[Influence of Operating Modes for the Alternating Anoxic/Oxic Process on Biological Nitrogen Removal and Extracellular Polymeric Substances of Activated Sludge].

Nitrogen removal, extracellular polymeric substances (EPS), and the chemical composition (protein (PN), polysaccharide (PS), and DNA) by the aerobic/anoxic (O/A) and the anoxic/aerobic (A/O) modes were studied in a sequencing batch reactor (SBR) fed with domestic wastewater. The results showed that the removal rates of NH4+-N were 97.5% and 98.0% in the two operating modes, respectively, and a removal efficiency of NH4+-N with high efficiency and stability was obtained. The nitrification rate was positively correlated with the nitrogen loading ratio. The influence of operating modes for the alternating anoxic/oxic mode on extracellular polymeric substances of activated sludge was evaluated. The EPS constituent in the A/O mode was slightly higher than the O/A mode. The operating mode had no effect on the contents of PN, PS, and DNA in tightly bound EPS (TB-EPS) and TB-EPS. However, PN and PS in loosely bound EPS (LB-EPS) and LB-EPS in the A/O mode were 1.38 to 1.56 times those of the O/A mode. In the two operating modes, PSs were the main constituents in the TB-EPS and EPS, while PNs were the main constituents in LB-EPS. The EPS content had a good linear correlation with the sludge settling performance.

[Effect of Temperature on Nitrogen Removal Performance and the Extracellular Polymeric Substance (EPS) in a Sequencing Batch Reactor (SBR)].

In this paper, the long-term effects of temperature on the nitrogen removal performance and the extracellular polymeric substance (EPS) in a sequencing batch reactor (SBR) treating synthetic wastewater was investigated under three temperature conditions (15℃, 25℃, 35℃). The results showed that high temperatures (35℃) could promote the establishment of short-cut nitrification processes and improve nitrogen removal performance greatly. Temperature had a significant impact on the EPS and its composition. With an increased temperature, the EPS and tightly bound EPS (TB-EPS) content decreased, while, loosely bound EPS (LB-EPS) increased slowly. TB-EPS became dominant in the EPS (the percentage of TB-EPS/EPS was 69.0%-79.5%), however, the ratio of TB-EPS/LB-EPS decreased from 3.8 (15℃) to 3.6 (25℃), and then to 2.2 (35℃) with a gradual increase in temperature. Moreover, protein (PN) and DNA in the EPS, TB-EPS, and LB-EPS decreased with an increasing temperature. Carbohydrates (PS) in the EPS and LB-EPS increased as temperature increased, nevertheless, PS in TB-EPS decreased. Furthermore, 25℃ was identified as the breaking-point temperature in the variation of PN, DNA and PS concentrations. At 15℃ and 25℃, PN was the main component in TB-EPS and LB-EPS. PS has the second highest concentration and DNA the least. However, PS were the dominant component at 35℃, with PN having the second highest concentration, and DNA having a subtle concentration. Moreover, at 15℃ and 25℃, the EPS content increased in the nitrification process and reduced in the denitrification process.

[Synergetic Inhibitory Effect of Free Ammonia and Aeration Phase Length Control on the Activity of Nitrifying Bacteria].

Three sequencing batch reactors (SBRs) labeled with R(Ahead), R(Exact) and R(Exceed) were employed to investigate the synergetic inhibition effect of free ammonia (FA) and length of aeration phase on the activity of ammonia-oxidizing bacteria ( AOB) and nitrite- oxidizing bacteria (NOB) after shortcut nitritation was achieved in the systems. The experiments were conducted under the conditions of three FA concentrations (0.5, 5. 1, 10.1 mg · L⁻¹) combined with three kinds of aeration time (t(Exact): the time when ammonia oxidation was completed; t(Ahead): 30 min ahead of the time when ammonia oxidation was completed; t(Exceed): 30 min exceeded when the time ammonia oxidation was completed). It was found that short-cut nitrification could be successfully established in three reactors with a FA level of 10.1 mg · L⁻¹. Meanwhile, the speed of achieving nitritation was in the sequence of R(Ahead) > R(Exact) > R(Exceed) with operational cycles of 56, 62 and 72, respectively. Compared to AOB, NOB in the three reactors was observed to be more sensitive to FA, resulting in AOB activity higher than NOB activity throughout the whole experimental period. Moreover, there was great difference in the activity coefficient ( η) between AOB and NOB. The activity coefficients of AOB were in the order of η(RExact) > η(RExceed) > η(RAhead) with the values of 104.4%, 100% and 85.8%, respectively. Nevertheless, the activity coefficients of NOB were in the order of η(RExceed) > η(RExact) > η(RAhead) with the values of 71.2%, 64.9% and 50.2%, respectively.

The differentially-expressed proteome in Zn/Cd hyperaccumulator Arabis paniculata Franch. in response to Zn and Cd.

The Zn/Cd hyperaccumulator Arabis paniculata is able to tolerate high level of Zn and Cd. To clarify the molecular basis of Zn and Cd tolerance, proteomic approaches were applied to identify proteins involved in Zn and Cd stress response in A. paniculata. Plants were exposed to both low and high Zn or Cd levels for 10 d. Proteins of leaves in each treatment were separated by 2-DE (two-dimensional electrophoresis). Nineteen differentially-expressed proteins upon Zn treatments and 18 proteins upon Cd treatments were observed. Seventeen out of 19 of Zn-responsive proteins and 16 out of 18 of Cd-responsive proteins were identified using MALDI-TOF/TOF-MS (matrix-assisted laser desorption/ionization time of flight mass spectrometry). The most of identified proteins were known to function in energy metabolism, xenobiotic/antioxidant defense, cellular metabolism, protein metabolism, suggesting the responses of A. paniculata to Zn and Cd share similar pathway to certain extend. However, the different metal defense was also revealed between Zn and Cd treatment in A. paniculata. These results indicated that A. paniculata against to Zn stress mainly by enhancement of energy metabolism including auxin biosynthesis and protein metabolism to maintain plant growth and correct misfolded proteins. In the case of Cd, plants adopted antioxidative/xenobiotic defense and cellular metabolism to keep cellular redox homeostasis and metal-transportation under Cd stress.