3.3. Comparison of methods for measuring changes in the rate of
biomethane production
Previously, the rate constant (kBMP) (Eq. (1)) has been calculated
as an indicator of hydrolysis speed during BMP tests (Monlau et al.,
2012). The current data set was used to evaluate the sensitivity of
kBMP to changes in rates of biomethane production by comparing
significant differences in kBMP. Significant differences at each time
point were examined (Table 4). Table 5 displays calculated values
for kBMP. The improvements to rates of biomethane production,
caused by the Ca(OH)2 pre-treatment, could be identified by a significant
rise in kBMP values. kBMP increased on average by 85.9%
from 3, 2 and 1.25 mmparticles sizes and 58.4% from 10 mm, when
compared to the corresponding milled-only samples. No significant
increase in kBMP values could be attributed to the use of enzyme
alone. However, previous analysis had shown that pre-treatment
significantly increased NmL-CH4 g-VS produced for 3, 2 and
1.25 mm particle sizes, at every digestion time point examined.
The lack of significant variation in kBMP between milled-only and