$cleansedstring = preg_replace('#\W#', '', $string);
// or
/**
* Helper function serving to clear string.
* @param $str
* @return mixed|string
*/
function academy_csv_export_clear_str($str) {
// Remove non breaking spaces
$str = str_replace(' ', '',$str);
// Replace all custom tags to HTML tags
$str = check_markup($str, 'rich');
// Remove all HTML tags
$str = strip_tags($str);
// Remove all tabs and carriage return symbols from string
$str = preg_replace("/[\t\r]/", "", $str);
// Replace several newlines in a row with one newline
$str = preg_replace("/\n+/", "\n", $str);
// Replace newlines with whitespaces with only newline
$str = preg_replace("/\n\s*/", "\n", $str);
// Remove non breaking spaces and new lines from start and end of the line
$str = trim($str, "\xC2\xA0\n");
return $str;
}