الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Nowadays, the world is looking for renewable energy sources that are both cost-effective
and environmentally friendly. The purified biogas is an important source of renewable energy
that can be used in place of fossil fuels. Anaerobic digestion is a biochemical method of
producing biogas that the organic compounds can be converted into a renewable energy source.
Anaerobic co-digestion, or AcoD, is regarded as a practical method for resolving substrate
property and system optimization issues in single-substrate digestion processes. Improving the
mesophilic anaerobic co-digestion process in the high solid state to improve the biodegradation
process and improve the production of biogas is the main aim of the research work of this
thesis. Anaerobic digestion is difficult for sewage sludge. The contents of the cells are
biodegradable, but they are protected by tough cell walls. Biomass also retains water, making
dewatering difficult. So, the conventional mesophilic anaerobic digestion process degrades VS
of sludge by about 40% at 30 and 40 days. Food waste is one of the best available feedstocks
for AcoD all over the world. It consists of carbon (C), hydrogen (H), nitrogen (N), oxygen (O),
and Sulphur (S) which indicates an important quantity of carbon is available in FW, which
makes it highly biodegradable. Generally, FW prevails with a high C/N ratio (11.1–36.4), while
the SS revealed a low C/N ratio (6–9), which can improve in the range of 20–30 by proper
mixing ratios.
In this research, the biological methane potential test is a preferred technique for
measuring the biodegradability and decomposition rate of organic substances. Sixteen digesters
models had been constructed to investigate the effect of thermal pre-treatment on the physical
characteristics, the performance of the biological degradation process, and the gas production
of the anaerobic co-digestion process in the high solid state. An electric oven is used for pretreatment of the well-mixed FW and SS individually at different temperatures of 100°C, 120°C,
140°C, 160°C, and 180°C. The food waste (FW) to sewage sludge (SS) ratio used in this
research is 1:2 (VS-based) to form a final total solids concentration of 11.20%. The inoculum
to substrate ratio was set at 1:1 (Volume-based). The biomethane potential test reactors had
been duplicated. The food waste and sewage sludge were covered before putting it in the pretreatment oven to prevent the evaporation of the water from the samples. After pre-treatment
the samples were cooled to the room temperature before mixing in order not to affect the
methanogenic microorganisms in the inoculum sludge inversely. The results show that thermal pre-treatment has changed the physical characteristics of
the food waste and sewage sludge mixture. As the pre-treatment temperature increased, the
viscosity of the food waste and sewage sludge reduced so it was improved noticeably, which
led to the improvement of the mixing process. One of the main challenges facing high solid
AcoD of the waste and sludge - in this research the total solids was 11.2% - is the mixing
process but the thermal pre-treatment might help to improve the mixing process because TP
reduce the viscosity and this lead to use low energy and not specialized mixers. After the
biomethane potential test, the final pH values were ranging between 7.23 and 7.72 which was
appropriate for anaerobic co-digestion because methanogenic bacteria are incredibly affected
by pH variations and require a pH of around 7.0 for optimal growth. The minimum achieved
volatile solids removal ratio is 44.77% in R1(120) and the maximum is 64.58% in R3(180).
These values are within the optimal values achieved by most of the studies that reported the
optimal temperatures for thermal pre-treatment range from 160 to 180°C, and that treatment
durations range from 30 to 60 minutes. The achieved TS removal Ratio ranges between 15.56
to 49.29% and it is higher if compared with the untreated reactor. As the pre-treatment
temperature increased, the removal ratio increased. COD removal ratio of the blank digester
was 39.54% and it was lower than the removal ratio of all other digesters. The achieved removal
ratio ranged between 42.59 and 53.33% in all reactors. the removal ratio increases along with
pre-treatment temperature for R3(T) but it increases up to 160 and 140 °C, and then decreases
for R1(T) and R2(T), respectively. The best reactor in COD removal is R1(160). The thermal
pre-treatment has an effect on the TOC removal. The TOC removal ratio increased as the TP
increased till the treatment temperature of 140℃ and the still approximately the same as the
temperature of TP increased till 180℃. The best case in removing the TOC was R2(140).
Finally, the results show that the pre-treatment increased the biogas production from
4385 ml for the untreated reactor (RB) to 5685 for the reactor R2(140) at 140°C and the
improvement in biogas production reaches 29.65% in the reactor R2(140) and the removal of
volatile solids was 58.90%. Therefore, after the biomethane potential test, the temperature of
140°C was found to be optimal to produce biogas. The optimal condition is to use a mixture of
pre-treated SS at the temperature of 140°C and untreated FW, so TP is recommended to be
used in anaerobic digestion of the mixture of food waste and sewage sludge.