Jianrong Zhu

The membrane fouling characteristics of MBRs with different aerobic granular sludges at high flux

This experimental work investigated the property of membrane fouling for different sludges at high flux 20 L/(m(2)h). The MBR with good aerobic granular sludge performed the longest operation time 61 days, and TMP rose up in a steady overall rate, while only 10, 14 and 19 days for bulking, flocculent and small granular sludge, respectively, which clearly demonstrated the good and complete aerobic granules greatly retarded the membrane fouling. The pore blocking resistance 76.21% was the key fouling factor for aerobic granules, but the cake resistance 61.23% or 79.02% was the main factor for flocculent or bulking sludge. The difference in EPS composition of membrane foulants between granules MBR and flocculent sludge MBR led to the different behaviour of fouling. Aerobic granules were quite stable during operation. These results suggested MBR with aerobic granules might be operated at high flux, which was very valuable for practical application.

Optimal cultivation and characteristics of aerobic granules with typical domestic sewage in an alternating anaerobic/aerobic sequencing batch reactor

The present work investigated some important factors for optimal aerobic granulation using typical domestic sewage as a substrate in a pilot-scale alternating anaerobic/aerobic sequencing batch reactor. High sludge concentration and low sludge loading, for the first time, were used for the reactor start-up. A vast number of small particles appeared on day8. Subsequently, several measures for controlling sludge concentration and sludge loading within an appropriate range were applied to optimize the granulation process. On day 45, complete sludge granulation was achieved. After 60days of operation, the aerobic granules always kept in stable state, with an average diameter of 750μm and the SVI(30) of 20-35ml/g. The COD, TN, and TP removal ratios were 92%, 81%, and 85%, respectively. The results demonstrated that it was feasible to form aerobic granules quickly using typical domestic sewage under optimal operation strategies, which was further proved by the results from denaturing gradient gel electrophoresis fingerprint.

Performance and role of N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) in aerobic granules

The present study investigated the relationship between N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) and the physico-chemical properties of aerobic granules. Stable mature granules were observed in SBR2 and SBR3 with average diameters of 0.96, and 1.49 mm, respectively. The sludge densities of aerobic granules in SBR2 and SBR3 were 1.0246, and 1.0201 g/mL, respectively, which were higher than that of flocculent sludge in SBR1 (1.0065 g/mL). The results showed that the activity of AHL-based QS in SBR2 and SBR3 amounted to 2.4- and 2.1-fold induction, however, that in SBR1 with flocculent sludge was 1.6-fold induction. In addition, the results also showed that the activity of AHL-based QS in the three reactors rose in the feast condition, and then dropped with the consumption of substrate. However, the activity of AHL-based QS in these three reactors recovered again in prolonged starvation. Furthermore, the results showed that the enhancement of AHL-based QS favored the extracellular polymeric substance production of microorganisms in activated sludge. Thus, it could be concluded that aerobic granules showed higher AHL-based QS than flocculent sludge, which resulted from the higher sludge density of aerobic granules than flocculent sludge. AHL-based QS was related to the metabolism energy in the feast condition; however, in prolonged starvation, microorganisms would emit more AHL-like molecules to protect themselves to resist starvation. Moreover, the enhancement of AHL-based QS favored the EPS component productivity of the microorganisms in activated sludge, which contributed to maintain the aerobic granular structure.

The role of N-acyl homoserine lactones in maintaining the stability of aerobic granules

In this study, porcine kidney acylase, as N-acyl homoserine lactones (AHLs)-degradation enzyme, was employed for the first time to directly investigate the role of AHLs in the structure stability of aerobic granules. Results clearly showed that inactivation of AHLs by AHLs-acylase could weaken the stability of aerobic granule. In the presence of AHLs-acylase, AHLs were degraded by hydrolyzing the amide linkage, which resulted in aerobic granular attachment potential and activity of AHLs-based quorum sensing significantly reduced. In addition, it was also found that inactivation of AHLs led to reduction of extracellular polysaccharides and protein (PN), especially PN, and induced extracellular polymeric substances matrix damaged, which was hostile to stability of aerobic granules. This study provided direct evidence that AHLs played a key role in improving aerobic granular stability, and a potential way to enhance long-term stability of aerobic granules.

The microbial attachment potential and quorum sensing measurement of aerobic granular activated sludge and flocculent activated sludge

The aerobic granulation process is involved in the attachment of microorganisms, and the quorum sensing (QS) is supposed to play an important role in microbial attachment. In this study, the attachment potential of aerobic granular activated sludge (AGAS) and flocculent activated sludge (FAS) was investigated. Results clearly showed that AGAS had stronger attachment potential than FAS. A bioassay with NTL4 proved that N-acylhomoserine lactones (AHLs) were produced in both sludge, but the AHLs content of AGAS was significantly higher than FAS. Additionally, the extracellular polymeric substances (EPS) measurements indicated that there were more proteins and polysaccharides in the hydrophobic EPS fraction of AGAS. Besides, the bacterial community structure of AGAS differed from FAS by PCR-DGGE. Some hydrophobic bacteria, such as Flavobacterium, exclusively existed in AGAS. It was speculated that the difference of attachment potential between AGAS and FAS was derived from the divergence of AHLs, EPS and microbial community.

High-rate nitrogen removal and its behavior of granular sequence batch reactor under step-feed operational strategy

Alternating anoxic/oxic (A/O) combined with the step-feed granular sequence batch reactor (step-feed SBR) was operated in laboratory scale to investigate nitrogen removal. The results showed that when the total inorganic nitrogen (TIN) and chemical oxygen demand (COD) levels were 55 and 320 mg/L in the influent, the TIN removal efficiencies were 89.7-92.4% in the step-feed mode and 48.1-59.5% in the conventional alternating A/O single-feed mode within a 360 min cycle. The pH and dissolved oxygen (DO) were used to optimize the process of denitrification and nitrification in the step-feed mode. The optimized operational condition was achieved by shortening the cycle time to 207 min, resulting in a nitrogen removal rate of 0.27 kg N/m3 d, which was much higher than those achieved using activated sludge systems. The dominant community in the aerobic granules was coccus-like bacteria, and filamentous bacteria were hardly found. Granules were well maintained throughout the 90 days of continuous step-feed operation.

The effect of metal ions on the microbial attachment ability of flocculent activate sludge

ABSTRACT As a kind of biofilm structure, microbial attachment was believed to play an important role in the aggregation and stability of flocculent activated sludge (FAS), and also its translation to aerobic granular activated sludge (AGAS). The aim of this study was to investigate the effect of Ca2+, Mg2+, Cu2+, Fe2+, Zn2+, K+, and Na+, which were frequently found in the biological wastewater-treatment systems on the microbial attachment of FAS, in order to provide a new strategy for the cultivation of FAS and AGAS. The results showed that different metal ions had different effects on the process of microbial attachment of FAS; in particular, Cu2+, Fe2+, and Zn2+ could increase the microbial attachment ability of FAS at appropriate concentrations, and disrupted the process at higher concentrations. Mg2+ would greatly enhance the microbial attachment of FAS at lower concentrations but then the biomass of attachment was fallen down to a level close to that of the control. However, Ca2+, K+, and Na+ always exhibited a positive impact on the microbial attachment of FAS. Besides, the concentration of FAS suspension and the culture time both had an effect on the microbial attachment of FAS. Moreover, the acyl-homoserine-lactones-based quorum-sensing system, the content of EPS, and the relative hydrophobicity of FAS had been greatly influenced by metal ions. As all these parameters had close relationships with microbial attachment process, changes in these parameters may affect the microbial attachment of FAS.

The biological effect of metal ions on the granulation of aerobic granular activated sludge

As a special biofilm structure, microbial attachment is believed to play an important role in the granulation of aerobic granular activated sludge (AGAS). This experiment was to investigate the biological effect of Ca(2+), Mg(2+), Cu(2+), Fe(2+), Zn(2+), and K(+) which are the most common ions present in biological wastewater treatment systems, on the microbial attachment of AGAS and flocculent activated sludge (FAS), from which AGAS is always derived, in order to provide a new strategy for the rapid cultivation and stability control of AGAS. The result showed that attachment biomass of AGAS was about 300% higher than that of FAS without the addition of metal ions. Different metal ions had different effects on the process of microbial attachment. FAS and AGAS reacted differently to the metal ions as well, and in fact, AGAS was more sensitive to the metal ions. Specifically, Ca(2+), Mg(2+), and K(+) could increase the microbial attachment ability of both AGAS and FAS under appropriate concentrations, Cu(2+), Fe(2+), and Zn(2+) were also beneficial to the microbial attachment of FAS at low concentrations, but Cu(2+), Fe(2+), and Zn(2+) greatly inhibited the attachment process of AGAS even at extremely low concentrations. In addition, the acylated homoserine lactone (AHL)-based quorum sensing system, the content of extracellular polymeric substances and the relative hydrophobicity of the sludges were greatly influenced by metal ions. As all these parameters had close relationships with the microbial attachment process, the microbial attachment may be affected by changes of these parameters.