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M. Rajin et al.
1 Introduction
Food waste has been recorded as the largest components of waste in the world as
reported by Zhang et al. (2014) and Capson-Tojo et al. (2016). Food waste is recognised as pollutants, since it readily decomposes, generates odours, and sometimes
causes illness under natural condition due to its high biodegradable organic compound and moisture content (Moon and Song 2011). The amount of food waste is
expected to keep increasing as the population growth and the development of worldwide economy increase (Agamuthu and Fauziah 2011). Therefore, a proper management of food waste is needed to avoid severe health problems and environmental
pollution.
Landfill disposal, incineration and anaerobic digestion are among the traditional
methods used for food waste treatment (Polprasert 2007). However, the approaches
of disposals for food waste management by landfills and incinerator have some drawbacks. Many countries fully banned the landfilling approach as well as the incinerator
where it produces intensive energy to the surrounding due to the high moisture content and can cause air pollution from the release of smoke from chimneys. Moreover,
incineration also decreases the economic value of the waste as it inhibits the recovery
of nutrients and valuable chemical compounds from the incinerated substrate. On the
other hand, the increasing number of food waste generated every year leads to insufficient area for landfill management (Kunwar et al. 2017). Thus, anaerobic digestion
has been considered as an attractive alternative to overcome these limitations.
Anaerobic digestion involves the degradation and stabilisation of organic materials under anaerobic conditions by microbial organisms. The degradation of organic
material will lead to the formation of biogas which is a mixture of carbon dioxide and
methane as renewable energy source and microbial biomass (Kelleher et al. 2002).
This technology is widely applied in waste management including food waste and
other organic waste treatments (Yaser 2014; Rajin 2018). Furthermore, the production of biogas from anaerobic digestion is one of the renewable energies that can be
used for heating and power generation.
Generally, there are four steps involved in anaerobic digestion which are hydrolysis, acidogenesis, acetogenesis and methanogenesis. Among these steps, hydrolysis is
known as the rate limiting step. During hydrolysis, the polysaccharides (macronutrients) are converted into monosaccharides (micronutrients) by extracellular microbial
enzymes. The slow degradation rate of crude lipid which includes floatable grease,
oil and fats in the food waste leads to low digestion efficiency and therefore inhibits
the digestion process. Various methods have been reported to improve the performance of anaerobic digestion system. Among them is the addition of enzymes to
accelerate the hydrolysis reaction of various types of substrates as reported by Meng
et al. (2017), Dors and Mendes (2013) and Kanmani et al. (2016). In these previous
works, commercial enzymes such as carbohydrases, proteases, and lipases have been
used to improve hydrolysis of food waste from various sources.
Therefore, this research was conducted to determine the feasibility of lipase to
be used in the anaerobic digestion system of Malaysian food waste. The effects of
M. Rajin et al.
1 Introduction
Food waste has been recorded as the largest components of waste in the world as
reported by Zhang et al. (2014) and Capson-Tojo et al. (2016). Food waste is recognised as pollutants, since it readily decomposes, generates odours, and sometimes
causes illness under natural condition due to its high biodegradable organic compound and moisture content (Moon and Song 2011). The amount of food waste is
expected to keep increasing as the population growth and the development of worldwide economy increase (Agamuthu and Fauziah 2011). Therefore, a proper management of food waste is needed to avoid severe health problems and environmental
pollution.
Landfill disposal, incineration and anaerobic digestion are among the traditional
methods used for food waste treatment (Polprasert 2007). However, the approaches
of disposals for food waste management by landfills and incinerator have some drawbacks. Many countries fully banned the landfilling approach as well as the incinerator
where it produces intensive energy to the surrounding due to the high moisture content and can cause air pollution from the release of smoke from chimneys. Moreover,
incineration also decreases the economic value of the waste as it inhibits the recovery
of nutrients and valuable chemical compounds from the incinerated substrate. On the
other hand, the increasing number of food waste generated every year leads to insufficient area for landfill management (Kunwar et al. 2017). Thus, anaerobic digestion
has been considered as an attractive alternative to overcome these limitations.
Anaerobic digestion involves the degradation and stabilisation of organic materials under anaerobic conditions by microbial organisms. The degradation of organic
material will lead to the formation of biogas which is a mixture of carbon dioxide and
methane as renewable energy source and microbial biomass (Kelleher et al. 2002).
This technology is widely applied in waste management including food waste and
other organic waste treatments (Yaser 2014; Rajin 2018). Furthermore, the production of biogas from anaerobic digestion is one of the renewable energies that can be
used for heating and power generation.
Generally, there are four steps involved in anaerobic digestion which are hydrolysis, acidogenesis, acetogenesis and methanogenesis. Among these steps, hydrolysis is
known as the rate limiting step. During hydrolysis, the polysaccharides (macronutrients) are converted into monosaccharides (micronutrients) by extracellular microbial
enzymes. The slow degradation rate of crude lipid which includes floatable grease,
oil and fats in the food waste leads to low digestion efficiency and therefore inhibits
the digestion process. Various methods have been reported to improve the performance of anaerobic digestion system. Among them is the addition of enzymes to
accelerate the hydrolysis reaction of various types of substrates as reported by Meng
et al. (2017), Dors and Mendes (2013) and Kanmani et al. (2016). In these previous
works, commercial enzymes such as carbohydrases, proteases, and lipases have been
used to improve hydrolysis of food waste from various sources.
Therefore, this research was conducted to determine the feasibility of lipase to
be used in the anaerobic digestion system of Malaysian food waste. The effects of