yanlış eklemişsiniz.
@mysqli_query($this->db_connect_id, "set collation_connection='utf8_unicode_ci'")
den sonra ; noktalı virgül olucak
herbirinden sonra noktalı virgülü unutmayınız!
@mysqli_query($this->db_connect_id, "SET NAMES 'utf8'");
@mysqli_query($this->db_connect_id, "SET CHARSET 'utf8'");
@mysqli_query($this->db_connect_id, "set character_set_client='utf8'");
@mysqli_query($this->db_connect_id, "set character_set_results='utf8'");
@mysqli_query($this->db_connect_id, "set collation_connection='utf8_unicode_ci'");
tekrar deneyiniz