Techno-economic and environmental assessment of wastewater management systems: Life cycle approach

The septic-tank and tanker (STT) system is a traditional wastewater management practice commonly used in many developing countries. The system is based on septic tanks that are pumped out by sewage tankers on a regular basis. Although the STT system is gradually being replaced by conventional gravity sewers (CGS), the high capital cost of this shift remains a major obstacle. This research aims to investigate the economic feasibility and environmental footprint of an alternative wastewater management system compared to existing sanitation systems. The study examines the small-bore sewers (SBS) system which utilizes the existing septic tanks to separate solids from gravity-conveyed effluent. A comparative assessment of the three systems (STT, CGS, and SBS) along with their treatment facilities was conducted on a residential area in the United Arab Emirates. Local design criteria of the SBS system were proposed based on current CGS guidelines and international SBS standards. A cost-integrated life cycle assessment (LCA) was carried out in order to evaluate the environmental and economic aspects of the three management strategies. The total present value of the SBS strategy was found to be significantly higher than those of STT and CGS, respectively. Moreover, a 67% smaller treatment plant was sufficient to serve the SBS effluent. The LCA results revealed that the CGS strategy imparted the highest damage to the environment in all impact categories considered including global warming potential, whereas, the STT system produced a higher impact than SBS in six out of the eleven tested impact categories. Overall, while the STT strategy was the least financially feasible, the CGS had the largest environmental footprint. The eco-efficiency assessment revealed that the SBS strategy was the most favored among the examined strategies.