Advanced oxidation processes (AOPs) are powerful methods that were traditionally used for treatment of hazardous materials. Based on their resourcefulness, these methods have recently found important applications in various processes of bioenergy production. Despite the growing interest in the application of AOPs in improving the production of bioenergy, there is no comprehensive documentation on how biofuels production operations have increasingly incorporated these oxidation processes. Therefore, the present study aims at reviewing the current state of the art and future prospects of applying AOPs in biofuels production. The usage of these processes in pre-treatment of lignocellulosic biomass, excess sludge, organic effluents, solid wastes and other substrates for energy production was reviewed. It was noted that wet air oxidation has high potential in pretreatment of lignocellulosic biomass for production of various energy types while sonolysis is most effective in biosolids pretreatment. Ozonolysis and photocatalysis are mostly used to selectively remove the colorants in organic effluents. However electrochemical oxidation has good performance in post-treatment of bioenergy effluents. Documented studies indicate that AOPs can be used to enhance trans-esterification thereby boosting biodiesel production. Moreover, they can be used to improve oil extraction from bio-algae to increase biodiesel yields. Comparative studies involving AOPs and conventional processes are necessary to determine their suitability for these applications. The possibility of using AOPs to upgrade low value biofuels to bio-products of higher value should be part of future investigations. A summarized criterion for evaluating the suitability of different AOPs in the production of biofuels is proposed in this study as a guide for their future usage. The main limitation of applying AOPs in bioenergy sector include high process costs due to costly chemicals and energy requirements. Further studies should investigate the possibility of integration of AOPs with conventional methods aimed at improving the process cost-effectiveness.

Biohydrogen can be produced from organic wastewater but the process is limited by low production yields. The aim of this review is to summarize the production strategies which are recently researched for enhancing biohydrogen yield and productivity from organic wastewater. The survey of published work indicates that the dark hydrogen fermentation is the most promising production mode. Current strategies geared towards improving biohydrogen production include: microbial culture immobilization, bioreactor modifications, the optimization of process conditions (temperature, pH, OLR and HRT), culture selection and enrichments, substrate choice, and the metabolic engineering of biohydrogen specialists. Comparative analysis of energy recovery from anaerobic digestion using vinasse-related substrates indicates that the production of methane has a higher energy yield than production of hydrogen. A sequential combination of biohydrogen and biomethanation production phases has the potential for even higher bioenergy recovery from organic wastewater.