Evapotranspiration tank for the treatment, disposal and resource recovery of blackwater

Abstract The development of simple and safe solutions for sanitation systems is required to reach goal 6 of the United Nations Sustainable Development Goals. Source separation is an important step towards simplification of domestic sewage treatment, enabling the treatment and reuse of blackwater (BW) in more compact and decentralized systems. The Evapotranspiration tank (TEvap) is a natural, soil and plants-based hybrid system, being a combination of an in-built septic tank with a constructed wetland, used for BW recovery aiming at zero liquid discharge. The objective of this work was to describe the system dynamics and to evaluate criteria for design and operation, based on the evapotranspiration rate and performance. The study was based on a 1490 days-continuous run of a real scale TEvap. A design equation for sizing based on local climate conditions was proposed. The specific methanogenic activity was determined (0.047 kgCOD · kgTVS −1 · d −1 ) and the applied biological loading rate was calculated. The results indicated that the TEvap could receive 740 L · d −1 providing a COD removal of about 90%. However, the volumetric capacity of the TEvap combined with the routine in the household showed to be 87 L · d −1 if zero liquid discharge was aimed. Understanding the routine of householders helps to decide whether to design the tank to cope with peak flows or to consider an infiltration trench for occasional overflow. When exposed to a peak flow, average COD removal was 75%. The slight accumulation of salts in the top soil did not affect the development of the plants.