This method convert to utf-8 the provided columns

        :param columns: list of columns to convert to
        :type columns: list of strings
        :return: original dataframe with converted strings
        :rtype: pandas.DataFrame

def enrich(self, columns):
        """ This method convert to utf-8 the provided columns

        :param columns: list of columns to convert to
        :type columns: list of strings
        :return: original dataframe with converted strings
        :rtype: pandas.DataFrame
        """

        for column in columns:
            if column not in self.data.columns:
                return self.data

        for column in columns:
            a = self.data[column].apply(self.__remove_surrogates)
            self.data[column] = a

        return self.data