Corn cob dry

Materials and Methods

Sample Material

Corncobs were harvested from an 111 day hybrid on October 26^th 2009 from a field near

Ames, Iowa. A modified John Deere 9860 combine separated cobs from the grain and stover.

The cobs were harvested at approximately 26% moisture w.b. and stored in polyethylene plastic

bags (three bags to prevent moisture exchange with the environment) in a cold room at 4˚C until

needed for the experiment. Foreign material and remaining stover were removed from the

samples by hand separation once the cobs were taken from storage.

Prior to testing all cob moistures were determined using a hot air oven for 24 hours and

103C (ASABE Standards, 2003).

The moisture content of the corn cobs were adjusted, as necessary, to obtain desired

levels for the experiment (15, 25 and 35% w.b.). If the moisture level had to be increased, the

samples were sprayed with a calculated amount of distilled water necessary to reach the desired

MC and then stored at 4˚C for 48 hours to allow the moisture to equilibrate within the material.

If samples needed to be dried, they were left in open air at ambient conditions, occasionally

weighed until the desired MC (weight) was achieved, usually few hours. Immediately before the

experiment was performed, sample MC was re-determined.
Experimental Apparatus

Three temperature-controlled chambers were used (model I-35LLVL Incubator, Percival

Scientific, Inc., Boone, Iowa) and set to one of the treatment temperatures (10, 20 and 30ºC),
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according to the treatment randomization. Each chamber contained one sample of each of the

three MC corn cobs used (15, 25 and 35 % w.b.). The individual sample size varied depending

on degradation rates from pre-experimental tests for the different temperatures and MCs. Large

samples with favorable microbial conditions had high rates of CO₂ evolution and exceeded the

full-scale capacity of the CO₂ measurement device, hence smaller sample sizes were needed for

these conditions. For this reason, sample size varied from 200 to 500 g of dry matter.

Within a chamber, individual samples were placed in a 15.2 cm O.D acrylic tubes

approximately 60 cm in height, capped with 15.2 cm flexible cap (Figure 1). At both ends, a

0.625 cm plastic hose coupler connected with tygon R-3603 tubing (Saint-Gobain Performance

Plastics Corporation, Akron, Ohio) through which air was provided to maintain aerobic

conditions and to carry away carbon dioxide produced by microbial activity. Three diaphragm

pumps (model MOA-P122-AA, Gast Manufacturing, Benton Harbor, MI) were used to pump air

through the system.