Colloidal Stability in Aquatic Systems: The Roles of Calcium and Natural Organic Matter

EPA Grant Number: U915560
Title: Colloidal Stability in Aquatic Systems: The Roles of Calcium and Natural Organic Matter
Investigators: Penisson, Adrian C.
Institution: The Johns Hopkins University
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 1999 through August 1, 2002
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1999) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Engineering


Colloids are ubiquitous in natural and technological aquatic systems and can significantly affect environmental quality in these systems. Most aquatic colloids are at least partially coated with natural organic matter (NOM). The objective of this research project is to provide the first comprehensive study of the effects of divalent cations (calcium, in particular) on the adsorption of NOM by aquatic colloids and the resulting effects on colloidal stability. The specific objective is to test the hypothesis that divalent cations affect colloidal stability through specific interactions with colloids and their adsorbed NOM layers that alter the amount and conformation of adsorbed NOM and the electrostatic properties of the colloids and NOM.


This study will be the first to integrate measurements of NOM adsorbed amount, NOM adsorbed layer thickness, electrophoretic mobility, and coagulation kinetics (colloidal stability) in the presence of calcium for positively and negatively charged metal oxide colloids. Because of the complex nature of natural aquatic colloids and NOM, an approach involving model systems is required. Judicious selection of model particles, model organic matter, and solution conditions (pH, ionic strength) will allow insight into the relative importance of hydrophobic effects, macromolecular effects, electrostatic effects, and specific chemical interactions among calcium, oxide surfaces, and NOM to be obtained. Potentiometric titrations will be used to determine the charge of the model particles and model NOM as functions of pH, ionic strength, and calcium concentration. NOM adsorption isotherms will be obtained in batch adsorption experiments by measuring the difference in the concentration of dissolved NOM before and after adsorption. The thickness of NOM adsorbed layers will be determined through photon correlation spectroscopy (PCS). The electrophoretic mobilities of the particles both before and after adsorption of NOM will be obtained using Doppler-shift electrophoresis. Coagulation of model colloids will be studied with both single-angle and multiple-angle static light scattering (SLS). These experimental results will be used to extend recently developed models that describe the amount and conformation of adsorbed NOM to systems that contain divalent cations.

Expected Results:

This research will lead to a greater understanding of the effects of calcium and NOM on colloidal stability, and therefore, better prediction of the behavior of pollutants in natural aquatic environments and the development of improved water treatment processes.

Supplemental Keywords:

adsorption, natural organic matter, NOM, calcium, divalent cations, colloids, colloidal stability., Scientific Discipline, Water, Environmental Chemistry, Engineering, Engineering, Chemistry, & Physics, Environmental Engineering, calcium, natural organic matter, electrophoretic mobility instrument, aquatic resources, divalent cations, colloid, static light scattering

Progress and Final Reports:

  • 2000
  • 2001
  • Final