0512_desalination_RO membrane autopsy


Title: RO membrane autopsy of Zarzis brackish water desalination plant

Journal: Desalination
Authors: Mohamed Karimea*, S. Bouguechab, B. Hamrounia
Corresponding author: Mohamed Karime,
a.    Laboratoire Eau et Technologies Membranaires, Facult? des Sciences de Tunis, 2092 Manar II, Tunisia Tel. +216 71 872 600; Fax +216 71 885008;                   
email: mohamed.karime@yahoo.com
b.    Laboratoire Eau et Technologies Membranaires, P?le Technologique de Borj-C?dria,
BP. 95, 2050 Hammam-Lif, Tunisia

The original and creativity of paper: This study pay an effort to identified fouling using membrane autopsy method. The proposed techniques were scanning electron microscopy, atomic force microscopy, infrared analysis and diffraction by X-ray. Since only hydrological measurement is not enough to completely gives the information about nature of fouling, thus this paper promoted the valuable technique for fouling tracking.

The classic operational problems during desalination process usually caused by a variety of fouling types: biofouling, organic fouling, inorganic fouling (including scaling) and particulate fouling. That will lead to loss of membrane performance (e.g. increase of pressure drop, decrease of flux, poor product quality). An effective control of fouling requires a good diagnosis and autopsy followed by image analysis. A number of techniques can be carried out to identify and quantify the membrane foulant, such as TOC (total organic carbon) measurement, SEM (scanning electron microscopy), AFM (atomic force microscopy), IR (infrared) analysis and diffraction by X-ray. This approach gives complete and conclusive information about the nature and origin of fouling. The membranes from the Zarzis desalination plant of brackish water were used as case study. It was conceived to respond to the needs of the Zarzis inhabitants. With a nominal capacity 15,000 m3/d, a conversion rate of 75%, with feed water salinity of 6000 mg/L. 
Results of fouling analysis by energy dispersive X-ray showed the presence of silica (56%), iron oxide (3%), calcium silicate (6%), calcium sulphate hydrate (3%), aluminium phosphate (3%) and clay (16%). The proportion of organic matter in the fouling layer (13%) has been identified by FTIR which showed the presence of polysaccharide and protein. Based on these results, the solutions to reduce fouling were suggested: 
? Sand filters must be regular maintenance.
? Apply an effective method of using an antiscalants, to inhibit precipitations of salts and a specific antiscalants for silica.
? External lid of cartridges filters corroded must be substitute on time.
? Set up the specific treatment for clay elimination, to prevent a hard layer formation on the membrane surface.
? Clean membranes on a regular basis when performances of plant are declined. 

Desalination process always operated as low efficiency caused by fouling. More effective way to reduce and prevent fouling is membrane autopsy, that could be identify the foulant composition and elucidate fouling mechanisms.  Moreover, the solutions for fouling elimination, based on acquired results, could be obtained: (i) reducing the concentration of microorganisms and/or reducing the concentration of nutrients by pre-treatment and/or (ii) performing preventive/ curative cleanings. A combination of pre-treatment and cleaning may be the way to prevent biofouling. 

Application & further study: 
The methodology and a systematically process to identify or diagnosis membrane fouling could be modified to track the seawater reverse osmosis fouling.  Moreover, this paper introduced the helpful instrument for fouling identification.

By Monruedee Moonkhum
Email: moon@gist.ac.kr

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