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Institutional Subscription. Free Shipping Free global shipping No minimum order. Covers all aspects of formation, organization, and use of microbial granules in wastewater treatment Integrates engineering, microbiology, and biotechnology of microbial granules Comprises of deep fundamental data as well as practical information for applications of microbial granules in wastewater treatment. Textile dyeing wastewater is also characterized by high salt content, which also imposes potential environmental problems. Sodium chloride and sodium sulfate constitute the majority of the total salts used.
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Magnesium chloride and potassium chloride are used as raw materials in lower concentrations EPA, Common characteristics of textile wastewater from cotton textile wet processing for different processing categories are shown in Table 1. The highest concentration of organic pollutants in terms of COD is generated from bleaching while the highest concentration of total solids comes from the desizing process. Metals such as copper, cadmium, chromium, nickel and zinc are also found in textile effluents, as they are the functional groups that form the integral part of the dye molecule IPPC, These include coagulation and flocculation Harrelkas et al.
While these methods are often costly, they remove the pollutants by transferring them from one phase to another. Some of them generate highly concentrated sludge, hence creating disposal problems Pearce et al. Excessive use of chemicals in dye treatment creates secondary pollution problems to the environment. Characteristics of textile wastewater Bisschops and Spanjers, ; Dos Santos et al. However, such technologies usually involve complicated procedures and are economically unattainable Chang and Lin, Among the available techniques, the one that can offer effective pollutant removal at a lower cost is the desirable alternative.
Of these, biological treatment is the obvious choice due to the relatively low operating cost. While a conventional aerobic biological process is incapable of treating textile wastewater, studies have shown that the integration of anaerobic and aerobic processes are able to provide complete mineralization of colored substances Knackmuss, ; Melgoza et al. It can be done by using either two separate anaerobic and aerobic reactors Khelifi et al. The wastewater is initially treated under an anaerobic condition followed by an aerobic condition. This is followed by complete mineralization under the aerobic condition.
Different forms of biomass i. The textile industry, in particular the wet industry, has been considered as one of the major water environment polluters. This is mainly due to the enormous amount of water and the complexity of the chemicals used in the manufacturing processes that end up in the wastewater. The poorly treated wastewater is still highly colored comprising of significant amounts of nonbiodegradable chemicals that are hazardous to the environment. Under anaerobic condition, some of the organics i.
The color will make a river inhabitable to a majority of aquatic plants and animals. While there are many technologies available in treating the wastewater, a majority of them are relatively expensive to be applied by the small and mid-size industries. Furthermore, many of the physico-chemical technologies only transform the pollutants from one form or one phase to another and therefore do not provide any ultimate solution to the problem.
A conventional aerobic bioprocess fails to treat the wastewater due to the non-biodegradable nature of the wastewater. However, recent research and advancement in biological processes show that there is a huge potential of these new findings in providing low cost yet efficient technology to solve the textile wastewater problem. Microbial granules form a self-immobilization community that is formed with or without support material.
They are defined as discrete macroscopic aggregates containing dense microbial consortia packed with different bacterial species.
Each biogranule consists of millions of microorganisms per gram of biomass Weber et al. According to Calleja , microbial granulation is a multicellular association in a physiological state that is causing the mixture of cells into a fairly stable and contiguous structure.
The main advantages of biogranules systems are mainly due to the biogranules good settling property and the fact that biogranules are formed without the need of any biomass carrier. The relatively large size and high-density biogranules give them a rapid settling rate, which enhances the separation of the treated effluent from the biomass and results in high solid retention time SRT Ahn and Richard, ; Liu and Tay, Due to a better settling rate, the system also shows low suspended solid content discharged in the effluent Wirtz and Dague, Within the biogranules, the microorganisms are closely lumped together, hence generating syntrophic associations between the cells.
This relationship occurs due to optimum distances between the cells at appropriate substrate levels and such condition enables high and stable performance of metabolism activities Batstone et al. The granulation system is first recognized in an up-flow anaerobic sludge blanket UASB system characterized by anaerobic biogranules. Much research has been carried out using innovative upflow sludge bed USB type reactors Bachman et al. The applications of anaerobic granulation systems have been successfully demonstrated particularly in removing biodegradable organic matter from industrial wastewaters Lettinga et al.
Later the attention has also been diverted to the development and applications of aerobic biogranules. The reason has been several drawbacks that have been observed in the anaerobic biogranules system, including long start-up periods, relatively high temperature requirements and ineffectiveness in dealing with nutrient and low organic strength wastewater Liu and Tay, Aerobic granulation systems have been used for organics, nitrogen, phosphorus and toxic substances removal, especially high strength wastewater Yi et al.
In most cases, the system is in the form of a sequencing batch reactor SBR Beun et al.
State of the art of biogranulation technology for wastewater treatment
The reaction phase of the system has been carried out either in anaerobic, aerobic or anoxic conditions, with or without mixing, depending on the purpose of the treatment. Bacteria normally do not aggregate naturally to each other due to repulsive electrostatic forces via the presence of negatively charged protein compounds of the cell wall Voet and Voet, However, under selective environmental conditions, microorganisms are capable to attach to one another and thus form aggregates.
Development of biogranules involves integration of physical, chemical and biological processes occuring in multiple stages Calleja, ; Liu and Tay, ; Linlin et al. The first stage of a biogranulation process is initiated by several forces, which include diffusion of mass transfer, hydrodynamic and gravitational forces, thermodynamic effects, as well as the tendency of cells to move towards one another. These forces result in cell-to-cell or cell-to-solid surface interactions. The second stage involves several physical forces e. Van der Waals forces, surface tension, hydrophobicity, opposite charge attractions, thermodynamic of surface free energy, bridges by filamentous bacteria , and chemical and biochemical forces e.
At this stage, the multicell connections are stabilized. The third stage is the maturing stage, which involves the production of substances that facilitate more cell-to-cell interactions; at this stage, highly organized microbial structures are formed.
Several mechanisms of metabolite production will also change, such as higher production of extracellular polymer, growth of cellular cluster, metabolite change and environmental-induced genetic effects. The final stage involves shaping of the three dimensional granules by hydrodynamic shear forces. Beun et al. Immediately after inoculation, bacteria and fungi will be dominating the reactor system.
At this early stage, mycelial pellets manage to retain in the reactor due to their good settling ability. Bacteria, which do not hold this characteristic, are discarded with the effluent. Due to the shear force imposed by air bubbles during the aeration phase, the filaments will be detached from the surface of pellets.
The pellets then grow bigger until they reach a diameter of up to mm. When the sizes of the pellets have grown even larger, self-defragmentation will take place due to the limitation of oxygen transfer in the inner parts of the grown pellets. The fragmented mycelial pellet will act as a matrix for bacteria to grow and form new colonies.
The bacterial colonies grow larger and will form granules. As the granules are formed, the whole system will be governed by bacterial growth. Schematic diagram of aerobic granulation developed without any carrier material Beun et al. Weber et al. Microscopic analysis has revealed that eukaryotic organisms play a key role in aerobic granule formation.
Stalked ciliates of the subclass Peritrichia and occasionally, the fungi, are found to be involved in the biogranulation process development. Development of biogranules seeded with anaerobic granular sludge in an SBR system has been demonstrated by Linlin et al. At the initial stage, the anaerobic granular seeds disintegrate into smaller flocs and debris due to the hydrodynamic shear force created by the air bubbles during the aerobic phase. Lighter and small sized flocs or debris will be washed out in the effluent during the decanting stage.
The remaining heavier anaerobic granules remain and act as precursors that initiate the growth of new aerobic granules. The optimal combination of the shear force and the growth of the microorganisms within the aggregates govern the stable structur of the biogranules Chen et al. The morphology of these aerobic granules is slightly different as compared to the aerobic granules as described by Beun et al.
Biogranules are known for their outstanding features of excellent stability and high removal efficiency making biogranulation an innovative modern technology for wastewater treatment. The size of the biogranules is an important aspect that may influence the stability and performance of the reactor system. Biogranules with bigger sizes can easily be defragmented under high shear force resulting in high biomass washout. Meanwhile, if the size is too small, the biogranules cannot develop good settling properties, resulting in higher suspended substances in the effluent.
Bigger biogranules with loose structure will be developed in an SBR system supplied with low superficial air velocity. Smaller biogranules but with high strength structures are observed being formed in systems aerated at higher superficial air velocity Chen et al. Granular sizes range from 0. The hydrodynamic shear force imposed through the aeration rate of the reactor system will control the development of biogranules Chisti, The size of biogranules is the net result of the balance between the growth and the hydrodynamic shear force imposed by superficial air velocity Yang et al.
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For the optimal performance and economic purposes, the operational diameter range for effective aerobic SBR granular sludge should be in the range of 1. The usual structure of an aerobic granule is normally spherical in shape with smooth surface areas, which can be influenced by the concentration and type of substrate used in the media compositions Zhu and Wilderer, ; Adav and Lee, Based on electron microscope SEM observations, glucose-fed granules appear with fluffy outer surface due to the predominance growth of filamentous bacteria.
On the other hand, the acetate-fed granules show a more compact microstructure with smooth surface. The non-filamentous and rodlike bacteria were observed dominating the acetate-fed granules that are tightly linked together Tay et al. Settleability of a biogranular sludge shows the capacity of the biogranules to settle within a specified period of time. Such properties will allow fast and clear separation between sludge biomass and effluent.
Good settleability of sludge biomass is desirable in wastewater treatment plants to facilitate high percentage of sludge retention in a reactor system. Superior characteristics of settleability assist to maintain the stable performance, high removal efficiency and can handle high hydraulic loading of wastewater Tay et al. Good settling property of biogranules is also shown by a low value of the SVI. The observed density of microbial aggregates is the consequence of balance interaction between cells Liu and Tay, When biogranules grow bigger, the compactness of the granules decreases.
This can be detected via a less solid and loose architectural assembly Toh et al. Biogranules with high physical strength can withstand high abrasion and shear force.
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The physical strength of the biogranules is expressed as an integrity coefficient. This coefficient is an indirect quantitative measurement of the ability of the biogranules to withstand the hydrodynamic shear force Ghangrekar et al. A good granular strength is indicated by an integrity coefficient of less than Biogranules are also characterized by high cell hydrophobicity and high EPS content. The former aspect is postulated to be the main triggering force in the initial stage of the biogranulation process and is a measure of the cell-to-cell interaction Liu et al.
The latter characteristic is postulated to be responsible for the aggregation between cells Liu et al. The presence of the EPS will enhance the polymeric interaction, which is one of the attractive forces that can promote the adhesion of bacterial cells. The networking between cell and EPS will assist the formation of biogranules Zhang et al. The application of hybrid biogranular system in treating textile wastewater is reported in this section. In this study, the development of biogranules during the treatment of textile wastewater is investigated. The changes on the physical characteristics of the biogranules as well as the system performance in the removal of organic compound and color intensity of the textile wastewater are further discussed.
The schematic representation of the reactor design is given in Figure 2. The design of the reactor is based on Wang et al. The column of the reactor has a working volume of 4 L with internal diameter of 8 cm and a total height of cm. The reactor is designed with a water-jacketed column for the purpose of temperature control. This can be achieved by allowing the circulation of hot water from a water heating circulation system to the water jacketed column of the system. The temperature of the heating system was set at 30 0 C.
Air was supplied into the reactor by a fine air bubble diffuser located at the bottom of the reactor column. The reactor system was equipped with dissolved oxygen and pH sensors for the continuous monitoring throughout the experiment. The wastewater was fed into the reactor from the bottom of the reactor. The decanting of the wastewater took place via an outlet sampling port located at 40 cm above the bottom of the reactor.
This means that only particles with settling velocity larger than 4. Particles having smaller settling velocity will be washed out in the effluent.
http://pamro.base17.io/1648-application-to-tracking.php All operations of peristaltic pumps, circulation of influent, air diffuser and decanting process were controlled by means of a timer. During the start-up period, 2 L of mixed sludge and 2 L of synthetic textile wastewater were added into the reactor system giving the working volume of 4 L with 5. The system was supplied with external carbon sources consisting of glucose, sodium acetate and ethanol with substrate loading rate of 2.
The operation of the system started with 5 min filling of wastewater entering from the bottom of the reactor. The operation then continued with the react phase followed by 5 min settling, 5 min decanting and 5 min of idle time. The react time varies depending on the hydraulic retention time set for the system. Figure 3 shows the steps involved in one complete cycle of the hybrid biogranular system. During the biogranules development, the HRT of the reactor was set for 6 hours for one complete cycle. This will give a react time of minutes.
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The react phase is divided into equal anaerobic and aerobic react periods. Table 2 shows the successive phase for one complete cycle of the reactor system. The operation of the reactor system was designed with intermittent anaerobic and aerobic react phases. The reaction phase started with an anaerobic phase followed by an aerobic phase. The reaction phase was repeated twice.
During the anaerobic react phase, the wastewater was allowed to circulate from the upper level of the reactor and returned back through a valve located at the bottom of the system. The circulation system was stopped at the end of the anaerobic phase. The circulation process is required to achieve a homogeneous distribution of substrate as well as a uniform distribution of the granular biomass and restricts the concentration gradient.
The DO concentrations remained low during the anaerobic condition 0. The superficial air velocity during the aerobic phase was 1. The system was operated without pH control causing variation in the range of 6. In order to observe the changes on the characteristics of the biogranules due to the variations of HRT during textile wastewater treatment, the development of biogranules with sizes in the range of 0.
The operation steps of one complete cycle of the reactor system are shown in Table 3. The physical characteristics of the biogranules including settling velocity, sludge volume index, granular strength were measured throughout the experiment.
Related Biogranulation Technologies for Wastewater Treatment: Microbial granules
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