Pathogens could easily spread this way since your collection bin would require to meet hygiene standards (i.e. cooling and rodent-free) and you would need to make sure the people treat the scraps they throw in right. And are not such with gastroenteritis or similar diseases.
If you had a magic wand which removes all pathogens, your approach becomes viable I guess.
The tagging system is good on paper but will be gamed by the advertisers in no time. Basically bad SEO (adding random text without context just to push the site rank) all over again.