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Desalination 195 (2006) 109118*Corresponding author.Wastewater reclamation by advanced treatment of secondaryeffluentsM. Petalaa, V. Tsiridisa, P. Samarasb*, A. Zouboulisc, G.P. SakellaropoulosaaChemical Process Engineering Laboratory, Department of Chemical Engineering, Aristotle University of Thessalonikiand Chemical Process Engineering Research Institute, 57001 Thermi-Thessaloniki, GreecebDepartment of Pollution Control Technologies, Technological Educational Institute of Western Macedonia, 50100 Kozani, GreeceTel. +30 (24610) 40161; Fax +30 (24610) 39682; email: psamaraskozani.teikoz.grcDivision of Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki,54124 Thessaloniki, GreeceReceived 4 May 2005; accepted 17 October 2005AbstractThe objectives of this study were the investigation of the performance of an advanced treatment system, for thereclamation of secondary municipal effluents, and the study of the environmental quality of treated effluents. Thesecondary effluents from a conventional activated sludge process were fed to an advanced wastewater treatmentsystem, consisting of a moving-bed sand filter, a granular activated carbon adsorption bed and ozone disinfection.The performance of this plant was evaluated by measuring the physicochemical, microbiological and ecotoxicologicalcharacteristics of reclaimed water. Sand filtration resulted in about 45% turbidity removal, while carbon adsorptionenhanced mainly the removal of organic content, i.e. the total organic carbon removal exceeded 80%. The qualityof treated effluents, obtained after ozonation by an ozone dosage of 26.7 mg/L, was found to comply with therespective US EPA proposed guidelines for urban reuse, food crop irrigation and recreational impoundments.However, a high ozone dose caused adverse effects on bacterium V. fischeri, possibly due to the formation ofsecondary oxidation byproducts. The annual cost of overall tertiary treatment process was evaluated to 0.24 /m3,indicating the relatively high cost of these processes. Nevertheless, such processes are required in order to producean effluent, with a high reuse potential.Keywords: Tertiary treatment; Reuse; Reclamation; Filtration; Ozonation; Ecotoxicitydoi:10.1016/j.desal.2005.10.0370011-9164/06/$ See front matter 2006 Elsevier B.V. All rights reserved.110M. Petala et al. / Desalination 195 (2006) 1091181. IntroductionWater resources shortage is going to deteriorateduring the forthcoming years, due to increasedwater demand; in addition long-term pollution isexpected to affect an ever-increasing number ofwater bodies. In the Mediterranean area, severalcountries are regularly facing significant waterdemand and supply imbalances, particularlyduring the summer period, due to simultaneousoccurrence of low precipitation, high evaporationand increased demands for irrigation and tourism1,2. In particular, several relevant problems ofwater shortage have been observed in coastaleastern areas, as well as in the most Aegean islandsof Greece 3,4. Consequently, planning, manage-ment and optimization of water resources repre-sent an essential issue of environmental protection.Wastewater reclamation and reuse may playan important role in the development of strategiesfor the utilization of water resources. Reclaimedwastewaters may be reused in various applica-tions, most commonly for irrigation of agriculturaland urban areas, in industrial plants (as coolingwater), as well as for enrichment of groundwaterbodies. Thus, wastewater reuse may strengthenwater savings generating supplementary watersources, which are especially important in areaswith limited rainfalls 5.Various advanced wastewater treatment tech-nologies have been proposed for the productionof effluents with a quality complying with thespecific applications of wastewater reclamationand reuse. The degree of treatment is mainlydetermined by the required use of reclaimed water6,7. Among the most common processes usedfor advanced treatment of activated sludge efflu-ents are filtration (depth, surface or membrane fil-tration), adsorption, reverse osmosis, ion exchangeetc., followed by disinfection using chlorine orozone 813. Filtration processes have been com-monly applied for removal of residual particulatematter from secondary treated effluents, improv-ing the performance of subsequently advancedtreatment steps, such as carbon adsorption, ultra-filtration and disinfenction. Furthermore, filtrationmay be regarded as a supplementary polishing stepfor the production of a constant quality effluent,which is not affected by the performance of theactivated sludge unit and by eventual variationsof secondary effluent quality 8.However, refractory organics and volatile or-ganic compounds are not removed by filtration,even if this process is coupled with chemicalcoagulation. The residual dissolved organic matterof treated wastewaters may be effectively removedby application of carbon adsorption, while ozona-tion contributes to the overall improvement of theeffluent quality, due to its high oxidative potential11,14. Furthermore, different membrane pres-sure-driven processes have been used for effectiveremoval of residual constituents, contained insecondary treated effluents, while subsequentdisinfection by application of UV, chlorine orozone, may provide water quality of even potablegrade 1517. Nevertheless, fouling problemsencountered during the operation of such systemsmay cause flux decline, expanding the operationalcosts and limiting their potential use.It appears that the treated effluent quality ismainly determined by three principal components:the required effluent limits, the correspondingsystem efficiency and the relevant treatment cost.High effluent quality is commonly related to acomplex treatment system of relatively high cost,whereas reclaimed water of low quality may beproduced by application of simple and ratherinexpensive techniques. As a result, a balanceshould be considered between the system effici-ency and the effluent requirements. The use ofphysical-chemical control parameters alone mayprovide an indication of effluent quality, accordingto the respective legislative guidelines; however,this type of analysis cannot be directly related tothe environmental impact of the effluents. Analternative method for the assessment of water andwastewater quality is application of specific bio-M. Petala et al. / Desalination 195 (2006) 109118111assays, i.e. tests using living microorganisms oraquatic organisms as indicators. Bioassays maybe used for the assessment of the direct effect oftreated effluents on aquatic organisms, thus re-flecting the overall environmental impact poten-tial. Most of applied bioassays are quite simple,inexpensive and may predict the interactionsamong the components of a mixture that cannotbe detected by the application of single chemicalanalysis.The objectives of this work were the exami-nation of reclamation potential of secondary efflu-ents, the optimization of operational parametersof a tertiary treatment system and the evaluationof treated effluent quality by using ecotoxic para-meters, in addition to commonly monitored phys-ical-chemical characteristics.2. Materials and methodsA full-scale advanced wastewater treatmentunit was used for reclamation of secondary efflu-ents produced by an activated sludge plant, locatedat Thessaloniki, northern Greece. The activatedsludge plant was serving about 12,000 inhabitantsand was fed by about 1000 m3/d of septage and1500 m3/d of sewage. This unit included a pretreat-ment step, two 1200 m3 aerated tanks, followedby two sedimentation basins and chlorination; thesludge treatment unit included sludge thickening,followed by dewatering using a filter press.The advanced wastewater treatment plant wasdesigned to treat about 8001000 m3/d of second-ary effluents for additional removal of suspendedsolids, and biological, organic and inorganic resid-ual pollutants. The secondary effluents prior todisinfection were introduced to the advanced treat-ment unit, which included a continuous upflowmoving-bed sand filter, an activated carbonadsorption unit and an ozone disinfection unit. Theflow diagram of the constructed tertiary treatmentplant for the tertiary treatment is shown in Fig. 1.2.1. Upflow continuous backwash (moving-bed)sand filterSecondary effluents were mixed with the co-agulant solution and were fed to a continuousmoving-bed sand filter (Hydrasand) through acentrifugal mechanical pump. The coagulationunit included a 500 L storage tank, equipped witha mixing device for the preparation of thecoagulant solution and a diaphragm pump for theaddition of the appropriate amount of coagulantto the influent. The coagulant was a commerciallyobtained polyaluminium chloride (Flopac 41,Nalco) and was used in a dose of about 15 g/m3of water. Mixing of influent with the coagulationsolution took place into a 4 m pipe, connectingthe secondary non-disinfected effluents manholewith the Hydrasand filter.The diameter of the sand filter unit was 2.54 m,the total height 6.33 m and the sand bed depthwas 2.00 m. The size of the sand varied between0.61.2 mm, while the uniformity coefficient(D60/D10) was equal to 1.45. Secondary effluentswere fed to the bottom cone of the sand filter andwere evenly distributed through the distributionlaterals. In the filtration zone, the wastewatermoved upwards, whereas the effective trappingof solids took place through a counter-current fil-tration process through the falling sand. Thetreated filtrate, reaching to the top of the sand filter,was discharged over the upper weir to the filtereffluent manhole.The contaminated sand fell to the bottom coneoutlet and was transferred by an external air-liftto the wash chamber at the top of the unit. Thefinal backwash of the sand was carried out througha counter-current flow with wash water, beforereturning in the upper distributor of the sand bed.The sand wash rate was controlled by the appro-priate compressed air flow rate.2.2. Activated carbon adsorption columnThe effluents from the sand filter were collected112M. Petala et al. / Desalination 195 (2006) 109118Fig. 1. Flow diagram of the advanced tertiary treatment unit.in the Hydrasand effluent manhole and weresubsequently fed to the activated carbon adsorp-tion column, through a centrifugal pump. The dia-meter of the adsorption bed was 2.1 m, and theheight of carbon bed was 4.9 m. Granular activatedcarbon (CC 60/1240 type) was supplied by CPLCarbonlink. The effluents from the sand filter wereintroduced on the top of the adsorption columnand were uniformly distributed to the activatedcarbon bed by the appropriate spraying devices,and moved downwards through the carbon bed,resulting to the enhanced removal of residualorganics due to adsorption. Backwash of activatedcarbon column took place manually, at increasedheadloss buildup; the maximum allowable pres-sure drop was 2 bar. Backwash water was fedthrough the bottom of the activated carbon bedand removed from the column top cover, collectedin a manhole and pumped back to the entrance ofthe activated sludge unit.2.3. Ozone disinfection unitThe effluent from the activated carbonadsorption column was subsequently fed to theozone disinfection unit, consisted of:Two ozone generators (OZAT CFS-6A,Ozonia) with a total production capacity of450 g/h ozone, receiving pure oxygen.A 15 m3 closed concrete tank, consisting oftwo separate compartments with a height ofabout 5.5 m. In the first compartment, waste-water came in contact to ozone, while the reac-tion and oxidation of residual pollutants andM. Petala et al. / Desalination 195 (2006) 109118113microorganisms took place at the second part.Two fine bubble ceramic diffusers, located atthe bottom of the first compartment were usedfor ozone distribution.A thermal destroyer of excess ozone, placedat the exit of the contact tank.A liquid oxygen storage tank with a capacityof 2500 m3 oxygen, capable to supply oxygenfor about 10 days.Four different ozone doses were examined(7.1, 15.4, 24.2 and 26.7 mg/L) in order to evaluatethe corresponding disinfection capacity and to im-prove the quality of water.2.4. Physicochemical, microbiological andecotoxicological analysesSecondary effluents and treated wastewatersamples were collected at the outlet of each tertiarytreatment process, i.e. sand filter, adsorption bedand ozonation tank, and were subjected to thedetermination of turbidity, absorbance at 254 nmwavelength, total organic carbon (TOC), ammonianitrogen (NH4+-N) and phosphate content (PO4-P).A UV-Vis spectrophotometer (UV-1201, Shimadzu)was used for the determination of UV absorbance(UV254), while the turbidity of the samples wasmeasured by a turbidity meter (Lab-Vis, Aqua-lytic). PO4-P, NH4-N and TOC determination wascarried out, according to Standard Methods forthe Examination of Water and Wastewater 18.The determination of microbiological parametersof samples, included the measurement of totalcoliforms/100 mL, feacal coliforms/100 mL andfeacal streptococcus/100 mL; these tests werecarried out according to the respective StandardMethods for the Examination of Water and Waste-water 18.The toxicity of various advanced treated watersamples was evaluated by using the marineluminescence bacteria Vibrio fischeri (Microtoxtest), according to the 82% test protocol 19. Thedifference between the light emitted by the testbacteria during their contact with a control aliquot,i.e. a non toxic sample containing only 2% NaCl,and the produced samples was evaluated induplicated experiments for a short exposure time,15 min, using the Microtox Model 500 analyzer(SDI).3. Results and discussion3.1. Operation of the advanced treatment unitAbout 45 m3/h of secondary effluent wereintroduced to the tertiary treatment unit. Thepolyaluminium chloride coagulant (Flopac 41) ina dose of 15 g/m3 of water was added to the influ-ent stream, and the mixture was pumped to thefiltration unit at a hydraulic loading of about10 m3/m2/h. The characteristic parameters of thesecondary effluents were 23.8 NTU turbidity,0.44 cm1 UV absorbance at 254 nm, 40 mg/LTOC, 17 mg/L NH4-N and 2.8 mg/L PO4-P. Re-moval efficiency observed during the subsequenttreatment processes of filtration and carbon ad-sorption is depicted in Fig. 2.The reduction of turbidity was about 45% aftersand filtration, while the activated carbon processincreased turbidity removal to more than 60%,due to the adsorption of organics, associated withsuspended solids 13. Lower turbidity reductioncapacities (around 15%) have been observed by020406080100Turbidity Abs 254nmTOCPO4-PNH4-NP a r a m e t e rR e m o v a l, %FiltrationFiltration/Carbon adsorptionFig. 2. Typical removal efficiencies during filtration, andfiltration/carbon adsorption processes of secondary ef-fluents.114M. Petala et al. / Desalination 195 (2006) 109118Jimenez et al. 9 during sand filtration of a pri-mary treated effluent, containing a high solid andorganic content. Hamoda et al. 8 found that thehighest total suspended solids (TSS) removal mayreach up to 70% after sand filtration, correspond-ing to a relatively high turbidity removal. Fur-thermore, Koning and Nieuwenhuijen 20 founda 60% reduction of secondary effluent turbidityafter filtration, which was decreased to 39% afterthe addition of an iron coagulant, due to the re-duced adsorptive coagulation of iron. The lowturbidity reduction after the addition of poly-merised coagulant PACl was attributed to therather high initial solid concentration of secondaryeffluents.The maximum allowable solid concentrationof influent for the adequate operation of the sandfilter was 100 mg/L (set by the manufacturer). Fur-thermore, the activated carbon adsorption processwas found to significantly improve the turbidityreduction in the overall treatment process, al-though the particle size distribution in the sandfilter effluent should move towards substantiallylower diameters 21.The 254 nm UV absorption values may be con-sidered as a rough indication of organic com-pounds contained in the reclaimed wastewater,mostly in the form of humic-like substances 22.The reduction of UV absorbance after sand filtra-tion did not exceed 20%, whereas the highest UVabsorbance reduction, slightly exceeded 70%, andwas observed at the outlet of activated carbon unit.TOC removal rate was lower than 10% duringsand filtration, whereas organic matter adsorptiontook place onto activated carbon sites, resultingin an overall TOC removal efficiency of more than80%. A similar COD removal capacity of about8% was observed by Jimenez et al. 9, after sandfiltration of primary treated effluents. As shownin Fig. 2, TOC removal values were about halfthe corresponding UV254 absorbance reductionrates after sand filtration, indicating that a smallfraction of the organic matter was associated tosuspended solids. Furthermore, the adsorptiononto activated carbon resulted in a lower overallreduction of UV absorbance than TOC, indicatingthat the carbon adsorption sites might retainorganic substances of different structure.The removal capacity of dissolved phosphorusdid not exceed 20%, during the addition of poly-aluminuim coagulant, followed by sand filtration,whereas the subsequent carbon adsorption did notfurther enhance the reduction of phosphorus.However, higher phosphorus removal efficiencieshave been reported by the addition of aluminiumsalts, resulting in the increased precipitation/re-moval of phosphates 13. The low phosphorusremoval capacity observed in this work could beattributed to the presence of high solids concentra-tion, to increased influent TOC content, and tothe alkaline pH of secondary effluents, higher than7.5, resulting to secondary competitive reactionstaken place between hydroxyl and phosphate ions,for the occupation of available adsorption siteson the respective precipitates 13,23,24. Ammo-nium nitrogen was only partially removed by sandfiltration and adsorption processes, and wasslightly exceeding 15%. In a similar work, Libertiand Notarnicola 25 did not observe a distinctiveammonium nitrogen removal during coagulationwith PACl and sand filtration of secondary ef-fluents.The treated water after carbon adsorption wasfed to the ozonation tank, where various ozonedosages were applied for the assessment ofozonation performance and the determination ofoptimum ozone concentration supply. Typicalremoval efficiencies of turbidity, UV254 absorb-ance, TOC and ammonium-nitrogen, are presentedin Fig. 3 as a function of ozone dosage.Ozone treatment at the lowest dose, 7.1 mg/L,resulted in a TOC reduction of about 50% and ina UV254 absorbance reduction around 20%. At thesame conditions, turbidity and ammonium-nitro-gen reduction were lower than 10%. Dissolvedphosphorus concentration was slightly increasedfrom 2.2 to 2.4 mg/L. Although this increase wasrather low, it was observed after ozonation andM. Petala et al. / Desalination 195 (2006) 109118115was not affected by ozone dosage. This behaviorcould be attributed to potential dissolution ofphosphate ions that were attached and adsorbedon particles dissociated during ozone treatment.The application of higher ozone doses resulted ina significant increase in turbidity removal,reaching up to 80%, at the highest ozone dosage,26.7 mg/L, resulting in an effluent of high quality,with a turbidity of 1.2 NTU. The UV254 absorbancevalues were significantly decreased by ozonation,at an ozone dosage of 15.4 mg/L, while the addi-tion of ozone dosages of 24.2 and 26.7 mg/L didnot further affect the removal of humic-like sub-stances; the highest UV254 absorbance removalefficiency slightly exceeded 60%. The maximumTOC removal capacity exceeded 80% at an ozonedosage of 24.2 mg/L, while at even higher ozoneconcentration, the TOC concentration in the efflu-ent remained almost constant. Ozonation was020406080100TurbidityAbs 254nmTOCNH4-NP a r a m e t e rR e m o v a l, %7.1 mg/L15.4 mg/L24.2 mg/L26.7 mg/LFig. 3. Typical removal values during ozonation of efflu-ents as a function of ozone doses.considered as an effective process for the removalof ammonium nitrogen; the application of15.4 mg/L ozone dose resulted in the highest nitro-gen reduction, up to 35%. However, disinfectionat higher ozone doses did not result in additionalnitrogen reduction.The principal microbiological parameters ofsecondary wastewaters and of treated samples arepresented in Table 1. The measured parametersincluded total and feacal coliforms, and feacalstreptococcus. A sufficient removal of pathogenswas observed by the application of the lowestozone dose, 7.1 mg/L, while the disinfection atthe highest ozone dose, 26.7 mg/L, eliminatedalmost all measured microorganisms. The ozona-tion at the lowest ozone dose resulted in the reduc-tion of secondary effluents total coliforms contentto about 2.6 logs, of feacal coliforms to about3.3 logs and of feacal streptococcus to 0.7 logs.These results were similar to those reported byLazarova et al. 26, indicating that high ozonedoses should be applied in order to achieve thestringent microbiological requirements of waste-water reuse. However, Liberti and Notarnicolashowed that coagulation and sand filtration ofsecondary effluents, followed by disinfection atan ozone dosage of 15 mg/L, was not sufficientfor the adequate removal of total coliforms 25,whereas Xu et al. stressed that ozone dosage wasthe key factor for the efficient performance of awastewater ozonation process, proposing that theoptimum disinfection treatment should be carriedat ozone dosages between 2 and 15 mg/L, depend-ing upon the quality of raw effluents 11.Table 1Typical microbiological parameters of non disinfected secondary effluents and of reclaimed wastewatersParameter Non disinfected secondary effluents Effluents after filtration, adsorption and ozonation with 7.1 mg O3/L Effluents after filtration, adsorption and ozonation with 26.7 mg O3/L Total coliforms/100 mL 93,000 240 2 Feacal coliforms/100 mL 43,000 21 2 Feacal streptococcus/100 mL 2,400 460 2 116M. Petala et al. / Desalination 195 (2006) 109118The ecotoxic properties of ozonated sampleson aquatic species V. fischeri are illustrated inFig. 4. The raw secondary effluents indicatednegative responses on V. fischeri, denoting theexistence of stimulation effects. Stimulationresults were also observed in samples collectedat the outlet of ozonation tank, when using thelowest dose, 7.1 mg/L. Stimulation effects, knownas hormesis, were attributed to the presence ofnutrients or trace contaminants in the samples, innon-lethal concentrations that might affect thebioluminescence activity of V. fischeri, requiringa more careful examination of sample charac-teristics and the respective interpretation of ob-tained results 27. Significant positive effectswere observed after disinfection at high doses ofozone. The disinfection at the highest ozone dose,26.7 mg/L, caused a 60% inhibition of V. fischeri.The toxic effects of high ozone doses wereattributed to by-products that might be formedduring the reaction of ozone with the residualpollutants, presented in the reclaimed wastewatersin trace concentrations. It should be stressed thatalthough almost complete removal of the micro-organisms was achieved at the highest ozone dose,the reclaimed water may cause adverse effects onaquatic life, according to the results of bioassays.This problem could be possibly faced by theretention of ozonated effluents in an appropriatebasin for 2448 h, as further studies have shown-40-200204060801007.115.424.226.7Ozone dose, mg/LEffect, %Fig. 4. Toxicity of treated effluents after ozonation onVibrio fischeri, using different ozone doses.that toxicity of samples is reduced by the storagetime 28.3.2. Operational cost of the advanced treatmentsystemThe annual cost of the treatment process wassubsequently estimated, including the investment,operation and maintenance costs, in order toevaluate the production cost of reclaimed water.The investment cost was estimated to 25,000 /y,considering a depreciation period of 10 years. Thiscost would include the construction costs of filtra-tion, carbon adsorption and disinfection units, theconstruction of electrical facilities building andthe operational cost for chemicals and power con-sumption. An operation time of 340 d/y was as-sumed, for the estimation of the operational cost.The operation cost of the advanced treatment unitincluded the power cost for the operation of eachtreatment process, the corresponding pumpingrequirements and the consumable expenses. Thecorresponding results are given in Table 2.The assessment of energy consumption wasperformed by considering 60% of the nominalpower of the corresponding mechanical devices.Energy consumption during coagulation wasattributed to the mechanical agitation of coagulantsolution, coagulant pumping and pumping ofsecondary effluents to the sand filtration column.The power consumed for ozone production by thegenerators included the operation of the thermaldestroyer and the cooling water system. Theoverall energy consumption was estimated toabout 16.36 kWh, corresponding to an annualpower consumption of 133,500 kW. The annualcost of required power was estimated to 6700 ,considering a unit price of 0.05 /kWh. Con-sumables included the cost for the liquid oxygenand nitrogen gas used for ozone generation, thechemical agent, polyaluminium chloride, used forcoagulation, and the activated carbon regenera-tion. For the adequate operation of the activatedcarbon column, an annual replacement of activat-ed carbon was considered. The corresponding costM. Petala et al. / Desalination 195 (2006) 109118117Table 2Power consumption regarding the operation of advanced treatment unitof consumables for each treatment process ispresented in Table 3; the overall consumable costwas 29,600 , while the overall labor cost wasestimated to 8100 /y.The total operating cost was estimated to44,400 /y. Assuming maintenance cost and con-tingencies of about 10% of the investment costand an additional cost of 5000 /y for monitoringanalyses, the total annual cost of tertiary treatmentwas estimated to 81,500 . Taking into accountthe flow rate of reclaimed water, the productioncost was estimated to 0.24 /m3. In general, theestimated production cost of reclaimed water washigh, but it corresponded to the production of ahigh quality reclaimed water and could be usedin various specific applications requiring clean water.Table 3Annual cost of consumables for the operation of advanced treatment unitUnit Percentage (%) of time during operation Power (kW) Energy consumption (kWh) Feeding pump 100 2.24 1.34 Coagulant agitator 100 0.75 0.45 Coagulant dosing pump 100 0.25 0.15 Activated carbon column feeding pump 65 15 5.85 Rejects pump 50 1.5 0.45 Compressor 40 2.24 0.54 Outlet pump 65 7.5 2.92 Ozone generators 100 5.6 3.36 Thermal ozone destroyer 100 1.5 0.9 Ozone cooling system 40 1.7 0.4 Total 38.28 16.36 Process Consumables Quantity Unit price Annual cost (/y) Coagulation Coagulant FLOPAC 41 15 kg/d 0.35 /kg 1,800 Activated carbon adsorption Activated carbon 6,000 kg/y 2.41 /kg 17,000 Ozonation Oxygen 230 m3/d 0.12 /m3 9,400 Ozonation Nitrogen 5.76 m3/d 0.73 /m3 1,400 Total 29,600 4. ConclusionsThe reclamation potential of municipal second-ary effluents was studied in this work by the appli-cation of an advanced treatment unit, includingsand filtration, activated carbon adsorption andozone disinfection. The efficiency of the advancedwastewater treatment plant was measured byvarious physicochemical, microbiological andecotoxicological parameters and the operationcapacity of each process was evaluated for theremoval of specific compounds.The continuous upflow sand filtration unit re-sulted in the removal of suspended solids and thereduction of turbidity (45%) and organic matter,while the dissolved phosphorus and ammonium118M. Petala et al. / Desalination 195 (2006) 109118nitrogen concentrations were not substantiallyaffected. The activated carbon column was effec-tive for the removal of organic compounds andturbidity; the effluent from the carbon adsorptioncolumn had TOC values lower than 10 mg/L.The effect of ozonation on organic matter re-moval was studied by the application of differentozone doses, between 7.1 and 26.7 mg/L. Furtherremoval of turbidity, up to 80%, and reduction ofUV254 absorption to 60% were observed at thehighest ozone dosage. Ozone disinfection waseffective for the removal of microorganisms; thecomplete removal of pathogenic microorganismswas observed, at high ozone dosages. However,the application of high ozo