RESUMEN
This work aims to evaluate the hydrodynamic properties of the sludge bed of Upflow Anaerobic Sludge Blanket (UASB) reactors based on its settleability and expansion characteristics. The methodologies used for the evaluation of the settleability of aerobic activated sludge, and for the expansibility of a sludge bed of Expanded Granular Sludge Bed reactors and Fluidised Bed Reactors were adapted and applied to the particular characteristics of the sludge of UASB reactors. An easy-to-build experimental set-up was developed to assess the parameters necessary for the equations of settleability and of expansibility. The results obtained from the sludges of seven differently operated reactors show that, for the treatment of low strength wastewater, settleability increased and expansibility decreased at decreased hydraulic retention time, from 6 to 1 h, and/or increased influent concentrations, from 136 to approximately 800 mg chemical oxygen demand/L. The results also show that it is useless to design an UASB reactor with a longer hydraulic retention time to cope with hydraulic shock loads, as a more expansible sludge will develop at such condition.
Asunto(s)
Reactores Biológicos , Hidrodinámica , Aguas del Alcantarillado/análisis , Purificación del Agua/instrumentación , Purificación del Agua/métodos , Cinética , Proyectos PilotoRESUMEN
The effects of hydraulic retention time (HRT) and influent COD concentration (CODInf) 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 CODInf 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 CODInf 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.
Asunto(s)
Reactores Biológicos/microbiología , Metano/metabolismo , Eliminación de Residuos Líquidos/métodosRESUMEN
Although many publications are available on the fate of estrone (E1), 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) during aerobic wastewater treatment, little is published on their fate under strictly anaerobic conditions. Present research investigated the digestibility of E1 and EE2, using digested pig manure, granular UASB sludge, UASB-septic tank sludge and activated sludge as inocula. Besides, actual concentrations were measured in a UASB septic tank treating black water. Under anaerobic conditions E1 is reduced to E2 but the extent of this reduction depends on type of inoculum. No significant loss of the sum of E1 and E2 and of EE2 was observed. Adsorption was responsible for a 32-35% loss of E1 and E2 from the liquid phase in the UASB septic tank and the effluent still contained considerable concentrations of respectively 4.02 microg/l and 18.79 microg/l for E1 and E2 with a large fraction present in conjugated form. No EE2 was detected in the UASB effluent.
Asunto(s)
Estradiol/análisis , Estrona/análisis , Etinilestradiol/análisis , Agua/análisis , Adsorción , Anaerobiosis , Animales , Biodegradación Ambiental , Reactores Biológicos , Estiércol/análisis , Oxidación-Reducción , Aguas del Alcantarillado/química , Porcinos , Eliminación de Residuos Líquidos/métodos , Contaminantes Químicos del Agua/análisisRESUMEN
The fate of oestrone (E1), 17beta-oestradiol (E2) and 17alpha-ethynyloestradiol (EE2) was investigated in a concentrated blackwater treatment system consisting of an UASB septic tank, with micro-aerobic post-treatment. In UASB septic tank effluent a (natural) total concentration of 4.02 microg/L E1 and 18.69 microg/L E2, comprising the sum of conjugated (>70% for E1 and >80% for E2) and unconjugated forms, was measured. During post-treatment the unconjugated oestrogens were removed to below 1 microg/L. A percentage of 77% of the measured unconjugated E1 and 82% of E2 was associated with particles >1.2 microm in the final effluent implying high sorption affinity of both compounds. When spiking the UASB septic tank effluent with E1, E2, EE2 and the sulphate conjugate of E2, removal in the micro-aerobic post-treatment was >99% for both E2 and EE2 and 83% for E1. The lower removal value for E1 was a result of (slow) deconjugation during the treatment, and in the final effluent still 40% of E1 and 99% of E2 was present in conjugated form. The latter was the result of incomplete deconjugation of the spiked E2(3S) in the post-treatment system.
Asunto(s)
Estradiol/análisis , Estrona/análisis , Etinilestradiol/análisis , Contaminantes Químicos del Agua/análisis , Purificación del Agua/métodos , Agua/análisis , Aerobiosis , Anaerobiosis , Biodegradación Ambiental , Purificación del Agua/instrumentaciónRESUMEN
In conventional environmental protection the parallel development of advanced technical solutions alongside ever more stringent environmental standards increasingly conflicts with the moral and practical imperatives to ensure sustainability and drastically improve the life conditions of the world's poor. Such priorities are far better tackled by technological and social innovations based on relatively simple and highly sustainable concepts: e.g., applying Natural Biological Mineralization Routes (NBMR) for wastewater and waste treatment, implementing Decentralized Sanitation and Resource Recovery and Reuse (DESAR3) where transport of waste(water)s is kept to an optimum level and pollutants valorized, etc. With developing countries now taking a lead in applying these concepts in public sanitation, the more prosperous countries will gradually abandon the expensive, vulnerable and non-sustainable conventional approaches to wastes treatment and environmental protection.
Asunto(s)
Salud Ambiental , Contaminantes Ambientales , Saneamiento , Abastecimiento de AguaRESUMEN
In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic shock loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to shock loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic shock load, or prior to the shock, a sufficient amount of sludge needs to be discharged from the reactor.
Asunto(s)
Anaerobiosis , Aguas del Alcantarillado , Concentración de Iones de Hidrógeno , Proyectos PilotoRESUMEN
The production of small amounts of well-stabilized biological sludge is one of the main advantages of upflow anaerobic sludge bed (UASB) reactors over aerobic wastewater treatment systems. In this work, sludge produced in three pilot-scale UASB reactors used to treat sewage under subtropical conditions was assessed for both stability and specific methanogenic activity. Stability of primary sludge from settling tanks and digested sludge from conventional sludge digesters was also measured for comparison purposes. Kinetic parameters like the hydrolysis rate constant and the decay rate constant were calculated. High stability was observed in sludge from UASB reactors. Methanogenic activity in anaerobic sludges was relatively low, probably due to the low organic matter concentration in influent sewage. Knowledge on sludge growth rate, stability, and activity might be very useful to optimize sludge management activities in full-scale UASB reactors.
Asunto(s)
Aguas del Alcantarillado , Anaerobiosis , Hidrólisis , Cinética , Metano/biosíntesis , Proyectos Piloto , Aguas del Alcantarillado/microbiología , Clima TropicalRESUMEN
Anaerobic biological degradation processes (AnDe), when properly integrated with complementary biological and physical methods, constitute the ideal route to a sustainable protection of the life environment. However unfortunately for a smooth implementation of AnDe-processes drastic conceptual innovations are urgently needed in the field of environment protection; the present highly centralized approach in the public sanitation sector (CENSA) need to be substituted by a concept that focuses on optimal decentralization, problem prevention, self-sufficiency, resource recovery and reuse, with coupling to agriculture practices at or nearby the location (DESAR). Although a variety of excellent DESAR-based systems already are available and anaerobic digestion and treatment methods have found successful full-scale application for waste and wastewater treatment, there still is potential to improve these systems. Interesting questions to be elucidated are the effect of trace elements and macro-nutrients, the sludge immobilization phenomenon and the effect of environmental factors like temperature, pressure, mixing. Therefore tentatively a lot of challenging interdisciplinary research is waiting to attain further profitable innovations.
Asunto(s)
Bacterias Anaerobias/metabolismo , Conservación de los Recursos Naturales , Eliminación de Residuos Líquidos/métodos , Agricultura , Biodegradación Ambiental , Reactores BiológicosRESUMEN
A dynamic model has been developed to describe the anaerobic digestion of solid cattle waste in an accumulation system (AC). To calibrate the model an experiment was carried out at a lab-scale AC at 50 degrees C. The predicted methane production shows a very good agreement (i.e. R2 = 0.998) with the experimental data. However less agreement is evident for the intermediates. After model validation the model was applied to study the effect of different aspect ratios on the system performance. An optimum aspect ratio of 2-3 could be determined.
Asunto(s)
Reactores Biológicos/microbiología , Estiércol , Metano/metabolismo , Modelos Biológicos , Animales , Bacterias Anaerobias/metabolismo , Bovinos , Ácidos Grasos Volátiles/metabolismo , Calor , Hidrólisis , Reproducibilidad de los ResultadosRESUMEN
In this investigation, the performance of Upflow Anaerobic Sludge Blanket (UASB) reactors treating municipal wastewater was evaluated on the basis of: (i) COD removal efficiency, (ii) effluent variability, and (iii) pH stability. The experiments were performed using 8 pilot-scale UASB reactors (120 L) from which some of them were operated with different influent COD (CODInf ranging from 92 to 816 mg/L) and some at different hydraulic retention time (HRT ranging from 1 to 6 h). The results show that decreasing the CODInf, or lowering the HRT, leads to decreased efficiencies and increased effluent variability. During this experiment, the reactors could treat efficiently sewage with concentration as low as 200 mg COD/L. They could also be operated satisfactorily at an HRT as low as 2 hours, without problems of operational stability. The maximum COD removal efficiency can be achieved at CODInf exceeding 300 mg/L and HRT of 6h.
Asunto(s)
Bacterias Anaerobias/metabolismo , Reactores Biológicos/microbiología , Eliminación de Residuos Líquidos/métodos , Brasil , Estudios de Evaluación como Asunto , Metano/metabolismo , Aguas del Alcantarillado/microbiología , Factores de TiempoRESUMEN
The inhibitory effect of phosphate on acetoclastic-methanogens was investigated for three different thermophilic (55 degrees C) anaerobic consortia. When 70 mM of phosphate was tested, acetoclastic methanogens was completely inhibited in "Eerbeek" sludge which is dominated by Methanosaeta-like methanogens. For the "Hoogezand" sludge the specific methanogenic activity dropped by 79%, indicating that any of the acetate-consuming methanogens present in the sludge was more resistant to the phosphate applied. The results demonstrated that the inhibitory effect of phosphate may affect both methane production rate and final methane concentration and might also be time dependent. This study indicates that the degree of inhibition is species-dependent, and even more resistant species may be affected during long-term experiments. Such inhibition is a matter of concern for researchers since misleading conclusions might be taken from growth and specific methanogenic activity tests when considerable concentrations of phosphate buffer are used and no interference is expected.
Asunto(s)
Metano/metabolismo , Methanosarcinales/efectos de los fármacos , Fosfatos/farmacología , Aguas del Alcantarillado/microbiología , Acetatos/metabolismo , Reactores Biológicos , Calor , Residuos Industriales , Methanosarcinales/metabolismo , Papel , Eliminación de Residuos LíquidosRESUMEN
Sludge flotation was reported to cause several operational problems in anaerobic systems including UASB reactors treating both strong domestic sewage and some industrial wastewater. This research is to investigate the effect of anaerobic digestion on scum-forming potential (SFP) of sludge and other physical-chemical properties. A simple test was developed to measure and compare the tendency of different sludge to form a scum layer. Results showed that anaerobic digestion affects chemical composition of sludge flocs and consequently, SFP, which was found to be inversely proportional to the degree of digestion (both SRT and temperature). It was suggested that higher protein concentration at elevated SRT and 25 degrees C increased the negative surface charge of sludge flocs and ,consequently, reduced the ability of sludge to attach to gas bubbles and float. Floc average size increased with increasing SRT and temperature, especially for sludge with 75d SRT at 25 degrees C. On the other hand, settling properties of sludge were negatively affected by increasing SRT to 75d at 25 degrees C. Filterability had a strong positive correlation with average floc size, but also polymeric constituents correlated positively with filterability at 25 degrees C.
Asunto(s)
Reactores Biológicos , Residuos Industriales , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Anaerobiosis , Filtración , Floculación , Tamaño de la Partícula , Aguas del Alcantarillado/química , Temperatura , Factores de TiempoRESUMEN
A 96 m3 UASB reactor was operated for 2.5 years under different conditions to assess the feasibility of treating strong sewage (COD(tot) = 1531 mg/l) at ambient temperatures with averages of 18 and 25 degrees C for winter and summer respectively. During the first year, the reactor was operated as a two-stage system at OLRs in the range of 3.6-5.0 kg COD/m3 d for the first stage and 2.9-4.6 kg COD/m3 d for the second stage. The results of the first stage showed average removals of 51% and 60% for COD(tot) and COD(ss) respectively without significant effect of temperature. The second stage reactor was unstable. The temperature affected sludge stabilization. During the second year, the first stage was operated as a single-stage UASB reactor at half of the previous loading rates. The results showed an average removal efficiency of 62% for COD(tot) during summer, while it dropped to 51% during wintertime. However, the effluent suspended solids were stabilized with VSS/TSS ratio around 0.50 all over the year. The sludge in the single-stage reactor was well-stabilized and exerted an excellent settlability. During the last three months of research, sludge was discharged regularly from the single-stage UASB reactor. The results showed no significant improvement in the performance in terms of COD(tot). Based on the results of the experiment, a single-stage UASB reactor operated at relatively long HRT is preferred above two-stage system at the Jordanian conditions.
Asunto(s)
Bacterias Anaerobias/metabolismo , Reactores Biológicos , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/instrumentación , Eliminación de Residuos Líquidos/métodos , Jordania , Oxígeno/metabolismo , Estaciones del Año , TemperaturaRESUMEN
Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 degrees C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 degrees C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 degrees C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.
Asunto(s)
Reactores Biológicos , Aguas del Alcantarillado/química , Adsorción , Aerobiosis , Bacterias Aerobias/metabolismo , Floculación , Residuos Industriales , Oxígeno/metabolismo , Papel , Tamaño de la Partícula , Polímeros/química , Aguas del Alcantarillado/microbiología , Resistencia al Corte , Temperatura , Eliminación de Residuos Líquidos/métodosRESUMEN
This paper reviews different theories on anaerobic sludge granulation in UASB-reactors that have been proposed during the past two decades. The initial stages of the formation of anaerobic granules follow the same principles as biofilm formation of bacteria on solid surfaces. There exist strong evidence that inert carriers play an important positive role in granulation. Most researchers conclude that Methanosaeta concilii is a key organism in granulation. Only the Cape Town Hypothesis presumes that an autotrophic hydrogenotrophic organism, i.e., Methanobacterium strain AZ, growing under conditions of high H(2)-pressures, is the key organism in granulation. Many authors focus on the initial stage of granulation, and only a few contributions discuss the latter stages in granulation: granule maturation and multiplication. Granule enhancing factors in the latter stages predominantly rely on manipulation of the selection pressure, through which selectively heavier sludge particles are retained in the UASB reactor.
Asunto(s)
Bacterias Anaerobias/fisiología , Reactores Biológicos , Methanosarcinales/fisiología , Aguas del Alcantarillado/microbiología , Tamaño de la Partícula , Aguas del Alcantarillado/química , Eliminación de Residuos Líquidos/métodosRESUMEN
The impact of humic acids and the humic model compound, anthraquinone-2,6-disulfonate (AQDS), on the biodegradation of carbon tetrachloride (CT) by anaerobic granular sludge was studied. Addition of both humic acids and AQDS at sub-stoichiometric levels increased the first-order rate of conversion of CT up to 6-fold, leading to an increased production of inorganic chloride, which accounted for 40-50% of the CT initially added. Considerably less dechlorination occurred in sludge incubations lacking humic substances. By comparison, very limited dechlorination occurred in sterile controls with autoclaved sludge. Accumulation of chloroform (1-10%) and dichloromethane (traces) also accounted for the CT converted. The accumulation of a chlorinated ethene, perchloroethylene (up to 9% of added CT), is also reported for the first time as an end-product of CT degradation. A humus-respiring enrichment culture (composed primarily of a Geobacter sp.) derived from the granular sludge also dechlorinated CT, yielding products similar to the AQDS-supplemented granular sludge consortium. The dechlorination of CT by the Geobacter enrichment was dependent on the presence of AQDS or humic acids, which were reduced during the assays. The reduced form of AQDS, anthrahydroquinone-2,6-disulfonate, was shown to cause the chemical reduction of CT when incubated in sterile medium. The results taken as a whole indicate that the formation of reduced humic substances by quinone-respiring microorganisms can contribute to the reductive dechlorination of CT.
Asunto(s)
Antraquinonas/metabolismo , Tetracloruro de Carbono/metabolismo , Aguas del Alcantarillado/química , Contaminantes Químicos del Agua/metabolismo , Ácidos Alcanesulfónicos/farmacología , Antraquinonas/antagonistas & inhibidores , Biodegradación Ambiental , Cloruros/metabolismo , Gentamicinas/farmacología , Geobacter/metabolismo , Sustancias Húmicas , Cinética , Neomicina/farmacología , Aguas del Alcantarillado/microbiología , Vancomicina/farmacologíaRESUMEN
The conversion routes of carbon monoxide (CO) at 55 degrees C by full-scale grown anaerobic sludges treating paper mill and distillery wastewater were elucidated. Inhibition experiments with 2-bromoethanesulfonate (BES) and vancomycin showed that CO conversion was performed by a hydrogenogenic population and that its products, i.e. hydrogen and CO2, were subsequently used by methanogens, homo-acetogens or sulfate reducers depending on the sludge source and inhibitors supplied. Direct methanogenic CO conversion occurred only at low CO concentrations [partial pressure of CO (PCO) <0.5 bar (1 bar=10(5) Pa)] with the paper mill sludge. The presence of hydrogen decreased the CO conversion rates, but did not prevent the depletion of CO to undetectable levels (<400 ppm). Both sludges showed interesting potential for hydrogen production from CO, especially since after 30 min exposure to 95 degrees C, the production of CH4 at 55 degrees C was negligible. The paper mill sludge was capable of sulfate reduction with hydrogen, tolerating and using high CO concentrations (PCO>1.6 bar), indicating that CO-rich synthesis gas can be used efficiently as an electron donor for biological sulfate reduction.
Asunto(s)
Reactores Biológicos , Monóxido de Carbono/metabolismo , Hidrógeno/metabolismo , Aguas del Alcantarillado/microbiología , Acetatos/metabolismo , Ácidos Alcanesulfónicos/farmacología , Anaerobiosis , Dióxido de Carbono/metabolismo , Inhibidores de Crecimiento/farmacología , Calor , Hidrógeno/análisis , Microbiología Industrial , Metano/metabolismo , Oxidación-Reducción , Sulfatos/metabolismo , Vancomicina/farmacologíaRESUMEN
The capacity of an anaerobic granular sludge for serving as an immobilizing mechanism for quinone-respiring bacteria was evaluated. The inoculum was continuously fed with a basal medium containing the humic model compound, anthraquinone-2,6-disulfonate (AQDS), as a terminal electron acceptor. Complete reduction of AQDS was achieved by the granular sludge for a prolonged period in an anaerobic bioreactor provided with a mixture of volatile fatty acids as a substrate. Phylogenetic analysis revealed the enrichment and immobilization of AQDS-respiring bacteria appearing as dominant organisms in the microbial population of the AQDS-supplemented reactor, compared to a reactor control operated under methanogenic conditions. The consistent quinone-reducing capacity observed in the consortium indicates that it is feasible to apply quinone-reducing microorganisms in continuous bioreactors and this ability can potentially be important in wastewaters rich in humic substances. The quinone reducing activity could also be applied to accelerate the conversion of xenobiotics susceptible to reductive biotransformations such as azo dyes and polychlorinated compounds in continuous bioreactors.
Asunto(s)
Bacterias Anaerobias/fisiología , Benzoquinonas/metabolismo , Reactores Biológicos , Indicadores y Reactivos/metabolismo , Modelos Teóricos , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Biotransformación , Oxidación-Reducción , Dinámica Poblacional , Xenobióticos/metabolismoRESUMEN
The thermophilic-anaerobic treatment of methanol-containing wastewater in an upflow anaerobic sludge blanket (UASB) reactor, was found to be quite sensitive to pH shocks, both acid and alkaline. The results of the recovery experiments of sludge exposed to an alkaline shock, indicated that the addition or deprivation of sodium bicarbonate (NaHCO3) in the medium, plays an important role in the competition of methanogens and (homo)acetogens for methanol. In addition, caution has to be taken when using NaHCO3 for buffering methanol-containing wastewaters, since its introduction in the system will favour (homo)acetogenesis when proper conditions are not established. Based on these results, a recovery strategy for methanogenesis was proposed where bicarbonate is supplied stepwise, and the reactor is operated in a batch mode. This strategy was found to be appropriate, i.e. the results revealed that the recovery of methanogenesis on methanol from a reactor upset or complete failure caused by pH shock is possible, even in systems where (homo)acetogens are outcompeting methanogens. The time and the number of feedings required will depend on the degree of deterioration of the sludge.
Asunto(s)
Bacterias Anaerobias/fisiología , Reactores Biológicos , Metanol/metabolismo , Bicarbonato de Sodio/química , Eliminación de Residuos Líquidos/métodos , Concentración de Iones de Hidrógeno , Dinámica Poblacional , TemperaturaRESUMEN
High NaCl concentrations (25 g x L(-1)) considerably decreased the methanol depletion rates for sludges harvested from two lab-scale sulfate reducing UASB reactors. In addition, 25 gNaCl x L(-1) strongly affected the fate of methanol degradation, with clear increase in the acetate production at the expense of sulfide and methane production. The addition of different osmoprotectants, viz. glutamate, betaine, ectoine, choline, a mixture of compatible solutes and K+ and Mg2+, slightly increased methanol depletion rates for UASB reactors sludges. However, the acceleration in the methanol uptake rate favored the homoacetogenic bacteria, as the methanol breakdown was steered to the formation of acetate without increasing sulfate reduction and methane production rates. Thus, the compatible solutes used in this work were not effective as osmoprotectants to alleviate the acute NaCl toxicity on sulfate reducing granular sludges developed in methanol degrading thermophilic (55 degrees C) UASB reactors.