Various carbon-rich solid catalysts are evaluated for the synthesis of biodiesel from waste frying oil. The study results showed that the use of activated carbon made of corn stalk could increase the biodiesel yield by 7%. The heterogeneous carbon-based catalysts made of lignocellulosic residues could successfully improve the quality of biodiesel properties. The results obtained revealed that the biodiesel properties, including relative density (852–900 kg·m−3) and kinematic viscosity (2.4–3.9 mm2·s−1), are in compliance with the standard limits of ASTM and the European Biodiesel Standard, suggesting that the biodiesel produced would be decent as a diesel fuel that potentially can minimize the serious damage of engine parts, and prolong the engine life.

Anaerobic co-digestion of oil palm empty fruit bunches with cow manure was studied. The research focus was on the evaluation of feeding different solid concentrations of the substrate in the on-going process of anaerobic digestion. The solid concentrations ranged from 0.5 to 12% TS. Results of the study showed that the maximum methane production could be reached with the reactor digesting substrates with 4 to 8% TS, in which the methane produced was from 1300 to 1400 mL per day. A significant drop of pH from 7.02 to 5.97 occurred when the reactor was digesting substrates with 10 and 12% TS. Acidic condition caused by organic matter overloads lowered the efficiency of organic conversion represented in the low removal of COD, which was only 22.4%. This finding is highly significant for the waste management industries in terms of dealing with the digester upset due to the digestion of large amount of organic wastes.

The performance of anaerobic co-digestion of cow manure and POME was evaluated. The anaerobic composting process was carried out by using semi-continuous reactors under the mesophilic condition (35 ± 1℃). The addition of POME to the on-going anaerobic composting of cow manure was applied stepwise within a cycle of HRT (20 days). Results showed that the anaerobic co-digestion reactor could produce methane at about six times higher (7.2 L CH4) than the control reactor (1.3 L CH4). An increasing of POME loaded to the on-going anaerobic composting cow manure culture (4% to 64%) did not affect pH of the culture in which pH was still stable between 7.11 and 7.5. Assessment of biodegradation efficiency revealed that nitrogen removal of the anaerobic co-digestion reactor was six times higher (21%) than the nitrogen removal of the control reactor (3.4%). This suggested that the anaerobic co-digestion reactor performed sufficiently well in which no organic acid as well as ammonia accumulated in the reactor that could be effective to decompose the organic matters.

The biotechnological production of lactic acid could be carried out via anaerobic acidification process. In order to achieve an optimal production of lactic acid, the role of inoculum would be essential. The current study aimed to investigate as well as evaluate the effect of inoculum concentration on the anaerobic acidification of coconut water waste for the production of lactic acid. Results showed that the addition of 20% inoculums to the reactor fermenting coconut water waste was sufficient for the optimal production of lactic acid. In the batch process anaerobic acidification of coconut water waste inoculated with 20% inoculums of Lactobacillus acidophilus culture had the yield of lactic acid production, which was about 1.62 mmol lactic acid/mmol glucose while under the continuous operation the yield of lactic acid production obtained, was about 1.15 mmol lactic acid/mmol glucose. During the acidification process in both batch and continuous modes pH dropped significantly from 5.1 to 3.7.

Anaerobic co-digestion of oil palm frond waste with cow-manure was evaluated. The study aimed to evaluate a stepwise organic load with an increase solid concentration to the on-going anaerobic digestion of cow manure. The anaerobic digestion process was operated in continuous mode under the mesophilic condition. Results showed that the maximum methane productivity of 1700 ml CH4∙day-1 was obtained when the anaerobic co-digestion of OPFW and cow manure was loaded with the substrate concentration between 4 and 8% TS. The pH culture dropped dramatically from 6.9 to 6.3 when substrate concentration was increased from 10 to 12% TS. The acidic pH had restricted the conversion of organic materials in which the COD removal was less than 25% removal. This study is exceedingly notable for the industrial development of waste management processes, which handle and treat tons of organic wastes daily.