Factors affecting the distribution of heavy metals in wastewater treatment processes: role of sludge particulate

The distribution of heavy metals, namely, Ag(I), Cd(II), Co(II), Cr(III,VI), Cu(II), Hg(II), Ni(II), Pb(II), and Zn(II) in 4 municipal wastewater treatment plants was evaluated as a function of several parameters including pH, COD, ionic strength and SS. Although there are variations in pH, alkalinity, COD and ionic strength, the results show that wastewater samples containing less than 5 g/L suspended solids concentration have similar characteristics. Correlations among heavy metal distribution (as the ratio between dissolved to total metals) and wastewater characteristics were attempted. Correlation between the parameters monitored and metal distribution is poor. In the case of pH, no apparent relationship could be seen. In general, increasing COD and ionic strength decreases the metal distribution. Metal distribution relies almost entirely on the concentration of solids in wastewater samples. Total metal removal in primary treatment process is lower than that reported in the literature. This could be attributed to the low average solids removal observed in the treatment plants investigated. Solids reduction at the effluent were larger than 80% and total metals removal was identical to that of the primary treatment process.