Evaluation of nutrients removal and typologies for successful operation and maintenance for hybrid natural pond treating municipal wastewater in Kigali

Abstract

The increase of population, urbanization and industrialization in Rwanda lead to the production of huge amount of wastewater. Sanitation is needed to save human health and the environment, as well as for long-term development. Poor sanitation and wastewater management methods, on the other hand, have damaged the ecosystem and most fresh water sources in developing countries including Rwanda resulting in waterborne diseases. Municipal wastewater contains nutrients and pathogens which may have negative impact on environment and human life. Natural treatment systems such as constructed wetlands and ponds are utilized to treat municipal wastewater also are highly efficiency when they are properly maintained. In Rwanda there is few natural systems for treating wastewater but there are no appropriate management mechanisms for those treatment systems in order to keep them in a sustainable manner. The objectives of this research were: (1) Evaluate the nutrients removal efficiencies and limitation of the hybrid natural pond treating municipal wastewater. (2) Evaluate the mechanisms of nutrients and pathogen removal in the systems based on their design and local climate and (3) Assess the appropriate methods for the system operation and maintenance based on local knowledge and technology. The grab samples were taken for four sampling points of Nyarutarama natural hybrid pond every week in a period of six weeks. During the monitoring period, temperature, pH, DO, and EC were measured on-site, nutrients and pathogens were determined in the laboratory and the key informant interviews were conducted. During the monitoring period of six weeks, the average removal efficiencies of the primary pond, secondary pond and CW: 4 NH -N(14%, 20% and 54%), 2 NO -N(28%, 38% and 45%), 3 NO -N(27%, 38% and 48%), TN (14%, 19% and 27%), 4 PO -P(38%, 46% and 57%), TP(39%, 46% and 56%), TC(36%, 83% and 58%), FC(43%, 81% and 57%) and E. Coli (42%, 90% and 57%) respectively. The results showed that the pathogens were highly removed but the effluent did not comply to the standards. Preliminary treatment, awareness raising for willingness to pay, improvement of the treatment systems area for their valorization and permanent and trained staffs to oversee the system operation and maintenance, these methods can be applied for sustainable management of natural treatment systems in a highly urban region.