RESUMEN
Stringent water treatment criteria and rapidly growing pollutant loads provoke the demand for retrofitting wastewater treatment plants towards a higher capacity. In this study, we assess a two stage alternating aeration (AA) bioreactor equipped with electroflotation (EF) clarifier, for nitrogen removal within a short hydraulic retention time (HRT). The EF under steady solids loading required a minimum unit height and gas: solids ratio of 0.006 for efficient clarification. The separated sludge blanket was further thickened with retaining stability when the cyclic solids loading was smaller than 1.0 kg m(-2). In the continuous operation of the bioreactor, the returned activated sludge concentration increased to more than 18,000 mg L(-1), while the effluent suspended solids concentration was lowered below 5 mg L(-1). Under influent chemical oxygen demand (COD)/total inorganic nitrogen (TIN) concentration of 300/30 mg L(-1), the TIN removal efficiency was near 70% with cycle time ratios of 0.17 and 0.27. Under higher influent COD concentration of 500mg L(-1), TIN removal efficiency was found to be 73.4% at a carbon:nitrogen (C:N) ratio of 10 and even higher (80.4%) at a C:N ratio of 16.6. The increased mixed liquor suspended solids concentrations (> 6000 mg L(-1)) under the high COD loading were efficiently maintained by using the EF clarifier. The results of this study demonstrate that an EF clarifier with a HRT of less than 1 h can support reliable nitrogen removal in the AA process that has a HRT of 6 h, even under increasing influent loadings.
Asunto(s)
Reactores Biológicos , Técnicas Electroquímicas/instrumentación , Nitrógeno/aislamiento & purificación , Aguas del Alcantarillado/análisis , Purificación del Agua/instrumentación , Reactores Biológicos/microbiología , Diseño de Equipo , Aguas del Alcantarillado/microbiologíaRESUMEN
Electroflotation (EF) was investigated as a final clarification of an activated sludge process, to intensify its novel clarification and thickening efficiency. During operation of a biological reactor combined with an EF clarifier, deterioration of clarification efficiency was observed. Scale deposition on electrodes caused a coarse electrode surface, significantly increasing the size of the electrolytic bubbles. The average bubble size was initially 34 microm and increased to 80 microm after bulk cell electrolysis for 150 h. X-ray diffractometry and scanning electron microscopy further characterized the scale deposition as a cluster of calcite (CaCO(3)) and brucite (Mg(OH)(2)). Switching the polarity of electrical current clearly alleviated the increase of bubble size, when applied before scale growth. Under the control of scale deposition, excellent clarification was observed, with the effluent turbidity consistently lower than 2 NTU. An efficient thickening, with the concentration of return activated sludge higher than 15 g L(-1), was additional advantage of the EF clarifier.
Asunto(s)
Electrólisis/métodos , Aguas del Alcantarillado/química , Reactores Biológicos , Electricidad , Electrodos , Eliminación de Residuos LíquidosRESUMEN
The alteration of physico-chemical properties of sediment organic matter (SOM) incubated under current-harvesting conditions as well as no-current producing conditions over 120 days using sediment microbial fuel cell systems was examined. The SOM was microbially oxidized under anaerobic conditions with an electrode serving as a terminal electron acceptor. It was found that SOM around the electrochemically-active electrodes became more humified, aromatic, and polydispersed, and had a higher average molecular weight, along with its partial degradation and electricity generation compared to that for the original sediment. These changes in SOM properties were analogous to those commonly observed in the early stages of the SOM diagenetic process (i.e. humification). Such a humification-like process was evidently more stimulated when electrical current was produced than no-current condition. These new findings associated with microbially-catalyzed electricity generation may present a potential for the energy-efficient remediation, monitoring, and/or management of the geo-environment.
Asunto(s)
Fuentes de Energía Bioeléctrica , Sedimentos Geológicos/análisis , AnaerobiosisRESUMEN
The aim of this study was to evaluate limiting factors affecting electricity output from sediment microbial fuel cells (sediment MFCs). In laboratory tests, various factors likely to be encountered in field application were divided into controllable and uncontrollable ones. Based on the findings, it could be suggested that the sediment MFCs can be operated with an anode to cathode area ratio of at least 5:1 and at high external loads (1000 ohms) when the cathode is closely placed to the anode, though DO concentration at the cathode must be kept above 3 mg/l. Furthermore, no significant effect on current production over a prolonged period was observed within the sediment temperature range of 20-35 degrees C, but was negatively affected by lower temperatures (10 degrees C). These observations provide important factors with respect to the construction and operation of sediment MFCs at field sites, which will aid in maximizing electricity output.
Asunto(s)
Fuentes de Energía Bioeléctrica/microbiología , Electroquímica/instrumentación , Electrodos , Sedimentos Geológicos/microbiología , Diseño Asistido por Computadora , Electricidad , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
In a two-electrode system, freshwater sediment was used as a fuel to examine the relationship between current generation and organic matter consumption with different types of electrode. Sediment microbial fuel cells using porous electrodes showed a superior performance in terms of generating current when compared with the use of non-porous electrodes. The maximum current densities with thicker and thin porous electrodes were 45.4 and 37.6 mA m(-2), respectively, whereas the value with non-porous electrodes was 13.9 mA m(-2). The amount of organic matter removed correlated with the current produced. The redox potential in the anode area under closed-circuit conditions was +246.3 +/- 67.7 mV, while that under open-circuit conditions only reached -143.0 +/- 7.18 mV. This suggests that an application of this system in organic-rich sediment could provide environmental benefits such as decreasing organic matter and prohibiting methane emission in conjunction with electricity production via an anaerobic oxidation process.
Asunto(s)
Fuentes de Energía Bioeléctrica/microbiología , Electroquímica/instrumentación , Electrodos , Agua Dulce/microbiología , Sedimentos Geológicos/microbiología , Transferencia de Energía , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
An automated image analysis procedure was developed to determine extended filaments length and floc area to evaluate settling characteristics of activated sludge. Digitized image obtained by Gram staining granted the first step of algorithm, segmentation, to be extremely clear and simple. The image analysis work could become more accurate and less time consuming one to be required only 1 minute of operation time per image. Filamentous bulking phenomenon of the biological sludge was induced in a laboratory-scale bioreactor system under an extreme operational condition, and the non-bulking and filamentous bulking sludge samples captured were examined with image analysis as well as traditional settling test. There existed a linear relationship between DSVI (Diluted Sludge Volume Index) and the extended filaments length. Similar results were also obtained with the extended filaments per floc area. The arithmetic mean extended filaments length showed an excellent linearity with the DSVI. It is believed that the image analysis algorithm developed in this study can be utilized for estimation of the extended filaments length and for evaluation of the settling characteristics of activated sludge effectively.
Asunto(s)
Algoritmos , Monitoreo del Ambiente/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Aguas del Alcantarillado/análisis , Aguas del Alcantarillado/química , Floculación , Aguas del Alcantarillado/microbiología , Factores de TiempoRESUMEN
Effects of humus soil particles on the dewaterability of activated sludge were investigated. Cations leaching increased proportionally with the dosage of humus soil, and the leaching was not significant after 2 h. Divalent cations, Ca2+ and Mg2+, leaching from the humus soil played an important role in improving dewaterability of the biological sludge. On the contrary, dewaterability was not affected or slightly deteriorated by the monovalent cations, K+ and Na+ leached from the humus soil. Improvement in dewaterability of the sludge by addition of humus soil was higher than that of equivalent cations mixture. It seemed that the decrease of supracolloidal bio-particles (1 to 100 microm in diameter) resulted in diminishing of the blinding effect on cake and filter medium. SRF (specific resistance to filtration) of the humus soil added sludge varied in parallel with the M/D (monovalent to divalent cation) ratio, and the M/D ratio could be utilized as a useful tool for evaluation of the sludge dewatering characteristics. Long-term effects of humus soil on the improvement of activated sludge dewaterability were clearly identified by continuous operation results of a bench-scale MLE (Modified Ludzack Ettinger) system combined with a humus soil contactor. On the other hand, dewaterability of the control sludge was only slightly improved by a decrease in M/D ratio of the wastewater influent.