Add a new user role, Comment Moderator, that allows any selected user to manage comments.
"Problem": WordPress only allows Administrators and Editors to moderate comments.
"Solution": "WPsite Comment Moderator" by http://www.wpsite.net/ adds a new user "role" named "Comment Moderator" that can also manage comments. Simply install this plugin, activate it, and assign any user the "Comment Moderator" role. That user will now be able to moderate comments (all comments or only his).
No other permissions of the user will change so rest assured this plugin will not interfere with anything else on your site.