Effect of low solids retention time and focused pulsed pre-treatment on anaerobic digestion of waste activated sludge

The interacting effects of Focused Pulsed (FP) treatment and solids retention time (SRT) were evaluated in laboratory-scale digesters operated at SRTs of 2-20 days. Anaerobic digestion and methanogenesis of waste activated sludge (WAS) were stable for SRT ? 5 days, but the effluent soluble organic compounds increased significantly for SRT = 2 days due to a combination of faster hydrolysis kinetics and washout of methanogens. FP treatment increased the CH₄ production rate and TCOD removal efficiency by up to 33% and 18%, respectively, at a SRT of 20 days. These effects were the result of an increase in the hydrolysis rate, since the concentrations of soluble components remained low for SRT ? 5 days. Alternately, FP pre-treatment of WAS allowed the same conversion of TCOD to CH₄ with a smaller SRT and digester size: e.g., 40% size savings with a CH₄ conversion of 0.23 g CH₄-COD/g COD_in.     

Vertical distribution of structure and function of the methanogenic archaeal community in Lake Dagow sediment

Detailed studies on the relation of structure and function of microbial communities in a sediment depth profile scarcely exist. We determined as functional aspect the vertical distribution of the acetotrophic and hydrogenotrophic CH4 production activity by measuring production rates and stable 13C/12C-isotopic signatures of CH4 in the profundal sediment of Lake Dagow. The structural aspect was determined by the composition of the methanogenic community by quantifying the abundance of different archaeal groups using 'real-time' polymerase chain reaction and analysis of terminal restriction fragment length polymorphism (T-RFLP). Methane production rates in the surface sediment (0-3 cm depth) were higher in August than in May, but strongly decreased with depth (down to 20 cm). The delta13C of the produced CH4 and CO2 indicated an increase in isotopic fractionation with sediment depth. The relative contribution of hydrogenotrophic to total methanogenesis, which was calculated from the isotopic signatures, increased with depth from about 22% to 38%. Total numbers of microorganisms were higher in August than in May, but strongly decreased with depth. The increase of microorganisms from May to August mainly resulted from Bacteria. The Archaea, on the other hand, exhibited a rather constant abundance, but also decreased with depth from about 1 x 10(8) copies of the archaeal 16S rRNA gene per gram of dry sediment at the surface to 4 x 10(7) copies per gram at 15-20 cm depth. T-RFLP analysis combined with phylogenetic analysis of cloned sequences of the archaeal 16S rRNA genes showed that the methanogenic community consisted mainly of Methanomicrobiales and Methanosaetaceae. The relative abundance of Methanosaetaceae decreased with depth, whereas that of Methanomicrobiales slightly increased. Hence, the vertical distribution of the functional characteristics (CH4 production from acetate versus H2/CO2) was reflected in the structure of the community consisting of acetotrophic (Methanosaetaceae) versus hydrogenotrophic (Methanomicrobiales) phenotypes.     

Fractionation of proteins and carbohydrates of extracellular polymeric substances in a membrane bioreactor system

The major operational problem associated with membrane bioreactors (MBR) is membrane fouling, for which extracellular polymeric substances (EPS) are primarily responsible. In this work both the soluble and bound EPS (i.e. SMP and EPS) produced in an MBR system operating under sludge retention times (SRT) of 10, 15, 20 and 33 days were fractionized by means of membranes having variable molecular weight cutoffs (300 kDa, 100 kDa, 10 kDa & 1 kDa). The results show that increasing the SRT leads to a reduction of SMP and EPS and that these reductions are more pronounced for the SRTs in the range 10–20 days. This reduction is more significant for carbohydrates than for proteins. The decrease of SMP and EPS with increasing SRT from 10 to 20 days led to a significant decrease of the level of fouling. The further increase of SRT to 33 days did not significantly impact on the level of fouling as the SMP and EPS concentrations did not change much.     

Anaerobic acidogenesis of primary sludge: the role of solids retention time

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate. (c) 1994 John Wiley & Sons, Inc.     

基于交叉抚育的雌性根田鼠对雄鼠尿气味的识别

通过交叉抚育建立同巢同胞、同巢非同胞、异巢同胞和异巢非同胞个体组成的室内繁殖种群,在断奶后（80日龄）分别取这些供体的新鲜尿作刺激物,在吕字型观察箱中观察和记录雌性根田鼠对雄鼠气味的行为响应,以研究根田鼠同胞识别的化学通讯机制。结果表明：（1）成年雌性根田鼠对雄性同巢同胞气味的接近潜伏期极显著短于对同巢非同胞气味的接近潜伏期（P〈0.01）,而其对两者的访问时间和嗅舔时间之间的差异并不显著（P〉0.05）;（2）雌鼠对雄性异巢同胞和异巢非同胞气味无明显偏好。其对两者的接近潜伏期、访问时间和嗅舔时间等行为响应均无显著差异（P〉0.05）;（3）雌鼠对雄性同巢非同胞和异巢非同胞的接近潜伏期差异并不明显（P〉0.05）,对两者访问时间和嗅舔时间的差别不大（P〉0.05）;（4）比较雌鼠对异巢同胞和同巢同胞气味的行为响应发现,其对后者的接近潜伏期显著短于前者（P〈0.05）,其对两者访问时间、嗅舔时间之间的差异未达到显著水平（P〉0.05）。这些结果表明,80日龄时,雌性根田鼠具有亲属识别能力,其同胞识别的机制可能为共生熟悉和表型匹配两种模式协同作用。     

T-cell subsets of the encephalitis induced by the superantigen Staphylococcal Enterotoxin A (SEA) in the Lewis rat: An immunohistochemical investigation

In the present investigation, T-cell subsets of the previously described superantigen-induced encephalitis [9] have been investigated in 16 Lewis rats in comparison with four controls. Three days after intracerebral injection of Staphylococcal Enterotoxin A (SEA) or saline, 1.5 × 10⁷ ConA-activated splenocytes were loaded i.v. animals were sacrificed after 0.5, 3 or 5 days, followed by immunohistochemical investigation of CD3, CD4 and CD8. Pronounced perivascular cuffing was identified 0.5 days after splenocyte injection and declined thereafter. The majority of the perivascular round cells consisted of CD8+ T-cells (65%) and CD4+ T-cells (10%). Less than 20% of the perivascular round cells were CD3+. The reduced expression of CD3 relative to e.g. CD8 is presumably due to the previous superantigenic stimulus. The presented data may be of relevance for the pathogenesis of infectious or autoimmune encephalitis, e.g. in multiple sclerosis.     

Effect of temperature on carbon and electron flow and on the archaeal community in methanogenic rice field soil

Temperature is an important factor controlling CH(4) production in anoxic rice soils. Soil slurries, prepared from Italian rice field soil, were incubated anaerobically in the dark at six temperatures of between 10 to 37 degrees C or in a temperature gradient block covering the same temperature range at intervals of 1 degrees C. Methane production reached quasi-steady state after 60 to 90 days. Steady-state CH(4) production rates increased with temperature, with an apparent activation energy of 61 kJ mol(-1). Steady-state partial pressures of the methanogenic precursor H(2) also increased with increasing temperature from <0.5 to 3.5 Pa, so that the Gibbs free energy change of H(2) plus CO(2)-dependent methanogenesis was kept at -20 to -25 kJ mol of CH(4)(-1) over the whole temperature range. Steady-state concentrations of the methanogenic precursor acetate, on the other hand, increased with decreasing temperature from <5 to 50 microM. Simultaneously, the relative contribution of H(2) as methanogenic precursor decreased, as determined by the conversion of radioactive bicarbonate to (14)CH(4), so that the carbon and electron flow to CH(4) was increasingly dominated by acetate, indicating that psychrotolerant homoacetogenesis was important. The relative composition of the archaeal community was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16S rRNA genes (16S rDNA). T-RFLP analysis differentiated the archaeal Methanobacteriaceae, Methanomicrobiaceae, Methanosaetaceae, Methanosarcinaceae, and Rice clusters I, III, IV, V, and VI, which were all present in the rice field soil incubated at different temperatures. The 16S rRNA genes of Rice cluster I and Methanosaetaceae were the most frequent methanogenic groups. The relative abundance of Rice cluster I decreased with temperature. The substrates used by this microbial cluster, and thus its function in the microbial community, are unknown. The relative abundance of acetoclastic methanogens, on the other hand, was consistent with their physiology and the acetate concentrations observed at the different temperatures, i.e., the high-acetate-requiring Methanosarcinaceae decreased and the more modest Methanosaetaceae increased with increasing temperature. Our results demonstrate that temperature not only affected the activity but also changed the structure and the function (carbon and electron flow) of a complex methanogenic system.     

Simulated resistance training, but not alendronate, increases cortical bone formation and suppresses sclerostin during disuse

Mechanical loading modulates the osteocyte-derived protein sclerostin, a potent inhibitor of bone formation. We hypothesized that simulated resistance training (SRT), combined with alendronate (ALEN) treatment, during hindlimb unloading (HU) would most effectively mitigate disuse-induced decrements in cortical bone geometry and formation rate (BFR). Sixty male, Sprague-Dawley rats (6-mo-old) were randomly assigned to either cage control (CC), HU, HU plus either ALEN (HU+ALEN), or SRT (HU+SRT), or combined ALEN and SRT (HU+SRT/ALEN) for 28 days. Computed tomography scans on days -1 and 28 were taken at the middiaphyseal tibia. HU+SRT and HU+SRT/ALEN rats were subjected to muscle contractions once every 3 days during HU (4 sets of 5 repetitions; 1,000 ms isometric + 1,000 ms eccentric). The HU+ALEN and HU+SRT/ALEN rats received 10 μg/kg ALEN 3 times/wk. Compared with the CC animals, HU suppressed the normal slow growth-induced increases of cortical bone mineral content, cortical bone area, and polar cross-sectional moment of inertia; however, SRT during HU restored cortical bone growth. HU suppressed middiaphyseal tibia periosteal BFR by 56% vs. CC (P < 0.05). However, SRT during HU restored BFR at both periosteal (to 2.6-fold higher than CC) and endocortical (14-fold higher than CC) surfaces (P < 0.01). ALEN attenuated the SRT-induced BFR gains during HU. The proportion of sclerostin-positive osteocytes in cortical bone was significantly higher (+121% vs. CC) in the HU group; SRT during HU effectively suppressed the higher proportion of sclerostin-positive osteocytes. In conclusion, a minimum number of high-intensity muscle contractions, performed during disuse, restores cortical BFR and suppress unloading-induced increases in sclerostin-positive osteocytes.     

离心力对制备沉积物间隙水中化合物浓度的影响

研究了离心力对间隙水化合物浓度的影响.将腐殖质掺入东湖沉积物样品,按泥:水=1:4(体积)比室温下静置30d,随后掺入铜,泥:水=1:4(体积)比静置10d,得到总有机碳含量在1.47%-.72%、铜含量在120-2700mg/kg(干重)的试验沉积物样品,用离心法制备沉积物中的间隙水.离心参数为3000r/min、200r/min、9000r/min、1000r/min和12000r/min,4 ℃下离心20min.间隙水中化合物浓度分析表明,随离心力升高,间隙水中铜、铁、总有机碳(TOC)含量逐渐降低,钙的含量略有增加,而锰的含量不受离心力变化的影响.根据上述分析结果,确定在腐殖质对沉积物中铜的毒性影响研究中,制备沉积物间隙水的适宜离心条件为:12000r/min、4℃下离心20min.       

Nucleopolyhedrovirus infection and/or parasitism by Microplitis pallidipes affected haemolymph titre of 20‐hydroxyecdysone in Spodoptera exigua larvae

This study examined the physiological effects of joint and separate parasitism and infection by the endoparasitoid Microplitis pallidipes Szépligeti and the nucleopolyhedrovirus (NPV), respectively, on haemolymph 20‐hydroxyecdysone (20‐E) titre in Spodoptera exigua (Hübner) larvae. The results indicated that in parasitized larvae, virus‐infected larvae (5.7 × 10³ and 5.7 × 10⁵ OB/ml) and parasitized larvae infected with virus at 5.7 × 10⁵ OB/ml, compared to healthy larvae, the 20‐E all declined during the first 3 days but began to increase from day 4 after treatment, while in jointly parasitized and infected larvae (5.7 × 10³ OB/ml), the 20‐E declined during the first 4 days but began to increase on day 5 after treatment. Meanwhile, compared to parasitized larvae, the 20‐E declined during the first 4 days but significantly increased on day 5 in jointly parasitized and infected larvae (5.7 × 10³ OB/ml), while significantly increased during the first 2 days but began to decrease from day 3 after treatment in jointly parasitized and infected larvae (5.7 × 10⁵ OB/ml). Finally, in larvae that were both parasitized and virus infected (5.7 × 10³ OB/ml), compared to just virus‐infected larvae (5.7 × 10³ OB/ml), the 20‐E was lower on days 3 and 4 but higher on other days after treatment; in larvae that were both parasitized and virus infected (5.7 × 10⁵ OB/ml), compared to just virus‐infected larvae (5.7 × 10⁵ OB/ml), the 20‐E was significantly higher at the first 2 days but lower from day 3 after treatment. Our results revealed that 2nd instar larval M. pallidipes in host bodies may release 20‐E into the haemolymph of S. exigua larvae and that NPV infection may stimulate S. exigua to release more 20‐E during its third to fourth instar larval moulting. We found that this stimulatory effect was greater with higher virus concentrations.     

贮藏时间对银杏花粉保护酶活性和萌发率的影响

研究了室温贮藏对银杏花粉萌发率及超氧化物歧化酶(Superoxide dismutase,SOD)、过氧化物酶(Peroxi-dase,POD)、过氧化氢酶(Catalase,CAT)活性的影响。结果表明,随着贮藏时间的延长,花粉萌发率由88．89％降到15．76％;贮藏15d之后超氧化物歧化酶活性降低了80％;过氧化物酶活性减少到原来的10％;过氧化氢酶活性也减少了70％。在室温贮藏条件下萌发率随保护酶活性的下降而降低。POD酶对花粉萌发率的影响比SOD、CAT酶显著。     

Estimation of extremely small field radiation dose for brain stereotactic radiotherapy using the Vero4DRT system

The purpose of this study was a dosimetric validation of the Vero4DRT for brain stereotactic radiotherapy (SRT) with extremely small fields calculated by the treatment planning system (TPS) iPlan (Ver.4.5.1; algorithm XVMC). Measured and calculated data (e.g. percentage depth dose [PDD], dose profile, and point dose) were compared for small square fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm² using ionization chambers of 0.01 or 0.04 cm³ and a diamond detector. Dose verifications were performed using an ionization chamber and radiochromic film (EBT3; the equivalent field sizes used were 8.2, 8.7, 8.9, 9.5, and 12.9 mm²) for five brain SRT cases irradiated with dynamic conformal arcs.The PDDs and dose profiles for the measured and calculated data were in good agreement for fields larger than or equal to 10 × 10 mm² when an appropriate detector was chosen. The dose differences for point doses in fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm² were +0.48%, +0.56%, −0.52%, and +11.2% respectively. In the dose verifications for the brain SRT plans, the mean dose difference between the calculated and measured doses were −0.35% (range, −0.94% to +0.47%), with the average pass rates for the gamma index under the 3%/2 mm criterion being 96.71%, 93.37%, and 97.58% for coronal, sagittal, and axial planes respectively.The Vero4DRT system provides accurate delivery of radiation dose for small fields larger than or equal to 10 × 10 mm².     

Growth and survival of uninjured and sublethally heat-injured Escherichia coli O157:H7 on beef extract medium as influenced by package atmosphere and storage temperature.

The effect of atmospheric composition and storage temperature on growth and survival of uninjured and sublethally heat-injured Escherichia coli O157:H7, inoculated onto brain heart infusion agar containing 0.3% beef extract (BEM), was determined. BEM plates were packaged in barrier bags in air, 100% CO2, 100% N2, 20% CO2: 80% N2, and vacuum and were stored at 4, 10, and 37 degrees C for up to 20 days. Package atmosphere and inoculum status (i.e., uninjured or heat-injured) influenced (P < 0.01) growth and survival of E. coli O157:H7 stored at all test temperatures. Growth of heat-injured E. coli O157:H7 was slower (P < 0.01) than uninjured E. coli O157:H7 stored at 37 degrees C. At 37 degrees C, uninjured E. coli O157:H7 reached stationary phase growth earlier than heat-injured populations. Uninjured E. coli O157:H7 grew during 10 days of storage at 10 degrees C, while heat-injured populations declined during 20 days of storage at 10 degrees C. Uninjured E. coli O157:H7 stored at 10 degrees C reached stationary phase growth within approximately 10 days in all packaging atmospheres except CO2. Populations of uninjured and heat-injured E. coli O157:H7 declined throughout storage for 20 days at 4 degrees C. Survival of uninjured populations stored at 4 degrees C, as well as heat-injured populations stored at 4 and 10 degrees C, was enhanced in CO2 atmosphere. Survival of heat-injured E. coli O157:H7 at 4 and 10 degrees C was not different (P > 0.05). Uninjured and heat-injured E. coli O157:H7 are able to survive at low temperatures in the modified atmospheres used in this study.     

Effects of delayed and extended antioxidant treatment on acute acoustic trauma

Abstract

Objective: Hair cell death caused by acute acoustic trauma (AAT) reaches a secondary maximum at 7–10 days after noise exposure due to a second oxidative stress. Therefore, this study tested the effects of a combination of hydroxylated alpha-phenyl-tert-butylnitrone (4-OHPBN), N-acetyl-L-cysteine (NAC) and acetyl-L-carnitine (ALCAR) on AAT when the duration of treatment was extended over the period of 7–10 days after noise exposure as well as when the initial treatment was delayed 24 to 48 h after noise exposure. Methods: Thirty chinchilla were exposed to a 105 dB octave-band noise centred at 4 kHz for 6 h and received the following treatments: (1) noise + saline (2–5) 4-OHPBN (20 mg/kg) + NAC (50 mg/kg) + ALCAR (20 mg/kg) intraperitoneally injected beginning 24 or 48 h after noise exposure twice daily for the next 2, 8 or 9 days. Auditory brainstem response (ABR) threshold shifts, outer hair cell (OHC) counts and organ of Corti immunohistochemistry were analyzed. Results: The combination administration decreased ABR threshold shifts, inhibited OHC loss and reduced 4-hydroxynonenal (4-HNE) immunostaining. Significant decreases in the threshold shifts and reduction in OHC loss were observed with a shorter delay before starting treatment (24 h) and longer duration (9 days) treatment. Conclusions: These results demonstrate that the administration of antioxidant drugs extended up to 10 days after noise exposure can effectively treat AAT in a chinchilla model. This may provide significant and potentially clinically important information about the effective therapeutic window for AAT treatment.     

Auditory-Motor Mapping Training: Comparing the Effects of a Novel Speech Treatment to a Control Treatment for Minimally Verbal Children with Autism

This study compared Auditory-Motor Mapping Training (AMMT), an intonation-based treatment for facilitating spoken language in minimally verbal children with autism spectrum disorder (ASD), to a matched control treatment, Speech Repetition Therapy (SRT). 23 minimally verbal children with ASD (20 male, mean age 6;5) received at least 25 sessions of AMMT. Seven (all male) were matched on age and verbal ability to seven participants (five male) who received SRT. Outcome measures were Percent Syllables Approximated, Percent Consonants Correct (of 86), and Percent Vowels Correct (of 61) produced on two sets of 15 bisyllabic stimuli. All subjects were assessed on these measures several times at baseline and after 10, 15, 20, and 25 sessions. The post-25 session assessment timepoint, common to all participants, was compared to Best Baseline performance. Overall, after 25 sessions, AMMT participants increased by 19.4% Syllables Approximated, 13.8% Consonants Correct, and19.1% Vowels Correct, compared to Best Baseline. In the matched AMMT-SRT group, after 25 sessions, AMMT participants produced 29.0% more Syllables Approximated (SRT 3.6%);17.9% more Consonants Correct (SRT 0.5); and 17.6% more Vowels Correct (SRT 0.8%). Chi-square tests showed that significantly more AMMT than SRT participants in both the overall and matched groups improved significantly in number of Syllables Approximated per stimulus and number of Consonants Correct per stimulus. Pre-treatment ability to imitate phonemes, but not chronological age or baseline performance on outcome measures, was significantly correlated with amount of improvement after 25 sessions. Intonation-based therapy may offer a promising new interventional approach for teaching spoken language to minimally verbal children with ASD.     

Activity, structure and dynamics of the methanogenic archaeal community in a flooded Italian rice field

Methane production was studied in an Italian rice field over two consecutive years (1998, 1999) by measuring the rates of total and acetate-dependent methanogenesis in soil and root samples. Population dynamics of methanogens were followed by terminal restriction fragment length polymorphism and real-time PCR targeting archaeal SSU rRNA genes. Rates of total and acetate-dependent methanogenesis in soil increased during the season, reached a maximum at about 70-80 days after flooding and then decreased again. In contrast, the size of the archaeal community remained relatively constant. Therefore, the seasonal changes in the methanogenic processes were probably not caused by changes in the size of the methanogenic community but in its activity. During the 1998/1999 winter period, a slight decrease in archaeal cell numbers was found. In both years, the dominant groups were methanogens affiliated with Rice cluster I, Methanosaetaceae, Methanosarcinaceae and Methanobacteriaceae. Correspondence analysis showed, however, that the archaeal community structure was different in 1998 and 1999. Methanogens with potential acetoclastic activity made up a larger fraction of the total archaeal community in 1999 (32-53%) than in 1998 (20-32%). Furthermore, the frequency of Methanosaetaceae relative to Methanosarcinaceae was significantly higher in 1999 than in 1998. This difference could be explained by the much lower soil acetate concentrations in 1999, to which Methanosaetaceae are physiologically better adapted than Methanosarcinaceae. Over the season, however, the composition of the archaeal community remained relatively constant and thus did not reflect the observed seasonal change in CH(4) production activity. The analysis of rice root samples in 1999 showed that the archaeal community structure on the roots was similar to that in soil but with acetoclastic methanogens being relatively less common. This observation is in agreement with domination of CH(4) production by H(2)/CO(2)-dependent methanogenesis on roots. Our study provided a link between size, structure and function of the methanogenic community in an Italian rice field.     

Effect of progesterone on basal LH and episodic LH and FSH secretion in heifers

Heifers between Days 6 and 10 of the cycle were allocated at random to groups of 8 and treated with (i) a 4% progesterone-releasing intravaginal device (PRID) + oestrogen capsule for 12 days; (ii) 4% PRID for 12 days; (iii) 20% PRID for 12 days; (iv) 4% for 14 days; or (v) 20% PRID for 14 days. Blood was obtained daily during treatment and at 2- or 4-h intervals for 72 h after removal of PRIDs. Some animals were sampled every 20 min for 4.676 h on the 3rd day after PRID insertion, and 1 day before and 36 h after removal of the PRID insertion, and 1 day before and 36 h after removal of the PRID. During progesterone treatment there was: (i) no correlation between concentrations of progesterone and LH within days; (ii) a significant negative correlation between progesterone and days (P less than 0.01) and also between progesterone and LH over days (P less than 0.01); (iii) the overall correlation co-efficient between LH and days was positive (P less than 0.05). The amplitude of LH or FSH episodes was not affected as progesterone concentrations declined during PRID treatment, but the number of LH (but not FSH) episodes was increased (p less than 0.01). After PRID removal, the amplitude of both LH and FSH episodes increased (P less than 0.01). We suggest that progesterone is part of a negative feedback complex on LH secretion in cattle and that this effect is apparently mediated through frequency of episodic LH release.     

Influence of sludge retention time on tolerance of copper toxicity for polyphosphate accumulating organisms linked to polyhydroxyalkanoates metabolism and phosphate removal

This study explored the influence of sludge retention time (SRT) on tolerance of copper invasion for polyphosphate accumulating organisms (PAOs) in an enhanced biological phosphorus removal (EBPR). The experimental data showed the anaerobic polyhydroxyalkanoates (PHA) storage for the sludge at 10d SRT was less influenced by copper invasion than those at 5d and 15d SRTs. The reaction of PAOs aerobically taking up phosphate for the sludge at 5d or 15d SRT almost ceased at 2 mg Cu L⁻¹, whereas PAOs in the sludge at 10d SRT retained half of the ability to take up phosphate. Both the PHAs degradation and synthesis rates decreased with increasing copper concentration, regardless of the SRTs. However, the copper inhibition of the former was greater than that of the later.