Incremental sanitation improvement strategy: comparison of options for Hanoi, Vietnam.

Urban sanitation issues should be tackled strategically, and may be addressed effectively when sewerage development is pursued in conjunction with complementary sanitation measures. Five sanitation improvement scenarios employing sewerage, night-soil collection-and-treatment (NSCT) system, and/or septic-tank improvement by annual desludging were analyzed from the perspective of COD loads, total nitrogen loads, and cost under the conditions found in Hanoi, Vietnam. Compared to the development of sewerage alone, the scenario of developing NSCT systems in a complementary manner with sewerage development was estimated to be the most effective for a rapid decrease of both COD and total nitrogen loads. However, it may be difficult in some cases to replace ordinary water-flush toilets by the micro-flush toilets that are used in NSCT systems. In this case, the scenario employing septic-tank improvement in conjunction with sewerage development may be effective for a rapid decrease of COD in locations where septic tanks are widely used under poor maintenance conditions and nitrogen pollution is not serious compared to COD. It was calculated that the two scenarios above would respectively require cost increases of 16 and 22% over the sewerage development scenario.