1.2 RESEARCH OBJECTIVES
The primary objective of this research was to investigate the effect that blending
un-dewatered grease trap waste with municipal wastewater sludge in anaerobic codigestion
reactors has on methane potential and system inhibition.
Specific objectives of this research included:
1. Determining the biochemical methane potentials of un-dewatered GTW,
MWS and mixtures of un-dewatered GTW and MWS at various ratios.
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2. Evaluating the effects of anaerobic co-digestion of MWS and undewatered
GTW on (i) biogas production, (ii) methane content, and (iii)
volatile solids reduction.
3. Examining the stability of anaerobic co-digestion of MWS and undewatered
GTW at increasing GTW feed ratios under semi-continuous
feed and mesophilic conditions (35 0C).
1.3 SCOPE
The research was conducted in two major phases as follows:
Phase Ι: Batch Experiments. The biochemical methane potentials of undewatered
GTW, MWS and mixtures of un-dewatered GTW and MWS
were determined through a series of biochemical methane potential (BMP)
tests. The standard BMP test procedure was modified to periodically
monitor the process parameters. A mathematical equation describing the
relationship between GTW feed ratio (on a VS basis) and methane
potential was fit to the experimental data from the current study and
previous BMP studies. The kinetic and performance parameter estimates
that provided the best fit to the experimental data were used to assist in the
interpretation of the batch experimental results.
Phase ΙI: Semi-continuous Feed Reactor Experiments. The performance of
mesophilic (35 0C) AcoD of MWS and un-dewatered GTW was
investigated in two semi-continuous feed anaerobic co-digestion reactor
systems. Methane potentials and VS reductions were determined at
increasing GTW feed ratios and compared with previously reported
performance data for AcoD of MWS and concentrated/dewatered GTW.
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Optimum and inhibiting GTW feed ratios on a VS basis were determined.
The risk of inhibition of the AcoD process using un-dewatered GTW and
dewatered/concentrated GTW as co-substrates was assessed. The effects
of digester effluent feeding on the recovery of digesters following upset
conditions was studied and compared with previously reported recovery
methods.
1.4 ORGANIZATION
The dissertation includes 5 chapters. Chapter 1 presents the problem statement,
research objectives and organization of the thesis.
Chapter 2 provides a comprehensive review on GTW management through AcoD.
Fat, oil, and grease deposition mechanisms in wastewater collection lines, performance
and upgrades of grease traps, characteristics of GTW, and the biochemistry of AcoD
processes were analyzed. In addition, AcoD of grease trap waste including process
performance, effects of various reactor configurations and pre-treatment methods,
recovery of the digester following upset, and mathematical modeling were examined.
Future research needs in GTW management, as well as research needs addressed in this
study, were evaluated.
Chapter 3 and 4 describe and examine experimental results. Chapter 3 presents an
investigation of the biochemical methane potentials of un-dewatered GTW, MWS and
mixtures of un-dewatered GTW and MWS at various ratios through a series of
biochemical methane potential (BMP) tests. Chapter 4 focuses on investigating the
performance and stability of mesophilic (35 0C) AcoD of MWS and un-dewatered GTW
from a set of semi-continuous feed reactor experiments.
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Chapter 5 includes conclusions based on the research findings in this dissertation
and provides recommendations for future research.