122
M. Rajin et al.
TOC (%) =
100 − Ash (%)
1.8
=
Organic matter (%)
1.8
(2.1)
2.3.2 pH and Conductivity
5 g of food waste sample was oven dried at 105 °C for 24 h. The mashed food waste
was mixed with 50 ml of distilled water, shaken at 130 rpm for 24 h and then filtered.
The solution was analysed by using a pH meter and conductivity meter (HI 9811-5).
2.3.3 Moisture Content
The food waste was dried at 105 °C for 24 h before determining the moisture content.
The initial and final mass of the mixture were recorded. The moisture content was
calculated by using Eq. 2.2.
Moisture content =
Initial Mass − Final Mass
Initial Mass
× 100%
(2.2)
3 Results and Discussions
3.1 Effect of Lipase Addition on Total Organic Carbon
Figure 3.1 shows the Total Organic Carbon (TOC) profile of the digestate obtained in
this work, for food waste with and without lipase. Total Organic Carbon (TOC) is used
as the energy source for microorganisms during digestion process and the degradation
of carbon illustrates the level of digestate maturity (Zhang et al. 2017). The decrease
in total organic carbon is related to the amount of carbon dioxide released. Carbon
dioxide released depends on the degree of utilisation of organic carbon through
microbial degradation (Kulikowska 2016). Furthermore, the decrease in total organic
carbon is related to the microbial respiration (Kulcu and Yaldiz 2004). Thus, a larger
decrease in total organic carbon shows higher degradation by microorganisms.
Based on Fig. 3.1, the average TOC value in this research was unsteady throughout
the digestion process. Initially, the TOC decreased from 55.41 to 55.26% for food
waste without lipase and 55.41–54.93% for food waste with lipase. After 20 days of
digestion, the TOC for food waste without lipase slightly decreased from 55.26 to
55.04%, while the TOC increased from 54.93 to 55.15% for food waste with lipase.
The TOC for food waste without lipase increased from 55.15 to 55.26% at day 40. On
the other hand, the TOC for food waste with lipase decreased from 55.15 to 55.06%
at day 30 and increased again from 55.06 to 55.09% at day 40.
During the first 10 days, both food wastes with and without lipase showed a
significant loss of total organic carbon. A high amount of organic carbon loss may
M. Rajin et al.
TOC (%) =
100 − Ash (%)
1.8
=
Organic matter (%)
1.8
(2.1)
2.3.2 pH and Conductivity
5 g of food waste sample was oven dried at 105 °C for 24 h. The mashed food waste
was mixed with 50 ml of distilled water, shaken at 130 rpm for 24 h and then filtered.
The solution was analysed by using a pH meter and conductivity meter (HI 9811-5).
2.3.3 Moisture Content
The food waste was dried at 105 °C for 24 h before determining the moisture content.
The initial and final mass of the mixture were recorded. The moisture content was
calculated by using Eq. 2.2.
Moisture content =
Initial Mass − Final Mass
Initial Mass
× 100%
(2.2)
3 Results and Discussions
3.1 Effect of Lipase Addition on Total Organic Carbon
Figure 3.1 shows the Total Organic Carbon (TOC) profile of the digestate obtained in
this work, for food waste with and without lipase. Total Organic Carbon (TOC) is used
as the energy source for microorganisms during digestion process and the degradation
of carbon illustrates the level of digestate maturity (Zhang et al. 2017). The decrease
in total organic carbon is related to the amount of carbon dioxide released. Carbon
dioxide released depends on the degree of utilisation of organic carbon through
microbial degradation (Kulikowska 2016). Furthermore, the decrease in total organic
carbon is related to the microbial respiration (Kulcu and Yaldiz 2004). Thus, a larger
decrease in total organic carbon shows higher degradation by microorganisms.
Based on Fig. 3.1, the average TOC value in this research was unsteady throughout
the digestion process. Initially, the TOC decreased from 55.41 to 55.26% for food
waste without lipase and 55.41–54.93% for food waste with lipase. After 20 days of
digestion, the TOC for food waste without lipase slightly decreased from 55.26 to
55.04%, while the TOC increased from 54.93 to 55.15% for food waste with lipase.
The TOC for food waste without lipase increased from 55.15 to 55.26% at day 40. On
the other hand, the TOC for food waste with lipase decreased from 55.15 to 55.06%
at day 30 and increased again from 55.06 to 55.09% at day 40.
During the first 10 days, both food wastes with and without lipase showed a
significant loss of total organic carbon. A high amount of organic carbon loss may