In this study, co-digestion of different organic wastes were conducted in
collaboration with Quasar energy group in order to determine the feasibility of methane
production from certain waste streams such as expired creamer, hand sanitizer and algae
waste. To fulfill the purpose, three specific objectives were to: (1) determine the methane
potentials of four different food wastes (expired creamer, expired beer, food processing
waste (FPW), and fat, oil, and grease (FOG)), (2) identify the suitable mixing ratios of
dairy manure with creamer and sludge cake with hand sanitizer in semi-continuous
anaerobic digestion, and (3) investigate the efficacy of the algae waste in co-digestion
with corn stover. The algae wastes were collected after lipid extraction.
Batch reactors were used to determine the methane potentials of four different
food wastes. All the batches were filled with 800 g digested dairy manure as seed and
200 g mixture of wastes. The co-digestions of dairy manure with different levels of food
wastes were also tested in order to obtain the best mixtures. The digestions of 100%
creamer, 100% beer, 100% FPW, 100% FOG as well as 100% dairy manure were also
tested. The percentage was based on the VS content of each component. Beer and FOG
showed higher methane yield than the FPW and creamer in the co-digestion with dairy
manure.
Laboratory 4-L reactors were discharged and fed daily for the semi-continuous
co-digestions. Constant mixing was achieved by magnetic stirrer. Three levels of hand
sanitizer were tested (0.08%, 0.17%, and 0.35%) at the organic loading rate (OLR) of 4 g
VS/L/d and hydraulic retention time (HRT) of 15 days. Three levels (37.0%, 54.3%, and
68.7%) creamer was co-digested with dairy manure. A very small amount of hand
sanitizer could improve the methane yield significantly in the co-digestion with sludge
cake. The highest methane production (2.16 L/L/day) was obtained with 0.17% hand
sanitizer addition, while 0.35% hand sanitizer addition caused upset of the digestion at
the HRT of 15 days. Higher methane production rate was obtained with increased
creamer addition up to 69%.
The solid-state co-digestions of algae waste and corn stover were conducted in
500 mL flasks. At the TS of 23%, the addition of algae waste deceased when the C/N
ratios of the mixtures (including seed) from 23 to 15. The highest methane yield (166.7
mL/g VSadded) was obtained at the C/N ratio of 23. The addition of algae waste failed to
improve the methane yield in the co-digestion with corn stover. The possible reason
could be the seed already provided sufficient nitrogen source.