Comparative assessment of sewage sludge disposal alternatives in Mashhad: a life cycle perspective.

Municipal wastewater treatment facilities produce a lot of sludge which is concentrated with different pollutants. The sustainable design of the sludge disposal alternatives is of crucial importance for touristic cities like Mashhad in Iran. Increasing sludge generation and its accumulation in the city and more stringent legislations highlight the challenge of sludge disposal, recently. This study compares different alternatives to reach maximum possible environmental benefits as well as the most cost-effective technologies. In this study, life cycle analysis (LCA) assesses different scenarios for disposal of sewage sludge which is aerobically treated and dewatered for two real case studies. Alteymore and KhinArab are wastewater treatment units in the city. The scenarios include incineration, composting, and landfilling alternatives. The incineration and landfill scenarios are the least interesting solutions according to different life cycle impact categories. The heavy metals' emission to the soil worsens their impacts. Also, lifecycle cost analysis reveals that composting scenario is more cost-saving than others. However, main disadvantage of the composting scenario is its contribution in freshwater eutrophication. To move towards sustainability, the composting scenario is here determined as the best scenario for sludge disposal in Mashhad.