Pre-dimensioning and technical, economic and environmental feasibility analysis of sub-river outfalls in Macapá and Santana cities, Amapá State, Brazil

Coastal cities in the Amazon lack basic infrastructure to treat and finally discharge urban domestic sewage. Implementing sub-river outfalls and waste-treatment pre-conditioning that significantly reduce pollution impact would be a sustainable alternative to cope with such an issue. The aim of the present research is to analyze the technical, economic and environmental feasibility of alternative projects applied to domestic waste’s proper destination in the coastal zone of Amapá State (ZCEA), Brazil. Infrastructure basic sizing and the current treatment provided to domestic waste discharged in Amazonas River, in natura, were taken into consideration for study conduction. Research methodology was applied as follows: (a) pre-sizing the main infrastructure elements of sub-river outfalls (EM); (b) assessing the reduction of impacts on quality of water in the metropolitan seashore of Macapá and Santana cities; (c) economic assessment based on the alternative implementation of underwater outfalls in Macapá’s Northern and Central zones, where one finds Amazonas River’s high self-depuration ability and regular bathymetry. Technical feasibility, mainly in Fazendinha and Santana cities, was not satisfactory due to topobathymetric unevenness and traffic jam in Santana Channel’s waterway. We have concluded that the self-depuration and sanitary features in Amazonas River’s assessed stretches are a sustainable, effective and competitive technology extremely favorable for the implementation of sub-river outfalls, given its simplicity and, most of all, adjustment to the regional socioeconomic reality.