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This study evaluates the performance o f Moratuwa-Ratmalana Biological Nutrient Removal
(BNR) plant during the dry period o f 2016. This treatment plant is 1st ever reverse A2/0
(anoxic/ anaerobic/ aerobic) treatment plant in Sri Lanka which was established by the National
Water and Drainage Board (NW DB) in 2013.
This study was confined to the dry period. This study was carried out to achieve two objectives.
First objective is to monitor and evaluate the overall efficiency o f the treatment plant in terms
o f removing pollutants from the influent. Second objective is to analyze nitrogen and
phosphorous removing ability in each compartment.
Samples were collected weekly for a stretch o f 15 weeks from February to May. The sampling
method utilized in this study was ‘grab sampling’ and ‘composite sampling’. First samples
from each three layers o f each o f the three compartments were collected through grab sampling
and then composite samples for each layer was prepared by using the grab samples. Composite
samples were used for final testing. In addition samples were also collected for influent and
effluent from the composite sampler which is located in the treatment plant.
The analysis was carried out to test for physical (pH, Temperature) and chemical (BOD, COD,
TSS, TP, TN) parameters o f each collected sample.
The performance evaluation has indicated that 88.52% COD removal, 97.05% TSS removal,
94.12% BOD removal, 84.23% o f TP removal and 81.65% o f TN removal efficiencies have
been achieved. A lso the analytical measurements obtained o f the treated effluent are
compatible with the discharge water quality standards issued by CEA, Sri Lanka. In addition it
was shown that each compartment o f the treatment plant meets the design expectations
regarding Nitrogen and Phosphorous removing abilities.
