Atık sulardaki tekstil boyarmaddeleri renginin devrettirilen koagülant (CaO-MgCO3) ile giderilmesi

Abstract

Bu çalışmada, atık sulardaki tekstil boyarmaddelerinin renginin klasik metal koagülantlarla tasfiyesinde ortaya çıkan problemlerin çözümü ve bu boyarmaddelerin renginin, ucuz, te mini kolay koagülantlarla ekonomik olarak tasfiyesi ve yeni koagülasyon metodlarmm geliştirilmesi amacıyla araştırmalar yapılmıştır. Birinci bölümde, çalışmanın amacı ve kapsamı belirtilmiş tir. İkinci bölümde, deneylerde kullanılan boyarmaddelerin ya pıları ve boyama özellikleri belirtilmiştir. Tekstil elyafları sınıflandırılarak, bu elyafların boyanmasiyle ilgili bilgiler verilmiştir. Üçüncü bölümde, tekstil boyarmaddelerinin koagülasyonu ile ilgili olarak, kolloid stabilitesi ve stabiliteye etki eden faktörler, elektriksel çift tabaka için Gouy-Chapman ve Stern modelleri incelenmiştir. Çift tabakada potansiyel enerji dağı lımı, çift tabakanın kalınlığı, çift tabaka üzerine iyonik şid detin ve zıt yüklü iyonların etkileri belirtilmiş ve çift ta baka modelinin kolloid stabilitesine uygulanmasiyle ilgili Ver- wey-Overbeek modeli incelenmiştir. Koagülasyçoıu sağlayan çift tabakanın sıkışması, adsorbsiyon ve çökelti âğı içine mekaniz maları açıklanmıştır. Tekstil atık sularından rengin giderilmesi ile ilgili ola rak yapılan çalışmalar, kullanılan maddeler, uygulanan metodlar ve elde edilen sonuçlar belirtilmiştir. Dördüncü bölümde, kullanılan boyarmaddeler, seçilen koagü- lantlar, araç ve gereçler hakkında bilgiler verilmiştir. (CaO- MgC(>3) ile koagülasyonun teorik esasları belirtilmiştir. Indantren Grey-GG Colloisol, Indantren Orange RR-Colloisol, Palanil Brilliant Blue BGF, Palanil Rubine BN, Basilen Yellow II M-2R, Bas ilen Turquoise M-2G, Reaktif Mavi 114, Reaktif Kırmızı 124, Direkt Orange 107, Direkt Siyah 117, Asit Mavi 40, Asit Sarı 17, Bazik Mavi 41, Bazik Kırmızı 2L boyarmaddelerinin (CaO- MgC03) ile koagülasyonu, etkili koagülasyon mekanizmaları, koa- gülantın geri kazanılması ve devrettirilmesiyle ilgili araştır malar yapılmıştır. Bu amaçla her boyarmaddenin MgC03 ve CaO ile ayrı ayrı, CaO dozajını 250 mg/lt de sabit tutup MgCÛ3 dozajı nı değiştirerek, MgCÛ3 ve CaO i stökiyometrik oranlarda kulla narak koagülasyonu incelenmiştir. Bu deneylerin sonunda en iyi renk uzaklaştırma verimi (MgC03~CaO) in stökiyometrik oranlarda kullanıldığı deneylerde elde edilmiş ve bu koagülant konsantras yonları arasından geri devir için optimum dozaj tayin edilmiş tir. Bu deneylerde koagülantlarla boyarmadde tanecikleri arasın daki reaksiyonlarda safsızlıklardan dolayı meydana gelebilecek etkileşmeleri ortadan kaldırmak için saf su kullanılmıştır. Musluk suyu ile hazırlanan boyarmadde çözeltisinin belir lenen geri devir dozajında (MgC03-Ca(OH)2) kullanarak yapılan ön deneyden elde edilen çökelti ile on defa geri devir deneyle ri yapılmış geri kazanılan ve devrettirilen koagülantm boyar maddenin koagülasyonunda etkinliği araştırılmıştır. Koagülan tm geri kazanılmasında CO2,, devrettirilmesinde %88 lik Ca(0H)2' kullanılmıştır. NaOH ilavesiyle pH'sı yükseltilen (pH>ll) boyarmadde çö zeltisinin devrettirilen koagülant ile beş defa geri devir de neyleri yapılarak, bu koagülantm yüksek pH'lı boyarmadde çözel tilerinin koagülasyonunda etkinliği araştırılmıştır. Aynı tür boyarmaddenin başka bir rengi ile hazırlanan çö zeltinin NaOH ilavesi ile pH sı yükseltilmiş (pH>ll) ve devret tirilen koagülant ile beş defa geri devir deneyleri yapılarak, bu koagülantm boyarmaddenin başka bir rengini gidermedeki et kinliği araştırılmıştır. Boyarmaddelerin hepsinin karıştırılmasiyle hazırlanan çö zeltinin NaOH ilavesiyle pH1 sı yükseltilmiş (pH>ll) ve devret tirilen koagülant ile beş defa geri devir deneyleri yapılarak bu koagülantm boyarmaddelerin karışımının koagülasyonunda et kinliği araştırılmıştır. Deney neticeleri verilerek, değerlendirilmesi yapılmış ve boyarmaddelerin karışımının koagülasyonunda elde edilen sonuçlar Ill esas alınarak koagülasyon masrafı ile ilgili hesaplar yapılmış tır. Beşinci bölümde elde edilen sonuçların kritiği yapılmış tır.

Textile mills discharged highly colored wastewaters. The discharge of highly colored waste not only is aesthetically displeasing, but also impedes light penetration, thus upsetting biological processes and productivity within a stream. In addi tion, many dyes may be toxic to some organisms and may cause direct destruction of aquatic communities. Biological treatment processes are largely in effective for remowing color from the waste. Consequently, treated waste effluents may contain appreciaple amounts of color when dischar ged. Treatment technology includes biological treatment, filtra tion and chemical coagulation. The coagulation process will be the primary mechanism responsible for color removal. Considerable research has been done on the removal of color from textile waste effluents. These studies involved the use of conventional metal coagulants, such as alum, lime, ferric sulfate, ferrous sulfate, ferric chloride, calcium chloride, sodium aluminate. In most cases, coagulation has been effective in removing color. The large volume of sludge produced must be disposed of. Disposing of the sludge is extremely difficult and costly. Treatment processes wastes are recognized today as an industriwide pollution problem that must be solved. The principal needs are to find effective and economical means to dispose of water treatment of sludge. In answer to these needs, an. entirely new system has been used utilizing calcium oxide-magnesium carbonate as the coagulants. Magnesium carbonate can be removed from the precipitated sludge and re cycled through the process. This recoverability may significantly reduce the chemical costs and sludge disposal problems. The purpose of this study was to investigate the use of dalcium oxide-magnesium carbonate for color removal from textile dye waste, recoverability of coagulant and effective coagulation mechanisms... ' Coagulation with (CaO-MgCOq) can occur by three different mechanisms. One mechanism is the precipitation of magnesium hydroxide. The Mg(0H)2, a gelatinous precipitate, aggregates colloidal particles and sweeps them out of suspansion. Two other meshanisms are double layer compaction and adsorbtion. Precipita tion of Mg(OH)? is the preferred mechanism because it can be accomplished at the magnezyum carbonate dosages under proper conditions. Precipitation is enhanced at pH values above 10.56; thus, CaCOEOp is used to raise and sustain the pH during coagula tion. The addition of sufficient Ca(0H)2 to a solution, containing MgC03, precipitate Mg(0H)2 and CaCC>3, carbonation of the sludge selectively solubilizes the magnesium as Mg(HCC>3)2 an^ magnesium can be recycled. Recovery of magnesium is achieved by reducing the pH = 7.0 and disolving the Mg(0H)2. The CO2 is used to ruduce pH. The solubilized Mg (11003)2 can be returned to the coagula tion process and precipitate by the addition of more Ca(0H)2. In this study, MgCÛ3 recovery and recycle has been repeated - by continued application of the principle presented. Precipitation of Mg(0H)2 requires the" combined use of CaO and MgC03. However, Ca(0H).2 and MgC03 are capable of serving as coagulants. It is also desirable to study the effectiveness of the individual chemicals for coagulating textile dyes. Consequent ly, separate CaO and MgC03 jar tests were conducted. CaO dosage was fixed at 250 mg/lt and MgC03 dosage was increased. This CaO dosage was found to be sufficient to main tain a pH above 11.0 during coagulation. MgC03 and CaO dosages were used together at stoichiometric ratio. Much higher color removal were achieved when MgCÛ3 and CaO are used together at the stoichiometric ratio. VI In these tests, distilated water was used. Because im purities ift the solution can be influenced the reactions between the chemicals and the dye particles. The feasibility of recovering magnesium carbonate follo wing coagulation and reusing this material to treat; subsequent, waste samples was investigated. For this purpose, recover}? and recycle tests were made tan times at the selected coagula.nt dosages » ' The pH of the, solution was rised above İL. 0 by adding 200 ing NaOH to 1 It of solution. Recovery and recycle tests were made five times at the selected coagulant dosages. These tests- were conducted for the other color of tne dye at the pH values above 11'. 0. Textile dyes were mixed and. p.H of this solution was rised by adding 200 mg of the NaOH to 1 It of solution. Coagulant recovery and recycle tests were made five times at the selected coagulant dosages..'?..' Laboratory tests were made on fourteen different dyes. Stock solutions were prepared by adding 75 mg of dye to 1 It of distilled water. The optimum dosages of reactants required for. color removal were determined by a jar test. One litre beaker, containing 800 ml of dye solution, was placed on a jar test apparatus. The desired dosage of MgC03 in the. form of a 100 ml solution, was added to the jars and mixed for four minutes at a stirring speed of 100 rev/min. when CaO was used together, this was followed by the addition of CaO. Six minutes were allowed for the addition and rapid mixing of the reactants at a stirring speed of 100 rev/min. The solution were then allowed to flocculate at 45 rev/min for 30 minutes. After the flocculation period, the samples were allowed to settle for two hours (one hour at recycle studies) and then an aliquot of suparnatant was pipetted from 3 cm below the surface of the each jar and analyzed for absorbance. The charac teristic wavelength for each dye was determined by running a scan of the dye on a Double-Beam UV-150-02 model spectrophoto meter and determining the wavelength of maximum absorbance. VII This wavelength was used for.all absorbance readings. Percentage of color removal was calculated by comparing the absorbance values for the solution after treatment to the absorbance value for the original dye stock solution. The recycle studies began with the coagulation using MgCC>3 and Ca(0H)2 (%88 pure) at the selected dosages at the stoichiomet ric ratios. After settling, approximately %90 of the supernatant was siphoned off jars and the remaining volume, which contained the precipitated Mg(0H)2 sludge} was placed on a magnetic stirrer for recorbonation. The sludge was mixed for 1 minute. Carbon dioxide gas was bubbled into the sludge, until a pH of approxi mately 7.0 was reached, at which point all the Mg(OH)-; should have been disolved, CO2 was produced from the reaction between the CaCÛ3 and HC1.. Neither calcium oxide nor magnesium carbonate proved effec tive in removing color when used alone. However, calcium oxide was relatively effective for the Acid Blue 40 and Basic Blue 2L dyes.. Much higher color removals werte achieved when magnesium. carbonate and calcium oxide were used together as stoichiometric. These results suggest that Mg(0H)2 precipitation was responsible. For these result, it was concluded that the effective coagulation mechanism was enmeshment in a precipitate mechanism. In the recycle studies, for the treatment of Indantren Grey GG Colloisol dye color removal of %98-99.8 and %99.6-99;8 (at high pH), for the treatment of Indantren Qrange RR-Colloisol dye color removal of %99.8-99.8, for the treatment of Palanil Bril liant Blue BGF dye, color removal of %99.6-99.8 and %99.4-99.6, for the treatment of Palanil Rub ine BN dye, color removal of %98.5-98.6, for the treatment of Bas ilen Yellow M2R dye, color removal of %88-89 and %95. 8-96.0, for the treatment of Basilen Turquoise M-2G dye, color removal of %99.3-99.6, for the treat ment of Reactif Blue 114 dye, color removal of %92.0-93.2 and %98.4-99.6, for the treatment of Reactif Red 124 dye, color removal of %98-99, for the treatment of Direct Orange 107 dye, color removal of %99.4-99.9 and %99.8-99,9, for the treatment of Direct Black 117 dye, color removal of %99.8-99.9, for the treatment of Acid Blue 40 dye, color removal of %97. 5-98.0, and %59-58.8, for the treatment of Asit Orange 19 dye, color removal VIII of %40, for the treatment of Basic Red dye, color removal of %56.2-56.6 and %45. 2-45.0, for the treatment of Basic Blue 41 dye, color removal of %99.4-99.5, for the treatment of mixed dyes, color removal of %99.4-99.8 were obtained. The high natural pH of the dye wastes from the textile mill made it ideally suited to magnesium carbonate-calcium oxide treatment. Various coagulants such as alum, lime and iron salts have historically been used for treatment of textile, dye waste. The results of this study indicate that the stoichio metric (MgC03~CaO) sistem is a viable alternative to some of the more conventional forms of chemical treatment.