The main purpose of processing liquid waste that is rich in organic materials is to get clean water both used again (re-use) and disposed of. Biogas products are produced mainly for processing large-capacity liquid waste. The processing stage consists of two stages namely primary and secondary processing. In primary processing, primary sludge will be produced from clarifier or settling tank. The liquid waste is passed to the clarifier or settling tank and the sludge deposit is produced. While in secondary processing, liquid waste is aerated to stimulate microbial growth. These microbes form a floc and settle into secondary sludge. The sludge or sediment must be treated at that location or transported to another place to be processed or disposed of.
The sludge processing unit usually consists of two or four stages. In sludge processing units, small capacity usually consists of only two stages, while large capacity can consist of a total of four stages. The stages of the process are: thickening, digestion (fermentation), dewatering (drying) and sterilization. In the processing unit, small capacity usually only consists of thickening and dewatering, then sludge is further processed elsewhere. Sterilization is only done when there are rules or orders to do it, so it is not done much. In large capacity processing units, the concentrated sludge is then anaerobically fermented to break down complex compounds with the help of microbes, reduce solid volatile and pathogens in the sludge, and simultaneously reduce the occurrence of foul odors.
The sludge fermentation produces biogas. Biogas production depends on sludge composition, residence time in fermentation equipment / digester, temperature and speed of microbial metabolism, which is carefully controlled. If the amount of biogas produced is only small, it is usually only flared or heated in the digester. Whereas if the amount of biogas produced is quite large, it can be used for cogeneration fuel sources. Electricity can also be produced and can be used for internal and external needs. Heat from electricity production can also be used to maintain the digester temperature so that the fermentation process can be optimal. Other options are used to produce renewable natural gas (RNG). RNG can then be used for a variety of purposes both for industry and households.
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| Tractor with Biogas Fuel |
Potential liquid waste for biogas production is from palm oil mill effluent. As the largest CPO producer in the world, Indonesia as first rank and Malaysia second rank, both of which are estimated to have more than 1500 palm oil mills, so the potential for biogas production is also very large. The processing of wastewater from oil palm mills includes large capacity, because the average palm oil mill has a capacity of 60 tons / hour FFB and produces 700 liters of liquid waste for every ton of FFB processed. The use of biogas can be used for energy sources in the palm oil mill. There are two ways that can be done on this matter, namely biogas is used to fuel the palm oil mill with existing equipment with only a few modifications, especially on the biogas burner. In this way palm kernel shells (PKS) and mesocarp fiber commonly used in energy sources can be reduced or even utilized for others.
Whereas the second method, namely biogas output is purified so that generator fuel (gas engine generator) can be used and electricity is used for the operation of the palm oil mill, while the steam needs for sterilization of palm oil mills can remain with the palm fiber and shell or biogas that is. In addition, if the biogas can be packaged in a tube (such as a 3 kg or 12 kg LPG tube) or tank, the use can be wider. Vehicles used to support the palm oil business can use biogas as fuel. Remote communities around oil palm mills who also often find electricity supply because it is very remote can use the biogas to fuel electricity generators. Various business and industrial activities can be done with the availability of electricity. This means also encouraging economic growth of the community surrounding the palm oil mill. Of course not only economic problems are stretching and developing, but also education, religion, health, and social affairs can also develop together well.
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