Background: This study aimed to assess the accumulation rates and potential agricultural value of residual sludge from the aerated lagoon wastewater treatment plant in Ouargla province, which has long faced issues of rising and pollution of ground water. The plant was constructed in 2009 to mitigate these problems. After more than a decade of operation, it is essential to determine the management strategies for the sludge accumulated in the basins to prevent harmful consequences on both the purification process and the environment.
Methods: To achieve this objective, we measured the thickness of the sludge accumulated at the bottom of the lagoon basins and estimated the total sludge volume in each basin. In addition to these quantitative measurements, sludge samples were collected from the basins and a series of physicochemical and bacteriological analyses were conducted.
Results: The results highlight the heterogeneous spatial distribution of sediments in the studied basins. Based on the average height of the accumulated sludge, dredging is necessary for basins F2, A3, and B2. The average annual accumulation rate calculated for the entire wastewater treatment plant is 30.95 cm/year. The sludge produced by this plant is dry and has low fermentability when stored. It contains 2.58% nitrogen and 0.55% phosphorus on a dry matter (DM) basis, with very low concentrations of heavy metals.
Conclusion: This sludge can help increase agricultural soil’s nitrogen, phosphorus, and potassium content. It appears to be safe regarding the following trace metals: copper, nickel, cadmium, mercury, lead, and zinc.