Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

M Robin Collins

Second Advisor

Thomas Ballestero

Third Advisor

James Houle

Abstract

Gravel roughing filters (GRFs) are used as a way to buffer small systems that are sensitive to contaminant spikes within influent waters, however they tend to fall short in the removal of contaminants such as arsenic or organic precursors. A possible solution to this shortcoming is the addition of granular Zero Valent Iron (ZVI) or Ion Exchange Resin to the GRFs. ZVI is non-proprietary and non-deleterious to biofiltration systems. Ion exchange resins are proprietary however they are non-deleterious to biofiltration systems. ZVI or resin can be added as a portion of the media in a vertical upflow filter and as a final filtration step in a horizontal filter. Our research shows the buffering capabilities that GRFs offer as well as some possible enhancements that can be added for additional treatment if desired.

When ZVI is used as a portion of media compared to its typical gravel media without a ZVI portion has many benefits. The iron media is inexpensive making it practical for small communities, enhances removal potential of arsenic and dissolved organic compounds, easily generated and regenerated suggesting a long lifespan, can be found in any geographic location, and in aerobic conditions with pH’s greater than 7 iron solubility is rendered to almost undetectable levels making treatment for dissolved iron unnecessary.

Prior research under Dr. M. Robin Collins has demonstrated how ZVI granular media surfaces’ removal potential for arsenic while this dissertation focused on the removal potential of organics along with its regeneration capacity. Bench-scale column challenges have shown that ZVI has the capacity to remove more than 50% of organic precursors from raw waters. Regeneration was successful at pH’s ranging from 10 to 12 and possibly getting better results as pH goes even higher.

Purolite A502p resin has shown incredible removal potential over an extended period of time. Three different empty bed contact times(2, 5 and 10 minutes) were run to for a total of 47 days testing the affect that the varying empty bed contact time would have on the DOC removals as well as how long the resin would last before becoming exhausted. The 2-minute column treated about 33,900 bed volumes and was determined to be exhausted once it no longer achieved greater than 10% DOC removals.

Two pilot sized surface-loaded horizontal gravel roughing filters (HGRFs) and two vertical gravel roughing filters (VGRFs) were constructed and installed in the pipe gallery of the UNH/Durham Water Treatment Plant. The two HGRFs are were used to evaluate Purolite A502p resin additions to the gravel media and their increased removals of dissolved organic carbon (DOC). Anion exchange resin was added to one of the HGRFs initially by means of a resin box which was easily constructed at the University of New Hampshire. GRF 1 acted as a control with no resin box or resin additions. This resin box was added to the final 7 inch portion of GRF 2 as a final treatment stage. Resin was added to the VGRFs in a similar manner. The resin was added to the final 3-4 inches of media.

Once the single HGRF and two VGRFs received the resin enhancements differences between the orientations became apparent. The HGRF was consistently outperforming both VGRFs regarding DOC and turbidity removals by more than 15%. The results of our experimentation lean to HGRFs being a more successful system for its intended purposes.

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