def METHOD_NAME(self, json_content, step_num):
    file_format = 'mass_balance_{0:06d}.json'
    filename = os.path.join(self.output_dir,
                            file_format.format(step_num))
    with open(filename, 'w', encoding='utf-8') as outfile:
        dump(json_content, outfile, indent=4)
    return filename