## 1 Introduction  
Strategies to produce renewable energy from organic waste have become a high priority topic in any energy, bioconversion, bioresource and sustainability conferences in the world. Conversion of organic and inorganic wastes into useful and valuable end products like biohydrogen, biomethane and bio alcohols are increasingly studied each year as many nations progressively working towards sustainable world development. This is because biohydrogen gas is a clean energy alternative and it acts as a good source of fuel to apply in fuel cells for electricity generation. Meanwhile, biomethane, another clean energy alternative for electricity and transportation, is produced from the anaerobic digestion process. Bio alcohols that include biomethanol and bioethanol that were produced by the action of enzymes and microorganism through fermentation would also be used as fuels for internal combustion engines. Renewable energy is an energy that can be replaced, sustainable and does not harm the environment as it is derived from non-nuclear and non-fossil sources [1]. Due to its high energy efficiency, hydrogen (H\({}_{2}\)) is considered one of the preferable biofuels among various renewable energy sources [2]. It is considered the best and most effective fuels for transportation. This is because, when H\({}_{2}\) is combusted (only water vapor is produced with the absence of carbon monoxide (CO), the energy yields are 2.75 times higher (122 kJ/g) than hydrocarbon fuels [3; 4]. This can minimize environmental problems and makes H\({}_{2}\) a future fuel, which has drawn significant attention to the world. Variousotechnologies such as dark fermentation (DF) can be used to generate H\({}_{2}\) in a green and environmental-friendly way using renewable resources [5; 6]. Theoretically, DF is a bioprocess whereby H\({}_{2}\) is produces by microorganisms (i.e., anaerobic bacteria) from organic wastes or wastewaters. Through the activities of fermentative hydrogen producing-bacteria (HPB; obligate anaerobes and facultative anaerobes), the DF process could utilize various types of wastewaters and organic wastes as a feedstock to produce H\({}_{2}\). The fermentative conversion of organic wastes in the DF process involves similar biochemical pathways as in anaerobic digestion (AD) for methane production. As compared to photo-fermutation, the DF process is independent on weather conditions and produce relatively higher H\({}_{2}\) production rate. The other type of fermentation that can use organic wastes is lactic acid fermentation. Compared to the DF process, one mole of glucose will produce two moles of lactic acid under a simple redox reaction with no production of gas as a byproduct. On the other hand, in the AD process, organic materials were converted into biogas, nutrients and some refractory organic matter under anaerobic condition by a mixture of symbiotic microorganisms [7]. AD consists of four steps, _viz._ hydrolysis, acidogenesis, acetogenesis and methanogenesis. Lactic acid fermentation only involves the first two steps [8]. The AD process could reduce pollution and odor as well as produce renewable energy in an effective waste treatment due to the microbiological conversion. Compared to fossil fuels, renewable methane does not contribute to carbon dioxide (CO\({}_{2}\)) emissions in the atmosphere [9]. The palm oil industry in Malaysia is still progressing after developing over the years [10]. It contributes largely to the country's foreign exchange earnings and increased Malaysian lifestyle [11]. In 1917, the oil palm cultivation begins at very slow growth. The plantation developed rapidly only after the last 50 years through cultivation large-scale investment in order to diversify the country's agricultural development [12]. Back then, Malaysia is known as the main producer of cocoa, rubber and coconuts. An inclination for oil palm has prompted a quick extension of its planted regions to the detriment of rubber and different products in the course of the most recent four decades.