Sludge removal from primary wastewater stabilization ponds with excessive accumulation: a sustainable method for developing regions

• Published in: Journal of water, sanitation, and hygiene for development Vol. 2; no. 2; pp. 68 - 78
• Main Authors: Oakley, Stewart M., Mendonça, Luciana Coêlho, Mendonça, Sérgio Rolim
• Format: Journal Article
• Language: English
• Published: London IWA Publishing 01.06.2012
• Subjects: Accumulation; Dewatering; Drainage systems; Drying; Evapotranspiration; Excavators; Ludwigia; Methods; Ponds; Regions; Removal; Sludge; Sludge drying; Stabilization; Stabilization ponds; Sustainability; Wastewater; Wastewater treatment; Honduras
• ISSN: 2043-9083; 2408-9362
• DOI: 10.2166/washdev.2012.093

Wastewater stabilization ponds have long been considered a sustainable treatment option for developing regions. Sludge buildup in primary ponds is also a sustainability issue since ponds must be desludged every 2–15 years depending on their design and solids loading. Pond systems in developing regions are often designed without a desludging plan and operated without the amortized desludging cost included in the operation and maintenance budget. This paper presents a method where sludge drying within a pond is effected by rooted plants; after drying, the sludge is removed with a mid-sized excavator. The method was tested in the desludging of a primary pond in Tela, Honduras, where sludge 4 m deep was dried to a solid (TS ≈ 18%) to a depth >1 m using the wetland plant Ludwigia octovalvis. The data suggest that both evapotranspiration and drainage through the root system contributed to dewatering. The total cost in 2011 US dollars was $13,716 or $4.47 m3 removed, which was paid from the municipality's general fund without external aid. The method presented is sustainable, and serves as a model for desludging operations where excessive sludge accumulation has occurred – a likely scenario in many primary ponds in developing regions.