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OXIDATION DITCH MANAGEMENT NEEDS AND LESSONS LEARNED: A CASE STUDY OF BAGMATI AREA SEWERAGE CONSTRUCTION PROJECT, NEPAL
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15809)Authors: Ram Deep Sah
Keywords: Oxidation Ditch, Secondary Clarifier, Foaming, Performance and Management
Kathmandu Valley, the political and cultural center of Nepal has undergone rapid urbanization
since 1970. It has a population of about 1.4 million. Out of this about 0.5 million have access to
some type of limited wastewater or septic tank effluent collection. Nepal's rural settlements and
the majority of urban areas do not have access to sewerage networks. The domestic wastewater
generated by these areas is discharged into local rivers without treatment. All industrial wastes in
most cases are also directly discharged into local water bodies without treatment.
The Pashupati and Guheshori Temple, visited every year by Hindu pilgrims from all over the
world, are situated on the bank of Bagmati River. Millions of pilgrims take bath in the holy river
Bagmati to wash off physical, moral and spiritual impurities.
In order to clean the Bagmati river, phase-wise construction work is being implemented and a
first Carrousel type Waste water Treatment Plant with four meter deep oxidation ditch having a
capacity 16.4 MLD has been constructed and put into operation in January 2002. It has been
observed that the average BOD5, COD, SS, Ammonia-N, Phosphorus removals are 91.33%,
81.62, 79.77%, 41.32% and 51.50% respectively.
The analysis reveals that 100 percent surcharge must be levied on the water bills, as sewer
service fees to generate revenues for operational and maintenance cost Nrs. 1,09,40,000
($139670) of the waste water Treatment plant.