|Khansa Luqyana Hapsari||University of Indonesia|
|Firyal Tharifa||University of Indonesia|
|Setyo Sarwanto Moersidik||Universty of Indonesia|
|Sandyanto Adityosulindro||Universitas Indonesia|
|Cindy Rianti Priadi||Universitas Indonesia|
Process instability often occurs in anaerobic digestion (AD) due to inhibitors, such as the high sodium content in food waste. Recent studies have reported that magnesium can reduce the sodium ion’s toxicity towards methanogens. This study aimed to analyze the effect of magnesium addition to Volatile Solids Destruction (VSD), Chemical Oxygen Demand (COD) reduction, and biogas production in AD of food waste. The experiment consisted of two phases, the control phase and the experimental phase, without and with MgSO4, respectively. The control phase results were: average COD reduction, VSD, and methane yield up to 80.9%, 87.6%, 340 mL CH4/gr VS/day, respectively. The experimental phase results were: average COD reduction, VSD, and methane yield up to 78.5%, 83.9%, 125 mL CH4/gr VS/day, respectively. Overall, the study’s results showed that MgSO4 had a negative impact on VSD and methane yield. The addition of MgSO4 seemed to cause instability in the AD system, which resulted in a decrease in the VSD value and a decrease in the methane concentration.
Biogas; COD; Inhibition; Methane; Solid waste; VSD
Waste management is a fundamental process for finding solutions to the problems arising from waste produced by individuals and industry (Pongrácz, 2002). Society’s awareness of environmental issues is considered to drive the search for waste disposal methods that are alternatives to landfills (Shukor et al., 2018). Anaerobic digestion (AD) is a widely used domestic waste processing method that is able to convert various biodegradable waste materials into energy (Wijayanti et al., 2018) through a biological anaerobic process that converts organic matter into biogas and digestate (Lin et al., 2018). In comparison to other aerobic technology, anaerobic processes, such as AD, offer several advantages, including low energy use and low sludge production; moreover, the produced biogas can function as an energy source. Furthermore, the anaerobic process does not have a strong odor because the process is carried out in an enclosed space (Abdel-Shafy & Richardson, 1996).
However, operational problems, such as instability in the system and fluctuating biogas productivity, are disadvantages of AD (Lin et al., 2018). Failure to maintain the balance between acid bacteria and methanogen bacteria is known to be the main cause of instability in the system (Demirel & Yenigün, 2002). Furthermore, various elements, such as sodium (Na), are believed to inhibit AD processes (Chen et al., 2008). The amount of Na concentration that can cause inhibition can vary. This is influenced by the type of feedstock and the operating parameters, which might be different in each reactor (Anwar et al., 2016). According to Alhraishawi and Alani (2018), an NaCl concentration of 3,100 mg/L or more has the potential to inhibit AD processes.
To counter Na toxicity, a mechanism known as antagonism can be implemented (Kugelman & McCarty, 1965). Antagonism is achieved by the presence of another cation that reduces the toxicity of other types of cations, which can reactivate enzymes that have been damaged due to an excess amount of the toxic cation. This may induce a stimulatory effect from one type of cation, which, in this case, is magnesium (Mg), which could act as an antagonist cation against Na (Kugelman & McCarty, 1965). The study conducted by Bashir and Matin (2004) found that the handling of Na inhibition at a concentration of 9,000 mg/L can be done by adding Mg, which can reduce the toxic effects of Na. Hence, in our study, we further analyzed the effect of the addition of Mg on Na toxicity in anaerobic waste treatment. Toward that end, we evaluated the following parameters: Volatile Solids Destruction (VSD) and Chemical Oxygen Demand (COD) reduction. Both VSD and COD reduction represent the efficiency of the AD process in reducing organic matter, depending on the methods and concentrations used in the process.
The increase in VSD is related to the increased production of biogas (Anwar et al., 2016). According to Budiyono et al. (2013), in an AD system, COD is consumed through microbial activity and is converted into methane (CH4). Both of these parameters are important because they represent the performance of the AD process.
The results of this experiment demonstrated that the addition of MgSO4 did not improve the performance of the AD process. The addition of a significant amount of MgSO4 caused a significant decrease in VSD (p < 0.05), as seen in the VSD value of 83.9% ± 0.04% obtained in the experimental phase and the VSD value of 87.6% ± 0.07% obtained in the control phase. Moreover, the addition of MgSO4 caused a significant decrease in the CH4 yield (p < 0.05), as seen in the CH4 yield of 125±107.2 mL CH4/gr VS/day obtained in the experimental phase and the CH4 yield of 339±156.5 mL CH4/gr VS/day obtained in the control phase. However, in this experiment, the addition of MgSO4 did not significantly influence the efficiency of COD reduction, as seen in the COD reduction of 78.5% ± 0.2% in the experimental phase and the COD reduction of 80.9% ± 0.12% ??in the control phase. Further study on the synergistic effect of MgSO4 must be analyzed in a complex food waste AD environment.
This research and its publication are supported by the Superior Applied Research Grant 2019 from the Higher Education and Research Ministry Indonesia (number NKB-1728/ UN2.R3.1/HKP.05.00/2019).
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