effluent, being either adsorbed to the GAC or biodegraded by the consortium. When 4-CP at 100 mg l−1 was fed to the column in open mode operation (20 mg g−1 GAC total supply), up to 27% was immediately available for biodegradation, the rest being adsorbed to the GAC. Biodegradation
continued after the system was returned to closed mode operation, indicating that GAC bound 4-CP became available to the consortium.
Biofilm batch cultures supplied with 10–216 mg 4-CP g−1 GAC suggested that a residual fraction of GAC-bound 4-CP was biologically unavailable. The consortium was able to metabolise
4-CP after perturbations by the addition of chromium (Cr VI) at 1–5 mg l−1 and nitrate at concentrations up to 400 mg l−1. The development of the biofilm structure was analysed by scanning electron microscopy and confocal laser scanning microscopy
(CLSM) techniques. CLSM revealed a heterogeneous structure with a network of channels throughout the biofilm, partially occupied
by microbial exopolymer structures.
Received: 17 March 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999 相似文献
5.
The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was
investigated. For peptone concentrations from 5 g l−1 to 20 g l−1 the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l−1 day−1 compared to 320 mg l−1 day−1 at 10 g l−1 peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH3/g peptone in the mesophilic cultures. If 0.5–6.5 g l−1 ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand
(COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures
were most active if around 1 g ammonia l−1 was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and
hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and
methane formation revealed a K
i (50%) for NH3 of 92, 95 and 88 mg l−1 at 37 °C and 251, 274 and 297 mg l−1 at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH3 than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 108 peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only
5.6 × 107 cfu/ml was observed.
Received: 24 April 1998 / Received revision: 26 June 1998 / Accepted: 27 June 1998 相似文献
6.
A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow
operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated
water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were
modeled using a modified Haldane equation, which resulted in the following kinetic constants: q
max = 0.41 mg PCP mg protein−1 day−1, K
S = 16 μg l−1, K
i = 5.3 mg l−1, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations
(above 1.1 mg PCP l−1). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and
energy. During continuous-flow operation, effluent concentrations below 2 μg l−1 were achieved at 268 min hydraulic retention time (t
HR) and 2.5 mg PCP l−1 feed concentration. An increase in loading rate by decreasing t
HR did not significantly deteriorate the effluent quality until a t
HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP
concentration and increasing t
HR resulted in an improved process recovery.
Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997 相似文献
7.
Production of sophorolipids from whey 总被引:5,自引:0,他引:5
Otto RT Daniel HJ Pekin G Müller-Decker K Fürstenberger G Reuss M Syldatk C 《Applied microbiology and biotechnology》1999,52(4):495-501
Sophorolipids, obtained by a two-stage process starting from deproteinized whey concentrate using Cryptococcus curvatus ATCC 20509 and Candida bombicola ATCC 22214, were compared to products from one-stage processes, using different lipidic compounds as substrates. Results
showed that above all carbon source and not cultivation conditions had a distinct influence on the composition of the crude
product mixture and therefore on the physicochemical and biological properties of the sophorolipids, such as, for example,
surface activity, cytotoxicity and stability against hydrolases. The results were completed by corresponding data for purified
mono- and diacetylated (17-hydroxyoctadecenoic)-1′,4′′-lactonized sophorolipids. Crude sophorolipid mixtures showed moderate
to good surface active properties (SFTmin 39 mN m−1, CMC 130 mg l−1), water solubilities (2–3 g l−1) and low cytotoxicities (LC50 300–700 mg l−1). In contrast, purified sophorolipids were more surface active (SFTmin 36 mN m−1, CMC 10 mg l−1), less water soluble (max. 70 mg l−1) and showed stronger cytotoxic effects (LC50 15 mg l−1). Incubation of crude sophorolipid mixtures with different hydrolases demonstrated that treatment with commercially available
lipases such as from Candida rugosa and Mucor miehei distinctly reduced the surface active properties of the sophorolipids, while treatment with porcine liver esterase and glycosidases
had no effect.
Received: 23 February 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999 相似文献
8.
Dilsen S Paul W Sandgathe A Tippe D Freudl R Thömmes J Kula MR Takors R Wandrey C Weuster-Botz D 《Applied microbiology and biotechnology》2000,54(3):361-369
A pH-auxostatic fed-batch process was developed for the secretory production of a fusion protein consisting of the pro-part
of Staphylococcus hyicus lipase and two synthetic human calcitonin (hCT) precursor repeats under the control of a xylose-inducible promotor from Staphylococcus xylosus. Using glycerol as the energy source and pH-controlled addition of yeast extract resulted in the production of 2000 mg l−1 of the fusion protein (420 mg l−1 of the recombinant hCT precursor) within 14 h, reaching 45 g l−1 cell dry mass with Staphylococcus carnosus in a stirred-tank reactor. Product titer and space-time yield (30 mg calcitonin precursor l−1 h−1) were thus improved by a factor of 2, and 4.5, respectively, compared to Escherichia coli expression-secretion systems for the production of calcitonin precursors. Two hundred grams of the fusion protein was secreted
by the recombinant S. carnosus on a 150-l scale (scale-up factor of 50) with a minimum use of technical-grade yeast extract (40 mg fusion protein g−1 yeast extract).
Received: 18 January 2000 / Received revision: 14 April 2000 / Accepted: 14 April 2000 相似文献
9.
Nitrogen (N) pollution is a problem in many large temperate zone rivers, and N retention in river channels is often small
in these systems. To determine the potential for floodplains to act as N sinks during overbank flooding, we combined monitoring,
denitrification assays, and experimental nitrate (NO3− -N) additions to determine how the amount and form of N changed during flooding and the processes responsible for these changes
in the Wisconsin River floodplain (USA). Spring flooding increased N concentrations in the floodplain to levels equal to the
river. As discharge declined and connectivity between the river and floodplain was disrupted, total dissolved N decreased
over 75% from 1.41 mg l−1, equivalent to source water in the Wisconsin River on 14 April 2001, to 0.34 mg l−1 on 22 April 2001. Simultaneously NO3− -N was attenuated almost 100% from 1.09 to <0.002 mg l−1. Unamended sediment denitrification rates were moderate (0–483 μg m−2 h−1) and seasonally variable, and activity was limited by the availability of NO
3− -N on all dates. Two experimental NO3− -N pulse additions to floodplain water bodies confirmed rapid NO3− -N depletion. Over 80% of the observed NO
3− -N decline was caused by hydrologic export for addition #1 but only 22% in addition #2. During the second addition, a significant
fraction (>60%) of NO3− -N mass loss was not attributable to hydrologic losses or conversion to other forms of N, suggesting that denitrification
was likely responsible for most of the NO3− -N disappearance. Floodplain capacity to decrease the dominant fraction of river borne N within days of inundation demonstrates
that the Wisconsin River floodplain was an active N sink, that denitrification often drives N losses, and that enhancing connections
between rivers and their floodplains may enhance overall retention and reduce N exports from large basins. 相似文献
10.
Inhibition of methane production from whey by heavy metals – protective effect of sulfide 总被引:1,自引:0,他引:1
A whey solution was used as a substrate for methane production in an anaerobic fixed-bed reactor. At a hydraulic retention
time of 10 days, equivalent to a space loading of 3.3 kg (m3 day)−1, 90% of the chemical oxygen demand was converted to biogas. Only a little propionate remained in the effluent. Toxicity tests
with either copper chloride, zinc chloride or nickel chloride were performed on effluent from the reactor. Fifty per cent
inhibition of methanogenesis was observed in the presence of ≥10 mg CuCl2 l−1≥40 mg ZnCl2 l−1 and ≥60 mg NiCl2 l−1, respectively. After exposure to Cu2+, Zn2+ or Ni2+ ions for 12 days, complete recovery of methanogenesis by equimolar sulfide addition was possible upon prolonged incubation.
Recovery failed, however, for copper chloride concentrations ≥40 mg l−1. If the sulfide was added simultaneously with the three heavy metal salts, methanogenesis was only slightly retarded and
the same amount of methane as in non-inhibited controls was reached either 1 day (40 mg ZnCl2 l−1) or 2 days later (10 mg CuCl2 l−1). Up to 60 mg NiCl2 l−1 had no effect if sulfide was present. Sulfide presumably precipitated the heavy metals as metal sulfides and by this means
prevented heavy metal toxicity.
Received: 8 October 1999 / Received revision: 3 January 2000 / Accepted: 4 January 2000 相似文献
11.
Water and surficial sediment samples of Lake Chascomús and its tributaries were analyzed in order to relate changes in diatom
community structure to chemical variables. Over the course of 13 months of sampling, the lake exhibited major changes in water
level (1.15–1.98 m average depth), total dissolved solids (821–1972 mg l−1), silica (0.098–8.22 mg l−1), and total algal biomass (21.4–145.9 μg Chl a l−1). However, despite these large fluctuations, the diatom species composition was relatively stable. The dominant species in
the water column was always Synedra berolinensis (68.9%–90.1% total frustules), with Fragilaria construens and F. brevistriata as subdominants. In the sediments the latter two species dominated the frustule counts. These results indicate an unusual
floristic stability of this eutrophic ecosystem, with persistent dominance by broadly tolerant, generalist species.
Received: April 24, 2001 / Accepted: January 23, 2002 相似文献
12.
The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol 总被引:5,自引:0,他引:5
A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam
(PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR),
packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation
rate of phenol (q
s
max) decreased in the order: PBRC (598 mg l−1 h−1) > PBR (PU, 471 mg l−1 h−1) > PBR (SG, 394 mg l−1 h−1) > FBR (PU, 161 mg l−1 h−1) > FBR (SG, 91 mg l−1 h−1). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick
layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed
to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized
in colloidal SiO2 enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic
packing.
Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000 相似文献
13.
P. Becker I. Abu-Reesh S. Markossian G. Antranikian H. Märkl 《Applied microbiology and biotechnology》1997,48(2):184-190
A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity
showed a maximum of 340 U l−1 h−1 at a dilution rate of 0.4 h−1. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity
measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation
of olive oil were determined. The maximal biomass output method led to a saturation constant K
S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μmax, of 1.0 h−1. Oxygen uptake rates of up to 2.9 g l−1h−1 were calculated and the yield coefficient, Y
X/O, was determined to be 0.29 g dry cell weight/g O2. From an overall material balance the yield coefficient, Y
X/S, was estimated to be 0.60 g dry cell weight/g olive oil.
Received: 8 January 1997 / Received revision: 30 April 1997 / Accepted: 4 May 1997 相似文献
14.
Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus 总被引:1,自引:1,他引:0
A. A. Tsygankov A. S. Fedorov T. V. Laurinavichene I. N. Gogotov K. K. Rao D. O. Hall 《Applied microbiology and biotechnology》1998,49(1):102-107
The influence of (NH4)2SO4 concentration and dilution rate (D) on actual and potential H2 photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H2 production in a photobioreactor was maximal (approx. 80 ml h−1 l−1) at D = 0.06 h−1 and 4 mM (NH4)2SO4. However, it was lower than the potential H2 evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h−1 l−1 at D = 0.03–0.08 h−1. Taking into account the fact that H2 production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting)
factor should be sought. One possibility is an inhibition of H2 production by the H2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H2 evolution in the vials or from its inhibition by the addition of H2; initial rates were restored in both cases after the vials had been refilled with argon. The actual H2 production in the photobioreactor at D = 0.06 h−1 was shown to increase from approximately 80 ml h−1 l−1 to approximately 100 ml h−1 l−1 under an argon flow at 100 ml min−1. Under maximal H2 production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H2 production and 50% for biomass synthesis.
Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997 相似文献
15.
An extractive membrane biofilm reactor for degradation of 1,3-dichloropropene in industrial waste water 总被引:4,自引:0,他引:4
Katsivela E Bonse D Krüger A Strömpl C Livingston A Wittich RM 《Applied microbiology and biotechnology》1999,52(6):853-862
A bacterial biofilm, capable of mineralising a technical mixture of cis- and trans-1,3-dichloropropene (DCPE), was enriched on the biomedium side of an extractive membrane biofilm reactor (EMBR). The membrane
separates the biomedium from the industrial waste water, in terms of pH, ionic strength and the concentration of toxic chemicals.
The biofilm, attached to a silicone membrane, is able to mineralise DCPE after its diffusion through the membrane. Five bacterial
strains with degradation capabilities were isolated from the metabolically active biofilm and further investigated in batch
experiments. Two of them, Rhodococcus erythropolis strains EK2 and EK5, can grow with DCPE as the sole carbon source. Pseudomonas sp. EK1 utilises cis-3-chloroallylalcohol and cis-3-chloroacrylic acid, whereas the metabolite trans-3-chloroacrylic acid represents a dead-end product of the pathway of this strain. The other two strains, Delftia sp. EK3 and EK4, although unable to grow with DCPE as the carbon source, can transform DCPE and its upper-pathway intermediates
at reasonable conversion rates. They may represent helper functions of the biofilm consortium, which mineralised up to 12.5 mmol
DCPE per hour per gram of biomass protein. Higher feed rates in the EMBR (up to 15 mmol per hour per 100-l bioreactor volume)
and shock loads corresponding to concentrations up to 1.8 mmol l−1 led to a significant increase in the freely floating bacterial biomass in the reactor medium (OD546= 0.2). At the standard operating feed rate of 1.8 mmol h−1, the free biomass concentration was very low (OD546= 0.04).
Received: 23 April 1999 / Received revision: 1 July 1999 / Accepted: 5 July 1999 相似文献
16.
Biotransformation of citronellol by the basidiomycete Cystoderma carcharias in an aerated-membrane bioreactor 总被引:1,自引:0,他引:1
The basidiomycete Cystoderma carcharias transformed citronellol into 3,7-dimethyl-1,6,7-octanetriol as the main product. 3,7-Dimethyl-6,7-epoxy-1-octanol was identified
as important intermediary product of the biotransformation, and the allylic diols 2,6-dimethyl-2-octene-1,8-diol, 3,7-dimethyl-5-octene-1,7-diol
and 3,7-dimethyl-7-octene-1,6-diol were found to be minor products. Microbial formation of rose oxide, a flavour-impact component,
was observed for the first time. The formation of the main products was inhibited by 70% after addition of 0.1 mmol l−1 cytochrome monooxygenase inhibitors. Formation of 3,7-dimethyl-1,6,7-octanetriol was effective in a bioreactor with aeration
over a coil of a hydrophobic microporous polypropene capillary membrane. Production rates of up to 150 mg l−1 day−1 were reached and led to a product concentration of 866 mg l−1 (conversion rate: 52%). The total loss of the added volatile substrate via the exhaust air was 4.5% when this aeration method
was used.
Received: 30 July 1998 / Received revision: 2 November 1998 / Accepted: 7 November 1998 相似文献
17.
E. Kostyál E.-L. Nurmiaho-Lassila J. A. Puhakka M. Salkinoja-Salonen 《Applied microbiology and biotechnology》1997,47(6):734-741
This study deals with combining the biologi cal removal of organic halogens with the removal of nitrogen from bleached kraft
pulp mill wastewater in fluidized-bed reactors under nitrifying and denitrifying conditions. Untreated and biotreated bleached
kraft pulp mill wastewaters had no detrimental effect on nitrification or denitrification. The nitrifying biofilm reactor,
pregrown on synthetic inorganic feed with ammonia, removed without a lag phase adsorbable organic halogens [7.2 mg Cl (g biomass
volatile solids)−1day−1] from bleached kraft pulp mill wastewater and selected chlorophenols from synthetic wastewater. Electron microscopical examination
of the biofilm showed that bacteria, morphologically similar to the nitrifying species Nitrosomonas or Nitrobacter, and Nitrosospira were dominant. The denitrifying fluidized-bed reactor, pregrown on nitrate and methanol, denitrified without a lag phase bleached
kraft pulp mill wastewater. Under denitrifying conditions, 35% of the total organic carbon content of untreated bleached kraft
pulp mill waste water was removed. The reducing power delivered by untreated bleached kraft pulp mill wastewater for denitrification
was 2 mmol electrons/mmol carbon mineralized. Dechlorination under denitrifying conditions was negligible.
Received: 21 November 1996 / Received revision: 27 January 1997 / Accepted: 1 February 1997 相似文献
18.
Bioenergetics and RNA/DNA ratios in the common carp (Cyprinus carpio ) under hypoxia 总被引:2,自引:0,他引:2
Zhou BS Wu RS Randall DJ Lam PK 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2001,171(1):49-57
Hypoxia caused by eutrophication occurs over large areas in aquatic systems worldwide. Common carp (Cyprinus carpio) exposed to hypoxia (1 mg · O2 · l−1 and 2 mg · O2 · l−1) for 1 week showed a significant reduction in feeding rate, respiration rate, faecal production and nitrogenous excretion
compared to those maintained at normoxia (7 mg · O2 · l−1). Fish exposed to hypoxia showed negative scope for growth (SfG), but no significant difference in the specific growth rate
was revealed after 1 week in both hypoxic groups. A significant reduction in RNA/DNA ratio was, however, clearly evident in
the white muscle of the 1 mg · O2 · l−1 treatment group, but not in the 2 mg · O2 · l−1 treatment group. Both specific growth rate and RNA/DNA ratio were significantly reduced when fish were exposed to severe
hypoxia (0.5 mg · O2 · l−1) for 4 weeks. At all levels of hypoxia, growth reduction was accompanied by a significant decrease in RNA/DNA ratio in white
muscle. Covariance analysis showed no significant difference between the slope of RNA/DNA ratio and growth rate under normoxic
conditions and 0.5 mg · O2 · l−1 for 4 weeks (F=1.036, P > 0.326), as well as 1.0 mg · O2 · l−1 and 2.0 mg · O2 · l−1 for 1 week (F = 0.457, P > 0.5), indicating that the RNA/DNA ratio serves as a biomarker of growth under all oxygen levels, at least under controlled
experimental conditions. SfG also appears to be more sensitive than the RNA/DNA ratio in responding to hypoxia in fish.
Accepted: 15 September 2000 相似文献
19.
During the process of producing cassava starch from Manihot esculenta roots, large amounts of cyanoglycosides were released, which rapidly decayed to CN− following enzymatic hydrolysis. Depending on the varying cyanoglycoside content of the cassava varieties, the cyanide concentration
in the wastewater was as high as 200 mg/l. To simulate anaerobic stabilization, a wastewater with a chemical oxygen demand
(COD) of about 20 g/l was prepared from cassava roots and was fermented in a fixed-bed methanogenic reactor. The start-up
phase for a 99% degradation of low concentrations of cyanide (10 mg/l) required about 6 months. After establishment of the
biofilm, a cyanide concentration of up to 150 mg CN−/l in the fresh wastewater was degraded during anaerobic treatment at a hydraulic retention time of 3 days. All nitrogen from
the degraded cyanide was converted to organic nitrogen by the biomass of the effluent. The cyanide-degrading biocoenosis of
the anaerobic reactor could tolerate shock concentrations of cyanide up to 240 mg CN−/l for a short time. Up to 5 mmol/l NH4Cl (i.e. 70 mg N/l = 265 mg NH4Cl/l) in the fresh wastewater did not affect cyanide degradation. The bleaching agent sulphite, however, had a negative effect
on COD and cyanide removal. For anaerobic treatment, the maximum COD space loading was 12 g l−1 day−1, equivalent to a hydraulic retention time of 1.8 days. The COD removal efficiency was around 90%. The maximum permanent cyanide
space loading was 50 mg CN− l−1 day−1, with tolerable shock loadings up to 75 mg CN− l−1 day−1. Under steady-state conditions, the cyanide concentration of the effluent was lower than 0.5 mg/l.
Received: 15 August 1997 / Received revision: 10 October 1997 / Accepted: 14 October 1997 相似文献
20.
Nitrate reduction by Citrobacter diversus under aerobic environment 总被引:17,自引:0,他引:17
A new aerobic denitrifier, Citrobacter diversus, was isolated from both nitrification and denitrification sludge. To monitor the variation in the concentration of nitrogen
oxides, aerobic denitrification by C. diversus was carried out in a batch reactor. When the nitrate concentration was greater than 180 mg N l−1, the nitrate reduction rate became stable. The effect of the C/N ratio on the denitrification activity was also investigated.
The results showed that the optimum denitrification activity was obtained when the C/N ratio was 4–5. The range of the C/N
ratio was higher than that for traditional anoxic denitrification. The effect of the dissolved oxygen concentration was further
studied; and it was found that the range of dissolved oxygen concentrations, both for specific growth rates and for specific
denitrification rates, was 2–6 mg−1. From these results, it can be concluded that both the concentration of dissolved oxygen and the C/N ratio are key factors
in the aerobic denitrification by C. diversus.
Received: 23 November 1999 / Received revision: 4 February 2000 / Accepted: 13 February 2000 相似文献