Upflow Roughing Filter and Upflow Slow Sand Filter

Effectiveness of combined upflow roughing filter and upflow slow sand filter to reduce turbidity in Citarum water as a source of drinking water

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Citarum is the longest river in West Java, Indonesia and is used as a source of drinking water by people and PDAM (Perusahaan Daerah Air Minum, Regional Drinking Water Company). Its turbidity is high and fluctuating. Citarum also receives domestic and industrial wastewater. Since the 1980s the people and government of Indonesia has issued Citarum water quality improvement programs such as MCC: Masyarakat Cinta Citarum, Clean River Program (Program Kali Bersih, Prokasih), GCB: Gerakan Cikapundung Bersih, Gerakan Citarum Bergeutar [bersih (clean), geulis in Sundanese is beautiful, lestari (sustainable) [1] and Citarum Harum on 2018 [2].

The Citarum Harum program improves quality of drinking water source for people, community and PDAM. However, Citarum water treatment is too expensive when using PDAM technology i.e. settler or prasedimentation, coagulation, flocculation, sedimentation, rapid sand filter (RSF). Configuration of these unit operations and processes are called conventional treatment and always use chemicals. Since the 1970s PDAM has applied conventional technology for their water treatment. PDAM does not have a new design and the Ministry of Public Works always implements a conventional treatment called IPA Kedasih (Instalasi Pengolahan Air Keluaran Direktorat Air Bersih) [3]. Therefore there is a hope in the future that the government and PDAM will use multistage filtration (MSF).

MSF is a combination of roughing filter (RF) and slow sand filter (SSF). MSF has been widely applied in developing countries in Latin America. This system was intensively researched in the last decades of the 20th century by IRC - CINARA (International Water and Sanitation Centre - Instituto de Investigacion y Desarollo en Abastecimiento de Agua) in Colombia. CINARA built a pilot plant in Puerto Mallarino. Its turbidity was 80 - 3,600 NTU, coliform bacteria was 63,000 - 500,000 Colony Forming Units (CFU) and final turbidity was 3 - 24 NTU (nephelometric turbidity units) [4]. Indonesia is a developing country but so far there is no PDAM from Sabang to Merauke use MSF.

Numbers of developing countries have implemented horizontal roughing filter (HRF) combined with slow sand filter [5]. Baker on 1981 wrote a book The Quest for Pure Water that HRF was also used to treat surface water from cistern by installed a gravel pack around it since the Middle Ages in former castle of Hohentrins in the Swiss Alpine valley of Rhine River [6]. HRF is applied because gravel produces large perviousness so that solid particle penetration is deeper and has much more space. HRF is able to extend the lifetime of downflow slow sand filter (DSSF) up to five times [7] and HRF has successfully treated raw water quality with turbidity 200 - 400 NTU [8].

In Ghana HRF is also used to treat highly turbid water [9]. HRF has been effectively made in developing countries such as Iran, Malaysia, India, Sri Langka [10]. HRF is also studied in Iran to treat surface water [11]. HRF is also able to treat various raw water in Kenya, Africa [12]. Roughing filter can treat highly turbid water (1,000 NTU) to generate 10 NTU for SSF in Myanmar [13]. Beside HRF, vertical roughing filter (VRF) is also developed viz. downflow and upflow and the filter media is completely submerged, different to HRF [14].

Japan has implemented VRF. Community Water Supply Support Center in Niigata, Japan studied a pilot plant on 2008 - 2010. Its treatment consisted of one settler (prasedimentation), five upflow roughing filters (URF) and one DSSF, and treated water from Kariyata and Shinano River. The pilot plant had three variations i.e five steps URF, three steps URF, multilayers URF. The last one was a DSSF. The video of pilot plant is available in this link [15]. Another URF study for rural water treatment with velocity 5 - 20 m/hour achieves turbidity efficiency 85 - 90% [16].

In addition to HRF and URF, available many roughing filters like dynamic gravel filter, upflow gravel filter in layers and series, downflow gravel filter in layers and series, and slow sand filter. All filter media are gravel, average diameter 0,5 - 3 cm and specific gravity 2,6 - 3,0. Gravel filters mainly improve physical water quality: as suspended solid are removed then turbidity reduced, the water becomes clearer. Bacteriological improvement can also be expected as bacteria and viruses are solids too, in size approx. 10 - 0.2 µm and 0.4 - 0.002 µm respectively. Bacteriological water quality can be improved to 60 - 99% [7]. Some research results on MSF, RF, and SSF are shown in table 1 [10].