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Fish waste (FW) and water hyacinth (WH) are biodegradable wastes that remain
underutilized and unexploited and cause a problem to the environment since the
existing disposal techniques result in environmental pollution and health risks.
Anaerobic Co-digestion of FW and WH can be used to improve biogas generation as a
source of energy to replace fossil fuel consumption. The conversion of wastes to energy
can provide an answer to environmental pollution, waste treatment and management,
and rising energy costs. The main objective of this study was the optimization of biogas
production from anaerobic co-digestion of FW and WH. The specific objectives were
to characterize the substrate, evaluate operating conditions to maximize the biogas
production, and determine the biogas yield model equation. The WH was collected
from Lake Victoria and FW from fish point Eldoret, Kenya, and the inoculum was
collected from the Moi University biogas plant. Laboratory scale experiments were
carried out in Moi University laboratories (Chemical and Process Engineering
Laboratory and Chemistry Laboratory) under mesophilic temperature (37 o C). The
physiochemical characteristics (Total solids, Moisture content, Volatile solids, and
Carbon to nitrogen ratio) of the substrate were tested using standard methods. Design-
Expert 13 was used for optimization and results analysis. RSM (Response surface
methodology) was used to examine the effects of operating parameters and identify
optimum values for biogas yield. Experimental variable levels for biogas were substrate
ratio (WH: FW, 25-75g), inoculum concentration (IC, 5-15g), and dilution (85-95mL).
The total weight of the substrate was 100 g. The total volume of the biodigesters was
made between 190-210 mL. The quantity of biogas produced was measured by the
water displacement method on daily basis (20 days). The initial analysis of FW was
61.78, 99.48, and 38.21% for MC, VS, and TS respectively while for WH was 94.4,
83.3, and 5.6 % respectively. The C/N ratio of FW (5.89) was out of range for the
accepted C/N ratio (20-30:1). However, the C/N ratio of WH (21.35) and inoculum
(23.47) was in a suitable range. Optimum values for maximum biogas yield of 690mL
with the highest methane yield of 68.15% were found to be WH: FW ratio, 25:75g, 15g
of IC, and 95 mL for dilution. The yield was 16.1% and 32.4% greater than FW and
WH mono-digestion, respectively. The biogas yield was expressed as function of
operating variables.The model was significant (P<0.05). All factors had significant
linear and quadratic effects on biogas while only the interaction effects of the two
factors were significant. The coefficient of determination(R 2 ) of 99.9% confirms the
good fit of the model with experimental variables. In conclusion, FW and WH were
potential feedstock for biogas production. AnCo-digestion of FW and WH feedstock
has been shown to enhance biomethane yield. Optimum values for RSM were within
the range of experimental results. Biogas yield decreased as substrate ratio increased.
FW had a lower C/N ratio, further study needs to consider co-digestion with other
higher C/N ratio substrates. |
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