Chemical Characterisation of Sludge Generated from Water Treatment Plants (WTPs) in Nigeria

Abstract

Sludge collected from four (4) selected water treatment plants in Nigeria was characterised chemically to ascertain its compositions and possible usefulness. The results indicated variations in physicochemical, nutrients, essential and non essential metals, and polycyclic aromatic hydrocarbons (PAHs) load among the studied stations. Ranges of mean values of physicochemical parameters were:  pH (7.2 – 8.1); electrical conductivity (480.0 – 988.0 µSCm-1); moisture content (12.8 – 24.6%); total organic carbon (6.9 8.9 %); ash (8.9 – 12.5%); organic matter (88.5 – 91.1%); total solid (206.5 – 689.2 mgL-1); total dissolved solids (78.2 – 439.8 mgL-1); total suspended solids (104.6 – 183.5 mgL-1); nitrogen (8.6 – 13.4 %); phosphate (0.6 – 2.4 mgL-1); ammonium ion (1.6 – 6.1 mgL-1); nitrate (6.9 – 14.9 mgL-1); and total PAHs (0.2 – 7.7 mgkg-1). Essential elements had mean ranges of 171.0 – 1219.7 mgkg-1K, 5623.3 – 15,821.5 mgkg-1Mg, 97,342.1 – 354,855.2 mgkg-1Ca, 273.5 – 432.0 mgkg-1Na, 8,548.1 – 15,316.6 mgkg-Fe, while non essential (trace) elements such as As, Cd, Co, Si and Pb were not detected in all the studied samples. The parameters evaluated were found to be within maximum permissible limit expected for sludge from water treatment plants by United States Environmental Protection Agency (USEPA). These findings reveal that the variation in levels of these properties (physicochemical, nutrients, essential and non essential elements, and PAHs) are largely dependent on the source of raw water used, and the method of treatments. However, the results indicated that sludge from the selected water treatment plants are rich in plant nutrients and can be exploited in the area of soil conditioning and plant fertilizer. Keywords Water treatment plants, sewage sludge, physicochemical properties, poly-aromatic hydrocarbons, characterisation