| dc.description.abstract | There has been an increase of confined animal feeding operations (CAFOs)
generating large amounts of manure. When this manure is not handled properly, it
generates greenhouse gases (GHGs), odors and water pollution. Anaerobic digestion (AD)
is touted as an acceptable approach to address manure management and associated
environmental problems. Biogas production from manure alone is limited by low volumes
of biogas yield, thus it has a poor economic reputation. Co-digestion of dairy manure with
other agricultural wastes has emerged as a promising strategy to enhance the economic
viability of AD. Among the agricultural wastes, canola meal (a by-product from extraction
of oil from canola seed) was considered as a potential candidate for co-digestion with dairy
manure. The purpose of this research was to investigate the suitability and appropriate
ratios of canola meal for anaerobic co-digestion with dairy manure.
In this study, various proportions of canola meal: dairy manure (100:0, 10:90,
40:60, 20:80, 0:100) by volume-basis were co-digested in 0.5 L batch bioreactors at a
temperature of 35±1 °c for 25 d. Two types of canola meal were used in the study; high oil
content (HOC) and low oil content (LOC) canola meal with oil contents of 8.0% and 2.5%,
respectively. For HOC, the total solids (TS) were high organic loading (HOL, 7.5±2% TS)
and low organic loading (LOL, 4.5±2% TS). LOC trials were done at HOL only. In
addition, the pretreatment of the canola meal with caustic solution and digestion at high
temperature (60±2°C) were evaluated. Results from this study indicated that at HOL, canola meal is not a viable candidate
for anaerobic co-digestion with manure as it lowers biogas production. Manure only
digestion performed better than bioreactors augmented with canola meal. The specific
methane yield was 352 L/kg VS for manure only and 84 L/kg VS for LOC canola meal
only digestion. Nonetheless, at LOL, both 10% and 20% HOC canola meal resulted in
increased specific methane of 535 L/kg VS and 445 L/kg VS, respectively. This is 78% and
48% higher than 300 L/kg VS obtained in manure only digestion. Hence, canola meal is
beneficial in dairy manure co-digestion at LOL.
At all organic loading levels, canola meal alone digestion had the lowest cumulative
biogas production (0.9 L per 0.35 L bioreactor) and specific methane yield (83 L/kg VS).
For HOL, the cumulative biogas yield and specific methane yield decreased as the canola
meal ratio increased, while at LOL, the decrease was only noted for bioreactors with 40%
canola meal. This is suspected to be caused by elevated levels of total volatile fatty acids
(VF As) of more than 4000 mg/L. Two factors are suspected to impact the accumulation of
VF As: the ratio of canola-to-manure in the bioreactor and the organic loading or oil content
in the canola meal. In future it will be necessary to look into ways of overcoming the
inhibition caused by elevated VF As. | en_US |
