Anaerobic Digestion of Organic Waste in UMS Campus …
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degradation. In this study, sewage sludge was used as inoculum, while Deressa et al.
(2015) used cow manure. Cow manure contains high lignocellulosic which is due
to the food consumed by the cow. Since cow is fed with grass, part of the grass that
indigestible will be excreted out in their manure. The presence of lignocellulosic
in manure inhibits the completion process of AD (Nielsen and Angelidaki 2008)
making the process in the non-optimal state. Hence, this might cause the low TS and
VS destruction in the previous study. Iacovidou et al. (2012) reported that digestion
of food waste with sewage sludge as inoculum causes high reduction of organic
content in food waste. Therefore, the type of inoculum used in AD is very important
in order to have a high degradation of solid wastes (Forster-Carneiro et al. 2008).
4 Conclusions
In this study, the physical and chemical characteristics of kitchen food wastes samples
were determined using FWRL (raw sample liquid) and FWDL (digested sample
liquor). Anaerobic digestion was chosen as a method of study as it can release
a significant amount of nutrients due to the breakdown of organic substances by
anaerobic bacteria. Determination of physical characteristics including pH, TS and
VS are very important as they affect greatly on the digestion performance and to
design the experimental work of anaerobic digestion. In this study the pH of the
food waste ranged between pH 6.30 and 7.10, suggests anaerobic digestion of food
waste does not highly dependent on chemical addition to control the pH, because
the optimum pH for anaerobic digestion was reported to be between pH 6.8and 7.2.
The presence of CaCO 3 , represented by eggshell may contribute to the pH values.
Chemical characteristics such as the concentration of Mg
2+ , NH 4
+ and PO 4
3− , on
the other hand, show that kitchen food waste contains high nutrients. Mg
2+ and
PO 4
3− increased after digestion, but not for NH 4
+ . At least there are two possibilities
which may cause the decreased in NH 4
+ and low PO 4
3− increased in FWDL, i.e.,
NH 4
+ may be converted to ammonia (NH 3 ) or struvite may be formed during the
AD process, when the molar ratio present in equimolar. Nevertheless, the P content
was very high both in FWRL and FWDL and if precipitated, 136 g struvite can be
formed from 1 g of food waste. This suggests that food waste is naturally high in
nutrient content. If we consider the amount of food waste generated in Tun Mustapha
Residences each day, about 0.34 kg struvite (340,816 mg struvite/g food waste) can
be potentially recovered. In this study, P recovery was also addressed as struvite
recovery because phosphate can be precipitated as struvite with the presence of
magnesium and ammonium ions. Anaerobic digestion was not only to stabilised
sludge and recover resources, but also to reduce waste volume. In this study the
total solids and volatile solids were successfully reduced with a high percentage of
40.11% and 76.51%, respectively, indicates that the type of food waste used in this
study was highly degradable and high in organic content. This destruction can help
in diverting waste from landfill and saving space, reduce unpleasant odour as well
as greenhouse gases release. This study is important as this is the first study was
141
degradation. In this study, sewage sludge was used as inoculum, while Deressa et al.
(2015) used cow manure. Cow manure contains high lignocellulosic which is due
to the food consumed by the cow. Since cow is fed with grass, part of the grass that
indigestible will be excreted out in their manure. The presence of lignocellulosic
in manure inhibits the completion process of AD (Nielsen and Angelidaki 2008)
making the process in the non-optimal state. Hence, this might cause the low TS and
VS destruction in the previous study. Iacovidou et al. (2012) reported that digestion
of food waste with sewage sludge as inoculum causes high reduction of organic
content in food waste. Therefore, the type of inoculum used in AD is very important
in order to have a high degradation of solid wastes (Forster-Carneiro et al. 2008).
4 Conclusions
In this study, the physical and chemical characteristics of kitchen food wastes samples
were determined using FWRL (raw sample liquid) and FWDL (digested sample
liquor). Anaerobic digestion was chosen as a method of study as it can release
a significant amount of nutrients due to the breakdown of organic substances by
anaerobic bacteria. Determination of physical characteristics including pH, TS and
VS are very important as they affect greatly on the digestion performance and to
design the experimental work of anaerobic digestion. In this study the pH of the
food waste ranged between pH 6.30 and 7.10, suggests anaerobic digestion of food
waste does not highly dependent on chemical addition to control the pH, because
the optimum pH for anaerobic digestion was reported to be between pH 6.8and 7.2.
The presence of CaCO 3 , represented by eggshell may contribute to the pH values.
Chemical characteristics such as the concentration of Mg
2+ , NH 4
+ and PO 4
3− , on
the other hand, show that kitchen food waste contains high nutrients. Mg
2+ and
PO 4
3− increased after digestion, but not for NH 4
+ . At least there are two possibilities
which may cause the decreased in NH 4
+ and low PO 4
3− increased in FWDL, i.e.,
NH 4
+ may be converted to ammonia (NH 3 ) or struvite may be formed during the
AD process, when the molar ratio present in equimolar. Nevertheless, the P content
was very high both in FWRL and FWDL and if precipitated, 136 g struvite can be
formed from 1 g of food waste. This suggests that food waste is naturally high in
nutrient content. If we consider the amount of food waste generated in Tun Mustapha
Residences each day, about 0.34 kg struvite (340,816 mg struvite/g food waste) can
be potentially recovered. In this study, P recovery was also addressed as struvite
recovery because phosphate can be precipitated as struvite with the presence of
magnesium and ammonium ions. Anaerobic digestion was not only to stabilised
sludge and recover resources, but also to reduce waste volume. In this study the
total solids and volatile solids were successfully reduced with a high percentage of
40.11% and 76.51%, respectively, indicates that the type of food waste used in this
study was highly degradable and high in organic content. This destruction can help
in diverting waste from landfill and saving space, reduce unpleasant odour as well
as greenhouse gases release. This study is important as this is the first study was