"Not generating any traffic from organic" is a poor measure of "low quality". It could hurt your site to remove content that isn't truly low quality, even if that content isn't getting any search engine referrals. Before you remove the content make sure it is also one of the following:
- Poorly written
- Out of date
- Unlikely to ever be useful to anybody
When you remove content from your site:
- Googlebot will come back and crawl those URLs forever.
- Users that have the content bookmarked will get error pages.
- Links to the content will be broken.
Ideally you would:
- Use "410 Gone" HTTP status
- Create a custom error page saying when and why the information was removed
- Provide a list of alternative content that might be useful instead.
- Implement "301 Permanent" redirects for content that has a replacement at a different URL. (But don't be tempted to redirect all the pages to a single destination such as your home page.)
If you have determined that the pages are truly useless low quality page and you have proper error handling in place, it is fine to remove all the pages at one time. It won't matter to search engines if the process is done slowly over time or all in one shot.