Assessment of the Polluting Status of Sludge from a Physicochemical Water Purification Unit and Their Impacts on the Soil: Case of the Yato Station (Littoral-Cameroon)

Abstract

The Yato physicochemical water purification station is located in Dibombari District Council in the Littoral-Cameroon region. It is one of the largest drinking water production stations in the Central African sub-region. This work aims to evaluate, through the quantification of the concentrations of Trace Metal Elements (TMEs), the polluting status of the sludge from this drinking water production station and their impacts on the soil. To achieve this objective, mixed samples of sludge from sludge treatment ponds (taken according to the technique described in GIDS-A003 point 6 as explained in the Solid and pasty waste sampling strategy of Code of Good Practice No. 2) and samples of sludge from primary settling basins (taken in transparent bottles in polyethylene terephthalate of 1.5L) were analysed. Likewise, three soil wells were carried out and soil samples were taken on two levels of alteration then sent to the laboratory where physicochemical and TME analyses were carried out. The characteristics of the samples that were analysed are: particle size, texture (sand, silt, clay), physiochemistry (pH, electrical conductivity, temperature, phosphorus, nitrogen) and TME (chromium, copper, zinc, manganese). The results obtained show that the polluting status of the sludge from the Yato station is proven because their pollution index by heavy metals is greater than 1. The pollution index greater than 1 in the sludge from the treatment basins is due to the strong concentrations of TME originating from the accumulation of waste of all kinds in this location. Overall, TME concentrations in soils decrease for the most part from the surface towards depth. All the TMEs studied (Zn, Mn, Cu, Cr) are present in all horizons. There is multiple contamination of sludge by TMEs because their pollution index is greater than 1 (IP>1). Although the sludge pollution indices are greater than 1, those of the different horizons are much lower than 1. Thus, since the TMEs decrease with depth, the subsurface horizons would be less affected by the pollutants contained in the station sludge. marking a real pollution of the surface layers.