The acute effects of erythromycin and oxytetracycline on enhanced biological phosphorus removal system: shift in bacterial community structure.

Since extensive application, an increasing amount of antibiotics has been released into wastewater treatment plants. In this study, the enhanced biological phosphorus removal (EBPR) system was fed with synthetic wastewater containing erythromycin (ERY) and oxytetracycline (OTC) for 7 days to evaluate the variations of solution ortho-P (SOP), volatile fatty acid (VFA), poly-bhydroxyalkanoates (PHAs), specific oxygen uptake rater (SOUR), and microbial community in the EBPR system. The obtained results showed that the P-removal efficiency decreased to 0.0%, and at the end of the experiment, only less than 20% of the VFA could be consumed. Besides, the variable processes of P and PHAs were destroyed. Moreover, to better grasp the inhibitory mechanism of antibiotics, microbial community compositions of activated sludge sampled in all reactors were investigated by high-throughput sequencing techniques. Results of comparative and evolutionary analysis revealed that high concentrations (5 and 10 mg/L) of ERY and OTC could seriously shift microbial communities, while combined antibiotics could induce more. Additionally, Accumulibacter and Competibacter were two primary microorganisms at the genus level in the EBPR system. Accumulibacter decreased seriously for exposure to antibiotics, while Competibacter increased in all experimental reactors especially in combined antibiotics reactor.

Understanding the performance of microbial community induced by ZnO nanoparticles in enhanced biological phosphorus removal system and its recoverability.

In this study, the impacts of ZnO Nanoparticles (NPs) on the microbial community in enhanced biological phosphorus removal (EBPR) system and its recoverability were investigated. High-throughput sequencing was applied to study the microbial community shift. Results show that the species richness in the EBPR system was reduced under the condition of ZnO NPs with high concentration (above 6mg/L). Evolution analysis suggests that higher concentration ZnO NPs induced more microbial community shift. According to the analysis on genus level, Competibacter was more impressionable than Accumulibacter after exposure to 2mg/L ZnO NPs. Nonetheless, this phenomenon could not be found as the concentration of ZnO NPs got higher (above 6mg/L). Accumulibacter could reach to the initial level after recover for 20days, whereas Competibacter could not recover even when the concentration of ZnO NPs was only 2mg/L. Interestingly, although the phosphorus removal (P-removal) process was re-achieved, the microbial community in reactors was irreversible.

Short-term performance of enhanced biological phosphorus removal (EBPR) system exposed to erythromycin (ERY) and oxytetracycline (OTC).

The effects of Erythromycin (ERY) and oxytetracycline (OTC), including individual and combinative effect, on enhanced biological phosphorus removal (EBPR) system within a short-term (24h) were evaluated in this study. Results showed that the P-removal efficiency decreased to 34.6% and 0.0% under the effect of ERY (10mg/L) and OTC (10mg/L) for 24h. OTC concentration higher than 5mg/L was sufficient to cause serious adverse impact on the EBPR performance. While the performance of EBPR system will be impacted by ERY above 10mg/L. OTC, due to its special antibacterial action to the gram-negative bacteria which most PAOs belong to, has more serious negative effect on the EBPR performance than ERY does. Moreover, in the combined antibiotics test, neither synergistic nor antagonistic effect was detected between ERY and OTC. Finally, ERY (10mg/L) and OTC (10mg/L) could inhibit the microorganisms' activity, while couldn't induce serious microorganisms death within 24h.

Long-term effect of low concentration Cr(VI) on P removal in granule-based enhanced biological phosphorus removal (EBPR) system.

In light of the fact that most wastewater in China contained both industrial and domestic wastewater, a 52-d systematical investigation was conducted on the long-term effect of low concentration Cr(VI) (0.3-0.8 mg L(-1)) on P removal performance of granule-based EBPR system in this study. The mechanisms were likewise discussed. Results showed that high Cr(VI) concentration (⩾0.5 mg L(-1)) could significantly inhibit P removal, while this phenomenon was not found when Cr(VI) concentration was less than (or equal to) 0.4 mg L(-1). Most of the granules was disintegrated and filamentous bacteria overgrew inducing sludge bulking occurred at 0.7 mg L(-1) Cr(VI). During the exposure test, the abundance of poly-phosphate-accumulating organisms (PAOs) significantly decreased while the populations of glycogen accumulating organisms (GAOs) and other bacteria increased. Both production and degradation of poly-ß-hydroxyakanoates (PHAs) were apparently inhibited. An improved polysaccharide/protein (PS/PN) ratio was observed with the increasing Cr(VI) concentration, implying excessive polysaccharide was secreted by microorganisms to support its resistance to the toxicity of Cr(VI). Besides, good linear regression between PS/PN ratio and the granule size (R(2)=-0.86, p<0.01) was obtained, indicating that high PS/PN was adverse to granule stability. Correlation analysis indicated that the accumulation of granules intracellular Cr was directly responsible for the observed inhibitory effect on P removal process. The long-term Cr(VI) treatment had irreversible effects on granule-based EBPR system as it could not revive after a 16-d recovery process.

The effect of COD loading on the granule-based enhanced biological phosphorus removal system and the recoverability.

In this study, the effect of varied COD loading (200, 400, 500, 600 and 800 mg L(-1)) on stability and recoverability of granule-based enhanced biological phosphorus removal (EBPR) system was investigated during continuously 53-d operation. Results showed that COD loading higher than 500 mg L(-1) could obviously deteriorate the granular EBPR system and result in sludge bulking with filamentous bacteria. High COD loading also changed the transformation patterns of poly-ß-hydroxyalkanoates (PHAs) and glycogen in metabolism process of polyphosphate-accumulating organisms (PAOs) and inhibited the EPS secretion, which completely destroyed the stability and integrality of granules. Results of FISH indicated that glycogen-accumulating organisms (GAOs) and other microorganisms had a competitive advantage over PAOs with higher COD loading. The community composition and EBPR performance were recovered irreversibly in long time operation when COD loading was higher than 500 mg L(-1).

Inhibition of free ammonia to the granule-based enhanced biological phosphorus removal system and the recoverability.

The inhibition of free ammonia (FA) to the granule-based enhanced biological phosphorus removal (EBPR) system and the recoverability from macro- to micro-scale were investigated in this study. FA was found to seriously deteriorate the EBPR performance and sludge characteristic (settleability and morphology). The FA inhibitory threshold of 17.76 mg NL(-1) was established. Acclimation phenomenon took place when poly-phosphate accumulating organisms (PAOs) were exposed for long time to constant FA concentration (8.88 mg NL(-1)). The repressed polysaccharides excretion could lead to breaking the stability and integrity of the granules. Therefore, the reduced particle size and granule disintegration were observed. The molecular analysis revealed that FA had a significant influence on the microbial communities and FA inhibition may provide a competitive advantage to glycogen accumulating organisms (GAOs) over PAOs. Interestingly, the community composition was found irreversible by recovery (Dice coefficients, 36.3%), although good EBPR performance was re-achieved.

The long-term effect of nitrite on the granule-based enhanced biological phosphorus removal system and the reversibility.

This study investigated the long-term effect of nitrite on the granule-based enhanced biological phosphorus removal (EBPR) system and the reversibility from macro- to micro-scale. Nitrite was found to seriously deteriorate the EBPR performance and result in severe sludge bulking. The inhibited polysaccharides excretion could lead to breaking the stability and integrity of the granules. Therefore, the reduced particle size and granule disintegration were observed. In this study, granules with lower ratio of proteins to polysaccharides (1.76) had better structure and function than the higher (3.84). Experimental results demonstrated that the microbial community structure was largely changed due to the presence of nitrite. In comparison, glycogen accumulating organisms (GAOs) had stronger resistibility and higher recovery rate than poly-phosphate accumulating organisms (PAOs). Interestingly, the community composition was unable to recover (Dice coefficients, 33.0%), although good EBPR performance was achieved only by propagating other types of PAOs.

[Effect of mixed carbon sources in the granulation process of EBPR system].

Activated sludge highly enriched of phosphorus accumulating organisms (PAOs) were seeded, and cultivated with mixed carbon sources of different propionate to acetate ratios, to obtain granule-based enhanced biological phosphorus removal (EBPR) system. The results showed that the granule growth rate was obviously increased as the proportion of propionate in the mixed carbon sources increased. After operating for 90 d, the volume average particle diameters of the mature granules were 550.64 microm, 599.41 microm, 642.38 microm, 680.99 microm and 745.08 microm, and the sludge volume indexes (SVI) of the mature granules were 30 mL x g(-1), 40 mL x g(-1), 50 mL x g(-1), 60 mL x g(-1) and 75 mL x g(-1), in the treatment of 0%, 25%, 50%, 75% and 100% propionate in mixed carbon sources, respectively. The phosphorus (P) removal performances of granule-based EBPR system cultivated with different carbon sources showed significant differences under the same P-loading. It was about 0.78 mg x g(-1), 2.29 mg x g(-1), 2.96 mg x g(-1), 3.23 mg x g(-1) and 3.77 mg x g(-1) of net P removed in the treatment of 0%, 25%, 50%, 75% and 100% propionate in mixed carbon sources, respectively, which resulted in the phosphorus removal efficiencies were 31.5%, 56.5%, 77.4%, 85.9% and 97.0%, respectively.

Effect of oligochaete worm body fluids on biological phosphorus removal in a bench-scale EBPR system.

During waste sludge reduction by oligochaetes, phosphorus (P) concentrations in the effluent have been noticed to increase. In the current study, batch experiments were carried out in order to provide explanations for this phosphorus release. The results indicated that increase in effluent phosphorus concentration might not be directly linked to the phosphorus in worm body fluids, as the phosphorus concentration in the system at the start of each operational period did not change significantly. However, the phosphorus removal efficiency rapidly dropped from 93.9% +/- 1.9% to 62.2% +/- 1.3% with increasing addition ofoligochaete worm body fluids. Furthermore, an increase in worm body fluids induced a remarkable enhancement ofanaerobic phosphorus release rate as well as anaerobic storage of poly-beta-hydroxyalkanoate (PHA). At a worm density (wet weight) of 14.4 g/L, the anaerobic phosphorus release rate was elevated by 31.1% +/- 2.8% and 57.3% +/- 4.6% at 2.5% and 5.0% worm death rate, respectively, compared with the control. The contribution of worm body fluids to PHA production was 39.3-67.7 mg/g of dead worm (wet weight), which was mainly attributed to the extra synthesis of poly-beta-hydroxyvalerate (PHV). Unfortunately, in the concomitant aerobic stage, inhibition of 3-hydroxybutyric acid (PHB) oxidation and ammonia utilization was observed along with the increasing addition of worm body fluids. Meanwhile, nitrite elevation was found at the beginning of the aerobic stage, which might be negative to the aerobic metabolic processes performed by phosphate-accumulating organisms (PAOs), namely PHB oxidation, phosphate uptake and ammonia utilization for biomass growth.

Impact of Cr(VI) on P removal performance in enhanced biological phosphorus removal (EBPR) system based on the anaerobic and aerobic metabolism.

Influence of Cr(VI) on P removal in enhanced biological phosphorus removal (EBPR) system was investigated with respect to the composition of poly-phosphate-accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), the transformation of poly-ß-hydroxyalkanoates (PHA) and glycogen, enzymes' activities, and the intracellular Cr. Whether EBPR system could revive after Cr(VI) shock was also explored. Results showed P removal performance was completely inhibited by Cr(VI) with the concentration more than 5 mg L(-1). PAOs were more sensitive to Cr(VI) than GAOs and the other bacteria were. PHA consumption, glycogen synthesis and adenylate kinase's activity had been inhibited by 5 mg L(-1) Cr(VI). Both adenylate kinase's activity and P removal efficiency were negatively correlated with the intracellular Cr. Recovery experiments revealed that P removal performance with 5 mg L(-1) Cr(VI) shock could revive after a 2-day recovery treatment, while systems with high level Cr(VI) (20 and 60 mg L(-1)) shock could not.

[Effects of composite substrates on the phosphorus removal in granule-based EBPR system and its optimization experiment].

Based on the mature granular sludge, effects of composite substrates [m(C)/m(N)/m (P)] on the process of phosphorus removal in granule-based EBPR system was conducted by the optimal mixed-carbon sources ratio. Results showed that it was observed with the expanded filamentous bulking to granular sludge in the system of R2 [m(C)/m(N)/m (P) = 400:10:5], R3 [m(C)/m(N)/m (P) = 600: 10:10] and R5 [m(C)/m(N)/m (P) = 400:20:15]. The presence of large amount of granular fragments led to the poor performance of R6 [m(C)/m(N)/m (P) =600:20:5], and it returned back after the particulate debris was removed off the system. The particle size of R3, R8 [m(C)/m(N)/m (P) = 400:30:10] and R9 [m(C)/m(N)/m (P) = 600:30:15)] gradually decreased from 0.8 mm to 0.3 mm, and other systems were similar to the initial size. More than 95 percent of the COD was consumed in the anaerobic stage in R1 [m(C)/m(N)/m (P) = 200:10:15], R4 [m(C)/m(N)/m (P) = 200:20:10] and R7 [m(C)/m(N)/m (P) = 200:30:5], and the phosphorus release/uptake rates fluctuated within the range of 60-100 mg x (g x h)(-1), 60-80 mg x (g x h)(-1) and 40-60 mg x (g x h)(-1), respectively. However, the COD consumption was mainly occurred in aerobic stage in other systems, and the phosphorus release/uptake rates gradually declined, even decreased to 0 mg x (g x h)(-1). Phosphate removal rate of each system was (from R1 system to R9 system) 83.5%, 52.8%, 7.1%, 96.7%, 19.7%, 72.2%, 79.7%, 28.1% and 48.7%, respectively. Finally, we also found that the optimal composite substrate condition for the granule-based EBPR system was the ratio of the m(C)/ m(N)/m (P) = 200:20: 15.

Simultaneous sludge reduction and nutrient removal (SSRNR) with interaction between Tubificidae and microorganisms: a full-scale study.

A symbiotic ecosystem between Tubificidae and microorganisms was established at a full-scale wastewater treatment plant (WWTP). In this ecosystem Tubificidae were inoculated, and then adhered to the outer layers of carrier materials in an oxidation tank. During the long-term treatment of sewage volumes of 20,000 m(3)d(-1), the excess sludge production rate was reduced from 0.21 to 0.051 kg m(-3) and sludge settleability was significantly improved. When the influent concentrations of COD, NH(4)(+)-N, PO(4)(-)-P, and SS were in the ranges of 130.0-459.0 mg L(-1), 14.2-27.5 mg L(-1), 1.6-7.0 mg L(-1), and 60.0-466.0 mg L(-1), respectively, the COD and SS removal efficiency was increased by 8.7% and 13.6% within the symbiotic system compared to the control without Tubificidae. In addition, NH(4)(+)-N and phosphorus removal efficiency can also be improved. The results showed that both sludge reduction and nutrient removal were enhanced simultaneously significantly within the system utilizing the symbiotic interactions of Tubificidae and microorganisms.

[Effects of C/P on the competition between PAOs and GAOs and PHAs metabolism in EBPR system].

Based on accumulating enrich phosphorus accumulating organisms (PAOs) in activated sludge and by fluorescence in situ hybridization (FISH) technique, the effects of C/P (25: 1, 20: 1, 15: 1 and 10: 1) on flora changes and polyhydroxyalkanoates (PHAs) metabolism in enhanced biological phosphorus removal (EBPR) system were systematically studied. The results show that after 10 days treatment (acetate as carbon source), the systems with C/P of 25: 1, 20: 1 and 15: 1 have good phosphate removal rate (> 88%); while for C/P of 10: 1 system, the phosphate removal rate was 0%. FISH results showed that the content of PAOs decreased from( 76.42 +/- 1.24) % to (10.40 +/- 0.97) % with C/P decreasing from 25: 1 to 10: 1, while glycogen accumulating organisms (GAOs) increased from (16.36 +/- 3.41)% to (34.25 +/- 2.59)%. In various C/P systems in the anaerobic, the production kinetic coefficients of PHB and PHV were K25: 1 > K20: 1 > K15: 1 > K10: 1 and K15: 1 > K20: 1 > K25: 1 > K10: 1, respectively. The PHB production in the proportion of PHAs decreased from 85% to 24%, while PHV increased from 15% to 76% with C/P decreasing from 25: 1 to 10: 1. For various C/P systems in the aerobic phase, their consumption kinetic coefficients of both PHB and PHV were K:20: 1 > K25: 1 > K15: 1 > K10: 1. PHB (the proportion of PHAs is 71% -75%) was the main consumption component in C/P of the 25: 1, 20: 1 and 15: 1 systems; while PHV(the proportion of PHAs is 71%) was the main consumption component in C/P of 10: 1 system. It is suggested that an increases of GAOs and decreases of PAOs in the EBPR system lead to the decreasing of PHB production and consumption, and to the increasing of PHV.

Removal of chloride ion from aqueous solution by ZnAl-NO(3) layered double hydroxides as anion-exchanger.

The layered double hydroxides (LDHs) containing nitrate as the interlayer anion has a high anion-exchange capacity in the presence of appropriate anions. In the light of this, ZnAl-NO(3) LDHs have been employed to remove chloride ion from aqueous solution in a batch mode. The influences of conditions for chloride ion uptake, including dosage of LDHs, pH of aqueous solution, and temperature on anion-exchange have been investigated, respectively. The thermodynamic parameters including Gibbs free energy (DeltaG(0)), standard enthalpy change (DeltaH(0)), and standard entropy change (DeltaS(0)) for the process were calculated using the Langmuir constants. It was found from kinetics test that the pseudo-second order kinetics model could be used to well describe the uptake process. An E(a) value of 10.27 kJ/mol provides evidence the anion-exchange process. The explanation of anion-exchange phenomenon has also been supported by X-ray diffraction and FT-IR spectra.