Distribution and fractionation of heavy metals in liquid and solid waste from selected industrial sites in Delhi

Abstract

The National Capital Territory (NCT) of Delhi is situated along the Yamuna river, a major newlinetributary of the river Ganges. It has a population of over 11 million people, and it hosts one newlineof the largest clusters of small-scale industries in India, generating waste of varying newlinecharacteristics and quantities. It is estimated that the city generates 2270million Htres of newlinewastewater and 6500 tonnes of solidwaste daily. The raw and partially treated wastewater newlineis often discharged into open drains, which link-up with others before emptying their contents newlineinto the Yamuna river, thus, resulting in the deterioration of its water quality. In this study, newlinewastewater, suspended matter, bed residues and solidwaste samples were obtained from newlineselected industrial sites (Jhilmil, Patparganj, Naraina and Mayapuri) within the NCT of newlineDelhi representing the lateral spread of the industrial zones on either side of the Yamuna newlineriver. Bulk estimation of heavy metals (Ni, Cu, Zn, Pb, Cr, Cd, Co, Mn, Fe and Hg) was newlinecarried out using GBC model 902 atomic absorption spectrophotometer. In addition, newlinesequential extraction was used to fractionate heavy metals (Ni, Cu, Zn, Pb, Cr, Cd, Co, Mn newlineand Fe) in solidwaste and bed residues into six operationally defmed phases: waster-soluble, newlineexchangeable, carbonate-bound, Fe-Mn oxides, organic-bound and residual. Also, newlinefractionation of phosphorus was carried out on solidwaste and bed residues in order to newlineestimate its potential mobility and availability. newlineThe results obtained show that the pH of the wastewater and solidwaste varied from highly newlineacidic to moderately basic. Wastewater samples with low pH levels had relatively high newlinemetal contents. In general, Jhilmil industrial site had higher levels ofNi, Cu, Zn, Pb, Mn, newlineCd, Co and Fein the wastewater compared with the other sites. As well, suspended matter newlinehad higher levels of metals compared with the bed residues. The spatial distribution of newlineheavy metals in solidwaste showed that Jhilmil had higher levels of Cu and Hg, while newlineNaraina had Pb, Ni, Cr, Co