Comparison of membrane fouling during short-term filtration of aerobic granular sludge and activated sludge

Aerobic granular sludge was cultivated adopting internal-circulate sequencing batch airlift reactor. The contradistinctive experiment about short-term membrane fouling between aerobic granular sludge system and activated sludge system were investigated. The membrane foulants was also characterized by Fourier transform infrared （FTIR） spectroscopy technique. The results showed that the aerobic granular sludge had excellent denitrification ability; the removal efficiency of TN could reach 90%. The aerobic granular sludge could alleviate membrane fouling effectively. The steady membrane flux of aerobic granular sludge was twice as much as that of activated sludge system. In addition, it was found that the aerobic granular sludge could result in severe membrane pore-blocking, however, the activated sludge could cause severe cake fouling. The major components of the foulants were identified as comprising of proteins and polysaccharide materials.

Community analysis of ammonia and nitrite oxidizers in start-up of aerobic granular sludge reactor

A lab-scale sequencing batch reactor （SBR） was set-up and the aerobic granular sludge was successfully incubated using anaerobic granular sludge as seed sludge. Nitrogen was partially removed by simultaneous nitrification and denitrification （SND） via nitrite with free ammonia （FA） of about 10 mg/L. The denaturing gradient gel electrophoresis （DGGE） method was used to investigate community structure of α-Proteobacteria, β-Proteobacteria, ammonia oxidizing bacteria （AOB）, and Nitrospira populations during start-up. The population sizes of bacteria, AOB and Nitrospira were examined using real-time PCR method. The analysis of community structure and Shannon index showed that stable structure of AOB population was obtained at day 35, while the communities of α- Proteobacteria, β-Proteobacteria, and Nitrospira became stable after day 45. At stable stage, the average cell densities were 1.1× 10^12, 2.2×10^10 and 1.0×10^10 cells/L for bacteria, AOB and Nitrospira, respectively. The relationship between characteristics of nitrifying bacteria community and nitrogenous substrate utilization constant was discussed by calculating Pearson correlation. Certain correlation seemed to exist between population size, biodiversity, and degradation constant. And the influence of population size might be greater than that of biodiversity.

Re-activation characteristics of preserved aerobic granular sludge

In some industrial plants, wastewater was intermittently or seasonally generated. There may be periods during which wastewater treatment facilities have to be set into an idle phase over several weeks. When wastewater was generated again, the activated sludge flocs may have disintegrated. In this experiment, re-activation characteristics of aerobic granular sludge starved for 2 months were investigated. Specific oxygen utilization rate(SOUR) was used as an indicator to evaluate the metabolic activity of the sludge. The results revealed that aerobic granular sludge could be stored up to two months without running the risk of losing the integrity of the granules and metabolic potentials. The apparent color of aerobic granules stored at room temperature gradually turned from brownish-yellowish to gray brown. They appeared brownish-yellowish again 2 weeks after re-activation. The velocity and strength of granules after 2-month idle period could be fully restored about 3 weeks after re-activation. Metabolic activity, however, dropped to 15 8 mg O_2/(g MLVSS·h), i.e. 74 % reduction after 2 months of storage. After restarting the reactor, it took 2 weeks that SOUR of up to 48 5 mg O_2 /(g MLVSS·h) was achieved. A stable effluent COD concentration of less than 150 mg/L was achieved during the re-activation process.

Molecular characterization of bacterial community in aerobic granular sludge stressed by pentachlorophenol

To characterize the effects of pentachlorophenol (PCP) on the performance and microbial community of aerobic granular sludge in sequencing batch reactor (SBR), the web-based terminal restriction fragment length polymorphism (T-RFLP) and real-time PCR (RT- PCR) techniques were used to explore the bacterial community structure. When PCP increased from 0 to 50 mg/L, the COD removal rate changed little, while the ammonia removal rate dropped from 100% to 64.9%. The results of molecular characterization showed t...

Screening and identification of functional bacterial attachment genes in aerobic granular sludge

The screening and identification of attachment genes is important to exploring the formation mechanism of biofilms at the gene level.It is helpful to the development of key culture technologies for aerobic granular sludge(AGS).In this study,genome-wide sequencing and gene editing were employed for the first time to investigate the effects and functions of attachment genes in AGS.With the help of whole-genome analysis,ten attachment genes were screened from thirteen genes,and the efficiency of gene screening was greatly improved.Then,two attachment genes were selected as examples to further confirm the gene functions by constructing gene-knockout recombinant mutants of Stenotrophomonas maltophilia;when the two attachment genes were knocked out,the attachment potential was reduced by 50.67%and 43.93%,respectively.The results provide a new theoretical principle and efficient method for the development of AGS from the perspective of attachment genes.

Cultivation and characters of aerobic granules for pentachlorophenol(PCP) degradation under microaerobic condition

Cultivation of aerobic granular sludge for pentachlorophenol(PCP) degradation under microaerobic condition(DO concentration was controlled at 0.2—0.7 mg/L) was studied in this paper. Anaerobic granules were selected as inoculum. The changes of appearance were observed and the variations of SVI, VSS/TSS, PN/PS and the size of sludge were measured during cultivating. The capabilities for degradation of PCP, AOX and COD_ Cr were also studied. Observations on mature granules were carried out by scanning electron microscope, and the results indicated bacillus was dominant on the surface of granules while in the inner of granules both bacillus and coccus were the dominant microorganisms. K, Na, Fe, Ca, Mg, Ni, Co, Mn, Cu and Zn were detected in the granules by element analysis.

Effect of seed sludge on characteristics and microbial community of aerobic granular sludge

Aerobic granular sludge was cultivated by using different kinds of seed sludge in sequencing batch airlift reactor. The influence of seed sludge on physical and chemical properties of granular sludge was studied; the microbial community structure was probed by using scanning electron microscope and polymerase chain reaction-denaturing gradient gel electrophoresis （PCR-DGGE）. The results showed that seed sludge played an important role on the formation of aerobic granules. Seed sludge taken from beer wastewater treatment plant （inoculum A） was more suitable for cultivating aerobic granules than that of sludge from municipal wastewater treatment plant （inoculurn B）. Cultivated with inoculum A, large amount of mature granules formed after 35 days operation, its SVI reached 32.75 mL/g, and SOUR of granular sludge was beyond 1.10 mg/（g.min）. By contrast, it needed 56 days obtaining mature granules using inoculum B. DGGE profiles indicated that the dominant microbial species in mature granules were 18 and 11 OTU when inoculum A and B were respectively employed as seed sludge. The sequencing results suggested that dominant species in mature granules cultivated by inoculum A were Paracoccus sp., Devosia hwasunensi, Pseudoxanthomonas sp., while the dominant species were Lactococcus raffinolactis and Pseudomonas sp. in granules developed from inoculum B.

Biodegradation of aniline by Candida tropicalis AN1 isolated from aerobic granular sludge

Aniline-degrading microbes were cultivated and acclimated with the initial activated sludge collected from a chemical wastewater treatment plant. During the acclimation processes, aerobic granular sludge being able to effectively degrade aniline was successfully formed, from which a preponderant bacterial strain was isolated and named as AN1. Effects of factors including pH, temperature, and second carbon/nitrogen source on the biodegradation of aniline were investigated. Results showed that the optimal conditions for the biodegradation of aniline by the strain AN1 were at pH 7.0 and 28–35°C. At the optimal pH and temperature, the biodegradation rate of aniline could reach as high as 17.8 mg/（L·hr） when the initial aniline concentration was 400 mg/L. Further studies revealed that the addition of 1 g/L glucose or ammonium chloride as a second carbon or nitrogen source could slightly enhance the biodegradation efficiency from 93.0% to 95.1%–98.5%. However, even more addition of glucose or ammonium could not further enhance the biodegradation process but delayed the biodegradation of aniline by the strain AN1. Based on morphological and physiological characteristics as well as the phylogenetic analysis of 26S rDNA sequences, the strain AN1 was identified as Candida tropicalis.

Cultivation of aerobic granular sludge in a conventional, continuous flow, completely mixed activated sludge system

Aerobic granules were formed in a conven- tional, continuous flow, completely mixed activated sludge system （CMAS）. The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen （DO） of the reactor were 2 h and 4.2 mg. L 1, respectively. The reactor was agitated by a stirrer, with a speed of 250r·min^-1, to ensure good mixing . The granular sludge had good settleability, and the sludge volume index （SVI） was between 50 and 90 mL ·g ^-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope （SEM） investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electro- phoresis （PCR-DGGE）. Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.

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.

Isolation and characterization of a strain with high microbial attachment in aerobic granular sludge

Aerobic granule is a special microbial aggregate associated with biofilm structure.The formation of aerobic granular sludge is primarily depending on its bacterial community and relevant microbiological properties.In this experiment,a strain with high microbial attachment was isolated from aerobic granular sludge,and the detailed characteristics were examined.Its high attachment ability could reach 2.34(OD600 nm),while other low attachment values were only around 0.06-0.32,which indicated a big variation among the different bacteria.The strain exhibited a very special morphology with many fibric fingers under SEM observation.A distinctive behaviour was to form a spherical particle by themselves,which would be very beneficial for the formation and development of granular sludge.The EPS measurement showed that its PN content was higher than low attachment bacteria,and 3 DEEM confirmed that there were some different components.Based on the 16 S rRNA analysis,it was identified to mostly belong to Stenotrophomonas.Its augmentation to particle sludge cultivation demonstrated that the strain could significantly promote the formation of aerobic granule.Conclusively,it was strongly suggested that it might be used as a good and potential model strain or chassis organism for the aerobic granular sludge formation and development.

Analysis of aerobic granular sludge formation based on grey system theory

Based on grey entropy analysis, the relational grade of operational parameters with aerobic granular sludge＇s granulation indicators was studied. The former consisted of settling time （ST）, aeration time （AT）, superficial gas velocity （SGV）, height/diameter （H/D） ratio and organic loading rates （OLR）, the latter included sludge volume index （SVI） and set-up time. The calculated result showed that for SVI and set-up time, the influence orders and the corresponding grey entropy relational grades （GERG） were： SGV （0.9935） 〉 AT （0.9921） 〉 OLR （0.9894） 〉 ST （0.9876） 〉 H/D （0.9857） and SGV （0.9928） 〉 H/D （0.9914） 〉 AT （0.9909） 〉 OLR （0.9897） 〉 ST （0.9878）. The chosen parameters were all key impact factors as each GERG was larger than 0.98. SGV played an important role in improving SVI transformation and facilitating the set-up process. The influence of ST on SVI and set-up time was relatively low due to its dual functions. SVI transformation and rapid set-up demanded different optimal I-I/D ratio scopes （10-20 and 16-20）. Meanwhile, different functions could be obtained through adjusting certain factors＇ scope.

Response of aerobic sludge to AHL-mediated QS:Granulation,simultaneous nitrogen and phosphorus removal performance

The effects of different species and concentrations’signal molecules on aerobic activated sludge system were investigated through batch experiments.Results showed that the fastest NH^(+)_(4)-N oxidization rate and the most extracellular polymeric substances(EPS)secretion were obtained by adding 5 nmol/L N-hexanoyl-l-homoserine lactone(C_(6)-HSL)into the aerobic activated sludge.Further study investigated the correlation among N-acyl-homoserine lactones-mediated quorum sensing(AHLs-mediated QS),nutrient removal performances and microbial communities with the long-term addition of 5 nmol/L C_(6)-HSL.It was found that C_(6)-HSL-manipulation could enhance the stability and optimize the decontamination performance of aerobic granular sludge(AGS)system.Microbial compositions considerably shifted with long-term C_(6)-HSL-manipulation.Exogenous C_(6)-HSL-manipulation inhibited quorum quenching-related(QQ-related)activities and enhanced QS-related activities during the stable period.The proposed C_(6)-HSL-manipulation might be a potential technology to inhibit the growth of harmful bacteria in AGS,which could provide a theoretical foundation for the realization of more stable biological wastewater treatments.

Resistance to salt stresses by aerobic granular sludge:sludge property and microbial community

Saline wastewater is regarded as a challenge for wastewater treatment plants because high-salinity conditions negatively affect on traditional biological technologies.Aerobic granular sludge(AGS)has gained attention as a promising technology for saline wastewater treatment because of its compact structure and the ability to withstand toxic loadings.Therefore,this study investigated the saltresistance performance,sludge properties and microbial community of AGS under low-salinity and high-salinity conditions,with the saline concentrations ranging from 0 to 50 g/L.The results showed that AGS could withstand long-term saline stresses,and the maximum salinity reached 50 g/L within 113 d.Under salinities of 10,30,and 50 g/L,the chemical oxygen demand(COD)removal efficiencies were 90.3%,88.0%and 78.0%,respectively.AGS also its maintained strength and aggregation at salinities of 10 and 30 g/L.Overproduction of extracellular polymeric substances(EPS)by non-halophilic bacteria that enhanced sludge aggregation.The compact structure that ensured the microorganisms bioactivity helped to remove organic matters under salinities of 10 and 30 g/L.At a salinity of 50 g/L,moderately halophilic bacteria,including Salinicola,Thioclava,Idiomarina and Albirhodobacter,prevailed in the reactor.The dominant microbial communities shifted to moderately halophilic bacteria,which could maintain aerobic granular stabilization and remove organic matters under 50 g/L salinity.These results in this study provide a further explanation for the long-term operation of AGS for treating saline wastewater at different salinities.It is hoped that this work could bring some clues for the mystery of salt-resistance mechanisms.

Aerobic granules cultivated and operated in continuous-flow bioreactor under particle-size selective pressure

A novel method based on the selective pressure of particle size （particle-size cultivation method, PSCM） was developed for the cultivation and operation of aerobic granular sludge in a continuous-flow reactor, and compared with the conventional method based on the selective pressure of settling velocity （settling-velocity cultivation method, SVCM）. Results indicated that aerobic granules could be cultivated in continuous operation mode by this developed method within 14 days. Although in the granulation process, under particle-size selective pressure, mixed liquor suspended solids （MLSS） in the reactor fluctuated greatly and filamentous bacteria dominated the sludge system during the initial operation days, no obvious difference in profile was found between the aerobic granules cultivated by PSCM and SVCM. Moreover, aerobic granules cultivated by PSCM presented larger diameter, lower water content and higher specific rates of nitrification, denitrifieation and phosphorus removal, but lower settling velocity. Under long term operation of more than 30 days, aerobic granules in the continuous-flow reactor could remain stable and obtain good chemical oxygen demand （COD）, NH4^＋-N, total nitrogen （TN） and total phosphorus （TP） removal. The results indicate that PSCM was dependent on the cultivation and maintenance of the stability of aerobic granules in continuous-flow bioreactors.

Nitrifying and denitrifying bacteria in aerobic granules formed in sequencing batch airlift reactors

The purpose of this study was to investigate nitrifying bacteria and denitrifying bacteria isolated from aerobic granules.Aerobic granules were formed in an internal-circulate sequencing batch airlift reactor(SBAR)and biodegradation of NH_(3)^(−)-N was analyzed in the reactor.Bacteria were isolated and determined from aerobic granules using selected media.The growth properties and morphology of bacteria colonies were observed by controlling aerobic or anaerobic conditions in the culture medium.It was found that bacteria in aerobic granules were diverse and some of them were facultative aerobes.The diversity of bacteria in aerobic granules was a premise of simultaneous nitrification and denitrification.