外文原文-印染纺织废水的生物和臭氧联合处理技术.pdf

Integrated biological and ozone treatment of printing textile wastewater Adriana Maria Lotito a Umberto Fratinoa Giovanni Bergnab Claudio Di Iaconic aDepartment of Water Engineering and Chemistry Politecnico di Bari via Orabona 4 70125 Bari Italy bCIDA s p a via Laghetto 1 22073 Fino Mornasco CO Italy cWater Research Institute National Research Council viale De Blasio 5 70132 Bari Italy h i g h l i g h t s Integrated ozone SBBGR treatment was tested for printing wastewater treatment An effl uent for direct discharge can be obtained with an ozone dose of 135 mg l A synergetic biological and chemical oxidation activity is observed Sludge production is low 0 17 kgTSS kgCODremoved a r t i c l ei n f o Article history Received 7 February 2012 Received in revised form 13 April 2012 Accepted 1 May 2012 Available online 11 May 2012 Keywords Printing wastewater treatment Textile wastewater Sequencing batch biofi lter granular reactor Ozone integration Synergetic oxidation a b s t r a c t Textile effl uents are among the most diffi cult industrial wastewaters to treat because of their composi tional variability and of the presence of numerous different chemicals intentionally designed to resist degradation Though biological technologies offer a cheaper and more environmental friendly alternative for the treatment of textile effl uents an additional step to remove recalcitrant compounds is still needed Integrated biological and chemical treatment is a rather new approach that allows improving treatment performance and stability without increasing too much treatment costs Ozone integration in a sequenc ing batch biofi lter granular reactor was tested at laboratory scale for treating a printing wastewater char acterized by high concentrations of surfactants and nitrogen The process was optimized in terms of applied organic load and ozone dose The results have shown that the process assures the possibility to comply with the limits for direct discharge for all investigated parameters by operating at an organic load value lower than 1 5 kgCOD m3d and with an ozone dose of 135 mg l A synergetic biological and chemical oxidation activity was observed with a ratio between ozone dose and COD removed lower than 0 75 Finally the process was characterized by a sludge production as low as 0 17 kgTSS kgCODremoveddue to the high biomass concentration in the biological system used 2012 Elsevier B V All rights reserved 1 Introduction The textile industry is one of the longest and most complex manufacturing industrial chains covering the entire production cycle from raw materials to semi processed products yarns woven and knitted fabrics with their fi nishing process to fi nal products carpets home textiles clothing and industrial use tex tiles 1 2 The main environmental issue arising from textile production primarily regards water pollution In fact the textile industry uses water as the principal medium for removing impurities applying dyes and fi nishing agents and generating steam 1 3 About 100 200 l of water per kg of textile product are consumed and are then quite completely discharged as aqueous effl uent because both water losses to the product and water evaporated during drying are negligible 1 4 Apart from the high volume of dis charged water the main concern regards the chemical load it car ries due to the high dosage of chemicals and auxiliaries as high as 1 kg per kg of processed textiles 1 Among the products ap plied during the process the highest environmental load arises from salts detergents and organic acids Even if dyestuffs do not represent a signifi cant load compared to other substances theycanconvey diffi cult to eliminateorganiccompounds adsorbable organic halogens AOXs metals and they are respon sible for the colour of the effl uent which is mainly an aesthetic problem but can also reduce light transmission to aquatic plants 1 5 1385 8947 see front matter 2012 Elsevier B V All rights reserved http dx doi org 10 1016 j cej 2012 05 006 Corresponding authors Tel 39 3403005056 fax 39 0805313365 A M Lotito tel 39 0805820525 fax 39 0805313365 C Di Iaconi E mail addresses adriana lotito libero it A M Lotito claudio diiaconi ba r it C Di Iaconi Chemical Engineering Journal 195 196 2012 261 269 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage Finishing processes give the higher contribution to global wastewater production and load 6 7 For this reason numerous studies have addressed the development of an effi cient and cost effective treatment for this type of wastewater including physicochemical methods which are effective but quite expensive 8 13 Moreover accumulation of toxic compounds in the sludge can create disposal problems while excessive use of chemicals can also lead to secondary pollution On the contrary biological pro cesses offer a cheaper and more environmental friendly alternative for the treatment of textile effl uents 1 14 15 Hence several inno vative attempts to achieve improved biological reactor design and utilize special dye degrading microbes have been carried out 15 Nevertheless biological treatment alone is not suffi cient to remove colour surfactants and the recalcitrant COD fraction to lev els for direct discharge Therefore additional specifi c steps like ozonation or advanced oxidation processes are still needed to achieve this goal 16 Ozone is one of the most attractive alterna tives as it is an extremely strong oxidant which reacts rapidly either by a direct reaction of molecular ozone or through a radical type reaction involving the hydroxyl radical produced by ozone decomposition in water moreover it does not produce any solid residue Hence it is widely applied as a fi nal polishing step or as a pre treatment 17 19 In the last years in contrast to the conventional pre or post treatment concepts a new approach to the use of chemical and biological oxidation processes has been adopted based on the abil ity of ozone to enhance wastewater biodegradability as ozonation rarely originates complete mineralization to carbon dioxide and water but mostly leads to partial oxidation sub products such as organic acids aldehydes and ketones If biological and chemical oxidation treatments are applied as an integrated process and not separately or in sequence the effectiveness of the two treat ments is synergetic rather than additive This would result in a more effi cient use of the chemical oxidant together with a more robust and stable biological treatment as the effects of toxic and inhibitory compounds in bioreactors are reduced 16 20 21 Furthermore as the textile sector is fragmented and heteroge neous dominated by a majority of small and medium enterprises the search for technologies for on site treatment is a hot research topic In this fi eld sequencing batch biofi lter granular reactor SBBGR can be used as an advanced biological treatment which offers stability resistance to shocks and simultaneous organic car bon and nitrogen removal 22 In addition this system allows bio logical degradation to be easily integrated with ozonation 23 When assessing the effectiveness of a new technology for textile wastewater treatment it is necessary to recall that fi nishing treat mentsincludenumerousdifferentprocesses suchaspre treatment dyeing printing coating laminating processes for conferring special characteristics to the fi bres anti felting waterproofi ng non fl ammability etc washing and drying each characterized by specifi c features and pollutants 1 While numerous studies have investigated treatment solutions for dyeing wastewater less attention has been paid to printing wastewater 24 25 Despite the composition of such wastewater strongly resembles the one of dyeing wastewater solid pollutants from printing paste and sol vents are present in higher concentrations 24 25 Moreover while dyeingwastewatercontainslownitrogenamounts whichresultsin a lack of nutrients to biomass when applying biological treatment on the contrary printing wastewater presents very high nitrogen concentrations due to the use of ammonia in pigment printing pastes and urea as a hydrotropic agent 1 This paper reports the results of a study aimed at evaluating the effectiveness of an integrated process based on SBBGR and ozona tion for treating textile printing wastewater The synergetic effect of biological and chemical oxidation which is achievable adopting the integrated approach has been evaluated as well 2 Materials and methods 2 1 Experimental setup and operation The lab scale plant consisted of a SBBGR biological unit equipped with an ozonation unit The system was completely auto mated and controlled by a programmable logic controller PLC The SBBGR was made up of a 1 m Plexiglas cylinder with inter nal diameter of 0 19 m The bed volume of about 9 l was fi lled with a plastic support material KMT k1 Kaldnes Norway 10 mm diameter 7 mm height 630 m2 m3 specifi c surface 950 kg m3 density 0 75 porosity kept between two sieves Reactor operated in up fl ow mode using a peristaltic pump with fl ow rate of 60 l h to feed wastewater from the bottom Two aerators in the liquid phase over the bed each with a fl ux of 150 Nl h provided dis solved oxygen to biomass through a continuous recycle 90 l h that assured also substrate distribution The opening of a motor ized valve made effl uent fl ow out from a port located in the liquid phase over the bed A washing step of the fi lter with compressed air was performed when head losses at the bottom of the bed ex ceeded an established threshold 3 m The ozonation unit consisted of a 5 l reactor equipped with a porous distributor of ozone An ozone generator Modular 8HC WEDECO with maximum capacity of 8 gO3 h produced ozone from pure oxygen The column was supplied with an ozone meter and a residual ozone destroyer The liquid phase from the biological reac tor was withdrawn into the ozonation column by means of a peri staltic pump with fl ow rate of 70 l h while the ozonated liquid was recycled in the biological reactor by gravity Before starting the experiments with the printing wastewater the reactor had treated a mixed municipal textile wastewater for 200 days A stratifi ed distribution of biomass was present at the beginning of the new experimental campaign with a mean concen tration of about 31 kg of total suspended solids per m3of bed 26 The experimentation was arranged in two main periods during the fi rst one period A 1 only biological treatment was performed while during the second period period B ozonation was inte grated During the last two weeks ozonation was stopped again to better compare the results obtained with biological treatment alone and with the integrated one period A 2 Period A 1 was aimed at acclimatizing biomass and at evaluat ing the maximum value of the organic loading rate OLR compat ible with a satisfactory removal level of biodegradable pollutants and nitrogen by adjusting the wastewater volume fed to the plant i e hydraulic load HL During this period SBBGR operated with 8 h treatment cycles consisting of three consecutive phases Fig 1a At the beginning of the cycle a certain volume of infl uent was added to the liquid volume retained in the SBBGR from the previous treatment cycle fi lling phase duration 8 10 min Then the biological degradation phase started with continuous recircu lation of the liquid phase through the biomass bed duration 455 457 min During the fi rst hour of this phase no air was provided for pre denitrifi cation while afterwards the liquid in SBBGR was continuously aerated to allow the biological removal of biodegrad able pollutants Finally the treated effl uent was drawn by gravity from SBBGR and the plant was ready to start a new treatment cycle drawing phase duration 15 min The integration of ozonation in SBBGR period B led to the modifi cation of plant confi guration and treatment cycle Fig 1b In particular a fourth phase i e aerobic degradation and ozona tion phase was inserted before the drawing one aimed at the re moval of recalcitrant pollutants During this phase the liquid in SBBGR was recycled through ozone reactor the ozonated liquid was then pushed back by gravity in the top of SBBGR and recircu lated through the SBBGR biomass Period B was split in three runs 262A M Lotito et al Chemical Engineering Journal 195 196 2012 261 269 B1 B2 and B3 each characterised by different aerobic degrada tion and ozonation phase time i e 30 60 and 60 min for runs B1 B2 and B3 respectively and transferred ozone dose values i e 45 135 and 90 mgO3 linf respectively HL throughout experimentation is shown in Fig 2 together with OLR HL was progressively increased during period A days 0 60 except for the last 15 days when a strong infl uent stock was used In the period between days 95 and 100 HL was reduced to allow biomass to recover after some biomass loss due to pump failure in the previous days Operational conditions applied during the different experimen tal periods are summarized in Table 1 2 2 Analytical methods Several parameters of infl uent and effl uent were measured two or three times per week to monitor treatment performance In par ticular standard methods were adopted to measure chemical oxygen demand COD biochemical oxygen demand BOD5 total and volatile suspended solids TSS and VSS total Kjeldahl nitrogen TKN ammonia N NH4 total surfactants non ionic bismuth active substances BIAS cationic CAT anionic methylene blue active substances MBAS total phosphorous P and pH 27 pH was monitored throughout treatment cycles no signifi cant variations were observed as it remained in the range 7 5 8 5 Total nitrogen TN was measured by means of a carbon analyzer model 5050 with an additional total nitrogen measuring unit model TNM 1 by Shimadzu Co Japan Oxidised nitrogen N NOx was calculated as the difference between TN and TKN To evaluate colour removal the absorbance of the samples was measured in quartz cuvettes with a 1 cm path length at three wavelengths 426 nm 558 nm and 660 nm and the decolouriza tion percentage was then computed Biomass concentration in the reactor was determined twice at the end of the biological treatment alone and at the end of period B after ozone integration In particular representative samples of biomass microbial samples were detached from two heights of the microbial bed top and bottom The volume of bed sampled was determined by counting the carrier elements and relating them to the number of carrier elements per litre of bed 1023 All the sludge present on the removed carriers was washed in a known volume of tap water and TSS and VSS were measured Fig 1 SBBGR sketch and cycle a biological treatment b integrated treatment Fig 2 Hydraulic continuous line and organic load squares applied throughout the whole experimental campaign A M Lotito et al Chemical Engineering Journal 195 196 2012 261 269263 Sludge volume index SVI was determined as an additional test to verify the development of granules evaluating their effect on the settling ability of the sludge 27 Ozone concentration in the gas stream at the inlet and outlet of the ozone reactor was measured by a UV analyzer ozone analyzer BMT 964 WEDECO Germany A standard calibration curve for the ozone produced by the ozone generator at different oxygen fl ow rates was established 28 The transferred ozone was subsequently computed as the integral of the difference between the produced ozone and the residual ozone measured during the treatment cycle The ratiobetweensuchvalue andthe volumeof wastewatertreated per cycle represented the transferred ozone dose The specifi c excess sludge production was computed by dividing theTSScomingoutofthereactor effl uent washingoperation micro bial samples by the amount of COD removed in the same period 2 3 Wastewater composition Wastewater was collected from the equalization tank of a fabric printing factory located in the textile district of Como Italy In such factory textile processing of different types of fabrics cotton silk polyester polyacrilic viscose acetate is performed consisting of a preparation step degumming for silk scouring followed by printing with reactive acid cationic and disperse dyes Final pro cesses include washing steaming and fi nishing softening Table 2 shows the composition average values and standard deviations of the printing wastewater which was provided in stocks of 1 m3 3 Results and discussion 3 1 Global treatment performance Fig 3 shows infl uent and effl uent concentrations of TSS COD TKN N NOx total surfactants and colour measured throughout the whole experimental campaign Moreover the total amount of nitrogen removed is presented Despite the variations in infl uent concentration low suspended solids concentrations below 15 mg l were always measured with removal effi ciencies even higher than 90 irrespective of the ap plied operational conditions HL and OLR thus demonstrating the high fi ltering capacity of the biofi lter Fig 3a However an in crease in effl uent concentrations which remained still lower than 30 mg l with consequent removal effi ciency deterioration was observed in the periods between days 85 and 95 and days 150 and 155 due to pump operating problems Quite constant COD effl uent concentrations mostly in the range 220 260 mg l were measured during period A 1 Fig 3b but the direct discharge limit of 160 mg l presently in force in Italy was not respected As expected this failure was due to the presence in the wastewater of a COD fraction recalcitrant to biological treat ment In fact regardless of the organic load applied during period A 1 see Fig 2 the COD concentration in the effl uent fell always in the same range On the contrary COD removal effi ciency was quite sparse 25 65 during period A 1 because of the strong var iation of the infl uent value i e 350 700 mg l When biological treatment was integrated with ozonation a reduction of the residual COD concentration was recorded In par ticular when the