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Oily-biological sludge (OBS) generated from petroleum refineries has high toxicity. Therefore, it needs an appropriate disposal method to reduce the negative impacts on the environment. The anaerobic co-digestion process is an effective method that manages and converts organic waste to energy. For effective anaerobic digestion, a co-substrate would be required to provide a suitable environment for anaerobic bacteria. In oily-biological sludge, the carbon/nitrogen (C/N) ratio and volatile solids (VS) content are very low. Therefore, it needs to be digested with organic waste that has a high C/N ratio and high VS content. This study investigates the use of sugarcane bagasse (SB) as an effective co-substrate due to its high C/N ratio and high VS content to improve the anaerobic co-digestion process with oily-biological sludge. The sugarcane bagasse also helps to delay the toxicity effect of the methane bacteria. Batch anaerobic co-digestion of oily-biological sludge was conducted with sugarcane bagasse as a co-substrate in twelve reactors with two-liter capacity, each under mesophilic conditions. The interaction effect of a C/N ratio of 20-30 and a VS co-substrate/VS inoculum ratio of 0.06-0.18 on the methane yield (mL CH4/g VSremoved) was investigated. Before the anaerobic digestion, thermochemical pre-treatment of the inoculum and co-substrate was conducted using sodium hydroxide to balance their acidic nature and provide a suitable pH environment for methane bacteria. Design and optimization for the mixing ratios were carried out by central composite design-response surface methodology (CCD-RSM). The highest predicted methane yield was found to be 63.52 mL CH4/g VSremoved, under optimum conditions (C/N ratio of 30 and co-substrate/inoculum ratio of 0.18).

A comprehensive review using natural rubber in the modification of bitumen used for road construction is presented in this paper. The sources, types and properties of natural rubber are discussed briefly. The methods used by researchers to add natural rubber as a modifier for bitumen are also discussed. A literature review of the effects of natural rubber on the physical, mechanical and rheological properties of bitumen and the performance of asphalt mixtures over the past three decades is presented along with the cost analysis of using natural rubber as a modifier in comparison to using other polymers. Researchers in the field of the highway and pavement engineering need to find a method to deal with the most common pavement distress by using local additives such as natural rubber. It is expected that a special, cost effective and long lasting natural rubber modified flexible for road pavements, which is also fatigue and rut resistant, will be developed in the near future. This will reduce the amount of expenses required for the annual maintenance of asphalt mixtures around the world.

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