Bu çalışmanın amacı sulardaki Fe(II) konsantrasyonunun filtre yük kaybı ve çıkış suyu kalitesine etkisini deneysel olarak incelemektir. Çalışma laboratuvar ölçekli iç çapı 30 mm ve yüksekliği 1000 mm olan pleksiglassdan imal edilmiş silindirik filtre kolonları kullanılarak gerçekleştirilmiştir. Kolonlara 0.50-0.59 mm çapları arasında ve 40 cm yüksekliğinde silisli kum doldurulmuştur. Çalışmada musluk suyu, dört farklı Fe (II) konsantrasyonu (0.5, 1.0, 2.5, 5.0 mg/L) ve iki farklı yükleme hızı (5.6, 11.20 m3/m2.saat) kullanılmıştır. Ham suyun alkalinite değeri, ani pH değişimlerine karşı 150 mg/L CaCO3 değerine ayarlanmıştır. Alkalinite ayarlamasında sodyum karbonat ve pH düşürmede karbondioksit kullanılmıştır. Filtre çıkış suyunda su kalitesini temsilen bulanıklık değeri ve filtrenin demir giderim verimini belirlemek için çıkış suyunda toplam demir(TFe) ölçülmüştür. Filtrede oluşan yük kayıpları ve filtre yatağı boyunca yük kaybı değişimi incelenmiştir. Sonuç olarak, 2.5 ve 5.0 mg/L gibi yüksek TFe konsantrasyonlarında yük kaybının 0.5 ve 1.0 mg/L’ye göre çok daha hızlı meydana geldiği ve tıkanmanın tüm filtre yatağı boyunca değil yoğun bir şekilde filtrenin üst kısmında olduğu, 0.5 ve 1.0 mg/L gibi düşük TFe konsantrasyonlarının yük kaybı oluşumunu çok az etkilediği, filtre çıkışında TFe’nin standart değerinin (0.2 mg/L) altında kalması açısından 2.5 ve 5.0 mg/L TFe konsantrasyonlarında 5.60 m/saat ve daha düşük filtre hızlarının uygulanmasının uygun olacağı belirlenmiştir. Anahtar Kelimeler: Filtrasyon, demir (II) oksidasyonu, yük kaybı, demir giderimi.The aim of this study is to determine the effect of Fe(II) concentration on filter headloss and effluent water quality. In the scope of the study, a plexiglas cylindrical columns having inner diameter of 30 mm and height of 1000 mm were employed in laboratory scale studies. These filter columns were filled with silica sands having 0.59 mm equivalent diameter, 2.64 g/cm3 density and shape factor of 0.80. It was ensured that the ratio between inner diameter of filter column and diameter of sand was greater than 50. Settling velocity of silica sand was calculated as 8.07 cm/s by column settling experiment results. The porosity of the sand was determined in the experimental study as 0.36. Filter columns were fed by a 100 L-tank. The oxygen required for the oxidation process was provided by a fine bubble diffuser set on the bottom of the tank. In this study, tap water having 2.5-3.5 mg/L of total organic carbon, 9.5-11 mg/L of dissolved oxygen and temperature of 15-16 0C was used. Alkalinity value of 90-110 mg CaCO3/L of tap water was adjusted to 150 mg CaCO3/L with sodium carbonate (Na2CO3). Increased pH value was decreased to 7.0 injecting carbon dioxide. To ensure Fe(II) concentration, desired ferrous ammonium sulfate (FeSO4(NH4)2SO4.6H2O) was added to water. Nitric acid ((HNO3)) was used to preserve iron samples for metal analysis. Perkin Elmer 2100 DV Induced Coupled Plasma Optical Emission (ICP-OES) was used for iron measurement. Cations and anions of tap water were measured by using DIONEX ICS?1500 Ion Chromatograph (IC). Experimental studies were carried out at four different Fe(II) concentrations (0.5, 1.0, 2.5 and 5.0 mg/L) and two different filter velocities (5.60 and 11.20 m/h). Turbidity and total iron concentration were measured at the influent and effluent of the filter. 0.81, 1.2, 7.0 and 15.0 NTU of turbidity in the filter influent were obtained by oxidation of Fe(II) in the feed tank. Turbidity in the filter effluent for 2.5 mg/L of iron concentration was increased for first 150 minutes and than decreased. It is thought that this was due to longer ripening period of the filter for 2.5 mg/L of iron concentration. On the other hand, it was observed that low filter velocities had to be applied for high iron concentrations and turbidity removal efficiency was not changed importantly in the high filtration velocities in the course of time. Total iron concentrations in the filter effluent were apparently decreased by the increasing filtration period. Although filter headloss was increased linearly at all iron concentrations, it was apparently high for 5.0 mg/L of iron concentration according to other concentrations (0.5, 1.0 and 2.5 mg/L). Headloss changes among filter bed height were investigated and it was noted that headloss curves among filter bed were very different. While headloss curves among filter bed height were parabolic for low filter velocities, they were in the shape of two linear curves at 90 minutes and longer for high filter velocities. While headloss was decreasing to 35 cm deep from top of the filter bed linearly, it was suddenly changed its direction following more step linearly. It was observed that headloss was increased by elevated filter velocities. The results obtained in this study can be summarized as follows: In the case of 0.5 and 1.0 mg/L total iron concentrations and a porosity of 0.36, iron removal can be achieved by rapid sand filters (5-15 m/h) ensuring water quality standards described in TSS-266 (TS-266, 1997) In the higher total iron concentrations such as 2.5 and 5.0 mg/L, headloss occurrence was more rapid than for 0.5 and 1.0 mg/L and clogging happened in top layers of the filter rather than among all the filter height. It was observed that low concentrations of total iron such as 0.5 and 1.0 mg/L did not affect filter headloss occurrence. It was determined that filter velocities lower than 5.60 m/h were more appropriate for 2.5 and 5.0 mg/L total iron concentrations to ensure filter effluent quality and TSS-266 standard. Turbidity removal efficiency was affected by Fe(II) concentration rather than filter velocities. Maximum filter operation time was calculated according to net headloss occurrence rate, filter velocity and raw water iron concentration using experimental results. It was found that the ratio between velocities 11.20 and 5.60 m/s was 0.5 for maximum operating times. Keywords: Filtration, ferrous oxidation, filter headloss, iron removal
