Decentralized Wastewater Treatment System (DEWATS) can be described as a low maintenance treatment system, treating small volumes of wastewater for reuse or discharge within National Standards. DEWATS generally treats domestic wastewater originating from individual or groups of dwellings, businesses or institutions that are located in close proximity to each other and the DEWATS site. Unlike conventional wastewater treatment plants, DEWATS promotes technologies that use natural processes and are simples in operation and maintenance. In DEWATS, natural treatment processes are achieved through methods that make use of physical principles combined with biological activities of microorganisms. Bacteria colonies in the treatment devices are generated from microbial populations that occur naturally in the wastewater.
The size of a DEWATS can range from individual onsite systems that serve one household or institution; to shared facilities that serve up to ten households or public/community facilities serving up to 2000 households. Since the distance between the point of origin and treatment of wastewater is small, elaborate collection systems and pumping equipment is avoided thereby reducing costs. This also allows for easier reuse of treated water which again makes the whole system cost efficient.
Typical DEWATS combine the following technical treatment steps in a modular manner.
(1) Primary Treatment
The primary treatment phase retains all settable solids and allow only dissolved solids to discharge.
In settler, sedimentation tank, septic tank or biogas settler.
Another type of primary treatment is sedimentation tank for collection and use of biogas generated from decomposition of settled organic particles.
(2) Secondary Treatment
Suspended and dissolved solids in the wastewater undergo anaerobic degradation due to contact with an active sludge blanket on the bottom of each chamber.
(3) Tertiary Treatment
It is the secondary and/or tertiary treatment phase and cleans the wastewater by biological conversion, physical filtration and chemical adsorption.
(4) Sludge Treatment
Sludge generated from primary and secondary treatment units can be dried applying on sand beds, which is also called sludge drying beds. De-sludging intervals can be set to coincide with the dry season in order speed up the drying process.
EXISTING DEWATS IN NEPAL
S.N.
Location Type
Year Built
1
Dhulikhel Hospital Hospital
1997
2
Dallu, Private House Domestic
1998
3
Kathmandu University Institutional
2001
4
ENPHO Laboratory Institutional
2002
5
Malpi International School Institutional
2002
6
Sushma Koirala Memorial Plastic &Reconstructive Surgery Hospital Hospital
2002
7
Kapan Monastry Institutional
2002
8
Private House at Dallu Domestic
2002
9
Septage Treatment, Pokhara Community
2003
10
Shuvatara School, Lamatar Institutional
2004
11
Surya Tobacco Industrial
2005
12
Private House, Bishal Nagar Domestic
2005
13
Sunga, Thimi Municipal
2006
14
Kirtipur Housing Community Community
2006
15
Kusunti Housing Community
2007
16
Ilam Polyclinic Hospital
2007
17
Sano Khokana Community Community
2008
18
Srikhandapur Community
2008
19
Monastry in Pharping, Dakshinkali Institutional
2009
20
Private House at Kirtipur Domestic
2010
21
Namo Bhudha Resort
2012
22
Thakuri Gaun Sub System
2009
23
Pipal Bot Sub System
2009
24
Srikhandapur Community Wastewater Treatment Plant
2008
25
Nala Community Wastewater Treatment Plant
2012
26
Panauti Wastewater Treatment Plant
2009
27
Chandeshwori Wastewater Treatment Plant
2009
28
Budole Wastewater Treatment Plant
2009
29
Landfill Site Wastewater Treatment Plant
2009
30
Gokarna Wastewater Treatment Plant(I)
2012
31
Gokarna Wastewater Treatment Plant(II)
2014
32
Gokarna Wastewater Treatment Plant (III)
2016
33
Kapan Monastry
2002
34
Satya Sai Sikshya Sadan
2014
35
School at Dallu
2010
36
Central Horticulture Center
2011
37
Neydo Monastry
2009
38
Kusunti Housing
2007
39
ICIMOD
2010
40
Ama Ghar
2010
41
Suvatara School
2004
42
Park Village Water Front Resort
2011
43
Hetauda Wastewater Treatment Kara Sub System
2009
44
Hetauda Waste Treatment Rapti II Sub System
2009
45
Hetauda Wastewater Treatment Rapti II Sub System
2009
46
Hetauda Industrial Wastewater Treatment Plant
2003
47
Bharatpur Wastewater Treatment Plant (C1)
2009
48
Bharatpur Wastewater Treatment Plant (C2)
2009
49
Surya Nepal Pvt. Limited (Staff Housing)
2005
50
Lumbini Medical College and Teaching Hospital
51
Sidhartha Childern and Women Hospital (AMDA)
52
Middle Marshyangdi Hydro Electric Power Station (Staff Quarter)
