Abstract
Surface water pollution is one of the serious environmental problems in urban centers ofNepal due to the discharge of untreated wastewater. Almost all conventional type wastewaterplants are not functioning well and practically not sustainable due to lack of regularmaintenance and high operation cost. To overcome this, Constructed Wetland (CW)technology for wastewater treatment arises as alternative technology in Nepal. Now, there are12 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 atvarious locations in Nepal. The performance evaluation was conducted through collection ofwastewater samples from inlet and outlet sources of treatment plants and measuringsignificant water qualities determining physical and chemical parameters such as BiochemicalOxygen 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 pollutionparameters. Performance of CW system were excellent for Kathmandu University (KU) andMalpi 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 ScaleWastewater Treatment Plant (Thimi) where the efficiency levels was 56% for BOD, 64% forCOD, 17% for Conductivity, 88% for TSS, 59% for TDS and 80% for TS. The results showthat, the CW systems are useful and efficient for waste water treatment in growing urbanareas. They are cost effective and easy to maintain. It is recommended that CW system couldbe replicate in other growing urban areas.
Highlights
Scientists have investigated the possibility of using wetlands to remove nutrients and suspended solids from polluted water
The wetlands herbs can reduce the levels of bacteria in waste water by secreting natural antibiotic substances from their roots, and they can sequester heavy metals and eliminate hydrocarbons
The Constructed Wetland (CW) technology is relevant for wastewater treatment due to the tropical climate at most places which is conductive to the growth of the rhizosphere
Summary
Scientists have investigated the possibility of using wetlands to remove nutrients and suspended solids from polluted water. The bulrushes, Schoenoplectus lacustris could remove large quantities of organic and inorganic substances from contaminated water. The wetlands herbs can reduce the levels of bacteria in waste water by secreting natural antibiotic substances from their roots, and they can sequester heavy metals and eliminate hydrocarbons. The basic mechanism of organic matter degradation in constructed wetlands is plant bacterial symbiotic reactions, in which gaseous oxygen photosynthetically produced or taken up for respiration by the plant is used by aerobic and facultative bacteria [I]. Some of the reasons for the need of introducing CW systems in Nepal are that they are modular and can be decentralized to even a single family level for sewage treatment; does not involve complicated mechanical components; does not demand high technical skill for operation and maintenance and construction uses locally available materials desirable for developing countries
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