Date of Award

Winter 2018

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

M. Robin Collins

Second Advisor

Paula Mouser

Third Advisor

Francesca Leasi

Abstract

Optimizing ripening periods and maintaining removal efficiencies when treating high-quality source waters are some of the main challenges of slow-rate biofiltration. The ripening period of biofilters treating carbon-limited source waters can be significantly longer than biofilters treating nutrient-rich source waters, especially during colder temperatures. Abrupt changes in the influent water quality, e.g. surface water to groundwater, can also impact biofilter active biomass, and consequently biofilter performance. This study aimed to investigate how to reduce ripening period and improve removal efficiencies of slow-rate biofilters treating low-carbon waters by (i) increasing the organic carbon loading of the source water, and (ii) adding ferric chloride to act as a biofilter aid at the beginning of the biofilter operation or when changing source waters. The organic carbon loading was expected to increase biofilter active biomass with subsequent improvement in E. coli removal, while ferric chloride was expected to quickly enhance the capture of the E. coli by coagulation mechanisms. DNA sequencing analysis was performed to evaluate the impact of organic carbon and ferric chloride amendments on microbial community composition.

This research was conducted at bench-scale levels at the University of New Hampshire. Two pilot studies were also conducted in Jamestown (CO) by ACE Engineering and in Salem (OR) by Carollo Engineers using the results from the bench-scale test. The final bench-scale experimental setup consisted of 6 single stage down-flow biofiltration units amended with various combinations of organic substrates and ferric chloride. The experimental run was conducted for 5 weeks. E. coli challenges were conducted at 3 and 5 weeks of biofilter operation. Several conclusions were reached at the completion of the biofilters runs including the following: (i) biofilter active biomass was increased in biofilters amended with organic substrates over the control; (ii) the addition of a readily biodegradable organic substrate, e.g. glucose-glutamic acid, resulted in a less diverse bacterial community compared to a more complex organic substrate, e.g. powdered milk, and favored the growth of fungi; (iii) the addition of low-dosages of ferric chloride also increased biofilter active biomass and increased the presence of positive-charged attachment sites for the removal of the negative-charged E. coli bacteria; and (iv) increasing E. coli removal was positively correlated to higher active biomass in biofilters amended with organic substrates and without fungal growth, and to ferric-ion accumulations in biofilters amended with ferric chloride.

Recommendations for future work include further investigations of: (i) the impact of various complex organic substrate amendments on biofilter microbial communities and subsequent treatment performance; (ii) the particle removal mechanism(s) associated with low ferric-ion accumulations to biofiltration systems; (iii) the role of filter depth on E. coli removal from biological-enhanced slow-rate biofilters; (iv) operational taxonomic units and water quality conditions that are conducive or deleterious for enhanced treatment performance; and (v) headloss development from organic substrate and ferric-ion amendments in slow-rate biofilters.

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