the variable is a string accord to var_dump, how can i pass it? is correct the way i do the query? DB is Msqli
public static function two()
{
    $risultato = modOne::one();
    var_dump($risultato);
    $ident = json_decode($risultato,true);
    $db = JFactory::getDBO();   
    $query=$db->prepare ("SELECT avatar AS memTotal FROM #__comprofiler WHERE id = ?");
    $query->bind_param("s", $ident);    
    $db->setQuery($query);
    $resulto = $db->query();
    return $resulto->fetch_object()->memTotal;
}
these return :
string(3) "751"
Fatal error: Call to a member functionbind_param()on a non-object
 
    