Abstract:
This dissertation describes an investigation into the performance of a waste
stabilization pond system designed to treat the wastewater at Digana village, near
Kandy. This system was designed, constructed and put into operation in 1980 as a
combination of anaerobic pond followed by a facultative and a maturation pond.
The main objective of this study was to evaluate the performance of the pond system
in relation to the design and to suggest methods of improving the efficiency. A
secondary objective was to prepare some guidelines for operation and maintenance of
the pond system.
With respect to the design, the only data available were that the pond system was to
function as an anaerobic, facultative and maturation pond in series, with the total HRT
of 21 days and expected to produce a final effluent BOD of less than 20 mg/l. Hence
the study concentrated firstly on determining the existing physical state and
capacities. Based on the outcome of the above study, interpond connections were
closed to operate only half the pond system to study the performance related to
removal of BOD, COD, TSS and Nutrients.
The study indicated that due to the capacity reduction caused by the accumulation of
sludge in combination with the entire flow being treated only by half the pond system,
the effective total HRT was only 6.27 days. Further it was revealed that the first pond
was not fully anaerobic, desirable algal species were absent and the anaerobicity in
the detention well contributed to the lowering of the final effluent quality.
However, the performance of the pond system was reasonably good inspite of a few
disadvantages. These shortcomings are identified and discussed in the report and
detailed recommendations have been made regarding the operation and maintenance
of the system in addition to suggestions made for immediate remedial measures to
improve the performance.
