Color removal from textile wastewater in modified fixed bed zeolite column reactor and regeneration of zeolite bed

Sabit yataklı modifiye zeolit kolon reaktörde tekstil atıksuyundan renk giderimi ve zeolit yatağın rejenerasyonu

Abstract

Textile industries consume large amounts of water and chemicals for dyeing processes and also dye wastewaters usually consist of a number of contaminants including acids, bases, dissolved solids, toxic compounds, and color. Reactive dyes are extensively used in textile dyeing processes, but about 20 to 40 % of these dyes remain in the effluents. The reactive (water-soluble) dyes cannot be easily removed by chemical coagulation/ flocculation because they strongly resist to biodegradation in an aerobic environment. Removal of reactive dyes from textile wastewater is considered as an important application of the adsorption process using low-cost adsorbents such as fly ash, chitosan, natural minerals against expensive adsorbents like activated carbon and polymer resins. The presence of 50 billion tons of natural zeolites of high quality, mainly those of clinoptilolite in Turkey, created an impetus for the utilization of clinoptilolite in wastewater treatment as a low cost adsorption material. In this study, color removal from real textile wastewater, which contains reactive dyes in a fixed bed column reactor, was investigated. In the studies, zeolites from Manisa-Gördes Region was used as a low cost adsorption material Adsorption of reactive dyes from the wastewater collected from a textile industry dye bath house effluent was researched using natural zeolite. The aim of this study was to investigate zeolites applicability to textile effluents for the removal of color, which contains reactive dyes in the fixed bed reactor and regenetability. The reactive dyes have negative sulfonate groups, which are repelled by the negatively charged zeolite surface. This induces a relatively low adsorption capacity for natural zeolite. For this reason, in order to increase the adsorption capacity, the surface of zeolite was modified with a typical quaternary amine surfactant hexadecyl trimethylammonium bromide (HTAB). In this respect, adsorption studies were carried out using modified zeolite in the fixed bed reactor and color removal performance of real textile wastewater was investigated. A series of tests were conducted by three stages as modification, color removal and regeneration. Each run consisted of modifying zeolite with HTAB in the column followed by removal of color from the real textile wastewater in the modified zeolite bed. Afterwards regeneration of modified zeolite column loaded with color was studied. At the end, in order to see the effect of regeneration on color removal, zeolite column once more modified. Finally, the real textile wastewater was given to modified zeolite column. Breakthrough curves for modification process were constructed under different conditions by plotting normalized effluent concentrations (C/Co) versus time (minute) or bed volumes (BV). Modification, color removal and regeneration studies were conducted by 1g/L HTAB concentrations a constant HTAB feeding flowrate of 0.025 l/min. and at a constant bed height of 25 cm (150 g of zeolite). Dimension of zeolite was 0.5-1 mm. and wastewater feeding flowrate was 0.025 l/min. Samples were taken every 30 minutes and analyzed using a visible spectrophotometer in 448 nm. In modification process, HTAB solution was pumped to the bottom of the column on the contrary of color removal process. In color removal studies, at a C/Co value of 0.1, the bed volume (BV) reached approximately 132 after 930 minutes running period in the modified fixed bed column. Empty bed contact time (EBCT) found to be 7 min. The results were successful for color removal as above the 100 BV at a C/Co value of 0.1 was accepted. Regeneration studies were performed at the condition of 60 oC at pH 12. The regeneration solution prepared as 10.5 l with 30 g/L NaCl solution and 3 g/L NaOH. The regeneration solution was pumped to the top of the bed using a pump that maintained both mixing and expansion of the bed. Thus, the flow in the bed accelerated, the desorption of color from clinoptilolite particles. In second modification after regeneration process, the zeolite column was needed less HTAB quantity comparing the first one. In color removal studies after regeneration process at a C/Co value of 0.1, BV reached approximately 55 after a 390 min. running period. Experimental results indicated that modification of zeolite column with the flowrate of 0.025 l/min and 1 g/l HTAB dosage was successful for color removal. The modified column showed a good performance by comparing the regenerated column for the color removal from the real textile wastewater. As a result, the information obtained from the present research will be applied to remove color from the textile industry effluents.

Özet

Bu çalışmada, sabit yataklı modifiye zeolit kolon reaktörde gerçek tekstil atıksularından zeolit ile adsorpsiyon uygulamasıyla renk giderimi araştırılmıştır. Doğal zeolitin adsorpsiyon kapasitesini arttırmak için zeolit yüzeyi, tipik kuaterner amin yüzey aktif madde hegzadesil trimetil amonyum bromür (HTAB) ile modifiye edilmiştir. Deneyler temel olarak modifikasyon, renk giderimi ve rejenerasyon olmak üzere üç ana kademeden oluşan toplam beş aşamada tamamlanmıştır. Kolondaki zeolit yatağın modifiye edilmesini takiben, tekstil atıksuyundan renk giderilmesi çalışılmıştır. Adsorpsiyon işleminden sonra doygun yatağın rejenerasyonu yapılmıştır. Rejenerasyonun etkinliğinin belirlenmesi amacıyla, zeolit yatak yeniden modifiye edilerek adsorpsiyon işlemi gerçekleştirilmiştir. Modifikasyon prosesinde kırılma eğrileri değişik HTAB konsantrasyonları için C/Co – süre ve BV (birim yatak hacmi başına arıtılan atıksu miktarı) olarak çizilmiştir. Renk gideriminde ise atıksuyun pik absorpsiyon değeri spektrofotometrede tespit edilmiş ve renk giderimi renk şiddeti olarak değerlendirilerek atıksulardan renk giderim kapasitesi, herhangi bir andaki absorbans değerinin başlangıç absorbans değerine oranı (bağıl renk şiddeti) olarak ifade edilmiştir. Modifikasyon, renk giderim ve rejenerasyon çalışmaları, 25 cm sabit yatak yüksekliğinde, 0.5–1 mm boyut aralığındaki 150 g zeolit ile 1 g/L HTAB konsantrasyonunda, 0.025 L/dk HTAB ve atıksu debilerinde yapılmıştır. Zeolitin adsorpsiyon kapasitesinin, atıksu debisine bağlı olarak belirli bir çalışma süresi sonunda azaldığı görülmüştür. 100 BV’ lik bir çalışma süresi verimli kabul edilirek 1 g/L HTAB modifikasyonu sonrası 0.025 L/dk atıksu debisi için renk giderimi başarılı olmuştur. Rejenerasyon çalışması pH 12 ve 60 oC’da gerçekleştirilmiştir. Doğal ve rejenere edilen zeolit için kırılma noktaları sırasıyla 930 ve 390 dakikada 132 BV ile 55 BV olarak gerçekleşmiştir