Assessment of performance characteristics of some constructed wetlands in Nepal

Abstract

Surface water pollution is one of the serious environmental problems in urban centers of
Nepal due to the discharge of untreated wastewater. Almost all conventional type wastewater
plants are not functioning well and practically not sustainable due to lack of regular
maintenance and high operation cost. To overcome this, Constructed Wetland (CW)
technology for wastewater treatment arises as alternative technology in Nepal. Now, there are
12 sub-surface flow CW systems in operation all over the country.
This study aims to checking the efficiency and performance evaluation of three CW located at
various locations in Nepal. The performance evaluation was conducted through collection of
wastewater samples from inlet and outlet sources of treatment plants and measuring
significant water qualities determining physical and chemical parameters such as Biochemical
Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Hydrogen ion concentration
(pH), Conductivity, Phosphorus, Total Suspended Solids (TSS), Total Dissolved Solids (TDS)
and Total Solids (TS).
The CW systems were found efficiently removing and reducing different pollution
parameters. Performance of CW system were excellent for Kathmandu University (KU) and
Malpi International School (Malpi) where the efficiency levels ranged between 82% to 96%
for BOD, 68% to 85% for COD, 91 % to 99% for TSS, 60% to 83% for TDS and for TS 84%
to 92%. The performance efficiency was relatively lower for Thimi Community Scale
Wastewater Treatment Plant (Thimi) where the efficiency levels was 56% for BOD, 64% for
COD, 17% for Conductivity, 88% for TSS, 59% for TDS and 80% for TS. The results show
that, the CW systems are useful and efficient for waste water treatment in growing urban
areas. They are cost effective and easy to maintain. It is recommended that CW system could
be replicate in other growing urban areas.