Inhibition of free ammonia to the formation of aerobic granules

Organic and nitrogen removal from landfill leachate in aerobic granular sludge sequencing batch reactors

Granule sequencing batch reactors (GSBR) were established for landfill leachate treatment, and the COD removal was analyzed kinetically using a modified model. Results showed that COD removal rate decreased as influent ammonium concentration increasing. Characteristics of nitrogen removal at different influent ammonium levels were also studied. When the ammonium concentration in the landfill leachate was 366 mg L(-1), the dominant nitrogen removal process in the GSBR was simultaneous nitrification and denitrification (SND). Under the ammonium concentration of 788 mg L(-1), nitrite accumulation occurred and the accumulated nitrite was reduced to nitrogen gas by the shortcut denitrification process. When the influent ammonium increased to a higher level of 1105 mg L(-1), accumulation of nitrite and nitrate lasted in the whole cycle, and the removal efficiencies of total nitrogen and ammonium decreased to only 35.0% and 39.3%, respectively. Results also showed that DO was a useful process controlling parameter for the organics and nitrogen removal at low ammonium input.

Understanding the granulation process of activated sludge in a biological phosphorus removal sequencing batch reactor

The granulation of activated sludge was investigated using two parallel sequencing batch reactors (SBRs) operated in biological nitrogen and phosphorus removal conditions though the reactor configuration and operating parameters did not favor the granulation. Granules were not observed when the SBR was operated in biological nitrogen removal period for 30d. However, aerobic granules were formed naturally without the increase of aeration intensity when enhanced biological phosphorus removal (EBPR) was achieved. It can be detected that plenty of positive charged particles were formed with the release of phosphorus during the anaerobic period of EBPR. The size of the particles was about 5-20 μm and their highest positive ζ potential was about 73 mV. These positive charged particles can stimulate the granulation. Based on the experimental results, a hypothesis was proposed to interpret the granulation process of activated sludge in the EBPR process in SBR. Dense and compact subgranules were formed stimulated by the positive charged particles. The subgranules grew gradually by collision, adhesion and attached growth of bacteria. Finally, the extrusion and shear of hydrodynamic shear force would help the maturation of granules. Aerobic granular SBR showed excellent biological phosphorus removal ability. The average phosphorus removal efficiency was over 95% and the phosphorus in the effluent was below 0.50 mg L(-1) during the operation.

Variations of both bacterial community and extracellular polymers: the inducements of increase of cell hydrophobicity from biofloc to aerobic granule sludge

To investigate the inducements of increase of cell hydrophobicity from aerobic biofloc (ABF) and granular sludge (AGS), in this study, as the first time the hydrophilic and hydrophobic bacterial communities were analyzed independently. Meanwhile, the effect of extracellular polymers (EPS) on the cell hydrophobicity is also studied. Few Bacteroidetes were detected (1.35% in ABF and 3.84% in AGS) in hydrophilic bacteria, whereas they are abundant in the hydrophobic cells (47.8% and 43% for ABF and AGS, respectively). The main species of Bacteroidetes changed from class Sphingobacteria to Flavobacteria in AGS. On the other hand, EPS is directly responsible to cell hydrophobicity. For AGS, cell hydrophobicity was sharply decreased after EPS extraction. Both quantity and property of the extracellular protein are related to hydrophobicity. Our results showed the variation of cell hydrophobicity was resulted from variations of both bacterial population and EPS.

Aerobic granulation for nitrogen removal via nitrite in a sequencing batch reactor and the emission of nitrous oxide

In this study, the granulation of nitrifying-denitrifying via nitrite process in a sequencing batch reactor (SBR) as well as N(2)O emission patterns was investigated. After 60 days of operation, 0.8 mm granules were obtained, and partial nitrification was achieved after NH(4)(+)-N was raised to 350 mg/L. Fluorescence In-Situ Hybridization (FISH) analysis indicated that a fairly large proportion of ammonia-oxidizing bacteria (AOB) was close to the surface but nitrite-oxidizing bacteria (NOB) were rarely found. Batch experiments showed that 64.0% of NH(4)(+)-N in influent was transformed into NO(2)(-)-N, which showed the granules had excellent partial nitrification ability. Inhibition of free ammonia (FA) and limited DO diffusion within granules may contribute to the development and stabilization of partial nitrification. This process did not simultaneously lead to increased N(2)O production. N(2)O emissions at the anoxic and aerobic phases were 0.06 and 13.13 mg N(2)O/cycle, respectively.

Selective inhibition of nitrite oxidation by chlorate dosing in aerobic granules

Partial nitrification was successfully achieved with addition of 5mM KClO(3) in the aerobic granules system. Batch tests demonstrated that KClO(3) selectively inhibited nitrite-oxidizing bacteria (NOB) but not ammonia-oxidizing bacteria (AOB). During stable partial nitrification, the influent pH was kept at 7.8-8.2, while the DO and temperature were not controlled in the SBR. When the NH(4)-N and COD levels were kept at 100mg/l and 400mg/l in the influent, the NH(4)-N and COD removal efficiencies reached 98.93% and 78.65%, respectively. The NO(2)-N accounted for 92.95% of the NO(χ)-N (NO(2)-N+NO(3)-N) in the effluent. Furthermore, about 90% of the chlorate was reduced to nontoxic chloride, thus it would not cause environmental problem. SEM showed that the main composition of the aerobic granules was bacilli and coccus bacteria. FISH analysis revealed that AOB became the dominant nitrifying bacteria, whereas NOB were detected only in low abundance. Chlorate could be used to control the development and maintenance of aerobic granules sludge for partial nitrification.

Involvement of ATP and autoinducer-2 in aerobic granulation

Aerobic granulation represents an important bacterium-to-bacterium self-immobilization process that has been exploited for the treatment of a wide spectrum of wastewaters, but the mechanism behind still remains unclear in a microbiological sense. This study investigated the possible involvement of ATP and autoinducer-2 (AI-2) in aerobic granulation. Results revealed that initiation of microbial aggregation is closely associated with the ATP content of biomass, whereas AI-2 of biomass would be essential for maturation of aerobic granules. Furthermore, it was found that the AI-2-associated coordination of microorganisms in microbial aggregates would be biomass density dependent. This study clearly shows the involvement of ATP and autoinducer-2 in aerobic granulation, and may be exploited further for enhancement or prevention of microbial aggregation in general, for example, rapid granulation for wastewater treatment or inhibition of biofouling in membrane bioreactor.

Long-term storage and subsequent reactivation of aerobic granules

This study investigated a seven month storage and the subsequent reactivation of aerobic granules. The granule size and structure integrity were remained during storage, whereas some cavities and pleats appeared on the surface and further deteriorated the settleability. Along with the reactivation, the physical characteristics and microbial activities of aerobic granules were gradually improved. Activities of heterotrophs and nitrifiers can be fully recovered within 16days and 11days, respectively. Nitrifiers decayed slower during storage and reinstated rapider during reactivation than heterotrophs. In fresh aerobic granules, the dominated ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were Nitrosomonas and Nitrospira, respectively. During storage, the initially dominated populations decayed rapider than the initially less dominated ones. Extracellular polymeric substances (EPS) significantly decreased within the first month, and then gradually accumulated during the last six months storage. Accumulation of EPS was an effective strategy for maintaining structural integrity of aerobic granules during long-term storage.

Extracellular polymeric substances and structural stability of aerobic granule

The contributions of individual components in extracellular polymeric substances (EPSs) on structural stability of phenol-fed, aerobic granules were examined. The roles of proteins, alpha- and beta-polysaccharides, and lipids were studied via their selective hydrolysis using enzymes, and the structural changes of granule were probed using in situ fluorescent staining and confocal laser scanning microscopy. Selective enzymatic hydrolysis of proteins, lipids, and alpha-polysaccharides had a minimal effect upon the three-dimensional structural integrity of the granules. Conversely, selective hydrolysis of beta-polysaccharides fragmented the granules. The beta-polysaccharides were expected to form the backbone of a network-like outer layer with embedded proteins, lipids, alpha-polysaccharides, and cells to support the mechanical stability of granules.

Influence of different substrates on the formation and characteristics of aerobic granules in sequencing batch reactors

The effects of different substrates on the aerobic granulation process were studied using laboratory-scale sequencing batch reactors (SBRs). Four parallel granules sequencing batch reactors (GSBR): R1, R2, R3, and R4 were fed with acetate, glucose, peptone and fecula, respectively. Stable aerobic granules were successfully cultivated in R1, R2, R4, and smaller granules less than 500 microm were formed in R3. Morphology and the physic-chemical characteristics of aerobic granules fed with different carbon substrates were investigated by the four reactors operated under the same pressure. The aerobic granules in the four reactors were observed and found that peptone was the most stable one due to its good settleability even after a sludge age as short as 10 d. A strong correlation was testified between the characteristics of aerobic granules and the properties of carbon substrates. The stability of aerobic granules was affected by extracellular polymer substances (EPS) derived from microorganism growth during feast time fed with different carbon substrates, and the influence of the property of storage substance was greater than that of its quantity. Optimal carbon substrates, which are helpful in the cultivation and retention of well-settling granules and in the enhancement of the overall ability of the aerobic granules reactors, were found.

Wind-driven surficial oxygen transfer and dinitrogen gas emission from treatment lagoons

Surficial oxygen transfer plays an important role, when analyzing the complex biochemical and physical processes responsible for ammonia and dinitrogen gas emission in animal waste treatment lagoons. This paper analyzes if currently known nitrogen biochemical pathways can explain the enigmatic dinitrogen gas emissions recently observed from the treatment lagoons, based on the amount of wind-driven oxygen that can be transferred through the air-water interface. The stoichiometric amounts of the maximum dinitrogen gas production potential per unit mass of O(2) transferred were calculated according to three most likely biochemical pathways for ammonia removal in the treatment lagoons-classical nitrification-denitrification, partial nitrification-denitrification, and partial nitrification-Anammox. Partial nitrification-Anammox pathway would produce the largest N(2) emission, followed by partial nitrification-denitrification pathway, then by classical nitrification-denitrification pathway. In order to estimate stoichiometric amount (i.e., maximum) of N(2) emission from these pathways, we assumed that heterotrophic respiration was substantially inhibited due to high levels of free ammonia prevalent in treatment lagoons. Most observed N(2) emission data were below the maximum N(2) emission potentials by the classical nitrification-denitrification pathway. However, one value of observed N(2) emission was much higher than that could be produced by even the partial nitrification-Anammox pathway. This finding suggests yet unknown biological processes and/or non-biological nitrogen processes such as chemodenitrification may also be important in these treatment lagoons.

Distribution of EPS and cell surface hydrophobicity in aerobic granules

This study described the distribution of extracellular polysaccharides (EPS) and hydrophobicity in aerobic granule as well as the essential role of EPS in maintaining the stable structure of aerobic granules. Aerobic granules showed a heterogeneous structure, which had an outer shell with high biomass density and an inner core having a relatively low biomass density. Results showed that the outer shell of aerobic granule was composed of poorly soluble and noneasily biodegradable EPS, whereas its core part was filled with readily soluble and biodegradable EPS. It was further found that the shell of aerobic granule exhibited a higher hydrophobicity than the core of granule. The insoluble EPS present in the granule shell would play a protective role with respect to the structure stability and integrity of aerobic granules.

State of the art of biogranulation technology for wastewater treatment

Biogranulation technology developed for wastewater treatment includes anaerobic and aerobic granulation processes. Anaerobic granulation is relatively well known, but research on aerobic granulation commenced only recently. Many full-scale anaerobic granular sludge units have been operated worldwide, but no report exists of similar units for aerobic granulation. This paper reviews the fundamentals and applications of biogranulation technology in wastewater treatment. Aspects discussed include the models of biogranulation, major factors influencing biogranulation, characteristics of biogranules, and their industrial applications. This review hopes to provide a platform for developing novel granules-based bioreactors and devising a unified interpretation of the formation of anaerobic and aerobic granules under various operation conditions.