Analysis of Sludge from Municipal Waste Water Treatment Process

Municipal waste water or sewage refers to water that has been used in urban and sub-urban area homes or businesses for washing, bathing and flashing toilets. Some also originate from industrial sources. The waste water is usually conveyed via a sewer system to a centralized waste water treatment plant (e.g. publicly owned treatment works or POTWs). At the POTW, the waste water passes through a series of treatment steps that may use physical, biological, or chemical processes designed to remove pollutants. The treatment steps may include preliminary, primary, secondary, and tertiary treatment.

Sludge originates from the process of treatment of waste waters. Due to the physical-chemical processes involved in the treatment, the sludge tends to concentrate heavy metals and poorly biodegradable trace organic compounds as well as pathogenic organisms (viruses, bacteria etc) present in waste waters. Sludge is, however, rich in nutrients such as nitrogen and phosphorous and contains valuable organic matter that is useful in when soils are depleted or subject to erosion. The organic matter and nutrients are the two main elements that make the spreading of this kind of waste on land as a fertilizer or an organic improver suitable.

This heavy metals tend to accumulate in the soil in which eventually are taken in by the crops and pose a threat to us since its this crops that most of us consume as our daily meals leading to bioaccumulation. The aim of this project is to determine whether the untreated sludge is safe for use since most of the farmers use this untreated sludge to improve their farm. The parameter of concern was the level of heavy metal concentration. Samples were collected from 5 points from Kariobangi treatment plant. The samples were digested through classical wet decomposition method and analyzed using the Atomic Absorption Spectroscopy for the heavy metals concentration. Results obtained showed that showed that the concentration of the analyzed metal was Cu (173.36 mg/Kg), Cr (1,532 mg/Kg), Cd (13.35 mg/Kg), Mn (761.81mg/Kg), and Pb (207.43 mg/Kg). The results obtained showed a high concentration of this metals and potential risks involved in there usage is evident.

 Key words: Sludge, heavy metals, Municipal waste water treatment and bioaccumulation

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