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On the effect of flocculation as pretreatment process and particle size distribution for membrane fouling reduction
No full textThis work deals with the feasibility of an olive vegetation wastewater purification process consisting of two consecutive steps: coagulation followed by membrane separation. The target of this work was to reach a purification grade of the wastewater compatible with the limits for the discharge into a Municipal sewer that is a COD value less than 500 mg L(-1). A feedstock with 55 g L(-1) of COD was used for the experimental work. In a first step, the feedstock was pretreated by a flocculation process using as coagulant aluminium sulphate or aluminium hydroxide. Then, the pretreated wastewater stream was purified by four consecutive batch membrane processes consisting of microfiltration, ultrafiltration, nanofiltration and reverse osmosis, each with a recovery rate of 90%. For each membrane, at different recovery values, the critical flux values were Measured. Finally, all the streams were analyzed by means of a nanosizer, capable to measure the Suspended particle size distribution in the samples from 0.8 nm Lip to 6.5 mu m. Flocculation changes the fouling outcome on the membranes by changing sensibly the particle size distributions of the solution. The membrane's performances are strictly dependant on the coagulant type used during the pretreatment operation. In order to develop full advantages on fouling issues, the particle size shift effect of the flocculation process should be carefully studied and evaluated, and needs fine-tuned optimization
A three year long experience of effective fouling inhibition by threshold flux based optimization methods on a nf membrane module for olive mill wastewater treatment
No full textThe operation of a spiral-wounded nanofiltration membrane module used continuously for three years in order to purify different pretreated olive mill wastewater streams will be discussed. The membrane module was for the first time used at the beginning of year 2006 on a batch pilot scale plant for critical flux studies and wastewater treatment in our laboratories. The olive mill wastewater is a waste stream produced by the olive oil mill factories, characterized by very high organic matter load and polyphenols concentration. Without fouling inhibition at all, nanofiltration membranes will reach zero-flux conditions within days. This is not the case of this nanofiltration membrane module, which was successfully operated continuously for three years during our laboratory work. This result was reached by proper fouling inhibition control, relaying on both critical flux measurements and the development of an optimized operation method. Although the critical flux theory was successfully applied to this system, it was not capable to explain the observed fouling behavior of the examined membrane system. The doubt to work on a membrane system that does not follow perfectly the critical flux laws grow throughout the years. In year 2011, Field et al. introduced the threshold flux concept as an extension to particular membrane systems treating real wastewater streams, and this latter theory fits to the observations made on olive mill wastewater. In this work, a revision of previously obtained results in terms of critical flux will be performed, using the threshold flux theory as discussion basis. In the examined system, both critical and threshold points were found at 7-8 bar depending of the used feedstock and membrane condition. Moreover, it will be checked why the adopted "critical flux" approach was successful in inhibiting fouling for so many years despite it was not the correct approach. Copyright © 2013, AIDIC Servizi S.r.l
Purification of a olive vegetation waste water stream by coagulation and membrane separation
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Ottimizzazione dei processi a membrana per il trattamento degli effluenti di provenienza dall’industria olearia
No full textAbout the validation of advanced membrane process control systems in wastewater treatment applications
Full text linkThis paper focuses on the validation of advanced control systems to use on either batch or continuous, new or existing membrane process plants, by use of a simulation software (Aspen Hysys).
In the last decade, membrane technologies resulted to be very appealing and shows positive market trends. One main drawback is membrane fouling, which affects productivity, selectivity and longevity of the process, which leads to both technical and economical failures: proper membrane process design and control is a difficult task to accomplish. This leads to overdesign the plant capacities by process engineers, making this technology less reliable and convenient.
Nowadays membrane processes are controlled by a constant permeate flow rate or constant applied operating pressure. These simple control strategy approaches are sufficient to operate the processes, but do not distinguish different fouling operating regions, and therefore do not avoid process failures due to fouling. Fouling may be described by the boundary flux theory in a convenient way, separating low-fouling operations from high-fouling ones.
The paper reports about the validation of an previously developed advanced membrane process control system based on the boundary flux concept on different wastewater feedstocks. The advanced control strategy by the use of a simulation software by Aspen Hysys, capable to predict boundary flux values by measurement of some key parameters, was validated and capable to set suitable set-point values to the feedback controllers in order to work at or below the boundary flux. As a consequence, the membrane process is always operated far from irreversible fouling issues. The developed approach was then successfully validated by experiments on lab scale
Il fouling delle membrane in relazione alle dimensioni particellari della corrente di alimentazione
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Development Of A Stationary Prediction Model About Critical Flux Reductions Of Membrane Modules After Fouling Transients
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