RESUMEN
This study aims at comparing low-pressure membrane fouling obtained with two different secondary effluents at bench and pilot-scale based on the determination of two fouling indices: the total fouling index (TFI) and the hydraulically irreversible fouling index (HIFI). The main objective was to investigate if simpler and less costly bench-scale experimentation can substitute for pilot-scale trials when assessing the fouling potential of secondary effluent in large scale membrane filtration plants producing recycled water. Absolute values for specific flux and total fouling index for the bench-scale system were higher than those determined from pilot-scale, nevertheless a statistically significant correlation (r(2) = 0.63, α = 0.1) was obtained for the total fouling index at both scales. On the contrary no such correlation was found for the hydraulically irreversible fouling index. Advanced water characterization tools such as excitation-emission matrix fluorescence spectroscopy (EEM) and liquid chromatography with organic carbon detection (LC-OCD) were used for the characterization of foulants. On the basis of statistical analysis, biopolymers and humic substances were found to be the major contribution to total fouling (r(2) = 0.95 and r(2) = 0.88, respectively). Adsorption of the low molecular weight neutral compounds to the membrane was attributed to hydraulically irreversible fouling (r(2) = 0.67).
Asunto(s)
Cromatografía Liquida/métodos , Monitoreo del Ambiente/métodos , Espectrometría de Fluorescencia/métodos , Eliminación de Residuos Líquidos , Purificación del Agua , Cromatografía Liquida/economía , Monitoreo del Ambiente/economía , Filtración , Presión , Espectrometría de Fluorescencia/economía , Calidad del AguaRESUMEN
Twelve years after the first full scale municipal application in Europe of membrane bioreactor (MBR) technology, the process is now accepted as a technology of choice for wastewater treatment, and the market is showing sustained growth. However early misconceptions about the technology are persistent and false statements are commonly encountered in articles and conferences, generating unnecessary research efforts or even fuelling either fascination or scepticism with regards to the technology, which is ultimately detrimental to the perception of the process by water professionals. We try to provide some factual and rational clarifications on ten issues which are often wrongly reported about MBR technology.
Asunto(s)
Reactores Biológicos , Membranas Artificiales , Contaminantes del Agua/aislamiento & purificación , Abastecimiento de AguaRESUMEN
This paper deals with the performance and the optimisation of the hydraulic operating conditions of the A3 Water Solutions flat sheet membrane technology in a MBR pilot-plant to achieve a satisfying fouling control and also a reduction in the required aeration. Two vertically stacked modules were tested at pilot-scale at Anjou Recherche under typical biological operating conditions (mixed liquor suspended solids concentration (MLSS) =10 g/l; sludge retention time (SRT) =28 days; food to microorganism ratio (F/M)=0.12 kg COD/kg MLSS/d). The use of a double-deck and of specific backwashes for this membrane technology enabled to achieve satisfying membrane performances for a net flux of 25 L h(-1) m(-2), 20 degrees C at a low specific aeration demand per membrane surface (SADm = 0.2 Nm(3) h(-1) m(-2)) which corresponds to a specific aeration demand per permeate volume unit (SADp) of 8 Nm(3) air/m(3) permeate, which is lower than reported for many commercial membrane systems. The mixed liquor characteristics (foaming, MLSS concentration) appeared to influence the fouling behaviour of the membranes but no correlation was found with the fouling rate. However, with the new operating conditions, the system is robust and can cope with fouling resulting from biological stress and daily peak flows for MLSS concentrations in the membrane tank up to 18 g/l.
Asunto(s)
Reactores Biológicos , Membranas Artificiales , Eliminación de Residuos Líquidos/instrumentación , Eliminación de Residuos Líquidos/métodos , Filtración/instrumentación , Filtración/métodos , Proyectos Piloto , Agua/química , Contaminantes Químicos del AguaRESUMEN
The objective of the study was to identify alternative cleaning reagents to chlorine for membrane permeability regeneration in MBR applications. Indeed, chlorine is prohibited in some countries because of the formation of by-products such as THM. The study was focused on the comparison of ten cleaning reagents performances and in particular on their ability to remove irreversible fouling. The tests were carried on with the A3 Water Solutions' Maxflow membrane (flat sheet membrane). A specific experimental protocol was defined at lab scale to develop an irreversible fouling by filtering sludge supernatant. The more promising reagents at lab scale were then tested on the A3 membrane continuously immersed in a MBR pilot plant functioning under typical biological conditions (MLSS=11 g/l; SRT=28 days). A full scale test was finally performed with hydrogen peroxide, one of the best reagents. Chlorine was taken as reference for all performed tests. The cleaning performances of the selected reagents were different at the different scales, probably due to the difficulty to obtain an irreversible membrane fouling at larger scales. This testing procedure will be reproduced with other membrane materials to have a better understanding of interactions between irreversible fouling, material nature and chemical reagents.
Asunto(s)
Reactores Biológicos , Indicadores y Reactivos , Membranas Artificiales , Color , Permeabilidad , Proyectos Piloto , Aguas del AlcantarilladoRESUMEN
Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m3 each. Both configurations included an anaerobic zone ahead of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or post-denitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50 microgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring a low dose of ferric salt ferric salt < 3 mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1 mg of phosphorus was biologically eliminated for 10 mg BOD5 in the influent. The post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.