印染废水处理会用工程设计外文文献(毕业翻译可以参考).pdf

Corresponding author The most effective pre treatment to nanofiltration for the recovery of print dyeing wastewaters Goksen Capara Ulku Yetisa Levent Yilmazb aEnvironmental Engineering Department bChemical Engineering Department Middle East Technical University 06 531 Ankara Turkey Tel 90 312 2105868 Fax 90 312 2646 email uyetis metu edu tr Received 23 November 2005 accepted 14 September 2006 Abstract This paper presents the determination of the best pre treatment method to nanofiltration NF for the recovery of print dyeing wastewaters PDW of the carpet manufacturing industry Chemical precipitation CP with optimum alum Al2SO4 18H2O dose was chosen among five alternatives 1 Dead end microfiltration MF 2 CP with optimum coagulant dose 3 CP with low coagulant dose and polyelectrolyte aid 4 CP with low coagulant dose followed by MF 5 CP with high coagulant dose followed by ultrafiltration UF In the selected process an optimum alum dose of 150 mg L provided color and turbidity removal efficiencies of 90 The effectiveness of the selected pre treatment method for flux control in post NF was also tested Perfect rejection of COD color and turbidity was achieved in NF accompanied by a stable flux decline of around 22 Moreover the flux decline was mainly due to concentration polarization rather than fouling indicating reversible flux decline Keywords Chemical precipitation Microfiltration Nanofiltration Print dyeing wastewater Ultrafiltration 1 Introduction Reclamation of textile wastewaters by mem brane processes has been extensively studied in the last decade due to the fact that textile industry consumes large amounts of fresh water with typi cal consumption rates of 200 500 L per kg of product and a heavy polluter generating waste waters with a broad range of chemical oxygen demand COD 50 5000 mg L suspended sol ids 50 500 mg L and variable color 1 2 High performances of membranes have been reported for textile wastewaters with almost complete re moval of COD and color and high recovery rates of water 3 9 The major problem with the application of the membrane technology is the flux decline which Desalination 212 2007 103 113 doi 10 1016 j desal 2006 09 020 0011 9164 07 See front matter 2007 Elsevier B V All rights reserved 104G Capar et al Desalination 212 2007 103 113 means decreased productivity Implementation of the right pre treatment process is very important to control the flux decline and hence maintain an efficient membrane separation process The most commonly adopted pre treatment processes for textile effluents are microfiltration MF ultrafil tration UF chemical precipitation CP sand filtration and ozonation 2 6 10 These processes may be implemented individually or in combina tion according to the characteristics of the par ticular wastewater Textile wastewaters are sub ject to a broad range of characteristics since there are many subcategories where different types and concentrations of dyes and chemicals are used Therefore each type of textile wastewater can be treated in a different combination of processes necessitating the investigation of each subcategory individually The original process water qualities are often achieved by nanofiltration NF or re verse osmosis RO applied after a suitable pre treatment process To this end this study aims to determine the most efficient pre treatment pro cess to NF for the recovery of print dyeing waste waters PDW of the carpet manufacturing indus try which was handled as a sample textile sub category Dead end MF UF and CP were consid ered as possible pre treatment alternatives and tested either alone or in combination 2 Materials and methods 2 1 Sample Six PDW samples were taken from the print dyeing line of a carpet manufacturing plant and mixed to prepare a composite mixture Table 1 which would compensate for the diverse charac teristics of individual samples The PDW samples are the wash waters of carpets dyed with a print paste which includes metal complex dyes and auxiliary chemicals which are citric acid antifoaming agent synthetic thickener and non ionic penetrant used for adjusting the pH and vis cosity and improving wetting respectively Table 1 Characteristics of the PDW mixture Parameter Mean value standard deviation COD mg L 391 10 UVA195 3 12 0 03 Color Pt Co 301 3 Turbidity NTU 41 1 4 Total solids mg L 603 13 Total hardness mg L as CaCO3 20 0 Conductivity S cm 700 0 Chloride mg L 15 0 pH 7 60 0 00 2 2 Experimental strategy Five alternatives depicted in Fig 1 were con sidered First the applicability of dead end MF was investigated to control flux decline in post NF The other alternatives were based on CP where it was tested alone or in combination with a membrane process When it was applied alone alum doses of 50 200 mg L were used to find the optimum dose and alternatively it was applied at lower doses of 50 100 mg L coupled with a non ionic polyelectrolyte PE Stockhausen Praestol 2500 at doses of 0 2 1 0 mg L Here the effi ciency of CP with inadequate alum doses were tried to be improved by the help of PE In sequen tial trains CP was applied at low alum dose of 50 mg L preceding MF to increase the filtration rate of post MF Alternatively CP was applied at high alum dose of 400 mg L preceding UF All the al ternatives were evaluated based on their perfor mances first and then the selection was made to wards the simplest and the cheapest one 2 3 Experimental methods 2 3 1 Dead end microfiltration A conventional vacuum filtration apparatus Millipore operating under a vacuum level of 550 mm Hg was used for testing the applicability of dead end MF The filter media namely Whatman G Capar et al Desalination 212 2007 103 113105 PDW Optimum Dose CP 50 200 mg L MF MF 1 0 m Low Dose CP 50 mg L CP 11 m 2 5 m 1 0 m Low Dose CP 50 100 mg L PE 0 2 1 0 mg L High Dose CP 400 mg L UF 50000 Da CP MF CP UF Fig 1 Pre treatment alternatives for PDW W1 W42 and GF B Table 2 were washed with 1 L of distilled water prior to the filtration of PDW The filtrates were collected and analysed for their color contents 2 3 2 Chemical precipitation A conventional jar test apparatus was used Samples were mixed rapidly for 1 min at 100 rpm for distributing the chemical homogeneously and then mixed slowly for 30 min at 30 rpm for pro moting floc formation Then sedimentation was provided for 1 h for the settlement of flocs The clear supernatants were analysed for their con stituents color turbidity and COD Table 2 Membrane specifications aMWCO Molecular weight cut off MgSO 4 rejection 99 Process Filter media Material Pore size MWCOa Effective membrane area m2 Whatman 1 Cellulose 11 m 0 0014 Whatman 42 Ashless cellulose 2 5 m 0 0014 MF Whatman GF B Glass microfiber 1 0 m 0 0014 UF Osmonics HZ 15 Polyethersulphone 50 000 Da 0 0155 NF DSS NFT 50 Thin film composite 0 1080 2 3 3 Ultrafiltration UF was tested by SEPA CF Module product of Osmonics which housed flat sheet membranes and provided cross flow filtration The specifica tions of the UF membrane Osmonics HZ 15 are given in Table 2 The inlet pressure was kept at 400 kPa gauge by the use of a pressurized nitro gen cylinder whereas the pressure on the retentate side was 100 kPa gauge yielding a trans mem brane pressure TMP of 250 kPa across the mem brane The samples were fed to the system at a flow rate of 0 9 L min by a pump The feed ve locity was found as 0 25 m s from the relevant figure provided by the manufacturer The experi 106G Capar et al Desalination 212 2007 103 113 ment was run in total recycle mode of filtration TRMF where both the retentate and permeate were returned into the feed tank to keep the feed volume and hence the feed characteristics con stant The experimental set up is presented in Fig 2 The test duration was 5 h in UF test and permeate was analyzed for COD color and tur bidity The operating temperature was measured periodically and it remained constant at 20 C 2 3 4 Nanofiltration NF was tested by a lab scale plate and frame module LabStak M20 product of DSS Company in cross flow operation The experimental set up is presented elsewhere 11 and the specifications of the NF membrane NFT 50 are given in Table 2 The NFT 50 membrane consists of three layers an ultra thin polyamide barrier layer a micro po rous polysulfone interlayer and a high strength polyester support It is a hydrophilic membrane with a contact angle of 40 Wilhemy Method The test was performed under a TMP of 590 kPa The operation temperature was kept at 17 0 0 5 C The samples were fed to the system at a Fig 2 Experimental set up for UF test in TRMF mode Membrane Module Feed Tank Permeate P P P Nitrogen Cylinder Feed Pump Retentate flow rate of 6 L min Three pairs of membranes were used making a total effective area of 0 108 m2 The membranes were chemically cleaned by cir culating nitric acid solution at pH 3 for 15 min followed by sodium hydroxide solution at pH 9 10 for 15 min The cleaning protocol was applied after each run Permeates were analyzed for their COD color turbidity total solids and total hard ness contents 2 4 Flux declines The permeate fluxes in NF tests were measured in four steps in order to determine the flux de clines 1 Initial clean water flux Jcwi The first flux determined with clean membrane which was subjected to an initial chemical cleaning pro cedure 2 Wastewater flux Jww The flux stabilized with respect to time during wastewater filtration 3 Clean water flux of the fouled membrane Jcwf The clean water flux measured with the fouled membrane 4 The clean water flux of the cleaned membrane G Capar et al Desalination 212 2007 103 113107 Jcwc The clean water flux measured with chemically cleaned membrane The extents of concentration polarization and fouling were determined via flux decline analy sis based on the following calculations Calculation Explanation Jcwi Jww Jcwi Total flux decline Jcwf Jww Jcwf Flux decline due to concentration polarization Jcwi Jcwf Jcwi Flux decline due to fouling irreversible reversible Jcwc Jcwf Jcwc Flux decline due to reversible fouling Jcwi Jcwc Jcwi Flux decline due to irreversible fouling 2 5 Analytical techniques COD was measured using HACH DR 2000 Model spectrophotometer at wavelengths of 620 high range and 420 nm low range respectively Color measurements were performed by the same instrument which was already calibrated for color measurement in terms of Pt Co at a wavelength of 455 nm Ultra violet absorbance UVA mea surements were performed by a Varian Cary 100 Model spectrophotometer at a wavelength of 194 nm at which the highest absorbance values were obtained Turbidity was measured with HACH Model 2100A turbidimeter Total solids content of the samples were determined by gravimetric analysis All the analyses were performed accord ing to the Standard Methods 12 except COD which was measured following USEPA approved HACH Method 8000 3 Results and discussion The performances of single and sequential pre treatment processes are compared in Table 3a and Table 3b respectively In dead end MF which simulates sand filtration a high color removal ef ficiency of 79 was achieved with the finest mi cro filter 1 0 m The removal efficiencies ob tained with 2 5 m and 11 m filter were still rela tively high 43 45 which is about half of that obtained with 1 0 m Table 3a However all these filter media were clogged rapidly within 5 10 min The highest filtrate volume was as low as 88 mL obtained by 1 0 m MF in a period of 30 min which yielded a cumulative filtration rate of 0 18 L h The rapid clogging of all the filter media indicated high solids load of the PDW which had complex characteristics due to the pres ence of synthetic fibers unfixed metal complex dyes as well as the residual printing paste which contained surfactants This composition may im ply a diverse particle size and molecular weight distribution Moreover the printing pastes are highly viscous fluids as they contain polymeric thickeners and hence they tend to gel which may contribute to the rapid clogging of the MF media These findings have indicated that dead end MF simulating sand filtration would not be an appro priate pre treatment process to be applied alone for PDW Successful results have been reported in literature for sand filtration as a pre treatment option for textile dyeing effluents where sand fil tration coupled with MF or UF was applied to the biologically treated effluents rather than untreated process wastewaters 4 13 These results revealed that dead end MF had to be replaced or combined with another process Hence CP was considered as the second alternative where CP with optimum coagulant dose optimum dose CP was applied In evaluating optimum dose CP alum dosages ranging from 50 to 200 mg L were tested and the performance was assessed in terms of color and turbidity removals since the major target at pre treatment was color and turbidity removals which would cause fouling of the post NF membrane In optimum dose CP the results presented in Fig 3 were obtained The highest color and turbidity removal efficiencies were achieved by an alum dose of 200 mg L However 150 mg L appeared as the optimum dose since the corresponding 108G Capar et al Desalination 212 2007 103 113 performance was already very high i e 95 and 94 for color and turbidity respectively The optimum alum dose was alternatively re placed with lower doses and coupled with poly electrolyte low dose CP PE in order to main tain the similarly high removal performances of optimum dose CP process As seen from Table 3a 50 mg L of coagulant had little success i e 28 color and 14 turbidity removal efficien cies were obtained The addition of 0 2 mg L of polyelectrolyte even reduced the removal rates of color and turbidity to 15 and 9 respectively On the other hand 0 2 mg L of polyelectrolyte had slightly positive effect on the removal effi ciencies at alum doses of 75 and 100 mg L which indicates that there is a threshold value of alum dose for a successful combination of coagulant and polyelectrolyte although the improvement was not significant At these low alum doses in Table 3a Comparison of pre treatment alternatives single processes a Not available b Alum 150 mg L c Polyelectrolyte 0 2 mg L Effluent quality Removal Process Color Pt Co Turbidity NTU Color Turbidity 1 Dead end MF MF 11 m 166 naa 45 na MF 2 5 m 171 na 43 na MF 1 0 m 63 na 79 na 2 Optimum dose CP A 150 b 15 2 5 95 94 3 Low dose CP PE A 50 217 35 3 28 14 A 50 PE 0 2 c 256 37 3 15 9 A 75 175 32 8 42 20 A 75 PE 0 2 166 27 9 45 32 A 75 PE 1 0 196 31 2 35 24 A 100 90 16 4 70 60 A 100 PE 0 2 93 16 0 69 61 A 100 PE 1 0 96 17 6 68 57 0 50 100 150 200 250 300 050100150200250 Alum dose mg L Color Pt Co 0 5 10 15 20 25 30 Turbidity NTU ColorTurbidity creasing the polyelectrolyte dose from 0 2 mg L to 1 0 mg L again adversely affected the removal performances achieved by alum alone Table 3a These results revealed that low dose CP PE did not perform as good as the optimum dose CP and therefore a new alternative was considered Fig 3 Effect of alum dose on color and turbidity removal G Capar et al Desalination 212 2007 103 113109 In the fourth alternative low dose CP was fol lowed by MF low dose CP MF where MF media having pore size of 1 0 m was used as it had the best performance among all the MF me dia tested In this case alum dose as low as 50 mg L was tested in order to see whether the filtration rate in post MF would be sufficiently increased or not The cumulative dead end filtration rate in single MF increased from 0 18 L h to 0 27 L h due to the preceding low dose CP stage in a pe riod of 30 min This corresponds to an increase of 56 which was considered to be insufficient to implement the MF process in industrial scale since the following membrane processes might require higher flowrates The low dose CP process im proved the removal performance of post MF as expected Table 3b The improvement in COD removal which was realized to be from 15 to 29 was more significant as compared to those achieved for color and turbidity Since the low dose CP was not effective to significantly increase the filtration rate in the following MF another al ternative process train was implemented finally where low dose of alum was replaced by a much higher dose and MF was replaced by UF Table 3b Comparison of pre treatment alternatives sequential processes Final effluent quality Removal Process COD mg L Color Pt Co Turbidity NTU COD Color Turbidity 4 Low dose CP MF MF 1 0 m 332 42 8 2 15 86 80 Low dose CP 50 mg L naa 217 35 3 na 28 14 Low dose CP MF 278 27 5 7 29 91 86 5 High dose CP UF High dose CP 400 mg L 332 48 7 4 15 84 82 UF 50 000 Da 282 9 2 9 28 97 93 High dose CP UF 239 3 0 4 39 99 99 a not available In the last alternative 400 mg L of alum high dose CP and an UF membrane Osmonics HZ 15 with a MWCO of 50 000 Da were used The performance of high dose CP UF is shown in Table 3b As seen high dose CP removed 15 of COD 84 of color and 82 of turbidity initially present in PDW These removals were realized to be less than those observed for the optimum dose 150 mg L possibly due to overdosing of the system by coagulant at the dose of 400 mg L and resulting charge reversal which in turn would deteriorate the coagulation performance It was observed that post UF increased the removal effi ciencies obtained by high dose CP alone and the extent of these increases was significant espe cially for color and turbidity The overall removal efficiencies achieved by the combined process train was 39 for COD and 99 for color and turbidity The high dose CP UF alternative was also evaluated in terms of flux decline since it directly affects the productivity In the UF experiment the flux decline with respect to the clean water flux Jcw was 10 initially and increased to 28 at the end of a filtration period of 1 h after which it 110G Capar et al Desalination 212 2007 103 113 remained constant Fig 4a However there was a slight fluctuation in the flux decline after 2 5 h of filtration and the flux decline decr