Editorial – Moving water pollution monitoring into the 21st Century
That polluted water can raise a stink wafted into public memory about a century-and-a-half ago, when the Thames River in London made its smelly presence felt to that country’s august Houses of Parliament. With almost unseemly haste, the City spruced up its sewage collection and treatment, the poor state of which was behind the Great Stink. The Royal Commission on Sewage Disposal picked biological oxygen demand as the definitive test for river pollution in 1908. Its protocol was to measure the depletion in oxygen levels in a given sample of water at 20◦C over five days. Thus, the BOD5 test is therefore the amount of oxygen required for aquatic microorganisms to stabilize decomposable organic matter under aerobic conditions and has been accepted globally as a means to ascertain organic pollution loads.
The test’s reliability depends on how the samples are collected, stored, transported and how soon they are tested. Dependence on established laboratory protocols has meant test has remained stuck in a time warp till recently. Now, there seem to be plenty of other faster ways to check for BOD, and they can be calibrated against laboratory results. These methods are nearly as accurate and in the long-term, cheaper. Conventional BOD testing relies on people to collect and bring in samples, leaving a large margin for error; this is why we have an absurd situation where pollution control boards claim the BOD in the Ganga River at Kanpur is 3!
We recently saw presentations on two such systems. One uses a special bacterial culture immobilized on a membrane. This is calibrated using glucose glutamic acid as a reference material and actually reads out the chemical oxygen demand. A custom-made algorithm converts this to a corresponding BOD reading. The system has been checked against BOD5 readings from laboratories and has been found to be accurate, with a maximum deviation of 7 per cent. The biggest advantage is it gives the BOD level within 15 minutes; compared to the conventional five-day test, this is instantaneous. There are other electro-chemical processes as well to measure oxygen concentrations in water.
The second method uses a spectrophotometer to give instant readings. In the conventional scheme of things water samples were collected and taken to a laboratory to be analysed by this device. Now, there are solid state probes that can be lowered into water, that scan and provide real-time data on water quality. These are again calibrated to BOD5 using potassium dichromate as a reference material. The capital cost for each such unit is high but running costs are low. Given that it takes Rs 5,000 for testing water for BOD, per sample, this method may actually turn out to be cheaper in the long run over a large number of tests. Another type of probe measures dissolved oxygen by emitting blue light of a certain wavelength that causes a sensing element to glow. The intensity and duration of the glow indicates the concentration of oxygen.
There is a rider – neither method is a replacement for laboratory tests. But they are faster and almost as good. Given the poor state of the agencies that have to regulate water quality these processes will help speed up testing and follow-up action. We hope the Central Pollution Control Board will use a judicious mix of conventional and new testing procedures to improve water quality.
We conducted a roundtable on monitoring water pollution. You can read the full report here.