Low-cost Options for Treating Faecal Sludges (FS) in Developing Countries - Challenges and Performance *

This article analyses and discusses the performances of low cost technology for treating faecal sludges (FS) in developing countries. The state of research shows two trends: where septic tanks are the predominant type of on-site sanitation (OSS) installations (like in many towns and cities in Latin America and Asia), septage is the only or predominant type of FS generated, and, the following pretreatment options might prove suitable: constructed wetlands with solids loading rates (SLR) ≤ 250 kg TS/m 2 /year, settling tanks/ponds (design based on solids accumulation rates and expected operation mode), or unplanted drying beds (SLR ≤ 200 kg TS/m 2 /year). Pre-treatment will, in the majority of cases, have to be followed by processes catering for the polishing by algal or macrophytes ponds or by constructed wetlands, separately or in combination with municipal wastewater designed with the same rules as for domestic wastewater. In many African cities, highly concentrated and biochemically unstable sludges, such as those from unsewered public toilets or single-pit latrines occur in considerable proportions. Their high ammonia content (400-4,000 mg NH4 + -N/L) inhibits algal growth in pond systems and might impair plant growth in constructed wetland. Appropriate low-cost treatment options for such FS need as yet to be developed.