Blackening and odorization of urban rivers: a bio-geochemical process

Abstract

Urban rivers constitute a major part of urban drainage systems, and play critical roles in connecting other surface waters in urban areas. Black-odorous urban rivers are widely found in the developing countries experiencing rapid urbanization. The mismatch between urbanization and sewage treatment is thought to be the reason of the blackening and odorization phenomenon. This phenomenon is likely a complex bio-geochemical process of which the microbial interactions with the environment are not fully understood. Here, we provide an overview over the major chemical compounds, such as iron and sulfur, and their bio-geochemical conversions during blackening and odorization of urban rivers. Scenarios explaining the formation of black-odorous urban rivers are proposed. Finally, we point out knowledge gaps in mechanism and microbial ecology that need to be addressed to better understand the development of black-odorous urban rivers.