Types of Anaerobic Treatment Plants Installed Worldwide

The key to successful application of anaerobic treatment is to un-couple the hydraulic retention time (of wastewater) and the solids retention time (of active biomass) in the reactor system. In order to achieve high system loading rates, short hydraulic retention times should be applied, whilst at the same time maintaining positive net solids (biomass) retention. Thus, various reactor designs were developed over the past two decades that are based on various ways of retaining biomass within the...

Disadvantages of Microbial Granulation

However, one disadvantage of aerobic granulation is a long start-up period of granule formation from the flocs of activated sludge. The formation of aerobic granules is very crucial for their applicability in wastewater treatment, while this process takes several weeks to start-up aerobic granular system from conventional activated sludge (Peng et al., 1999 Beun et al., 2000 Tay et al., 2001c Moy et al., 2002). Another potential disadvantage is the risk of accumulation of pathogenic...

Solids Retention Time

Solids retention time (SRT), so-called sludge age, is one of the design parameters in a continuously activated sludge process. Pan (2003) investigated the role of SRT in aerobic granulation in SBR, and found that the sludge age of 20 days or longer is favorable for the formation and maintenance of stable aerobic granules with good settleability and activity (Fig. 5.6). As noted by Liu and Tay (2002), in more than 100 years of Fig. 5.6. Microscope images of granules flocs at different SRTs (Pan,...

Upflow Velocity and Hydraulic Retention Time

In a UASB reactor, upflow velocity and hydraulic retention time (HRT) is inter-related and serves as a selection pressure on microbial ecology. It has been observed that anaerobic granulation can proceed well at relatively high liquid upflow velocity, but does not occur under conditions of low hydrodynamic shear (Alphenaar et al., 1993 Arcand et al., 1994 O'Flaherty et al., 1997 Alves et al., 2000). According to Alphenaar et al. (1993), granulation in UASB reactors is favored by a combination...

References

Operational trends in UASB reactor bed stability and during initiation of granulation (eds. Tilche, A., & Rozzi, A.), Proceeding of the Fifth International Symposium on Anaerobic Digestion, Bologna, Italy, 99-103. Alphenaar, P.A., Visser, A., & Lettinga, G. (1993). The effect of liquid upflow velocity and hydraulic retention time on granulation in UASB reactors treating wastewater with a high-sulphate content. Bioresour. Technol., 43, 249-258. Alves,...

Bacterial Diversity and Functions in Aerobic Phenoldegrading Granules

Aerobic granules can be viewed as a special form of biofilm, but without carriers for biofilm attachment. Growth environments for biofilm communities are different from planktonic communities, and micro-bial communities in attached biofilms have been shown to be highly distinct from the suspended biomass, even within a single reactor system. Recognizing the diversity and the linkages among the key functional groups in any given biological system can lead to better ways to model and understand...

Anaerobic Migrating Blanket Reactor AMBR

Recently, Angenent and Sung (2001) developed a novel anaerobic wastewater treatment system, namely anaerobic migrating blanket reactor (AMBR), which is a continuously fed, compartmentalized reactor without the requirement of elaborate gas-solid-separation and feed-distribution systems. It was found that granules in an AMBR tended to be darker in color, smaller, and denser than granules in a UASB reactor operated under conditions similar to those in the AMBR. The internal structure of AMBR is...

Microbial Diversity of Granules Grown in Glucosecontaining Model Wastewater Studied by FISH with Groupspecific

Bacterial populations, associated with the development of aerobic granules in glucose-containing model wastewater, were monitored by a combination of FISH with rRNA-targeted fluorescence in situ hybridization with group specific probes and CLSM (Table 7.5). A column-type sequential aerobic sludge blanket reactor (SASBR) was inoculated with activated sludge from a municipal plant and fed with synthetic wastewater containing glucose as the main carbon source. The reactor biomass initially...

Formation of Phenoldegrading Granules from Acetatefed Granules

Phenol is a major environmental pollutant, and phenol concentrations of up to 10,000 mg L-1 have been reported in many industrial wastewaters (Fedorak and Hrudey, 1988). Phenol removal by biological methods is generally preferred to physico-chemical methods because of lower costs and the possibility of complete mineralization. However, phenol-containing wastewater is difficult to treat as microbial activity can be inhibited due to the toxicity exerted by high concentrations of the substrate...

Advantages of Microbial Granulation

Microbial granulation is a process exploited in biological wastewater treatment whereby bacteria are organized into highly structured suspended granules that are capable of removing biodegradable organic matter, nitrogen, and phosphorus. Parts of microbial granule, probably, have coordinated physiological functions, i.e. cell growth, metabolism, interactions, biosynthesis, transport, consumption, and storage of nutrients. Microbial granulation differentiated from flocculation and formation of...

Feast Famine Regime

SBR for cultivation of aerobic granules is operated in a sequencing cycle of feeding, aeration, settling, and discharging of supernatant. In SBR, the aeration period actually consists of two phases a degradation phase in which the substrate is depleted to a minimum, followed by an aerobic starvation phase in which the external substrate is no longer available. Thus, it is likely that microorganisms in SBR are subjected to a periodic feast and famine regime, called periodic starvation (Tay et...

Secondary Minimum Adhesion Model

Secondary minimum adhesion model is based on the DLVO theory for colloidal particles, which proposes that reversible adhesion takes place in the secondary minimum of the DLVO free energy curve. The Gibbs energy of the reversible adhesion is relatively small, and there is always a separation distance between the two adhering bacteria. Thus, the reversible adhesion can change to irreversible adhesion at the primary minimum by overcoming the energy barrier or by protruding fibrils or fimbriae,...

Development of a Kinetic Model for Metal Biosorption

Aerobic granules are microbial aggregates with a strong and compact structure. Liu et al. (2003a) investigated the biosorption kinetics of heavy metals by aerobic granules. Figure 11.1 shows the adsorption profiles of cadmium by aerobic granules in the course of batch tests (Liu et al., 2003a). It can be seen that the amount of cadmium adsorbed gradually increased as a function of contact time until a stable level. It had been assumed that functional groups or biopolymers on cell surface would...

Inert Nuclei Model

The inert nuclei model for anaerobic granulation was initially proposed by Lettinga et al. (1980). In the presence of inert microparticles in a UASB reactor, anaerobic bacteria could attach onto the particle surfaces to form initial biofilm, namely embryonic granules. Subsequently, mature granules can be further developed from the growth of these attached bacteria under given operating conditions. The inert nuclei model suggests that the presence of nuclei or microsize biocarrier for bacterial...

Surface Tension Model

According to the thermodynamic theory, microbial granulation is a creation process for a new granule-liquid interface by disrupting preexisting individual bacteria-liquid interface, and a molecular contact between the two adhering bacterial surfaces is involved. The free energy of adhesion (AGadh) can be expressed as follows (Rouxhet and Mozes, 1990) AGadh 20 - rl1 2)(rl1 2 - r 2) rc is the surface free energy of bacteria, rl is the surface free energy of liquid, and rs is the surface free...

Anaerobic Continuous Stirred Tank Reactor CSTR

The most common bioreactor type used for anaerobic digestion is the continuously stirred tank reactor (CSTR). Vanderhaegen et al. (1992) cultivated anaerobic granules in (CSTR), and found that granular sludge disappeared within three weeks when the reactors were incubated statically instead of being shaken. The hydrodynamic shear force appeared to be necessary for maintaining the integrity of granular sludge, and anaerobic granulation may not be reactor type-dependent, but related to the way by...

Development of Nitrifying Granules

Yang et al. (2005) cultivated nitrifying granules in at various substrate N COD ratios in the range of 5 100-30 100 by weight. It was found that nitrifying granules could form at all the tested substrate N COD ratios and the characteristics of nitrifying granules were found to be substrate N COD ratio-dependent. The Formation of Nitrifying Granules Nitrifying granulation was found to be a gradual process from the dispersed seed sludge through the tiny aggregates to the mature spherical granules...

Phylogenetic Identification and Evaluation of Biosafety of Selected Strains

Full 16S rRNA gene sequences were obtained for microbial strains B and F, respectively. The sequences of strain B was 99.4 identical to Klebsiella pneumoniae Gene bank access number is AY292866.1 , and strain F was 99.9 identical to Pseudomonas veronii Gene bank access number is AY512619.1 . The sequences were of 1338 and 1408 bases in length, respectively. Both isolates belong to subclass of y-Proteobacteria. A disadvantage of wastewater treatment with microbial granules in comparison with the...

General Model for Anaerobic Granulation

For bacteria in an anaerobic culture to form granules, a number of conditions have to be fulfilled. The contributions of physical, chemical, and biological factors to granulation process could not be considered separately. So far, no model seems able to depict the entire anaerobic granulation process reasonably. Based on the existing mechanisms for formation of anaerobic granules, a general four-step model to better describe anaerobic granulation is proposed as follows. Step 1 Physical movement...

Local Dehydration and Hydrophobic Interaction Model

Under normal pH conditions, the outer surfaces of bacteria are hydrated. Such a water layer on the surfaces of bacteria would prevent one bacterium to approach another. It has been believed that under normal physiological conditions, strong hydration repulsion is the main force keeping the cells apart, thus local dehydration of the short-distance-apart surfaces would be a prerequisite for cell-to-cell aggregation. The local dehydration and hydrophobic interaction model as proposed by Wilschut...

Aerobes and Facultative Anaerobes in Granules

Relation of detected OTUs to oxygen was inferred from their phylogenetic identification (Table 7.3). Table 7.3. Distribution of OTUs by relation to oxygen Table 7.3. Distribution of OTUs by relation to oxygen of clones found in the following library Relation to oxygen, gliding motility in the closest species Table 7.3. Distribution of OTUs by relation to oxygen Cont'd Table 7.3. Distribution of OTUs by relation to oxygen Cont'd Mean frequencies SD of OTUs related to obligate aerobes,...

Nitrogen Removal under Alternating Aerobic Anaerobic Conditions

Microbial granules for carbon oxidation and nitrogen removal can also be developed in SBRs operated under alternating aerobic-anaerobic conditions (Qin et al., 2004b, 2005). The microbial granules cultivated under alternating aerobic-anaerobic conditions even exhibited a better settleabil-ity than those developed under pure aerobic conditions. It was found that over 95 of influent COD was removed within the first half hour of aerobic phase. Along with the COD elimination, the NH4+-N...

Improved Stability of Aerobic Granules by Selecting Slowgrowing Bacteria

Since aerobic bacteria grows much faster than anaerobic bacteria, the stability of aerobic granules appears to be poorer than that of anaerobic granules developed in upflow anaerobic sludge blanket (UASB) reactor. Obviously, the poor stability of aerobic granules would limit its application in wastewater treatment practice. Existing evidence shows that the stability of biofilms is closely related to the growth rate of bacteria, i.e. a higher growth rate of bacteria resulted in a weaker...

Technologies For Wastewater Treatment

Joo-Hwa Tay, Stephen Tiong-Lee tayt, Liu Yu, Show Kuan Yeow and BIOGRANULATION TECHNOLOGIES FOR WASTEWATER TREATMENT Volume 1 Waste Materials in Construction Science and Engineering of Recycling for Environmental Protection G.R. Woolley, J.J.J.M. Goumans and P.J. Wainwright (Editors) Volume 2 Geological Disposal of Radioactive Wastes and Natural Analogues W. Miller, R. Alexander, N. Chapman, I. McKinley and J. Smellie Volume 3 Principles and Standards for the Disposal of Long-lived Radioactive...

Internal Circulation Reactor IC

In industrial practice, one major limitation of UASB reactors is the washout of seed sludge during the start-up period. In order to overcome the washout-related operation problem in conventional UASB system, Pereboom and Vereijken (1994) presented a modified design of two-stage UASB reactor, namely the internal circulation (IC) reactor. The IC reactor consists of two inter-connected UASB compartments on top of each other. In the first stage located in the bottom part of the IC reactor, most...

Syntrophic Microcolony Model

The bioconversion of organics into methane proceeds through a series of complex biochemical changes, and little is known about the individual Fig. 1.1. Simplified pathways of methane fermentation of complex wastes. Fig. 1.1. Simplified pathways of methane fermentation of complex wastes. steps involved due to the many pathways available for an anaerobic community. Figure 1.1 illustrates simplified pathways of methane fermentation of complex wastes by various routes. The microbial species...

Chemical Conditions

Ionic composition and presence of polymer in the anaerobic system are believed to have significant roles in the forming granules through various mechanisms and models. The effects of various cations and polymers are discussed in the following sections. Divalent and trivalent cations have positive effects on flocculation of dispersed sludge. Commonly used divalent cations are calcium and magnesium while iron can be used as both a divalent or trivalent cation depending on its oxidation state....

ECP Bonding Model

The ECPs can mediate both cohesion and adhesion of cells, and play a vital role in maintaining structural integrity of microbial matrix. On the other hand, the metabolic blocking of exopolysaccharides synthesis would prevent microbial aggregation (Schmidt and Ahring, 1994 Cammarota and Sant'Anna, 1998). It had been reported that ECPs could change the surface negative charge of the bacteria, and thereby bridge two neighboring cells physically to each other, and with other inert particulate...

Role of Extracellular Polymeric Substances EPS in Aerobic Granulation

Extracellular Bacteria Images

Extracellular polymeric substances (EPS) are sticky materials secreted by cells, and may play an important role in cell adhesion phenomena, formation of matrix structure, microbial physiology, and improvement of long-term stability of granules (Schmidt and Ahring, 1994 Tay et al., 2001c Liu et al., 2004b McSwain et al., 2005). High polysaccharide content could facilitate cell-to-cell interaction and further strengthen microbial structure through the formation of a polymeric matrix. The...

Selection Pressuredriven Aerobic Granulation

Many factors have been known to affect the formation of aerobic granules in sequencing batch reactor (SBR) as briefed earlier. Compared with continuous microbial culture, the main feature of SBR is its cycle operation, i.e. each cycle consists of filling, aeration, settling, and discharging. In SBR, the settling time is likely to exert a selection pressure on the sludge particles. Only particles that can settle down within a given settling time would be retained in the reactor, otherwise they...

The Future of Anaerobic Granulation

Anaerobic treatment is well over 100 years old. Its initial development was for the treatment of domestic wastewaters, it then progressed in application to separate sludge digestion, then to treatment of dilute industrial waste-waters. Several processes have been developed that accomplish efficient treatment of wastewaters at short detention times. The anaerobic granulation system has been known for its unique ability to convert highly objectionable wastes into useful products. With global...

Expanded Granular Sludge Bed Reactor EGSB

Anaerobic sludge bed (and in particular the EGSB) reactor systems can be started up within a few days with granular seed sludges, and they may be applied across a wide range of conditions and strengths of wastewater (Lettinga, 1996). EGSB systems are particularly suited to low temperatures (10 C) and very low strengths (very much smaller than 1000 mg L) and for the treatment of recalcitrant or toxic substrates. New insights into the anaerobic degradation of very different categories of...

Consideration on the Proton Translocation Dehydration Theory

The proton translocation-induced dehydration of bacterial surface is considered a key element of the proton translocation-dehydration theory. In accordance with the chemiosmotic mechanism on most of the aerobic bacteria, ATP is generated by oxidative phosphorylation, in which process electrons are transported through the electron transport system (ETS) from an electron donor (substrate) to a final electron acceptor (O2). The molecules directly using the H+ gradient built up by electron...

Amplified Ribosomal DNA Restriction Analysis ARDRA

The amplified 16S rDNA, full-length inserts 1500 bp), were selected for restriction enzyme digestion to define restriction fragment length polymorphism (RFLP) patterns using restriction endonuclease Cfol (Promega, USA). To determine the similarities of bacterial populations present in three clone libraries, comparisons of the RFLP types within and among each of clone libraries were performed using GelCompar II (version 1.5) software. The constituent populations in the aerobic granules were...

Upflow Anaerobic Sludge Blanket Reactor UASB

The sludge blanket concept was first used in the Reversed Flow Dorr Oliver clarigester which is a modified version of the contact process. Unlike the contact process, it is unmixed and feed flows upward through a dense bed of flocculated bacteria. Flocs collect in the settling compartment and return to the reactor by gravity. Dorr Oliver clarigester improvements due to the biomass loss in effluent led to the upflow sludge blanket process and the UASB process. The UASB has an integrated 3-phase...