Industrial water pollution in a surface water system in Colombo, Sri Lanka
Surface waters are increasingly polluted by the industries in Colombo, Sri Lanka.
Among these the food and drink industries are prominent in urban Colombo. To
understand the extent of pollution of the inland surface waters a project was undertaken
in the San Sebastian canal, which runs through the heart of Colombo, and
the connecting waterways. It entailed the chemical and physical monitoring of the
surface waters and the waste water discharges of the industries. The results indicated
that the San Sebastian canal was a highly polluted canal with a very low dissolved
oxygen level. The oxygen sag was very marked at the industrial discharges. Most
of the industries, by nature of the highly organic waste waters in addition to being
untreated failed to meet the specified standards of discharges into inland surface waters.
The rainfall-pollutant and the rainfall-lag analysis indicated the poor dilution
of these strong waste waters, and the low assimilative capacity of the highly polluted
canal system. Hence, the San Sebastian canal polluted the receiving river Kelani, into
which it discharges in the east, and the Beira lake in the west, where the polluted
waters are pumped from the canal to maintain the level of the lake.