Table 3 shows a good number of improvement options to clean the production at ammonia and urea production in sample fertil- izer plants. Air pollution can be prevented by using natural gas continuously under the ‘material purification’ option, which is found to be used at the time of ammonia production in the sample plants. In ammonia production, there are three improvement options: ‘improving maintenance procedure’, ‘recovery at plant’ and ‘waste-stream segregation’. But these options are not found in practice in the sample fertilizer plants.