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