Notice of RetractionPilot Study on Hybrid Biological Filter-Coagulation-Submerged Ultrafiltration Membrane for Drinking Water Treatment
Two parallel hybrid processes (Biological filter Coagulation/Ultrafiltration(BCUF) and Coagulation/Ultrafiltration(CUF)) for treating slightly polluted surface water were carried out in this experiment. In the process of BCUF, transverse flow water-dropping aerated biological filter was used as a primary pretreatment, and coagulation was used as the subsequent pretreatment of Ultrafiltration(UF). In the CUF process, coagulation was the unique pretreatment of UF. Turbidity was removed nearly completely in both two hybrid processes, and in the BCUF, effective ammonia nitrogen removal (87.1%) was also achieved mainly through the biological nitrification carried out in the biological filter, however, only 25.6% removal of ammonia nitrogen was achieved in the process of CUF. The removal rates of CODMn, TOC, DOC, UV254, AOC and BDOC were 55.2%, 87.8%, 71.0%, 61.1%, 91.4% and 89.3% respectively in the process of BCUF, which were much higher than that in the process of CUF. The biological pretreatment could improve the biological stability significantly and relieve the membrane fouling which made the transmembrane pressure (TMP) arising velocity lower. The pretreatment of biological filter and coagulation could remove the organic molecules in the range of 5000-500Da. Results showed the water-dropping aerated biological filter was fit for the pretreatment of UF.
Immersed membrane filtration for the production of drinking water: combination with PAC for NOM and SOCs removal
Abstract The use of microfiltration (MF) or ultrafiltration (UF) processes is expanding rapidly as an alternative to conventional clarification and filtration processes to meet increasingly stringent regulations related to the treated water quality and in particular to pathogens such as Giardia and Cryptosporidium. The membranes used in these processes do not remove color, natural organic matter (NOM) or synthetic organic chemicals (SOCs). MF and UF must be combined with other conventional technologies such as activated carbon adsorption and coagulation to overcome some of these limitations. In this context recent advances in immersed membranes configurations offer an opportunity to develop new combined treatment processes. In most of these systems, shell-less hollow fiber membranes are directly immersed in the reaction vessel receiving the water to be purified and operated under slight negative pressure (whereas they are traditionally housed in pressure vessels in conventional MF and UF systems). The membranes represent a positive barrier between a “reaction zone” where adsorption, biodegradation or coagulation can be carried out and the water treated. The system offers a great flexibility of operation by allowing operation at high suspended solids concentrations and to adapt the type and age of the suspension to the required treatment. The association of immersed membranes and powdered activated carbon provides the following benefits: (1) better physical removal of NOM and SOCs through optimal use of PAC, (2) biological removal of the biodegradable fraction of NOM, (3) reduced sludge volumes, and (4) absolute containment of the PAC within the system independent of process conditions. The very high concentration of PAC (10–20 g/L) carried in the reactor offers the required buffer capacity. The present research program, carried out at Compagnie Generale des Eaux Research Laboratory (in Maisons-Laffitte, France), has examined the use of immersed membranes for significantly enhancing SOCs and NOM removal at bench and pilot scales. An on-site pilot-study was conducted in Granville (Normandie) over one year to evaluate the immersed membrane process on river water. The process was first evaluated as a polishing microfiltration/PAC slurry reactor, after conventional coagulation/flocculation and sedimentation. In a second phase, the process was directly used on raw water with in-line coagulation; in that case, the coagulated matter and the PAC were allowed to co-exist in the membrane tank. The results of these studies show that the combination of immersed membranes with PAC and/or coagulant provides (1) excellent water quality through significant enhancement of particulate matters as well as NOM and SOCs removal, (2) excellent response to variations of the feed water quality and (3) suitability for plant upgrading by conversion of existing clarifiers or sand filters into membrane reactors.
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.