Influence of Effective Size and Level ... (Anggraini, A., et al.) Online version available at http://journal.ugm.ac.id/index.php/ajse 47 Sejarah: Received: October 7, 2014 Accepted: November 26, 2014 First published online:3 December 30, 2014 Keywords: slow sand filter grain size distribution operation mode effective size supernatant layer Abstract Slow sand filtration has been admitted as an old method of water treatment and has been widely used in the world. This type of sand filter is prominent in its simplicity, low cost, and effectiveness. The term effectiveness refers to the performance on removing particulate matter and microorganisms. There are some significant factors should be considered in the system of slow sand filtration, such as grain size distribution of media, sand type, bed depth, operation mode of filter, and filtration rate. This study focuses on the influence of different effective size of media and operation mode in slow sand filtration especially on removing turbidity. Grain size distribution is represented by the effective size (d10) and uniformity coefficient (Cu). In regard to the operation mode, both sizes were operated under intermittent operation mode and were compared in two different level of supernatant layer: decreasing level and constant level. Laboratory scale experiments were conducted using four filter columns. Two filter columns were filled up with Rhein sand in different effective size of d10 0.075 mm and d10 0.50 mm. Uniformity coefficient Cu 2.5 and curvature coefficient Cc 1 were the same for both d10. Every column was fed with the same concentration of artificial raw water. The artificial raw water was created from Heilerde (clay from Germany) which passed 0.063 mm sieve opening mixed with tap water. Fine grain size tends to be easier to be controlled in regard to filtration rate, and vice versa for the coarse grain size. Surprisingly, the coarse grain size was able to remove turbidity as good as the fine grain size. Permeability of column was also tested and it decreased along with the addition of Heilerde. INFLUENCE OF EFFECTIVE SIZE AND LEVEL OF SUPERNATANT LAYER IN SLOW SAND FILTER PERFORMANCE Anggraini, A. K.*, Fuchs, S., Silva, A. Institute for Water and River Basin Management, Department of Aquatic Environmental Engineering, Karlsruhe Institute of Technology, Gotthard-Franz-Str. 3, Bldg. 50.31, D-76133, Karlsruhe, Germany. *Corresspondence : agustina.anggraini@student.kit.edu 1. Introduction Slow sand filtration has been used since the beginning of 19 th century (Huisman and Wood, 1974). It is not only a simple and low cost water treatment method but also effective on water purifying. Visscher (1990) resumes the effect of slow sand filtration as follows: reduces turbidity to < 1 NTU; reduces fecal coliform up to 95‐100% to 99‐100%; reduces organic matter 60‐75%; largely removes iron and manganese; and reduces 30‐95% heavy metals. Moreover, the significant effect of slow sand filtration is the reduction of chlorine use. Slow sand filtration performance is influenced by many factors, such as biological layer (schmutzdecke); grain size distribution of media; sand type; bed depth; filter operation mode; and filtration rate. Different condition of the combination of those factors will lead into different performance. As an example, sand which is not too coarse combined with certain thickness can provide very good purifying process (Hazen, 1908). However, Sadiq et al. (2004) proves that finer grain size combined with certain bed depth and filtration rate might produce low removal efficiency. This study reports on the influence of different grain size distribution, represented by the effective size (d 10 ), and operation mode to the filter performance, especially on the different level of supernatant layer. There are four combinations: fine grain size with constant level supernatant layer; fine grain size with decreasing level supernatant layer; coarse grain size with constant level supernatant layer; and coarse grain size with decreasing level supernatant layer. According to Crites and Tchobanoglous (1998) in Tyagi (2010), grain size distribution of media represented by effective size (d 10 ) and uniformity coefficient (C u ) has a significant role in the performance of slow sand filtration. Hazen (1931) as mentioned in Barrett et al. (1991) states that the fine grain size determine the characteristic of the sand filter and confirms that the finer the d 10 , the higher the removal efficiency. Fine grain size can also avoid the deeper penetration into the bed that makes it difficult to be eliminated by surface scrapping (Hazen, 1908) (Huisman and Wood, 1974). Associated with head loss, Boller and Kavanaugh (1995) claim that the coarser the grain is, the larger the pores will be. Larger pores will lead into higher head loss. For slow sand filtration, Huisman and Wood (1974); Visscher (1990); and Environmental Protection Agency (1995) recommend the value of d 10 0.15 mm – 0.35 mm and C u < 3. Hazen (1908) suggests that it will be better not to employ sand coarser than 0.35 mm. In the other hand, Bellamy et al. (1985) find out that coarser sand may have high percentage of bacteria removal. Normally, filtration rate in slow sand filtration is in the range of 0.1 – 0.4 m/h (Huisman and Wood, 1974). Visscher (1990) recommends the value of 0.1 – 0.2 m/h for the filtration rate as the slow filtration rate would give satisfactory effluent. This statement is enhanced by Di Bernardo and Escobar Rivera (1996) who claim that higher filtration rate does not only produce worse result but also lower filtration period. In contrast, Muhammad et al. (1996) prove that the slow sand filter keeps giving reasonably good filtrate operated at higher filtration rate. The data of Sadiq et al. (2004) shows that the high filtration rate may produce better effluent. Filtration rate, besides is affected by grain size distribution, it can be controlled by the way the filter is operated by controlling the level of the supernatant layer. Supernatant layer level can be kept constant or decreasing in the filtration process. Based on Di Bernardo and Alcócer Carrasco (1996), there is no significant influence on the filters during the ripening period for both conditions of supernatant level.