A feasibility study on sustainable wastewater treatment using Constructed wetlands – an example from Cochabamba, Bolivia
The city Cochabamba in Bolivia faces increasing environmental problems and health risks due to insufficient wastewater treatment in peri-urban areas. This study evaluates the treatment efficiency of a horizontal subsurface flow (HSF) constructed wetland, built by the foundation AGUATUYA, and investigates the applicability of the method in Cochabamba. The wetland reduces BOD5 by 80–97 %, COD by 80–90 % and turbidity by 50–80 %. It is largely anaerobic causing low nitrogen removal. Faecal coliform bacteria are reduced by 90 % but the effluent does not meet treatment requirements. The wetland has two sections containing gravel and plastic media respectively. The plastic medium has significantly higher surface area per bed volume but analyses showed little difference in treatment efficiency. To investigate the difference, the wetland outlet has to be redesigned. Tracer experiments showed a large variation in transport time for the gravel section but could not be determined for the plastic section. Nominal retention time was 6.2 and 8 days for the gravel and the plastic section respectively. Reuse of treated wastewater reduces consumption of potable water and energy. HSF wetlands require little energy, construction material and maintenance. They are a good alternative in low-income areas like peri-urban Cochabamba.