Bioenergy Production from Agro-Industrial Wastewater Using Advanced Oxidation Processes as Pre-Treatment

Agro-industrial activities generate large volumes of wastewater. When this wastewater is discharged to the environment without proper treatment, it represents a serious problem. Bioenergy production can be conducted using wastewater, but the presence of some recalcitrant compounds may require a pre-treatment step. Advanced oxidation processes (AOPs) were traditionally used to treat hazardous materials but have recently been applied in various bioenergy production processes. AOPs are highly competitive water/wastewater treatment technologies and their application in the bioenergy sector is increasing as a pre-treatment process. Despite the increasing interest in using AOPs to enhance biofuel production, there is a lack of comprehensive documentation on their integration into biofuel production operations. This critical review highlights the application of AOPs as pre-treatment for agro-industrial wastewater (AIW) to enhance bioenergy production. It was noted that AOP applications can reduce the COD, VS, TS and total polyphenols, resulting in an improvement in their biodegradability. Moreover, these processes help remove hemicellulose and lignin contents, increasing the production of biogas, biodiesel and bioethanol. Among the different AOPs presented in this work, wet air oxidation showed promise for pre-treating lignocellulosic biomass to produce various energy types, while sonolysis and ozonation proved effective as a biosolid pre-treatment. Ozonolysis, Fenton reagents and photocatalysis are commonly used to selectively remove phenolic compounds and colorants from organic effluents. The high energy requirements and chemicals reagents costs are identified as obstacles to the application of AOPs in bioenergy production. Further studies should investigate the integration of AOPs with other treatment processes to improve the cost-effectiveness.