Grantee Research Project Results
1998 Progress Report: Fate and Transport of Heavy Metals in the Subsurface: Effects of Polymer-Surfactant Aggregates
EPA Grant Number: R826188Title: Fate and Transport of Heavy Metals in the Subsurface: Effects of Polymer-Surfactant Aggregates
Investigators: Dentel, Steven K. , Cha, Daniel K. , Huang, C. P.
Institution: University of Delaware
EPA Project Officer: Aja, Hayley
Project Period: September 1, 1997 through August 31, 2000
Project Period Covered by this Report: September 1, 1997 through August 31, 1998
Project Amount: $295,582
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals
Objective:
Concentrations and loadings of heavy metals are key criteria in recently implemented regulations concerning biosolids application to land. Although it has been assumed that biosolids offer a medium that enhances the ability of a soil to immobilize metals, the interactions of biosolids with soils are complex, and the mechanisms that may be responsible for the ability of biosolids to immobilize metals are poorly understood. We hypothesize that polymer-surfactant aggregates (PSAs) are a unique ingredients in biosolids that enhances immobilization of heavy metals. In biosolids, PSAs are formed by combination of the surfactants present in biosolids-due to the high concentrations of anionic soaps and detergents in waste water-with the cationic polymers used to chemically condition the biosolids prior to dewatering. The primary objective of the proposed research is therefore to examine the metal binding effects of polymer-surfactant combinations added to soils, particularly in comparison to soils with neither, or with one, of the two additives.Progress Summary:
The presence of both polymer and surfactant in a soil system can engender a variety of different effects. Not only are the polymer and surfactant present themselves, but micelle-like surfactant structures are created well below the conventional CMC. At and near the charge equivalence point, a PSA is formed as a new solid phase. At higher ratios of surfactant to polymer, monomeric and then micellar surfactant is found in the solution phase. Moreover, below and above the charge equivalence point, the PSAs will have a net electrical charge and are likely to be more soluble and capable of ionic interactions with other solution components. The complexity of the system necessitates a fundamental research on PS interactions. Sodium dodecyl sulfate (SDS) is used as the representative synthetic, anionic surfactant and Percol 757, commonly used in sludge conditioning, is utilized as the cationic polymer. Reproducible preparation and characterization of systems containing polymer and surfactant has required much effort. Although we have not obtained quantitative results to date, the necessary preparation techniques are now developed. In addition, visual observation of these systems indicates quite interesting properties that warrants discussion.
The behavior of the SDS-Percol 757 (in 0.01 NaNO3) system at different concentrations, mode of addition and mixing type were examined. Reproducibility, apparent time to equilibrate, and macroscopic properties (phase separation) were assessed.
In no mixing conditions and at surfactant/polymer addition sequence, nearly all polymer added was insoluble up to the end of the experiment. The formed structure was white and strictly cylindrical, retaining the evident geometry of polymer solution flow ejected from the syringe. The SDS-Percol 757 complex retained this structure long time as it very slowly collapsed toward the bottom of the beaker. The precipitate formed was very adhesive which was why the use of any stirring device become problematic. The solubilization of a polymer is a relatively slow process which, in practical application, requires considerable mixing. In the absence of mixing, phase separation occurred instead of diffusion and dissolution. It may be concluded that due to the high electrostatic and hydrophobic interactions between anionic SDS and cationic Percol 757, the structure is very tight and mixing is necessary to improve solubilization of the complex. Alternatively, the polymer may be brought to a fully dispersed state to which a surfactant stock solution is added. When the addition sequence was reversed in this manner, a totally different picture was observed. Addition of surfactant initiated the formation of whitish, small structures throughout the solution. Use of a blender, at high speed; was found to overcome adhesion difficulties.
Future Activities:
After completing the initial phase of the research -an understanding of the properties of polymer and surfactant solutions, alone and then in combination- the behavior of polymer-surfactant solutions in more complex environments that include metal and colloidal components will be investigated.Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
heavy metals, polymers, surfactants, soil, sludge, biosolids, groundwater, environmental chemistry, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Hydrology, Environmental Chemistry, Chemistry, Fate & Transport, Engineering, Chemistry, & Physics, fate and transport, cationic polymers, soil , wastewater treatment, subsurface, biosolid surfactants, metal binding, polymer surfactant aggregates, anionic soaps, sludge, heavy metalsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.