text: the present invention comprises two major parts : i ) production of metal oxides using the separated flocs after flocculation treatment in a contaminated water and ii ) microwave treatment to the pre - treated water to cause a photocatalytic reaction with the assistance of the remaining hydrolyzed metal compound . as used herein , the term “ contaminated water ” refers to any water which requires water treatment , including surface water , groundwater and wastewater . fig1 is a schematic diagram showing a preferred embodiment of the method for recovering organic - inorganic element - doped metal oxides from the separated flocs after flocculation treatment of contaminated water . the contaminated water is supplied to the flocculation basin ( 1 ), and thereto , a hydrolysable metal compound is added as a coagulant . the optimum concentration of the metal compound depends on the characteristics of the contaminated water . flocculation mechanisms to aggregate particles into the separable floc are complex . when the hydrolysable metal compound is added , rapid mixing leads to the charge neutralization so that the aggregation of particles occurs . slow mixing leads to the growth of heavy flocs ( 2 ) which easily settle down due to the gravity force . here , the hydrolysable metal compound of the present invention includes a hydrolysable titanium compound , a hydrolysable aluminium compound , a hydrolysable iron compound , a zinc compound , a copper compound and a zirconium compound . the hydrolysable metal compound is generally provided as a chloride or sulfate salt . for example , the titanium compound may be any one selected from the group consisting of titanium trichloride , titanium tetrachloride , titanyl sulfate , titanium sulfate , titanium oxysulfate , titanium iron sulfate and titanium oxychloride . in addition , titanium alkoxides may be used . as a hydrolysable iron compound , iron chloride and iron sulfate can be mentioned . as a hydrolysable aluminium compound , aluminum chloride and aluminum sulfate can be mentioned . of these metal compounds , the hydrolysable titanium compound is more preferred due to a wide range of synergistic effects , which will be more fully illustrated in the following . the separable floc ( 2 ) is separated from the pre - treated water . the separated floc ( 2 ) is further subjected to a calcination process to produce an organic - inorganic element - doped metal oxide according to the preferred embodiment of the present invention , calcination of the separated floc formed by the hydrolysable titanium compound in the contaminated water produced white organic - inorganic element - doped titania at a temperature in the range of 500 - 1000 ° c . for temperature of less than 500 ° c ., the black titania is obtained due to remaining organic matter . more than 1000 ° c ., the energy consumption is high . thus , the 500 - 650 ° c . of temperature range is most advantageous with respect to energy requirement and photocatalytic activity . titania produced such ways will be referred to hereinafter as “ photocatalyst from contaminated water ( pfw )” products . the pfw has both an amorphous and anatase . the primary size is 10 nm as a crystalline anatase . fig2 is a schematic diagram showing more preferred embodiment of the method for recovering organic - inorganic element - doped metal oxide with the separated flocs after flocculation treatment from contaminated water , wherein the pre - treated water is further subjected to a microwave treatment to involve a photocatalytic reaction with the assistance of the residual hydrolysable metal compounds in the pre - treated water . after ticl 4 flocculation treatment , the separated floc ( 2 ) is separated and the pre - treated water is discharged from the tank . due to imperfect separation and / or dissolution , the pre - treated water still has some residual hydrolysable titanium compound . then , the pre - treated water is heated with microwave to endow an improved photocatalytic property to the remaining hydrolysable titanium compound and the pre - treated water is irradiated with ultraviolet ( uv ) light . this leads to a photocatalytic reaction , which additionally degrades the remaining organic matter present in the pre - treated water . this process results in high synergistic effect in terms of the use of the remaining titanium compound and the higher removal of organic matter in water treatment . the present invention will be illustrated in terms of the following non - limiting examples . removal of organic matter by hydrolysable metal compounds as a coagulant the experiments using synthetic wastewater were conducted . the composition of the synthetic wastewater used in this study is presented in table 1 . this synthetic wastewater represents effluent organic matter generally found in the biologically treated sewage effluent ( seo et al ., 1997 ). the synthetic wastewater will be referred to hereinafter as a contaminated water . tannic acid , sodium lignin sulfonate , sodium lauryle sulfate , peptone and arabic acid contributed to the large molecular weight ( mw ) size organic matter , while the natural organic matter from tap water , peptone , beef extract and humic acid consisted of the small mw organic matters . the mw of the mixed synthetic wastewater ranged from 290 to about 34100 daltons with the highest fraction at 940 - 1200 daltons . the weight - averaged mw of the wastewater was approximately 29500 daltons . the concentration of the contaminated water was 10 . 05 mg / l and the ph was 7 . 3 . flocculation was carried out by standard jar tests . the contaminated water was placed in a two - liter container . the sample was stirred rapidly for 1 minute at 100 rpm , followed by 20 minutes of slow mixing at 30 rpm and 30 minutes of settling . the hydrolysable metal compounds ( ticl 4 , fecl 3 and alum ) were used . first , it is essential to investigate the optimal doses of different coagulants , the variation of ph and organic removal . fig3 shows the removal of organic matter with ticl 4 flocculation . the concentrations of the coagulant were varied from 2 . 70 to 14 . 04 ti - mg / l . as shown in fig3 , the organic removal was about 70 % at 9 . 786 ti - mg / l . a photo of ticl 4 flocculation is shown in fig4 . as shown in fig5 and fig6 , the optimum concentrations of fecl 3 and alum were 13 . 77 fe - mg / l and 8 al - mg / l , respectively . compared with fecl 3 and alum flocculation , the organic removal by ticl 4 flocculation was approximately equivalent by up to 70 %. this suggests that the ticl 4 compound proposed in the present invention is a novel effective alternative coagulant . high pressure size exclusion chromatography ( hpsec , shimadzu corp ., japan ) with a sec column ( protein - pak 125 , waters milford , usa ) was used to determine the mw distributions of organic matter . the separation ranges are between about 1000 and 30000 daltons . the effluent was made of pure water with phosphate ( ph 6 . 8 ) and nacl ( 0 . 1 m ). the detection limit of uv was 0 . 001 per cm . standards of mw of various polystyrene sulfonates ( pss : 210 , 1800 , 4600 , 8000 , and 18000 daltons ) were used to calibrate the equipment . a fluorescence detector was also used to identify protein - like substances at excitation ( 279 nm ) and emission ( 353 nm ). standards of polystyrene sulfonates with different mw ( pss : 210 , 1800 , 4600 , 8000 , and 18000 daltons ) at lower concentration were used to calibrate the equipment . details on the measurement methodology are given elsewhere ( her , 2002 ). fig7 and fig8 describe mw distribution and florescence chromatogram of organic matter after ticl 4 , fecl 3 and alum flocculation at the optimum doses , respectively . all three coagulants showed a similar trend of organic removal . they removed practically all of the large mw organic matter such as tannic acid , sodium lignin sulfonate , sodium lauryle sulfate and arabic acid . further , the flocculation was also helpful in removing some of the small mw compounds ( 860 - 1000 daltons ) such as peptone , beef extract and humic acid . however , the smallest mw range of compounds in the range of 250 daltons was not be removed by flocculation . the removal of protein - like substances , as indicated by fluorescence chromatogram , also showed a similar removal trend . the decantability test of the separated floc was conducted in measuring the head of the floc in terms of length ( cm ) ( fig9 ). iron floc separated faster than ticl 4 and alum . the decantability was found to be in order of fecl 3 & gt ; ticl 4 & gt ; alum . the colors of fecl 3 , ticl 4 and alum flocs were black , brown and gray , respectively . the mean size of the ti , fe and al flocs was 47 . 54 μm , 42 . 50 μm and 16 . 91 μm , respectively . the decantability was proportional to the floc size formed . fig1 shows photos of titania material produced by calcination at different temperatures . as the temperature increased , the color of powdered tio 2 has changed from black to white . this may be due to the effect of remaining organic matter . the pfw titania was compared with p - 25 tio 2 powder ( degussa , germany ), which is commonly used commercially available product . the pfw titania was identified on the edx graph as shown in fig1 . table 2 presents the weight fraction of doped element in pfw titania . carbon was present in all temperature ranges and mainly ti , c , o and p atoms were detected . in addition , many trace elements ( si , fe , al , v , ca , na , cr , cl , s , ni , and br ) were also found . when 9 . 786 mg of ti concentration ( as the hydrolysable ticl 4 compound ) was dosed , 17 . 86 mg of the pfw titania was experimentally recovered . equation 1 shows the mass balance : thus , the impurity was 1 . 78 mg in the pfw titania particles made by this invention . the weight percentage of the impurity was 9 . 97 %. based on this mass balance , for a medium size ( 25000 m 3 / d ) plant , about 446 . 5 kg / d of the pfw titania could be produced . fig1 shows x - ray diffraction ( xrd ) images ( rigaku , japan ) of the pfw titania to identify the particle structure . all the xrd patterns were analyzed with mdi jade 5 . 0 ( materials data inc .). the anatase crystal indicated 25 °, 38 ° and 48 ° of diffraction peak . on the other hand , the rutile crystal included 27 °, 36 ° and 41 ° of diffraction peak . the anatase pattern was found from more than 600 ° c . at lower temperature , remaining organic matter interfered with crystalline titania production . at 1000 ° c ., the anatase structure changed into rutile . although there are a variety of compounds in the contaminated water , only genuine titania structures were investigated . here , the narrower xrd pattern of annealed sample at 1000 ° c . was found compared with that at 600 ° c . this may be due to the grain growth of titania ( tonejc et al ., 2001 ). based on the result of liao et al ., the transformation temperature of anatase to rutile at ambient pressure is about 550 ° c . however , in this study , the transformation temperature exceeded over 800 ° c . this may be due to impurities in the pfw titania . the flocs with fecl 3 and alum indicated different trends . in the case of alum , only al 2 o 3 was obtained at 1000 ° c . ( fig1 ). interestingly , berlinite ( alpo 4 ) could not be made from alum flocs . on the other hand , the flocs after fecl 3 flocculation were found to be different structures ( hematite ( fe 2 o 3 ) and grattarolaite ( fe 3 ( po 4 ) o 3 or fe 3 po 7 ) ( fig1 ). a zinc oxide , a copper oxide and zirconium oxide by a zinc compound , a copper compound and a zirconium were also made . fig1 shows optical transmittance (%) of p - 25 and pfw photocatalysts using uv - vis - nir spectrophotometer ( cary 500 scan , varian , usa ). the p - 25 photocatalyst absorbed the majority of uv light ( less than 417 nm wavelength ). the pfw photocatalyst however absorbed not only uv light but also visible light ( from 600 nm to 400 nm ). this suggests that the pfw photocatalyst can be used with the sources of solar irradiation and interior lighting ( such as fluorescent light ). the result is similar to that of asahi et al ., ( 2001 ). asahi et al ., ( 2001 ) reported that tio 2 − x n x noticeably absorbs the light at less than 600 nm . photocatalytic reaction by the remaining titanium compound in the pre - treated water after flocculation followed by microwave treatment fig1 presents the effect of microwave retention time with photoreactor after ticl 4 flocculation from the contaminated water . retention time of 0 min , 1 min , 5 min and 10 min microwave corresponds to temperature of 20 ° c ., 38 ° c ., 75 ° c . and 105 ° c . after microwave heating , all the samples were cooled down to room temperature . methylene blue ( c 16 h 18 cln 3 s . 3h 2 o ) was used as representative organic matter and added at room temperature after microwave heating process to investigate photocatalytic activity . the pseudo first order equation was used to determine the rate constant ( k ) ( equation 2 ). in the equation 2 , c 0 = an initial concentration , c = the concentration of the reactant ( mg / l ), t = the illumination time ( h ), and k = the apparent photodegradation rate constant ( h − 1 ). the overall rate is presented in fig1 . the overall rate constant ( k ) with microwave treatment for 10 min was 2 . 7 times higher than that without microwave treatment . this may be due to the production of a photoactivity with the pre - treated water after ticl 4 flocculation followed by microwave treatment . according to the above examples , the use of titanium compounds as an alternative coagulant instead of iron and aluminum salts is proposed . flocculation with ticl 4 as a coagulant removes 70 % of organic matter , which is equivalent to removal of organic matter by the most - widely used coagulants ( fecl 3 and alum ). the removal trend of molecular weight distribution and protein - like substance of organic matter by ticl 4 flocculation is also similar to that by fecl 3 and alum flocculation . the pfw titania is mainly doped with c , p and various trace elements ( si , fe , al , v , ca , na , cr , cl , s , ni , and br ). the weight percentage of impurities in the pfw titania is 9 . 97 % and 18 g / m 3 of pfw titania is produced in the experimental conditions . the pfw photocatalyst can be used with the sources of solar irradiation and interior lighting . the anatase pattern is found over 600 ° c . calcinations temperatures . at 1000 ° c ., the anatase structure changes to rutile . for alum flocculation , al 2 o 3 is made at 1000 ° c . cacination temperature . on the other hand , the floc after fecl3 flocculation is found to be different crystals ( hematite ( fe 2 o 3 ) and grattarolaite ( fe 3 ( po 4 ) o 3 or fe 3 po 7 ). another method proposed is to cause a photocatalytic reaction using the remaining hydrolyzed metal compounds in the pre - treated water followed by microwave treatment . the overall rate constant ( k ) with microwave treatment for 10 min is three times higher than that without microwave treatment . it should be noted that the embodiments of the present invention described herein have been given for the purpose of illustration and examples . those skilled in the art will realize that changes and modifications may be investigated thereto . it is not intended to limit the invention of any of the precise embodiments disclosed . tchobanoglous g . and burton f . l . 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