Demo 2 – Low maintenance blackwater treatment system for rural developing areas

Background

Treating blackwater in areas not connected to central sewage systems is a major challenge, as untreated wastewater poses risks to both public health and the environment due to its high pathogen load. In many warm-climate regions, evapotranspiration tanks have emerged as a low-cost, low-maintenance solution that enables safe treatment with zero liquid discharge. Despite their widespread use, the system remains understudied, with limited scientific literature and few controlled laboratory assessments. Strong practical results are already seen in the field, but this lack of data creates uncertainty about how efficiently evapotranspiration tanks perform under different conditions, underscoring the need for clearer design guidance and further research..

Description

RPTU University of Kaiserslautern-Landau (RPTU) and the Nelson Mandela University (NMU) will jointly implement an evapotranspiration tank, a low-maintenance, plant-based system for treating household blackwater. The tank is fully sealed and filled with layered materials, topped with fast-growing plants that naturally draw and evaporate water. At its core is an anaerobic chamber that receives incoming wastewater. This chamber allows solids to settle and partially break down, protecting the filter layers from clogging. From there, the water flows upward through coarse recycled material, gravel, and sand until it reaches the topsoil. In the upper layer, most of the water is removed through plant uptake and natural evaporation, enabling a zero-discharge system. The surface vegetation not only drives water loss but can also be harvested to remove nutrients such as nitrogen and phosphorus stored in the plant biomass.