Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. George Nakhla

Abstract

This thesis demonstrated the feasibility of using ultrasonication to solubilize the particulate matter, suppress the growth of methanogens, and enrich the biohydrogen producers, thus overcoming the main challenge of biohydrogen systems i.e. long-term stability and contamination with methanogens. Furthermore, this work emphasized the benefits of applying ultrasonication inside a bioreactor over using it as a pretreatment for biohydrogen and biomethane production from wastes. The results of this work showed that sonicating hog manure at specific energy (SE) of 500 kJ/kg TS resulted in a 20% increase in methane production and 36% increase in VSS destruction. The viability of using ultrasonication as a pretreatment method for elimination of methane producers and enrichment of hydrogen producers has been confirmed at SE of 79 kJ/g TSS. Moreover, hydrogen production in a novel sonicated biological hydrogen reactor (SBHR), which comprised a continuous stirred tank reactor (CSTR) connected with an ultrasonic probe at the bottom of the reactor, was about 85% higher than that in a conventional CSTR. On the other hand, an extensive comparative study of five different mesophilic systems (single and two-stage with and without sonicated feed, and two-stage; SBHR followed by methane reactor) was undertaken using food waste. The results showed that sonication inside the reactor in the first stage showed superior results compared to all other systems with respect to hydrogen production, methane production, and VSS destruction. The study also confirmed the advantages of two-stage mesophilic digestion of food wastes over single-stage systems, as reflected by VSS destruction efficiencies in the range of 51% - 59% versus 36% - 44% at a short SRT of 7 days.

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