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

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.