Spatiotemporal variation in urban wastewater pollution impacts on river microbiomes and associated hazards

Authors: Andualem Mekonnen Hiruy, Jemila Mohammed, Mihret Mersha Haileselassie, Kishor Acharya, Giacomo Butte, Alemseged Tamiru Haile, Claire Walsh, David Werner

In Addis Ababa and its environs, most urban wastewater is discharged into rivers without treatment. In this study bacterial hazards were investigated in the Akaki catchment, which is home to 5 million people. The study related urban wastewater characteristics to the prevalence of faecal, antibiotic resistant, and potentially pathogenic bacteria in rivers of the Akaki catchment across six locations, for the dry and wet season. 

Spatiotemporal variation in bacterial hazards across the catchment was up to 6 log units. From the sequencing data, notable bacterial genera in the dry season included wastewater pollution indicators Arcobacter and Aeromonas, whereas soil erosion may explain the greater prominence of Legionella, Vicinamibacter, and Sphingomonas during the wet season. In conclusion, multiple bacterial hazards were of concern for river water users in the Akaki catchment, and elevated in the dry season, when the river water is being used for irrigation of vegetable fields that supply the markets of Addis Ababa. This reflects inadequate treatment and limited dilution of urban wastewater by the natural river flows during periods of low rainfall.