You are hereMemcache setting for drupal 7
Memcache setting for drupal 7
There is some slight change in default settings.php memcached setting for drupal 7, here is the setting you need to add to bottom of your file and you are ready to go.
$conf['cache_backends'][] = 'sites/all/modules/memcache/memcache.inc';
$conf['cache_default_class'] = 'MemCacheDrupal';
$conf['memcache_key_prefix'] = 'TD';
$conf['cache_default_class'] = 'MemCacheDrupal';
$conf['memcache_key_prefix'] = 'TD';
