Concept note on ZLD of city sewage-a tale of two cities - Orange County and Chennai - Explored

Habitations whether small or mega are inherent with mythologies and realities. The classical example is River Ganga. Human dead sometimes partly burnt are consigned to it and still it is revered for a holy dip. The National Cancer Registry Programme (NCRP) of the Indian Council of Medical Research (ICMR) observes that "We know that the incidence of cancer was highest in the country in areas drained by the Ganga. We also know why" (Anitban Ghosh, Times of India, Oct 17, 2012) and DS Bhargava, a retired hydrology professor who has spent a lifetime on experiments on Ganga saying "organic material usually exhausts a river's available oxygen and starts putrefying, but in the Ganges, an unknown substance, or "X factor" acts on organic materials and bacteria and kills them and oxygen levels at 25 times higher than any other river in the world". But it is not the case in other rivers. The Yamuna river sewage pollution is so high that the Agra city water treatment plant (WTP) with this river as source has a sewage treatment technology (STT) as pre-treatment before the WTP. The day may not be far off before this STT-WTP becomes a standard practice given that the country is still struggling with only 33 % of urban population with sewerage and that too not all of this sewage treated and almost all rural faeces getting dispersed into the environment. It is time to implement the zero liquid discharge (ZLD) in sewage than the minuscule industrial wastes. Such a ZLD in sewage is proven in Orange County in USA. The imminent candidate for its replication appears to be the Chennai habitation to save potential water famine there.