Does html_entity_decode replaces   also? If not how to replace it?

Quote from html_entity_decode() manual:

You might wonder why trim(html_entity_decode(' ')); doesn't reduce the string to an empty string, that's because the ' ' entity is not ASCII code 32 (which is stripped by trim()) but ASCII code 160 (0xa0) in the default ISO 8859-1 characterset.

You can use str_replace() to replace the ascii character #160 to a space:

<?php
$a = html_entity_decode('>&nbsp;<');
echo 'before ' . $a . PHP_EOL;
$a = str_replace("\xA0", ' ', $a);
echo ' after ' . $a . PHP_EOL;

html_entity_decode does convert   to a space, just not a "simple" one (ASCII 32), but a non-breaking space (ASCII 160) (as this is the definition of  ).

If you need to convert to ASCII 32, you still need a str_replace(), or, depending on your situation, a preg_match("/s+", ' ', $string) to convert all kinds of whitespace to simple spaces.

YES

See PHP manual http://php.net/manual/en/function.html-entity-decode.php.

Carefully read the Notes, maybe that s the issue you are facing：

You might wonder why trim(html_entity_decode(' ')); doesn't reduce the string to an empty string, that's because the ' ' entity is not ASCII code 32 (which is stripped by trim()) but ASCII code 160 (0xa0) in the default ISO 8859-1 characterset.