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Where the poop goes: A visit to the technical marvel of a Yokohama sewage plant

Sewage sludge processing tanks are seen at a Yokohama municipal water reclamation center in the city's Tsurumi Ward on Aug. 6, 2021. (Mainichi/Yoshiki Koide)

YOKOHAMA -- Books can take you to some unexpected places. One recent volume titled "Unchi no Yukue," or "where the poop goes," inspired a sudden intertest in exactly what happens to our waste, and then a visit to a Yokohama sewage treatment center, where all that smelly stuff is transformed into some of the basic resources of everyday life.

    If you lined all the sewage pipes in Yokohama up end-to-end, you'd just about get to New York City. And every day, the city's people and businesses produce enough wastewater to fill Landmark Tower -- an enormous skyscraper along the waterfront and a Yokohama icon -- 1.2 times.

    Some of that effluent comes here, to the Northern Second Water Reclamation Center in Yokohama's Tsurumi Ward, where microbes are used to process it, separating it into clean water and sludge. The clean water is discharged into Tokyo Bay, or reused such as in the facility's toilets.

    The sludge goes next door to a facility whose name translates roughly as "northern sludge resource conversion center." And conversion is what they do there, in 12 33-meter-tall egg-shaped tanks that have become the symbol of the center. The cream-colored tanks' shape makes it difficult for the sludge to build up on the bottoms, and the gases produced as the sludge ferments are siphoned off as fuel for incinerators, electric generators and other uses, after sulfur has been removed.

    A center worker told me, "Tokyo Bay, where we release the processed water, is a closed water system. So we're very sensitive about maintaining the water quality and preventing 'red tides' (algae blooms) by severely regulating the phosphorus, nitrogen and other compounds."

    After my reporting trip to the center, I found myself recalling some nasty smells from my childhood and my youth: old drop chute toilets on trains, the primary school squat toilets (and their attendant splashback), and the riverboats that used to take pungent loads of human waste out to sea. How easy and pleasant we have it now, I thought, and was filled with appreciation for the workers and the advancement of technology.

    (Japanese original by Yoshiki Koide, Yokohama Bureau)

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