Factors influencing the behavior of land applied biosolids

Abstract

Using biosolids from the Hampton Roads Sanitation District (HRSD), laboratory studies were conducted to provide an insight into the behavior of this material when it is applied on land. The interaction and affinity of the biosolids for heavy metals was determined by packing reactor columns with known amounts of the biosolids and passing through the packed columns aliquots of several heavy metal solutions including, cobalt, copper, lead, iron, manganese, and zinc. The process was repeated until the retention capacity of the columns was reached. Solution parameters were varied to allow investigations of the influence of pH, ionic strength, and inter-elemental effects. The affinity of the biosolids for each metal was determined by calculating the mass of the metal that was adsorbed on the biosolids (removed from the solution) per gram of the biosolids. Using batch and reactor column procedures, samples of the biosolids were fractionated to determine water soluble, exchangeable, adsorbed, organically bound, carbonate, and sulfide fractions and to determine the lability, mobility, and availability of the heavy metal and other contaminants in those fractions. A fractional distribution extraction protocol was specifically conducted for the lead-biosolids complex to provide an insight into the lability and bioavailability of the biosolids-bound lead. The affinity of metal ions for the biosolids was found to increase in the order Pb>Fe>Cu>Zn>Ni>Mn>Co. Correspondingly, synergistic effects of the different metals led to characteristic decreases in the respective binding capacities. A decrease in system pH led to a decrease in the binding capacity, a trend that was also observed when the ionic strength increased. Using lead as a model, fractionation studies revealed that adsorption of lead by biosolids is mainly associated with the carbonate fraction.

Chemical fractionation of Cu, Zn, Cd, Cr, and Pb in sewage sludge amended soils at the end of 65-d sorghum-sudan grass growth

“…Recent fractionation study of Urasa and Mwebi in reactor packed columns also revealed that adsorption of lead in biosolids amended soils mainly associated with the carbonate fraction. [15] It should be noted that there are several other soil factors and environmental conditions which affect the chemical association of Pb in soils. Sequential fractionation studies conducted by Elsokkary et al [26] in highly contaminated alkaline Nile Delta soils of Egypt indicated that most of the Pb accumulated in the organic matter as sulfide fraction and attributed this phenomenon was mainly due to high affinity of Pb towards organic matter.…”

“…[5,[10][11][12][13][14][15] To have a thorough understanding of the behavior and factors controlling the dynamics of trace elements in soils amended with various types of soil amendments including WWTS, research studies were focused by utilizing various analytical protocols. [10][11][12] Selective sequential extraction procedures have been commonly used for studying trace element mobility and availability in soils.…”

“…Scientists utilized sequential extraction technique with various extractants to extract various chemical forms of these elements in the solid phase. [5,[10][11][12][13][14][15] Such assessments assume that trace element bioavailability decreases with each successive extraction step in the procedure. Therefore, trace elements in water-soluble and exchangeable fractions would be readily bioavailable to the environment, whereas the trace elements in the residual fractions are tightly bound and would not be expected to be released under natural conditions. Even though various procedures have been developed and utilized, these procedures are not quite specific, and overlapping could occur among metal fractions.…”