[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.

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.

[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.