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Challenges and Potential Impacts of Wastewater Treatment in Kathmandu, Nepal
Aruna Shrestha

Last modified: 2017-08-22

Abstract


The study is based on wastewater treatment at Guheswori Wastewater Treatment Plant (WWTP), established 1995 with an objective of keeping Bagmati River and its tributaries clean by preventing the direct discharge of solid and liquid wastes into the river. The treatment capacity of 0.19 m3/s (17.3 million litres per day) and service area is 537 hectares covering upper Bagmati basin (Jorpati, Bouddha, Chabahil, Gokarna, Tusal, Mitrpark, Gaurighat and Pashupati). The design period of this plant is 25 years. The treatment plant involves activated sludge treatment system. The mechanical bar rack eliminates large objects from the influent, and inorganic particles like sand are removed in the grit chamber. Then wastewater is biologically treated in two carrousel 15 type oxidation ditches, each with three aerators. From the oxidation ditches, wastewater flows into two secondary clarifiers for the settling of solids. Up to 2,500 MLSS sludge is pumped from the clarifiers back to the oxidation ditches to be metabolized by microorganisms, and any excess sludge is wasted to one of fourteen drying beds. The different factors like economic, technical, and social factors are affecting the efficiency of the treatment plant. The lack of energy due to the frequent power cut led the partial function of the treatment plant. The partial functioning of the treatment plant could not give a satisfactory result. Also, the amount of wastewater generation is higher than the capacity of the treatment plant. For this reason, only certain about 30% of wastewater is being treated and rest of the 70% untreated wastewater is directly discharged into the river. Thirteen different parameters were assessed of both influent and effluent. The parameters like BOD5 and TSS were reduced by 87% and 75% respectively. But other assessed chemical parameters like nitrate, phosphate, total alkalinity, total hardness, chloride, ammonia and COD are not reduced so efficiently, may be due to the absence of tertiary unit in the treatment plant. The presence of chemical parameters in water may affect the organisms in the water by depleting the oxygen content of the water since ammonia; nitrogen and nitrate are the main oxygen depleting nutrients. Also the presence of phosphate, plant nutrient will emphasize the blooming of the phytoplanktons and the eutrophic condition in the river will increase the turbidity which will deplete the oxygen further. Also, the presence of these chemical parameters causes continuous foaming in the river water and this foaming prevents the surface water to intake atmospheric oxygen into it. So the stakeholders need to expand the capacity of Guheswori Wastewater Treatment Plant.

Keywords: Wastewater, treatment, Efficiency, Bagmati River, pollution

 


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