Copenhagen’s sewage system was built in the 1850s and it was indeed considered to build a two-pronged solution. There was much resistance against this because

Copenhagen’s sewage system was built in the 1850s and it was indeed considered to build a two-pronged solution. There was much resistance against this because it would eliminate a whole industry of “night men” (poop collectors), as well as people drying and trading it as fertilizer. So they build a single-pronged solution that was initially only allowed to be used for rain water. https://ing.dk/artikel/ingenioerer-maatte-kaempe-haardt-faa-indfoert-kloakker-i-koebenhavn https://ing.dk/artikel/ingenioerer-maatte-kaempe-haardt-faa-...