Recognizing the challenges of anaerobic digestion: Critical steps toward improving biogas generation

•Three strategies for enhancing AD of organic wastes are presented.•Balancing biomass composition can ensure the optimum digestion process.•Both macro and microelements adjustment can diminish digestion time.•Carbon source DIET promoting additives improve AD via adsorption potential.•Neutral red can increase biogas generation by promoting DIET potential. Anaerobic digestion (AD) is one of the most promising technologies that can break the complex organic substrate into biogas. However, biogas production from biomass waste and its utilization for energy applications are still challenging due to the complex physical and chemical properties of organic waste, which affect the metabolic pathways and methane content. Consequently, attentions have focused on opportunities for further improvement in biogas yield and quality. This review identified the technical challenges associated with AD and potential solutions for improving biogas production. The critical steps toward improving biogas generation were identified as balancing the waste composition; adjusting nutrient content using trace elements; and using direct interspecies electron transfer (DIET) promoting additives. Direct interspecies electron transfer (DIET) promoting additives such as activated carbon, biochar and phenazine have shown a considerable effect on biogas production. These additives facilitate the electron transfer via direct interspecies electron transfer and improve digestibility via adsorption potential. The last section of the review describes a case study of the potential of using biochar and neutral red (phenazine) additives in one of the commercial landfills in the North Island of New Zealand. The results of this case study indicate that application of “neutral red” in the landfill site can significantly improve biogas generation for a period of 70 years.