PERFORMANCE EVALUATION OF EXTRINSIC FACTORS AFFECTING GRANULATION IN SEWAGE (original) (raw)
Related papers
2011
Decades of investigations and explorations in the field of anaerobic wastewater treatment have resulted in significant indications about the role importance of sludge granules in biodegradation anaerobic process. It is believed that the development of anaerobic granules is reflecting an important role on the performance of reactor. An overview on the concept of up-flow anaerobic sludge bed UASB reactor operation as well as the main parts that reactor consists of is briefly explained in this paper, whereas the major theories of anaerobic granules formation are listed by related researchers. The correlations and compositions of such sludge granule have been specifically explained. It is believed that the extracellular polymer (ECP) is totally responsible of bacterial cell correlations and the formation of bacterial communities in the form of granules. In addition, the dependable factors for the performance of anaerobic granules formation process e.g. temperature, organic loading rate, pH, and alkalinity, nutrients, and cations and heavy metals have been discussed in this paper. Strong evidences proved that the process of gas production in the form of biogas is related to the methanogens activities, which are practically found in the core of granules. The aim of this review is to explore and assess the mechanisms of granules initiation and development inside UASB reactor.
Water Science and Technology, 1999
Four techniques (microscope sizing, calculation from settling velocities. image and laser analysis) are available nowadays for determining the particle size distribution of upflow anaerobic sludge blanket (UASB) reactor sludge. These techniques present however the disadvantage of being either tedious, imprecise or expensive and hardly applicable in full scale treatment plants. There was then the need for a simple and low cost technique. In this study, a granulometry procedure based on manual humïhsievïng was evaluated. It was shown that no solid loss occured during the screening and that the particle size profiles were reproducible when performed with sludge samples of 5. 10.25 and 150 ml. but not I ml. Only the results between 10 and 25 ml were however fully identical. It was shown also that the sieving could be performed on sludge samples stored for as long as 50 days at refrigerator temperature and that tap water could be use for [he wash' and backwash operations without any impact ori the particle size profile. The granulometry obtained by image analysis was not comparable to that given by sieving. Ne\,ertheless. no evidence of granule erosion could be found. In any case, the technique allowed us to follow [he evolution of sludge granulometry perfectly over lime. As a consequence. the manual humid sieving appears to be an adequate technique for determining the granule size distribution of UASB sludges. Q 1999 Published by Elsevier Science Lid on behalf of the IAWQ. All rights reserved.
2013
The upflow anaerobic sludge blanket (UASB) process is known to be energy conservative biotechnology. Its low cost and low skill requirement render it to be a viable technology for reducing organic pollution loads. However, this system is facing a challenge in the treatment of low-strength wastewater especially inoculated with non-granular sludge. This work was performed to emphasis an in-depth understanding of an UASB reactor start-up process inoculated with digested slurry for treating synthetic wastewater of chemical oxygen demand (COD) around 700-1000 mg/L. The lab scale reactor with an effective volume of 9.97 L was operated under ambient temperature (24-35 0 C). At the end of start-up period that lasted for 84 days, this system achieved 90.8% COD removal and a biogas evolution of 4.72 L/d (457 L / kg COD removal) at an organic loading rate (OLR) of 1.293 kg COD/ m 3 d. Concurrently, the volatile fatty acids (VFA)/ alkalinity ratio was found as 0.184. It confirms the stability o...
Upflow Anaerobic Sludge Blanket Reactor: Modelling
2011
Anaerobic treatment is widely used around the world as a biological stage in both domestic and industrial wastewater-treatment plants. The two principal advantages of anaerobic over aerobic treatment are the production of biogas, which can be used as fuel, and the lower rate of biomass production, which results in lower maintenance costs for the plant. The upflow anaerobic sludge blanket (UASB) reactor is an attractive alternative for regions in hot climates since it works better under mesophilic conditions and it does not need any supporting structure for the development of microorganisms, which grow in the form of granules. In this thesis, a model describing the UASB reactor behaviour with respect to substrate degradation, microorganism growth and granule formation was developed. The model is transient and is based on mass balances for the substrate and microorganisms in the reactor. For the substrate, the processes included in the model are dispersion, advection and degradation of the organic matter in the substrate. The reaction rate for the microorganisms includes the growth and decay of the microorganisms. The decay takes into account the microorganism dying and the fraction of biomass that may be dragged into the effluent. The microorganism development is described by a Monod type equation including the death constant; the use of the Contois equation for describing the microorganism growth was also addressed. An equation considering the substrate degradation in the granule was required, since in the UASB reactor the microorganisms form granules. For this, a stationary mass balance within the granule was carried out and an expression for the reaction kinetics was then developed. The model for the granule takes into account the mass transport through the stagnant film around the granule, the intraparticle diffusion, and the specific degradation rate. The model was solved using commercial software (COMSOL Multiphysics). The model was validated using results reported in the literature from experiments carried out at pilot scale. A simplified model was also developed considering the case in which the microorganisms are dispersed in the reactor and granules are not formed. The UASB reactor is then described as formed by many well-stirred reactors in series. The model was tested using experimental results from the literature and the sensitivity of the processes to model parameters was also addressed. The models describe satisfactorily the degradation of substrate along the height in the reactor; the major part of the substrate is degraded at the bottom of the reactor due to the high density of biomass present in that region. This type of model is a useful tool to optimize the operation of the reactor and to predict its performance.
Water Science and Technology, 1999
In the present study an upflow anaerobic sludge blanket (VASB) reactor and an expanded granular sludge bed (EGSB) reactor were operated with different substrates under the same conditions. Ethanol. diluted beer (as a brewery effluent model) and wastewater from a coffee industry were tested. Ethanol was fed at two different concentrations: 0.5 and IO gCOD/I. Beer was diluted to a concentration of 3gCODn and coffee wastewater had a concentration of approximately 7 gCOD/1. During the operation, samples of sludge were taken from both reactors to measure TSS. VSS. size distribution and methanogenic activity. Batch assays were performed in a third reactor using ethanol at two different superficial velocitIes to measure substrate uptake. The overall COD removal for ethanol at 500 gCOD/1 in EOSB and VASB reactors was similar (around 80% for a sludge loading rate of 0.8 gCOD/day/gVSS). Granular sludge experienced an important development in its characterisllcs dunng the operation with ethanol. Superficial velocity showed a positive effect on COD removal for ethanol below 5m1h. There were no big differences in the removal rates during the operation with coffee wastewater. Probably 10 thiS effluent the process is limited by the reaction kmetics instead of by the mass transfer. due to the complex nature of the waste. With diluted beer. EGSB reactor showed a better performance than the VASB.
Granulation during the start-up of a UASB reactor used in the treatment of low strength wastewaters
Biotechnology Letters, 1997
A glucose-based wastewater was efficiently degradaded by acidogenic bacteria, with a glucose removal efficiency close to 90%, and although a distinctive granular structure could not be observed, fluffy conglomerates developed in an Upflow Anaerobic Sludge Blanket (UASB) reactor. Subsequently, the pre-acidification of the wastewater promoted the granulation process. An enrichment in methanogenic bacteria was observed on the microscope and was confirmed by an increase in the specific methanogenic activity from 0.1 up to 0.5kgCOD/kgVSS.day. Such dynamics of microbial communities was also verified through changes in the polysaccharide and protein content, as well as in the electrophoretic mobility of the biomass.
2005
This work presents an analysis of the changes observed in granule characteristics of sludge in the treatment of synthetic wastewater at a concentration of about 500 mgCOD/L in batch, fed-batch (ASBR) and continuous (UASB) bench-scale reactors under similar experimental conditions. Physical and microbiological properties of the granules were characterized as average particle size and sedimentation time and by optical and epifluorescence microscopy. Several samples were analyzed in order to identify the morphologies. Granules from sequencing batch and fed-batch reactors, either with or without mechanical mixing, did not undergo any physical or microbiological changes. However, during the experiment granules from the UASB reactor agglomerated due to the formation and accumulation of a viscous material, probably of microbial origin, when operated at low superficial velocities (0.072, 0.10 and 0.19 m/h). When the superficial velocity was increased to 8.0-10.0 m/h by means of liquid-phase recirculation, the granules from the UASB reactor underwent flocculation and the microbiological characteristics changed in such a way that the equilibrium of microbial diversity in the inoculum was not maintained. As a result, the only reactor that maintained efficiency and good solids retention during the assays was the ASBR, showing that there is a correlation between maintenance of microbial diversity and operating mode in the case of anaerobic treatment of lowstrength wastewaters.