Abstract
Bathroom-rich greywater coming directly in contact with virgin soil for years contaminates soil and alters its properties. The degree of alteration of soil properties may also depend on geological settings from which the soil was formed. The present study was designed to investigate the physico-chemical and geotechnical properties of greywater-contaminated soil (GCS) in different soils of basement complex formation. Soil samples were collected from greywater discharge zones and control soil (CS) in two locations (Mapo in Ibadan, Oyo State and Isolu in Abeokuta, Ogun State, Nigeria) at the depths of 0.5, 1.0 and 1.5 m from the surface, and the soil properties were analysed following standard procedures in the laboratory. The experiment consists of two modes: CS with no presence of greywater and GCS. The results of this study showed that alteration of most analysed properties depends greatly on sampling depth. There is increased in soil pH, cation exchange capacity, dry density (DD), saturated hydraulic conductivity (Ksat) and shear strength (SS) in GCS at Mapo over their control values, while porosity, Atterberg limits (ALs), plasticity index and moisture content (MC) were reduced relative to the CS at all sampling depths. However, only bearing ratio improved at each sampling depth in GCS at Isolu, while alterations in other analysed properties did not follow clear trend. Correlation coefficient showed positive correlation between % clay and AL, porosity and ALs; MC and ALs at 1% level, while negative correlation exists between DD and ALs, % sand and ALs as well as Ksat and ALs at the two locations. Two-way ANOVA showed that there is a significant difference at 5% level (p < 0.05) based on sampling depths for most analysed properties except SS, organic matter and soil resistivity. Further investigation is needed to study the trend of alteration of soil properties with depth on GCS at other soil types and geological formations.
Highlights
The soil has considerable but restricted capacity to process pollutants, so that when that capacity is reached, the soil may turn into a deposit or a vector in the transmission of pollutants to the environment (Gavrilescu 2014)
Clay and silt particles in soil derived from quartzite rock (Mapo) ranged from 12.5 to 30.9% and 8.9 to 13.9%, respectively, and were classified as sandy loam/sandy clay loam based on analysed depths
The LL and PL values of Mapo greywater-contaminated soil (GCS) at each sampling depth reduced compared to their values in control soil (CS)
Summary
The soil has considerable but restricted capacity to process pollutants, so that when that capacity is reached, the soil may turn into a deposit or a vector in the transmission of pollutants to the environment (Gavrilescu 2014). The practice constitutes health hazard to aquatic ecology and the transmission of pathogens from polluted water to human food chain (Mohamed et al 2018a). This may not be unconnected to the distribution of pollutants such as chemical agents, surfactants and pathogens that drain into surface waters. The build-up of heavy metals and OMPs in soil contaminated with greywater may cause toxicity through the food, chain thereby causing detrimental health risks on humans and animals after long exposure period (Arjoon et al 2013; Edokpayi et al 2017). Surfactant which can be anionic, cationic or non-ionic based on their different chemical properties can be adsorbed, transported or degraded in porous media (Weil-Shafran et al 2006)
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