HYDERABAD: Hyderabad’s lakes have high content of Total Organic Carbon (TOC). TOC gives an idea of the total organic matter present in water bodies. While naturally several types of organic matter are present in lakes, high levels of TOC are indicative of organic matter getting mixed in water bodies due to letting in of municipal and industrial waste water.
Researchers from Jawaharlal Nehru Technological University-Hyderabad, in an endeavour to find out TOC levels, took water samples from five lakes from the city including Durgam cheruvu, Chinna Maisamma cheruvu, Khajaguda cheruvu, Timmidikunta cheruvu and Malaka cheruvu.
After analysing the samples it was found that the level of TOC in these lakes ranged between 66 - 77 parts per million(ppm). The drinking water standards demand that TOC should be less than 10 ppm. Among the five lakes, Durgam cheruvu had the highest levels of TOC.
Dr MVsS Giridhar of the Centre for Water Resources, JNTU-Hyderabad, says, “High TOC levels will definitely have an impact on the overall quality of the lake.
Microorganisms present in the water bodies will consume more oxygen from the water to break down the organic carbon and as a result the levels of dissolved oxygen will also decrease in the water body. This will ultimately affect the aquatic life in these lakes and also the overall ecosystem.”
He added, “TOC is naturally present as well as comes from manual sources. As residential and industrial waste water continues to be directly let in lakes without treatment they increase the organic matter in lakes resulting in rise of TOC in water.”
One way the JNTU-H researchers found to reduce the TOC levels in lakes is by using the traditional water clearing agent, alum. Alum and ferric chloride are well known coagulants. The researchers found that using alum resulted in a decrease of TOC levels in water samples. However, the decrease was just around 15 per cent. Alum is being used to reduce TOC levels as part of treatment of waste water in some countries.
However, Dr Shashidhar of Department of Civil Engineering at IIT Hyderabad, said, “Use of alum for reducing TOC levels might not prove practical. Large amounts of alum will have to be used for cleaning lakes. Moreover, this will leave sludge which will have to be cleared again. There are other ways like aeration for remediation of water with high TOC levels. It is more important that the sewage is not let into lakes directly and also the illegal dumping of effluents is controlled so that the lakes do not degrade further.”