Performance of uasb reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste (original) (raw)
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Anaerobic digestion of long-chain fatty acids in UASB and expanded granular sludge bed reactors
Process Biochemistry, 1993
Solutions of sodium caprate and sodium lam-ate were digested in upj7ow anaerobic sludge bed (UASB) reactors inoculated with granular sludge and in expanded granular sludge bed (EGSB) reactors. UASB reactors are unsuitable if lipids contribute 50% or more to the COD of waste water: the gas production rate required to obtain sufficient mixing and contact cannot be achieved. At lipid loading rates exceeding 2-3 kg COD m-3 day-', total sludge wash-out occurred. At lower loading rates the system was unreliable, due to unpredictable sludge fi'otation. EGSB reactors do fulfil the requirements of mixing and contact. They accommodate space loading rates up to 30 kg COD m-j day-' during digestion of caprate or laurate as sole substrate, at COD removal eficiencies of 83-91%, and can be operated at hydraulic residence times of 2 h without any problems. Augmentation of granular sludge in lab-scale EGSB reactors was demonstrated. The new granules had excellent settling properties. Floating layerformation, as well as mixing characteristics in full-scale EGSB reactors require further research.
Anaerobic treatment of fish meal process waste-water in a UASB reactor at high pH
Applied Microbiology and Biotechnology, 1992
The influence of high pH on anaerobic degradation of fish process waste-water with a high total ammonia concentration was investigated in an upflow anaerobic sludge blanket (UASB) reactor. More than 99% of volatile fatty acids and trimethylamine in the process waste-water were degraded up to pH 7.9. Above pH 7.9 only the conversion of acetate was slightly decreased. At pH 8.3 serious disintegration of the granules occurred leading to process failure. Increasing the pH changed the physical characteristics of the granules leading to decreased density, size, and volatile solids content. After 4 months of acclimatization to high pH in the reactor, the specific methanogenic activity of the granular biomass was the same from pH 7.1 to 8.5. At pH 8.3 and 8.5, acclimatization had improved the specific activity by 25 and 50%, respectively. However, the acclimatized biomass generally showed a decreased activity (60%) at all pH values tested below the acclimatization pH.
Water Science & Technology, 2009
The effects of hydraulic retention time (HRT) and influent COD concentration (COD Inf) on Specific Methanogenic Activity (SMA) and the biodegradability of an anaerobic sludge need to be elucidated because of the discordant results available in literature. This information is important for the operation of anaerobic reactors and design of the sludge post-treatment unit. For this study, sludge samples obtained from eight pilot-scale Upflow Anaerobic Sludge Blanket (UASB) reactors were tested. The reactors were fed with municipal wastewater and operated with different sets of HRT and influent concentrations until the steady state was established. The results show that at a lower HRT, sludge with relatively higher SMA develops. A slight trend of declining SMA at increasing COD Inf was found for reactors operated at longer HRTs; however, further experiments are necessary for more definitive conclusions. The sludge from reactors operated at longer HRTs and with lower COD Inf resulted in lower biodegradability. Results also showed that it is ineffective to design a UASB reactor with a longer HRT to cope with organic shock loads.
2012
Anaerobic treatment of liquidized food waste (LFW) was carried out in an upflow anaerobic sludge blanket reactor (UASBR) by stepwise increase in organic loading rate (OLR) and temperature. The chemical oxygen demand (COD), total organic carbon (TOC), biogas and methane production were measured at hydraulic retention time (HRT) of 10 to 4d, and start up strategy of the reactor was monitored for 10 weeks. Thermophilic condition was achieved by increasing the temperature from 30 to 558C, and pH was maintained at 7 6 0.5 throughout the experiment. Maximum COD removal efficiency was 93.67% (r 5 0.84) at an OLR of 12.5 g-COD/LÁd and 4d HRT. Maximum TOC removal efficiency was 79.14% (r 5 20.94) at an influent TOC concentration of 3.59 g/L. Biogas and methane yield were recorded to a maximum of 1.364 L/g-COD removed Ád (r 5 0.81), 0.912 L/g-COD removed Ád (r 5 0.83), and average methane content of biogas was 63%. The reactor was fully acclimatized at 558C and achieved stability with high removal efficiency and biogas production. An OLR of 12.5 g-COD/LÁd and HRT of 4 days were suitable for the treatment of LFW in UASBR.
Journal of Biotechnology, 1996
A high rate anaerobic treatment of palm oil mill effluent (POME) was achieved in a two-stage up-flow anaerobic sludge blanket (UASB) reactor. The acidogenic reactor acclimated rapidly to the wastewater and was tolerant to a suspended solids (SS) concentration of 5.4 g 1-r in the influent wastewater. Loading was gradually increased over a period of 100 days resulting in a satisfactory hydrolysis and acidification giving a maximum rate of acid production of 4.1 g I-' d _ ' acetic acid at a loading rate of 16.6 g I-' d-' COD at a hydraulic retention time of 0.9 days. An increase in alkalinity throughout the acclimatization maintained the effluent from the reactor at around pH 5.8. The methanogenic reactor was initially fed on dilutions of the effluent from the first stage reactor after pH adjustment. The loading was gradually increased, and then stepwise, to 60 g I-' dd' COD at which point COD removal efficiency had declined significantly and an accumulation of long-chain volatile fatty acids was observed. It was concluded that the reactor could work efficiently up to loadings of 30 g l-' dd' COD, whilst producing a good methane yield and a COD reduction of greater than 90%. Effluent recirculation alleviated the need for alkali additions to the feed of the methanogenic reactor and a direct coupling of the two reactors was achieved towards the end of the experimental run of 175 days. Both reactors showed granule formation with distinct morphological characteristics; these were observed to be formed after 80 days in the acidogenic reactor and after I IO days in the methanogenic reactor.
Inhibition of Volatile Fatty Acid Production in Granular Sludge from a UASB Reactor
Journal of Environmental Science and Health, Part A, 2005
Inhibition of volatile fatty acids (VFA), namely acetate, butyrate, and propionate, on the activity of acetoclastic methanogens within a full-scale upflow anaerobic sludge blanket (UASB) reactor was investigated using specific methanogenic activity (SMA) test. SMA tests were carried out at acetate concentrations in a range of 1000-25,000 mg l −1 , butyrate concentrations in a range of 3000-25,000 mg l −1 and propionate concentrations between 500-10,000 mg l −1 . Maximum potential methane production (PMP) rates were obtained as 389 ml CH 4 gTVS −1 .d −1 at 3000 mg l −1 acetate concentration, 432 ml CH 4 gTVS −1 ·d −1 at butyrate concentration of 5000 mg l −1 , and 162 mlCH 4 gTVS −1 .d −1 at 1000 mg l −1 propionate concentration. App. 50% and 100% inhibition occurred at acetate concentrations of 13,000 mg l −1 and 25,000 mg l −1 , butyrate concentrations of 15,000 mg l −1 and 25,000 mg l −1 , and propionate concentrations of 3500 mg l −1 and 5000 mg l −1 , respectively.
Water Environment Research, 2007
In the present study, characteristics of the granular sludge (including physical characteristics under stable conditions and process shocks arising from suspended solid overload, soluble organic overload, and high temperature; biological activity; and sludge kinetic evaluation in a batch experiment) developed in an upflow anaerobic sludge blanket fixedfilm reactor for palm oil mill effluent (POME) treatment was investigated. The main aim of this work was to provide suitable understanding of POME anaerobic digestion using such a granular sludge reactor, particularly with respect to granule structure at various operating conditions. The morphological changes in granular sludge resulting from various operational conditions was studied using scanning electron microscopy and transmission electron microscopy images. It was shown that the developed granules consisted of densely packed rod-(Methanosaeta-like microorganism; predominant) and cocci-(Methanosarsina) shaped microorganisms. Methanosaeta aggregates functioned as nucleation centers that initiated granule development of POME-degrading granules. Under the suspended solid overload condition, most of the granules were covered with a thin layer of fiberlike suspended solids, so that the granule color changed to brown and the sludge volume index also increased to 24.5 from 12 to 15 mL/g, which caused a large amount of sludge washout. Some of the granules were disintegrated because of an acidified environment, which originated from acidogenesis of high influent organic load (29 g chemical oxygen demand [COD]/L Á d). At 608C, the rate of biomass washout increased, as a result of disintegration of the outer layer of the granules. In the biological activity test, approximately 95% COD removal was achieved within 72 hours, with an initial COD removal rate of 3.5 g COD/L Á d. During POME digestion, 275 mg calcium carbonate/L bicarbonate alkalinity was produced per 1000 mg COD removed / L. A consecutive reaction kinetic model was used to simulate the data obtained from the sludge activity in the batch experiment. The mathematical model gave a good fit with the experimental results (R 2 . 0.93). The slowest step was modeled to be the acidification step, with a rate constant between 0.015 and 0.083 hours 21 , while the rate constant for the methanogenic step was obtained to be between 0.218 and 0.361 hours 21 . Water Environ. Res., 79, 833 (2007).
When treating municipal wastewater, the disposal of sludge is a problem of growing importance, representing up to 50% of the current operating costs of a wastewater treatment plant. Although different disposal routes are possible, anaerobic digestion plays an important role for its abilities to further transform organic matter into biogas (60-70 vol% of methane, CH 4 ), as thereby it also reduces the amount of final sludge solids for disposal whilst destroying most of the pathogens present in the sludge and limiting odour problems associated with residual putrescible matter. Anaerobic digestion thus optimises WWTP costs, its environmental footprint and is considered a major and essential part of a modern WWTP. The potential of using the biogas as energy source has long been widely recognised and current techniques are being developed to upgrade quality and to enhance energy use. The present paper extensively reviews the principles of anaerobic digestion, the process parameters and their interaction, the design methods, the biogas utilisation, the possible problems and potential pro-active cures, and the recent developments to reduce the impact of the problems. After having reviewed the basic principles and techniques of the anaerobic digestion process, modelling concepts will be assessed to delineate the dominant parameters. Hydrolysis is recognised as rate-limiting step in the complex digestion process. The microbiology of anaerobic digestion is complex and delicate, involving several bacterial groups, each of them having their own optimum working conditions. As will be shown, these groups are sensitive to and possibly inhibited by several process parameters such as pH, alkalinity, concentration of free ammonia, hydrogen, sodium, potassium, heavy metals, volatile fatty acids and others. To accelerate the digestion and enhance the production of biogas, various pre-treatments can be used to improve the rate-limiting hydrolysis. These treatments include mechanical, thermal, chemical and biological interventions to the feedstock. All pre-treatments result in a lysis or disintegration of sludge cells, thus releasing and solubilising intracellular material into the water phase and transforming refractory organic material into biodegradable species. Possible techniques to upgrade the biogas formed by removing CO 2 , H 2 S and excess moisture will be summarised. Special attention will be paid to the problems associated with siloxanes (SX) possibly present in the sludge and biogas, together with the techniques to either reduce their concentration in sludge by preventive actions such as peroxidation, or eliminate the SX from the biogas by adsorption or other techniques. The reader will finally be guided to extensive publications concerning the operation, control, maintenance and troubleshooting of anaerobic digestion plants.
Aquaculture, 2008
Intensive recirculating aquaculture systems (RAS) produce high volumes of biosolid waste. The high salinity of brackish/marine sludge limits its use in landfill sites and waste outflows and it is a source of pollution. A reduction in sludge mass would therefore minimize the potential environmental hazard and economic burden stemming from its disposal. The aims of the current study were: 1) to characterize brackish aquaculture sludge (BAS) from three RAS in order to test for potentially suitable treatments, and 2) to test the BAS's suitability for anaerobic digestion in an upflow anaerobic sludge blanket reactor (UASB). Brackish sludge from three intensive RAS was collected periodically and analyzed for a variety of physical and chemical parameters. The mean sludge electrical conductivity and pH values ranged from 4.0 to 8.6 mS cm − 1 and 7.0 to 7.7, respectively. A low sludge redox potential averaging −80 mV and dissolved oxygen concentrations of less than 1 mg l − 1 indicated the existence of anaerobic conditions. Volatile solids comprised 56 to 76% of the dry weight and the sludge volume index ranged from 44 to 69 ml g − 1 . High concentrations of total nitrogen and total carbon were also observed, resulting in a C:N ratio ranging between 8.1 and 10.3. Toxic and/or inhibitory compounds for methanogenesis such as nitrites, nitrates and sulfides were almost absent. Sludge BOD 5 ranged from 10 to 30% dry weight. These data suggest that BAS may be used in anaerobic digestion and methanogenesis without pretreatment. This concept was tested by digesting aquaculture sludge in UASB reactors. Despite the high sulfate and phosphate concentrations in the BAS, these were found not to be inhibitory to methanogenesis. Up to 70% sludge-mass reduction and an average of 40% methane production were demonstrated.
Kinetics and characteristics of 70 °C, VFA-grown, UASB granular sludge
Applied Microbiology and Biotechnology, 1999
We studied in batch reactors the kinetics and characterization of 70 °C, volatile fatty acids (VFAs)-grown, upflow anaerobic sludge blanket granular sludge with 55 and 35 °C sludge as reference. The half-saturation constant (K s), the inhibition constant (K i), the maximum specific methane production rate (μCH4max), and the inhibition response coefficient (n) of the 70 °C sludge were 6.15 mM, 48.2 mM, 0.132 h−1, and 2.48, respectively, while no inhibition occurred at 55 and 35 °C, where the K s was 3.67 and 3.82 mM, respectively. At 70 °C, the highest initial specific methanogenic activity (ISMA, 0.311 gCH4-COD per gram volatile solids per day) on VFAs was about 12–15% lower than that on acetate and three to four times less than the ISMA for the 55 and 35 °C sludge. In the acetate conversion study, residual acetate (79 mg l−1) at 70 °C was three to five times higher than that at 55 and 35 °C. Further, the methane produced as percentage of the acetate consumed at 70 °C (89%) was lower than that at 55 (95%) and 35 °C (97%). At 70 °C, 10% of the ISMA remained after 15 days of starvation as compared to 26% (55 °C) and 92% (35 °C) after 30 days of starvation. Thus, the kinetics of the 70 °C granular sludge seem to differ from those at 55 and 35 °C.