Published at : 25 Nov 2019
Volume : IJtech
Vol 10, No 6 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i6.3613
Muhammad Irpan Sejati Tassakka | Environmental Engineering Study Program, Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Brilyana Bela Islami | Environmental Engineering Study Program, Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Farah Nurul Anisa Saragih | Environmental Engineering Study Program, Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Cindy Rianti Priadi | Environmental Engineering Study Program, Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Indonesia currently has a waste generation
problem arising from the fact that sixty percent of the waste it produces is
organic waste (OW). The scope for anaerobic digestion (AD) of OW has not yet
been optimized, with many reactors not functioning properly. The purpose of
this study is to determine the suitability of food waste with an organic
loading rate (OLR) of 8–14 kgVS/m3day to produce the highest
volatile solids destruction (VSD) and methane. A semi-continuous pilot-scale
dry AD of 0.5 m3 was run for 134 days in mesophilic conditions. The
results showed that the feedstock was suitable for dry AD due to the high total
solids (TS) (23.2–27.1%) and organic content (volatile solids of 90–95% TS).
Meanwhile, the optimum OLR was 10 kgVS/m3day with a VSD of 92.2% and
a methane yield of 127 LCH4/grVSday. In addition, OLR 10 kgVS/m3day
had the highest stability, as shown by the pH value of 6.52 and ammonia
concentration of 848 mg/l. The VSD values fell with respect to the OLRs of 12
kgVS/m3day and OLR 14 kgVS/m3day, to 90.42% and 86.73%,
respectively.
Biogas; Inhibitor; Municipal waste; Renewable energy
The amount of municipal solid waste (MSW)
generated in Indonesia is approximately 175,000 tons/day, where 60–74% is
organic waste (OW). OW is generally generated by domestic, commercial, and
institutional premises (Dong et al., 2010). The incorrect treatment of OW can lead to
serious cases of environmental contamination, including Escherichia coli outbreaks and contaminated ground and surface
water. Having organic solids that account for 61% of the waste, a moisture
content of 78%, and volatile solids (VS) of 81% TS (Wang
et al., 2014) means there is potential
for treatment by anaerobic digestion (AD). Based on ecosystem sustainability,
AD is the most efficient method of OW treatment. AD offers the ability to reduce
a high quantity of OW in a small area and is a relatively faster method than
composting. Additionally, AD is considered a source of renewable energy due to
the production of methane, which can be utilized as biogas, and it is suitable
for sustainable social-economic development (Tetteh et al., 2018). It comprises the four stages of
hydrolysis, acetogenesis, acidogenesis, and methanogenesis.
Indonesia has very little
experience in the field of AD for MSW. From a previous survey, the very few
facilities that are in operation mostly do not produce methane (Priadi et al., 2015). One of the indicators of AD processing is based on
the efficiency with which organic matter is decomposed,
which is usually measured by volatile
solids destruction (VSD). Generally, a higher VSD value indicates higher
production of methane as biogas (Nagao et al., 2012). However,
VSD has an upper limit, where methane production declines due to the value of
VSD exceeds the limit. The decline happens due to inhibitor accumulation caused
instability of AD. Fluctuating
feedstock and low COD in recirculated leachate may also result in very low
biological activity and then lead to low biogas production. These conditions
can be overcome by operating AD with the optimum organic loading rate (OLR).
Thus, to improve AD performance, the OLR should be adjusted according to the
MSW specific to Indonesia so that the waste degradation process can be
streamlined and made more efficient.
OLR represents the daily quantity of OW used
as feedstock in a continuous system. The optimum
value indicates the total nutrients needed for microorganism growth and
metabolism (Dong et al., 2015). Excess OLR
can induce accumulation of volatile fatty acids (VFA), shock loading on the
reactor, and a low pH (Lin et al., 2011; Dai et
al., 2013). A low OLR, however, can
lead to the microorganisms lacking the required nutrients, unstable growth,
death, and the production of inhibitors to generation such as ammonia (Dai et al., 2013; Dong et al., 2015). The value of OLR
depends on the type of AD reactor, such as a one- or two-stage and a wet or dry
AD. The OLR in wet AD using household OW has been found to either vary within
the range of 2–10 kgVS/m3day
(Aslanzadeh et al., 2014) or to be below 7
kgVS/m3day (Kothari et al., 2014). Meanwhile,
dry AD has a higher OLR than wet AD, with a range of 7–15 kgVS/m3day (Fagbohungbe et al., 2015) or 12–15 kgVS/m3day (Kothari et al., 2014). Dry AD has the ability to attain a
higher OLR and process a greater volume of OW by up to > 60% (Mattheeuws & Baere, 2011). There are several
advantages of implementing dry AD, such as the small volume, thus making it
suitable for hydrophobic substrate (Fagbohungbe et
al., 2015), VSD at 40–75%, low
hydraulic retention time (HRT), high and consistent biogas production (Kothari et al., 2014), and good tolerance
to shock loading. Nevertheless, the optimum OLR for dry AD is needed in order
to produce a good level of VSD and methane, specifically in the context of
using OW in Indonesia. Accordingly, this
study aims to determine the optimum OLR needed to produce VSD using a
semi-continuous pilot-scale dry AD.
With a high TS and organic content, a mixture of OW and CM is
suitable for use in dry AD. The optimum OLR in this experiment was 10 kgVS/m3day,
which gave a VSD of 92.2% or 179 g/l and a methane yield of 127 LCH4/kgVSday.
The operation is likely to be more stable with temperature, pH, and ammonia
values of 28.7oC, 6.52, and 848 mg/l, respectively. Thus, the
optimum OLR obtained for AD can produce high VSD and serve as a solution to the
problem of OW in Indonesia.
This research was funded by Grant of
Indonesian Directorate of Research and Higher Education, Number 1149/UN2.R12/HKP.05.00/2016. Meanwhile, the conference was
financially supported by Grant of Indonesian Directorate of
Research and Higher Education, Number NKB-1728/UN2.R3.1/HKP.05.00/2019. Special
thanks are due to the laboratory of the
Environmental Engineering Study
Program at Universitas Indonesia.
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