Technologies for a Sustainable Environment Research Title: Chemical-Free Softening of Hard Water Using Harvested Rainwater or Snowmelt Graduate Student: John E. Greenleaf ( Lehigh University)

Research Objectives:

The primary objectives of the proposed research are to investigate the details of an environmentally attractive process which will very efficiently remove temporary hardness without requiring any chemicals for regeneration or production of sludge. According to information available in the open literature, the proposed process will be the first one to utilize rainwater or snowmelt as an efficient regenerant.

Potential Relevance and Future Applications:

Removal of temporary hardness from water is a treatment or pre-treatment practiced in a wide variety of drinking water plants. With the recent growth in pressure-driven membrane processes (e.g., reverse osmosis, nanofiltration), removal of hardness through pre-treatment has attained special significance for the protection of the relatively delicate membranes. The two universally practiced processes in this regard are lime softening and ion exchange. While lime softening produces voluminous sludge to be disposed of, ion exchange process generates highly concentrated brine or acid as a waste regenerant stream. Residuals management will continue to be a major concern with these processes

One of the generic goals in every segment of the water industry is to reduce or eliminate "residuals" without compromising with the treated water quality. In this regard, the proposed process offers unique opportunities to achieve complete and fast removal of hardness without producing any residual waste. The key features which make the process very distinct from the existing technologies are as follows:

• The process takes advantage of the unique properties of the ion exchanger fibers in a way that CO2 sparged rainwater or snowmelt can be used as the sole regenerant, thus producing virtually no waste. The complete absence of alkalinity in rainwater or snowmelt makes them ideally suited as a regenerant. If necessary, the harvested rain water or snowmelt can be chlorinated prior to long-term storage without any adverse effect on the process.

• The physical configuration of the process is exactly the same as that of any fixed-bed adsorption process. The proposed process, does not, therefore, introduce any operational complexity.

• Scientifically, the proposed process takes advantage of the fast kinetics of ion-exchange fibers unattainable with more popular resin beads. The sizes (i.e., foot prints) of the units may very likely be smaller than conventional treatment units.
  
  
• According to information available in the open literature, use of rainwater or snowmelt has never been practiced as a regeneration ingredient to date. Volume of regenerant needed is less than ten percent compared to the volume of hard water treated for softening.

• A host of water industries may benefit from the outcome of the proposed softening process. The current research thrusts of AWWARF do not address the specific performance enhancement in regard to the elimination of residuals for softening processes.

Primary Objectives:

· To provide experimental evidence about the long-term viability of the proposed sustainable process for multiple cycles of operation using ion exchange fibers at least from three different sources;

· To confirm that harvested rainwater or snowmelt can be a viable regeneration medium upon sparging with carbon dioxide;

· To investigate sorption/desorption kinetics of ion exchange material in order to develop an insight into the overall viability of the process;

· To identify important process design parameters (e.g., overall mass-transfer coefficient, Ca2+/H+ selectivity; empty bed contact time) for scale-up of the process:

Recent Publications

DeMarco, M.J., SenGupta, A.K., Greenleaf, J. (2003) "Arsenic removal using a polymeric/hybrid inorganic sorbent", Water Research, 37, 164-176.

Cumbal, L., Greenleaf, J., Leun, D., and SenGupta, A.K. "Polymer supported inorganic nanoparticles: characterization and environmental applications", Reactive Polymers, (2003), 54, 167-180.

Greenleaf, J.E., Cumbal, L., Staina, I., and SenGupta, A.K. "Abiotic As(III) oxidation by hydrated Fe(III) oxide (HFO) microparticles in a plug flow columnar configuration", Trans IChemE, (2003), Vol. 81, Part B, 87-98.