-

Indonesia, a Southeast Asian country has some regions where water cannot be easily accessed by people. One of these regions is Gunung Kidul District, Yogyakarta Special Province. Geomorphologically, Gunung Kidul is covered by a karst formation that incorporates over hundreds of interconnected caves. Owing to these cave structures, rainfall and surface runoff infiltrate rapidly and form underground flow systems that finally end up at the coastline. However, due to the lack of an appropriate water resources management, inhabitants of Gunung Kidul do not have safe access to the underground water sources. An IWRM project has been implemented to address the problem and to find sustainable solutions. As a result of the first stages of the project, underground water was damming up. Thus, water can be pumped up to the surface and then it can be distributed to the surrounding people. Nevertheless, water needs to be treated before its distribution. Slow sand filtration (SSF) was deemed as an appropriate technology to be applied in this area and to remove suspended solids (Silva, 2010). Process efficiency was monitored taking into account turbidity. Therefore, the present study was aimed to evaluate the performance of SSF considering other parameters i.e. total coliforms and E.coli removal in regard to filter media (grain size distribution and sand type) and operation mode (intermittent mode and hydraulic loading rate (HLR)).Two methodological approaches were used in this research i.e. literature review and laboratory work. Bacteria removal was analyzed considering two different filter media (Rhine and Lava sand) with three different grain size distributions. Filter column experiments were conducted intermittently and using two different HLRs. The overall performance of the columns regarding bacteria removal was 1.6 – 4.7 log-units or 97.7 – 99.998% removal of total coliforms and 1.6 – 5 log-units or 97.6 – 99.999% removal of E. coli. The best performance with a more consistent result was attained by filter column F4 which consisted of Lava sand and had the configuration C2 (d10 = 0.07 mm and Cu = 4.2). This filter column achieved 4.7 log-units removal of total coliforms and 5.0 log-units removal of E. coli. In terms of filter media, grain size distribution and sand type played an important role at removing bacteria. A higher removal was achieved by the filter columns filled with Lava sand and consisted of configuration C2 (d10 = 0.07 mm and Cu = 4.2). Apart from filter media, the filter performance under intermittent operation mode was observed. Intermittently operated slow sand filtration (SSFi) with HLR of 0.1-0.2 m/h had a negative effect on bacteria removal. A decrease and non-constant bacteria removal after both < 24 hours and > 24 hours interval occurred in the sand filter. Under the same operation condition but with HLR of 0.03 m/h, a relatively constant and high removal of bacteria was achieved. All mechanisms i.e. straining, adsorption, and purification mechanism actively took part within the sand bed. Those mechanisms seem to play a significant role at improving the bacteria removal in slow sand filtration as well.

Kata Kunci : Slow Sand Filtration, Bacteria Removal, Filter Media, Intermittent Operation