cultured in open ponds in a tropicalenvironment. In order to investigatethe causes of this phenomenon,Chlorella was cultivated under con-trolled conditions and the cake resis-tance was measured by batch filtra-tion in dead-end mode. Thefiltration resistance was found to be afunction of environmental condi-tions. Algae could grow favourablyand offered low specific cake resis-tance (Rcs) on the order of 1011 m/gfor the culture temperature from28°C to 35°C. The algal growth wasinhibited and the specific cake resis-tance increased to the order of 1012

m/g below or above this optimumtemperature range. Strong solar radi-ation, coupled with high tempera-tures, also inhibited the growth ofalgae and resulted in higher specificcake resistance. The specific cakeresistance of algae cultured at differ-ent temperatures increased with theamount of the extracellular organicmatter (EOM) extracted by 0.1 NNaOH. For this reason EOM, ratherthan bacteria present in the mono-algal culture, was considered to bethe primary factor affecting the cakeresistance. The specific cake resis-tance increased drastically afteractively growing cells were stored innutrient-free water under dark con-ditions. However, the resistance wasslightly decreased when the algal cellswere stored in NSIII nutrient mediain a dark room, indicating the effectof nutrient availability on the changeof the specific cake resistance underthe light-limiting conditions. EOMextracted from the cells kept in thenutrient-free water contained lesssugar than the fresh culture, whereasthe EOM extracted from the cellsstored in the NSIII media containedmore sugar. The molecular distribu-tion of the EOM shifted from below1000 kDa before storage to morethan 2000 kDa after storage in boththe nutrient-free and NSIII media. S. Babel, S. Takizawa, H. Ozaki:Water Research 36(5) 1193–1202(March 2002).

Exergy analysis of an ROdesalination plant An exergy analysis of a 7250-m3/dayreverse osmosis (RO) desalinationplant in California was conducted byusing actual plant operation data,and an alternative design was investigated to improve its perfor-mance. The RO plant is described indetail, and the exergies across themajor components of the plant are

calculated and illustrated using exer-gy flow diagrams in an attempt toassess the exergy destruction distribu-tion. The primary locations of exergydestruction were the membranemodules in which the saline water isseparated into the brine and the per-meate; the throttling valves where thepressure of liquid is reduced; pressuredrops through various process com-ponents; and the mixing chamberwhere the permeate and blend aremixed. The largest exergy destructionoccurred in the membrane modules,and this amounted to 74.07% of thetotal exergy input. The smallest exer-gy destruction occurred in the mix-ing chamber. The mixing accountedfor 0.67% of the total exergy inputand presents a relatively small frac-tion. The second law of efficiency ofthe plant was calculated to be 4.3%,which seems to be low. The analysisof the alternative design was based onthe exergy analysis. It is shown thatthe second law of efficiency can beincreased to 4.9% by introducing apressure exchanger with two throt-tling valves on the brine stream, andthis saved 19.8 kW electricity byreducing the pumping power of theincoming saline water.Y. Cerci: Desalination 142(3)257–2661 March 2002

Pervaporation of water–dye and alcohol–dyeIn this research, a novel phosphazeneheteropolymer (HPP) was synthe-sized that contained three differingpendant groups – 2-(2-methoxy-ethoxy)ethanol (MEE), 4-methoxy-phenol and 2-allylphenol. Theresulting polymer is an amorphouselastomer with good film-formingproperties where MEE and 4-meth-oxyphenol pendant groups influ-enced the hydrophilicity and the sol-vent compatibility of the polymer.Sorption studies were performed tocharacterize the polymer in terms ofHansen solubility parameters. Addi-tionally, group contributions wereused to predict the Hansen parame-ters for the polymer and these datacompared favourably with theobserved solubility behaviour with15 solvents that ranged from hydro-carbons to water. Homopolymerssynthesized from MEE and 4-methoxyphenol were also studied forsolubility, revealing different behav-iour, with each representing a limitin hydrophilicity – MEE formed awater-soluble hydrophilic polymerand 4-methoxyphenol yielded a

hydrophobic polymer. Membranesformed from HPP were character-ized for use as pervaporation mem-branes using five different feeds.There are water–dye, methanol–dye,2-propanol–dye, water-2–propanoland water–methanol. Fluxes ofmethanol and isopropanol weregreater than those for water. For thealcohol–water separations, the alco-hol was the favoured permeate in allcases with higher fluxes observed forhigher alcohol feed concentrations,however, separation factors declined. C.J. Orme, M.K. Harrup, J.D.McCoy, D.H. Weinkauf, F.F.Stewart: J. of Membrane Science197(1–2) 89–101 (15 March 2002).

Productivity improve-ments for small-size ROdesalination plantsThis detailed study was carried outfor the determination of the watercost in small-size reverse osmosis ROdesalination plants in remote areas.Data from desalination plants inthree Greek islands were used for aperiod of three years. The actualexpenses for these plants were exam-ined thoroughly and as a result thereal cost per cubic metre of water wasestimated. An evaluation of the effi-ciency of two different energy recov-ery systems was conducted by usingfactual operating data. The introduc-tion of new technologies, automa-tion, data acquisition and remoteoperation can be used to reduce thelabour and maintenance cost forsmall-size RO desalination plants.The increase in labour productivityhas proved to be the direct result ofthe introduction of a low costSCADA system to the RO plant. S.A. Avlonitis: Desalination 142(3)295–304 (1 March 2002).

Chitosan-cellulose composite membrane for purification of biopolymersA composite chitosan-cellulose mem-brane was prepared by coating chi-tosan on filter paper. Physical proper-ties of the composite membrane andits application in affinity membraneimmunoadsorption (IgG to immobi-lized Protein A) were examined. Thechitosan and porogen (polyethyleneglycerol, or PEG) contents in the chi-tosan preparation solution have a sig-nificant effect on porosity of themembrane and the flow rate of waterthrough the membrane. The effect ofthe evaporation time of the solution

(after coating) on the flow rate wasalso determined. The compositemembrane with a relatively large flux(3.2 ml/min/cm2 at 12.5 psi) andapproximately 1 µm pore size wasprepared by using a 0.5% chitosansolution containing 15.0% PEG, andevaporating the solution for 3 hoursat room temperature after coating.The composite membrane that wasobtained provided tensile strengthlarger than the plain cellulose sup-port, in both wet and dry states. Thehydroxyl groups on the compositemembrane were modified with an11-atom spacer arm to link Protein Aas an affinity ligand. For comparison,the plain filter paper was also linkedwith Protein A using the samemethod. The amount of Protein Aimmobilized was 1.36 mg/ml and6.29 mg/ml membrane on the plainfilter paper and the composite mem-brane respectively. The compositemembrane provided a relatively highdynamic binding capacity of humanIgG at 14.9 mg/ml membrane, whichis four-fold higher than that of theplain filter paper.L. Yang, W.W. Hsiao and P. Chen:J. of Membrane Science 197(1–2)185–197 (15 March 2002).

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