Variability of Metal and Metalloid Content in Sludge as Affected by Sources and Seasons

Abstract

This study evaluated the effect of seasonal variation on metal and metalloid content in sewage sludge
collected from eight different sewage treatment plants (STPs) of Delhi-NCR during summer (June, 2018),
rainy (August, 2018) and winter seasons (January, 2019). The micronutrients and pollutant elements content
in the sludge varied greatly among the sources and between the three seasons. On an average, micronutrients
viz. iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) content in the collected sludge samples in the
sources and seasons were 1.48%, 236, 1216 and 314 mg kg-1, respectively. The pollutant elements, i.e.
cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni) and arsenic (As) content in sludge samples were 2.85,
48.4, 88.6, 38.6 and 2.49 mg kg-1, respectively. Sludge collected from Delhi Gate Nala, Keshopur and
Nilothi tended to have higher pollutant elements compared to the Narella, Pappankallan and Okhla sludge
mainly because Delhi Gate Nala, Keshopur and Nilothi sludge is derived mainly from industrial area while
the other three sources are a combination of domestic and industrial residues, leading to lower pollutant
element concentration. Respect to seasonal variation, higher concentration of micronutrients and pollutant
elements were recorded in rainy and summer season, respectively. Content of the metal and metalloid
recorded in sludge was within the permissible limit as prescribed by USEPA (75, 85, 4300, 840, 75, 420
and 7500 mg kg-1 for As, Cd, Cu, Pb, Ni, and Zn, respectively). It may be concluded from the present study
that sewage sludge generated from STPs of Delhi-NCR can be used as potential source of plant nutrients,
particularly in the face of escalating price of chemical fertilizers.