The megacity of Calcutta has no sewage treatment plant. Instead, the majority of its wastewater flows east out of the city in a canal towards the Ganges and the Bay of Bengal. There, the wastewater is put to two uses: one, as fertilizer for hundreds of farms; two, it flows into huge settling ponds where it serves as a food source for algae and other organisms, which in turn are eaten by fish and prawns. In other words, it’s an ecosystem, with human waste at the base of the food pyramid. Many of the prawns are sold for good prices on the export market. I won’t try to claim that the water is completely clean by the time it flows into the Ganges, but after it’s made its way through the whole series of fish ponds, it’s much cleaner than when it started.
Along the way, the whole system supports a community of over 100,000 fish and conventional farmers living in dozens of villages. This system has been in place since the 1850s. While the West was busily developing the system of treatment plants where waste is treated with chemicals, the bheris have been steadily producing hundreds of tons of vegetables and fish every year. While not applicable everywhere, there’s no doubt that many cities in the developed world could build a similar system.
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