Hydro-biological characterization and efficiency of natural waste stabilization ponds in a desert climate (city of Assa, Southern Morocco)

The city of Assa is located in a Saharian area characterized by an arid climate and water scarcity. Like any other Saharian city in a developing country, the city is facing the challenges of rapid urbanization and the need to improve wastewater treatment and management. The main objective of this work is to assess the performance of waste stabilization ponds in an arid area. This evaluation concerns microbiological and physico-chemical monitoring over three and twelve months respectively. Microbiological results indicate bacterial elimination rates of over 90% in autumn–winter due to the effectiveness of facultative ponds with 20–25 days of retention time, water clarity, ponds depth, and high sunlight exposure and penetration. Physico-chemical parameters surpass the Moroccan standards for reuse except Ph and T0 by 20–30%, this wastewater is relatively loaded with various pollutants, especially high organic load and low oxygen content. Statistical analysis has been made by principal component analysis (PCA), and confirms that dissolved oxygen, total suspended solids, COD and BOD5 do not reach the threshold for discharge into the natural environment, and moreover their reuse. For the improvement of the quality of these waters, it is legitimate to provide an upgrade of this plant by a tertiary treatment with maturation ponds.