The impact of manhole toilets, and what I found out about sewage systems.
A disaster prevention news report introduced manhole toilets. It explained that since manholes lead to sewage lines, there is no problem with putting toilet waste directly into them. It is a logical way to set up emergency toilets. Is that so, manholes?
Actually, back in my student days, out of mere curiosity, I once obtained a qualification for "oxygen-deficient hazardous work." I wanted to know how to deal with oxygen deficiency after attending live music events in basements—which we called gigs back then. I took a few days of training, passed the written exam, and got certified. As a result, I learned how to prepare for entering places where oxygen might be low and what to do if oxygen levels actually dropped, but I also realized that it couldn't be applied to basement gigs. While I felt it wasn't very practical for me personally, the qualification for entering manholes, wine cellars, and the like remained unused.
Since I only studied it for a few days 40 years ago, I have mostly forgotten it. After all, I didn't even link manholes to toilet drainage. In my daily life, I had the image that manholes were mainly for rainwater drainage. Like those dangerous videos on the news where a manhole cover pops off during heavy rain. But that's right, manhole covers are apparently marked with words like "Rainwater," "Sewage," or "Combined." I'm starting to feel like I've seen those before.
"Rainwater" is just for rainwater, while "Sewage" is for household wastewater, including toilets. "Combined" is for both. My spouse, who used to do river surveys as a student, would often say jokingly while we were walking along the river, "Isn't household wastewater flowing in here?" and I would just reply, "Maybe so." I had the image of water from a kitchen sink, but household wastewater includes toilets and baths too. In other words, manhole toilets are only installed at "Sewage" or "Combined" manholes.
In areas where sewage systems are developed, sewage is transported to treatment centers and discharged into rivers and the like. I thought sewage systems were almost fully widespread in Japan, but as of the end of fiscal year 2024, the national sewage coverage rate is 81.8%, and the population coverage rate for sewage treatment is 93.7%. It's not 100%. I guess there are various places and circumstances. If the sewage coverage rate in Kanagawa Prefecture is 97.2% and in Tokyo is 99.7%, it seems unlikely that household wastewater is flowing directly into the rivers I walk along. However, there are some prefectures where the figures are quite low. Is that really the case in Japan?!
In other words, there are still places without sewage systems and without manholes. I assume that in such places, they don't just discharge it directly into rivers, but store it in tanks. Surely.
Speaking of sewage, a common thing you hear about kitchen sinks is "don't pour boiling water down them." This is a drainage pipe issue, as it might damage pipes made of heat-sensitive materials. I sort of thought, "I'm sure my place is fine," but apparently, gray or dark gray pipes are standard PVC, while black or brownish-black pipes are made of heat-resistant material. Oh no, I'm sure mine are the standard gray. Oh, that's bad.
Other things that are not allowed include oil, vegetable scraps, food waste, chemicals, hair, and fallen leaves. It seems like hair and fallen leaves from outside will inevitably get in to some extent no matter how hard you try. In the case of a garbage disposal, food waste is fine because it is processed in a dedicated treatment tank before being discharged into the sewage system. It seems that the sludge separated in the dedicated tank for the disposal is incinerated at a separate treatment facility.
While I was at it, I looked up what shouldn't be put into a garbage disposal: raw fish, chicken skin, edamame pods, banana peels, eggshells, corn husks, onion skins, pineapple cores and peels, fresh flowers, raw rice, etc. However, it seems that depending on the type of disposal, some of these might be okay. Large vegetables and fruits should be cut into pieces of about 3 centimeters. Fibrous items should be processed in small amounts. Also, bleach-based detergents are apparently not good either. That means I've been a bit careless until now. I need to be more considerate, as it affects not just my own disposal but the entire apartment building. I'll reflect on this.
Sewage systems are a great invention and indispensable to life, but I was a bit vague about how they work and how to use them. I was able to learn a little bit, so thank you, manhole toilets.