Microbial community structure and population dynamics of granules developed in expanded granular sludge bed (EGSB) reactors for the anaerobic treatment of low-strength wastewater at low temperature (original) (raw)
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Bioresource Technology, 2007
This study presents the performance characteristics of a plug Xow phase separated anaerobic granular bed baZed reactor (GRABBR) fed with brewery wastewater at various operating conditions. The reactor achieved chemical oxygen demand (COD) removal of 93-96% with high methane production when operated at organic loading rates (OLRs) of 2.16-13.38 kg COD m ¡3 d ¡1. The reactor conWguration and microbial environment encouraged the acidogenic dominant zone to produce intermediate products suitable for degradation in the predominantly methanogenic zone. Noticeable phase separation between acidogenesis and methanogenesis mainly occurred at high OLR, involving a greater number of compartments to contribute to wastewater treatment. The highly active nature and good settling characteristics of methanogenic granular sludge oVered high biomass retention and enhanced methanogenic activities within the system. The granular structure in the acidogenic dominant zone of the GRABBR was susceptible to disintegration and Xotation. Methanogenic granular sludge was a multi-layered structure with Methanosaeta-like organisms dominant in the core.
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Anaerobic reactors have acquired a new relevance in recent years due to their ability to generate methane from biodegradable wastewaters-thereby producing clean energy. Methane capture in this way prevents the outflow of the greenhouse gas to the air, which otherwise occurs when anaerobic conditions develop in drains and outfalls carrying wastewater. About 80% of the world's anaerobic wastewater treatment systems are estimated to be based on the UASB technology. The performance of a UASB reactor revolves round its sludge bed which gets expanded as the wastewater is made to flow vertically upwards through it. It is the micro flora attached to the sludge particles which acts upon the sewer water. Hence the quality of bio-fuels sported by the sludge particles, and the tightness of the sludge-wastewater contact are the factors which, principally, govern the success of a UASB reactor. Early in the development of UASB technology, it was realized that granular sludge of appropriate par...
High-rate anaerobic treatment of wastewater under psychrophilic conditions
Journal of Fermentation and Bioengineering, 1995
The start-up and operation of an expanded granular sludge bed (EGSB) reactor under psychrophilic (lo-12'C) conditions was studied. The reactor was seeded with mesophilic methanogenic granular sludge and fed with a mixture of volatile fatty acids (VFA). Chemical oxygen demand (COD) removal efficiencies exceeded 90% at imposed organic loading rates up to 12 g GOD-Z-1-d-1 at lO-12'C using influent concentrations ranging from 500 to 800 mg COD .I-'. The applied hydraulic retention time (HRT) was between 2.5 and 1.6 h and a liquid upflow velocity of 10 m. h-l was applied. The effect of temperature on the specific VFA conversion rates was assessed using hatch activity assays for the seed sludge and the sludge cultivated in the reactor. The optima temperatures for substrate conversion of sludge exposed to long term psychrophilic conditions were similar to those of the original mesophilic inoculum. Both sludges exerted an optimum substrate conversion rate at 35 40%. The temperature dependence of acetate conversion between 10°C and 40°C could he described by an Arrhenius derived model. Propionate, butyrate and VFA mixtures degrading activities for the same temperature range could be described by a aquare root model. The specific activities of the sludge in the reactor increased in time indicating enrichment of methanogens and acetogens even at low temperature.
Bioresource Technology, 2019
This study was carried out to investigate the relationship between the methane producing pathways and the characteristics of anaerobic granules treating municipal wastewater. For this purpose, two pilot scale upflow anaerobic sludge blanket reactors with different granule size distribution (1-2 mm and 3-4 mm) were investigated at operating temperatures of 20°C and 28°C for 239 days. There was an increased and stable biogas production when temperature was elevated to 28°C likely due to reduction in methane solubility. Larger granules had multi-layered internal microstructures with higher acetoclastic methanogenic activities (250-437 mL CH 4 g −1 VS d −1) than smaller granules (150-260 mL CH 4 g −1 VS d −1). The relative abundance of acetoclastic methanogens of larger granules was higher, confirming acetoclastic methane producing pathway was more prominent. However, there was no significant difference in the performance of the two reactors because they were operating below their capacities in terms of organic loading rate to volatile solids ratio.
Water Science & Technology, 2008
In this study, a lab scale EGSB reactor was operated for 400 days to investigate the influence of temperature-decrease on the microbial characteristic of retained sludge. The EGSB reactor was started-up at 15°C seeding with 20°C-grown granular sludge. The influent COD of synthetic wastewater was set at 0.6–0.8 gCOD/L. The process-temperature was stepwise reduced from 15°C to 5°C during 400 days operation. Decrease of temperature of the reactor from 15°C to 10°C caused the decline of COD removal efficiency. However, continuous operation of the EGSB reactor led the efficient treatment of wastewater (70% of COD removal, 50% of methane recovery) at 10°C. We confirmed that the both acetate-fed and hydrogen-fed methanogenic activities of retained sludge clearly increased under 15 to 20°C. Changes of microbial profiles of methanogenic bacteria were analyzed by 16S rDNA-targeted DGGE analysis and cloning. It shows that genus Methanospirillum as hydrogen-utilizing methanogen proliferated due...
Bioresource Technology, 2010
Granular biofilms underpin the operation of several categories of anaerobic wastewater treatment bioreactors. Recent studies have demonstrated the feasibility of treating both industrial and domestic wastewaters at their discharge temperatures (usually <18°C), thereby avoiding the heating expenses of mesophilic (20-45°C) or thermophilic (45-65°C) treatments. Previous low-temperature trials used mesophilic inocula and little information is available on the viability of low-temperature anaerobic granulation. Six laboratory-scale, expanded granular sludge bed bioreactors (R1-6) were operated at 15°C (R1-2 and R4-5) and 37°C (R3 and R6). R1-3 were fed glucose-based wastewater and R4-6 were fed volatile fatty acid-based wastewater. Quantitative real-time PCR and qualitative denaturing gradient gel electrophoresis of 16S rRNA genes identified the dominance of Methanomicrobiales (mainly Methanocorpusculum-like organisms) during low-temperature granulation. Granulation only occurred in glucose-fed bioreactors. The results suggest that (i) granulation is feasible in low-temperature bioreactors; (ii) carbohydrate decomposition likely favoured granulation, (iii) Methanocorpusculum-like organisms play a critical role in low-temperature granulation.
High‐rate ethanol production at low pH using the anaerobic granular sludge process
Biotechnology and Bioengineering, 2021
In this study, we investigated the operational performance and product spectrum of glucose-fermenting anaerobic granular sludge reactor at pH 4. A selective environment for the growth of granules was implemented by the introduction of a 2 min settling phase, a hydraulic retention time of 6 h and a solid retention time of 12 ± 3 days. The fermentation products were ethanol, lactate, and volatile fatty acids (VFA) with yields of 0.55 ± 0.03, 0.15 ± 0.02, and 0.20 ± 0.04 gram chemical oxygen demand (gCOD)/gCOD glucose, respectively. The obtained product spectrum was remarkably different from the VFA-dominated product spectrum reported in a previous study when the same system was operated at higher pH (4.5-5.5). The shift in product spectrum coincided with a shift in the microbial community structure with the dominance of eukaryotic Candida tropicalis, Pichia jaroonii, and prokaryotic Lactobacillus species instead of the Clostridia species obtained at higher pH-values. The control of the microbiomes and the associated product spectra provides bioprocess engineers with the option to tailor a suitable precursor compound mixture for subsequent chain elongation fermentation or PHA biopolymer production.
Role of sludge volume index in anaerobic sludge granulation in a hybrid anaerobic reactor
Research Article- CHEMICAL ENGINEERING JOURNAL, 2016
Sludge Volume Index (SVI) Denaturing Gel Gradient Electrophoresis (DGGE) Quantitative Polymerase Chain Reaction (qPCR) Scanning Electron Microscopy (SEM) a b s t r a c t This work focuses on microbial granulation in hybrid anaerobic reactors (HAR). Five HARs were used in two sets of experiments and all were seeded with the same inoculum. The volume of inoculum added was 10%, 20%, 30%, 40% and 50% in the first and 13%, 15%, 18%, 23%, and 27% in the second set of experiment. The volume of inocula added affects the sludge volume index, which in the present study proves to be important parameter for granulation. The results suggest that if SVI during the reactor start-up is kept between 150 and 210, reactors were able to form granules. Outside this range in the present setup , no granulation was observed due to increased biomass wash-out, causing decreased SRT. Higher methane production was achieved in reactors with good granulation. The DGGE profiles show that the non-granulating systems had lesser diversity, due to increased wash out. Archaeal profile gave better correlation for granulation. Granulating reactors were rich in aceticlastic methanogens over hydrogen utilizing groups, especially Methanosaetaceae. Both Methanosarcina and Methanosaeta are required for better granulation as confirmed quantitatively. Bacterial profile of granulating reactors were rich in acetogens. SEM (Scanning electron microscopy) pictures show that granules are dominated by Methanosaeta-like microbes. Thus, the sludge characteristics at the start-up are of vital importance as they influence the sludge quality developed during the reactor operation and also the microbial communities retained.
Celebrating 40 years anaerobic sludge bed reactors for industrial wastewater treatment
In the last 40 years, anaerobic sludge bed reactor technology evolved from localized lab-scale trials to worldwide successful implementations at a variety of industries. High-rate sludge bed reactors are characterized by a very small foot print and high applicable volumetric loading rates. Best performances are obtained when the sludge bed consists of highly active and well settleable granular sludge. Sludge granulation provides a rich microbial diversity, high biomass concentration, high solids retention time, good settling characteristics, reduction in both the operation costs and reactor volume, and high tolerance to inhibitors and temperature changes. However, sludge granulation cannot be guaranteed on every type of industrial wastewater. Especially in the last two decades, various types of high-rate anaerobic reactor configurations have been developed that are less dependent on the presence of granular sludge, and many of them are currently successfully applied for the treatment of various kinds of industrial wastewaters worldwide. This study discusses the evolution of anaerobic sludge bed technology for the treatment of industrial wastewaters in the last four decades, focusing on granular sludge bed systems.